PRUNE RESEARCH REPORTS - California Dried Plums Prune... · 2016 . PRUNE RESEARCH REPORTS ....
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2016 PRUNE RESEARCH REPORTS Published January , 2017 by the California Prune Board (California Dried Plum Board) **Not for Publication and not to be cited without authorization of author(s)
Transcript of PRUNE RESEARCH REPORTS - California Dried Plums Prune... · 2016 . PRUNE RESEARCH REPORTS ....
2016
PRUNE RESEARCH REPORTS
Published January, 2017by
the
California Prune Board
(California Dried Plum Board)
**Not for Publication and not to be cited without authorization of author(s)
An instrumentality of the Department of Food and Agriculture, State of California
C A L I F O R N I A D R I E D P L U M B O A R D
3840 Rosin Court Phone (916) 565-6232 Suite 170 Fax (916) 565-6237 Sacramento, CA 95834 www.CaliforniaDriedPlums.org
January 15, 2017
Dear Reader:
This report summarizes the results to date of the 2016 research projects conducted by University
of California and other researchers. California Dried Plum Board (CDPB) funding for these
projects totaled $345,076.
I would like to extend my thanks to Joe Turkovich who once again served as Chairman of the
CDPB Research Subcommittee. Joe makes a considerable investment of time and provides
strategic guidance to ensure that expenditures are directed in a way that can deliver the most
cost-effective and beneficial results to prune growers and the industry. After many years of
leadership to the Subcommittee Joe has recently stepped aside to focus on his new responsibilities
as Chairman of the California Dried Plum Board. I am pleased to announce that John Taylor now
brings his depth of knowledge and experience to serve as the Research Subcommittee Chair.
Along with the commitment of these recognized leaders, the Research Program would not function
without the assistance of Franz Niederholzer, U.C. Extension Orchard Systems Farm Advisor, who
serves as our University Liaison, Rick Buchner, U.C. Extension Prune Workgroup Chairman and
Gary Obenauf, President of Agricultural Research Consulting, who coordinates these projects.
The contributions of the 2016 – 2018 Research Subcommittee members listed below are
appreciated. If you have any questions about individual research projects, please contact Gary
Obenauf at (559) 449-9035.
Sincerely,
Donn Zea
Executive Director RESEARCH SUBCOMMITTEE
Members
Amarel Jr., Bob Righero, Pete
Bozzo, Matt** Singh, Ranvir
Dugan, Concetta Strong, James
Kelly, Matt Taylor, John*
Kettmann, Mark Turkovich, Joe
Kolberg, Bob Vereschagin, Mike
Loquaci, Dave Ward, Melvin
Micheli, Nick Wohletz, David
* Chairman ** Vice-Chairman
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TABLE OF CONTENTS
Manager Letter/CDPB 2016 Research Subcommittee
CDPB 2016 Research Budget Summary ................................................................................................... 1
2016 Prune Workgroup Meeting Agenda .............................................................................................. 2-3
REPORTS
Varietal Improvement
Dried Plum Cultivar Development and Evaluation.
85 CPB 3. DeJong, T.M. and S. J. Castro ........................................................................................... 4-17
Research Results for the Year 2016: Genomic Profiling and Development of a Comprehensive
Catalog of Plum Germplasm Using Genotyping-by-Sequencing (GBS). 15 CPB 1.
Zhebentyayeva, Tetyana, Chris Dardick, Chris Saski, Ralph Scorza, Ann Callahan, Michael
Rovelandro and Ted Dejong ............................................................................................................. 18-23
Rootstocks
2016 Field Evaluation of Prune Rootstocks. 09 CPB 2. Buchner, Rick, Joe Connell, Franz
Niederholzer, Katherine Pope, Carolyn DeBuse, Cyndi Giles, Ted DeJong, Sarah Castro, Luke
Milliron, Chuck Fleck and Allan Fulton ....................................................................................... 24-31
2016 Field Evaluation of Prune Rootstocks. 16 CPB 1. Pope, Katherine, Rick Buchner, Franz
Niederholzer, Ted DeJong, Sarah Castro ...................................................................................... 32-36
Flower and Fruit Development
Managing Heat at Prune Bloom ‘French’ Prune, 2016. 08 CPB 2, Niederholzer, Franz,
R. Buchner, D. Lightle, K. Pope and L. Milliron. ....................................................................... 37-41
Bloom and Postbloom Prune Management Practices for More Consistent Production of High
Quality Prunes. 16 CPB 2, Niederholzer, Franz, R. Buchner, D. Lightle, K. Pope and
L. Milliron. ................................................................................................................................... 42-47
Use of Cover Crops to Mitigate Heat at Bloom. 16 CPB 3, Lightle, Dani and Franz
Niederholzer. ................................................................................................................................ 48-50
Nutrition
Development of Nutrient Management Tools for Dried Plums (Year 3). 14 CPB 2, Brown,
Patrick, Franz Niederholzer and Amber Bullard. ........................................................................ 51-63
Diseases
Epidemiology and Management of Blossom, Leaf, and Fruit Diseases of Prune. 07 CPB 6.
Adaskaveg, Jim .................................................................................................................................. 64-72
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Diagnosis, Etiology, Epidemiology and Management of Canker Diseases in Dried Plums.
13 CPB 2. Michailides, Themis J., Young Luo, Franz Neiderholzer, David P. Morgan, Dan Felts
and Ryan Puckett. ........................................................................................................................73-86
Investigating Incidence and Type of Wood Decay Fungi in California Prune Orchards. 15 CPB 2.
Johnson, Bob, Franz Neiderholzer, Dave Doll, Florent Trouillas, Matteo Garbelotto, Neil
McRoberts and Dave Rizzo .........................................................................................................87-93
Miscellaneous
California Dried Plum Board Research Reports Database. 10 CPB 2.Rindell, Krista, Janet Zalom and
Crisosto, Carlos................................................................................................................................... 94-95
Tree Crop Intern Program. 12 CPB 2. Niederholzer, Franz. ............................................................. 96-97
Life Cycle Assessment: A Tool for Quantifying the Environmental Impacts of Plum and Prune
Production. 16 CPB 4. Marvinney, Elias, Sonja Brodt and Alissa Kendall. ................................... 98-104
2016 Prune Research Tour. Buchner, Richard P. and Franz Niederholzer. .................................. 105-106
Prune research is on the web site http://ucanr.org/sites/driedplum and is searchable.
California Dried Plum Board 2016 Research Proposals
2016 CDPB
Project 2015 Report Request
Number Pages Project Title/Project Leader Reference Pages (2015)
Varietal Improvements
85 CPB 3 1-4 Prune Cultivar Evaluation and Development- 4-19 121,031$
Ted De Jong-UC Davis (119,550)$
14 CPB 1 FasTrack Breeding for the Development of 20-24 -$
Plum Pox Virus Resistant Plum Varieties for the (76,146)$
California Dried Plum Industry-Ralph Scorza-
USDA/ARS Kearneysville, WV
15 CPB 1 5-12 Genomic profiling and development of a 25-34 25,000$
comprehensive catalogue of plum germplasm 35-36 (25,000)$
using Genotyping-By-Sequencing (GBS) -
Tetyana Zhebentyayeva, Clemson University,
South Carolina
09 CPB 2 Field Evaluation of Prune Rootstocks- 37-55 -$
Rick Buchner-UC Tehama County -$
16 CPB 1 13-15 Field Evaluation of Prune Rootstocks- 4,295$
Katherine Pope-Wolfskill New
Flower and Fruit Development
08 CPB 2 16-17 Managing Heat at Bloom-Franz Niederholzer- 56-59 10,500$
UC Sutter County -$
16 CPB 2 18-20 Bloom and Postbloom Prune Management 12,000$
Practices for More Consistent Production of New
High Quality Prunes-Franz Niederholzer-
UC Sutter County
16 CPB 3 21-24 Using Cover Crops to Mitigate Heat at Bloom/ 8,000$
Dani Lightle-Glenn County New
Nutrition
14 CPB 2 25-30 Development of Nutrient Management Tools 60-67 10,000$
for Prunes-Patrick Brown-UC Davis (10,000)$
Diseases
07 CPB 6 31-34 Epidemiology and management of brown rot 68-77 20,000$
and rust of prune – Development of an (20,000)$
integrated program with new fungicides
and optimal timing-Jim Adaskaveg-UC Riverside
13 CPB 2 35-43 Diagnosis, Epidemology and Management 78-89 44,396$
of Canker Diseases in Dried Plums- (43,896)$
Themis Michailides-UC Parlier
15 CPB 2 44-50 Investigating Incidence and Type of Wood 90-92 10,312$
Decay Fungi in Stone Fruit - Dave Rizzo - (6,497)$
UC Davis
Miscellaneous
10 CPB 2 51-53 California Dried Plum Research Reports 107-108 1,500$
Database-Carlos Crisosto-UCDavis (1,500)$
12 CPB 2 54-55 Tree Crop Intern-Franz Niederholzer-UC 109-110 34,812$
Sutter County -$
16 CPB 4 56-58 Life Cycle Assessment (LCA) of Prune 111-113 20,230$
Production-Elias Marvinney-UCDavis New
Contingency Reserve 23,000$
New
Research Total 345,076$
(310,200)$
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2016 California Dried Plum/Prune Research and Workgroup Meeting
Hosted by the California Dried Plum Board – Donn Zea Executive Director and Gary Obenauf, Research
Director
Wednesday, December 14, 2016 9:30 am to 5:00 pm and Thursday, December 15, 2016, 9:00 am to
12:30 pm.
Meeting Location: California Farm Bureau office (same as last year). The California Farm Bureau office is
located at 2300 River Plaza Drive Sacramento Calif. 95833. Take I-5 to the Garden Highway exit. After
exiting I-5 take Garden Highway west to the stoplight at Gateway Oaks Drive. Right on Gateway, then
first left to River Plaza Drive. Map and directions are also available at [email protected].
Hotel Location and Reservations: Hilton Garden Inn Sacramento South Natomas, 2540 Venture Oaks
Way Sacramento, Calif. 95833 (916) 568 5400. The Hilton Garden Inn offers complimentary van shuttle
service to the Sacramento Intl airport from 5am to 11pm and includes a full "Cook to Order" breakfast. If
you need sleeping rooms for December 13 and/or 14 please call Pam Conine at the CDPB 916-565-
6232 no later than December 5th.
If you plan to attend please RSVP by Friday 12/9/16 to Richard Buchner [email protected] so we get
1) an accurate lunch count and 2) an accurate dinner count.
Agenda for Wednesday 12/14/16 Day one:
9:30 – 9:35 Introduction to the 2015 Prune Research Conference and Workgroup. Richard P. Buchner
,UCCE Farm Advisor Tehama, Glenn and Butte counties.
9:35 – 10:20 California Dried Plum Board 2017 California Prune Industry Summit . Donn Zea, Executive
Director California Dried Plum Board.
10:20- 10:40 California Dried Plum research priorities survey. Gary Obenauf, research director California
Dried Plum Board.
10:40 – 11:00 Break
11:00 – 11:30 How Prunes’ Web of Nutrients Support Healthful Diets. Mary Jo Feeney , Consultant to
the Food and Agriculture Industries.
11:30 – 12:00 Epidemiology and Management of Brown Rot and Rust of Prune. Development of an
Integrated Program with New Fungicides and Optimal Timing (07 CPB 6). Dr. Jim Adaskaveg, Professor
Plant Pathology UC Riverside.
12:00 – 1:00 Lunch -compliments of the California Dried Plum Board. Lunch presentation, California
Dried Plum Research Reports Database (10 CPB 2) and Tree crop Intern Program Update (12 CPB 2). Dr.
Carlos Crisosto and Megan Haug, Fruit and Nut Research and Information Center UCD.
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1:00 – 1:30 Diagnosis, Epidemiology and management of Canker Diseases in Dried Plums (13 CPB 2). Dr.
Themis Michailides, Plant Pathology UC Kearney Ag Center Parlier.
1:30 – 2:00 2016 Conditions in California Prune orchards, Cytospora, Virus and/or cultural factors???
Round table discussion including Adaskaveg, Michailides , prune advisors and Industry.
2:00 – 2:20 Managing Heat at Bloom( 08 CPB 2). Dr. Franz Niederholzer, UCCE Farm Advisor Sutter,
Yuba and Colusa Counties.
2:20 -2:40 Fruit Thinning and Retain applications for Fruit set, report and discussion. Dr. Franz
Niederholzer UCCE Farm Advisor Sutter, Yuba and Colusa Counties.
2:40 – 2:50 Break
2:50 – 3:35 Prune Cultivar Evaluation and Development, G16N-19 release or not ( 85 CPB 3), Dr. Ted
DeJong and Sara Castro, Plant Science UC Davis.
3:35 – 5:00 Prune tasting and evaluation. Dr. Ted DeJong and Sara Castro, Plant Science UC Davis.
5:00 Adjourn for dinner at the Hilton Garden Inn compliments of the California Dried Plum Board.
Agenda for Thursday 12/15/16 Day Two
9:00-9:15 TBA
9:15 – 9:30 TBA
9:30-10:00 Nutrient Management tools for Prune, Orchard Nitrogen survey ( 14CPB2). Dr. Franz
Niederholzer, UCCE Farm Advisor Sutter, Yuba and Colusa Counties.
10:00 -10:30 Field Evaluation of Prune Rootstocks( 09 CPB 2). Richard P. Buchner, UCCE Farm Advisor
Tehama, Glenn and Butte counties.
10:30 -10:40 Break
10:40-11:10 Investigating Incidence and Type of Wood Decay Fungi in California Prune Orchards ( 15
CPB 2). Bob Johnson, graduate project supervised by Dr. Dave Rizzo Plant Pathology UCD.
11:10-11:40 Phosphoric Acid issues, monthly sampling to document fruit content and develop a base
line. Richard P Buchner, UCCE Farm Advisor Tehama, Glenn and Butte counties.
11:40 – 12:00 Discussion regarding a prune research tour probably in May 2017. Richard P. Buchner,
UCCE Farm Advisor Tehama, Glenn and Butte counties.
12:00 - 12:30 Wrap up and Adjourn. Lunch on your own.
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DRIED PLUM CULTIVAR DEVELOPMENT AND EVALUATION
T.M. DeJong and S.J. Castro
INTRODUCTION
California is the world leader in dried plum production, but is almost entirely dependent on the use of a single cultivar, the Improved French prune. This monoclonal situation lends itself to vulnerability to widespread disease, pest outbreaks and annual, statewide variations in yield caused by variable weather conditions that can negatively or positively affect fruit set and/or fruit retention. In addition to the risks of a monoculture system, the entire industry harvests and dehydrates the crop within a few weeks since the entire crop has a similar developmental pattern. The development of new, acceptable or superior, dried plum cultivars will increase the efficiency of California dried plum production and give some protection against the risks involved with a monoculture. The California dried plum industry is also facing increasing marketing competition from other regions of the world and must seek ways to reduce production costs to stay competitive. Thus the industry would also benefit from the development of new dried plum cultivars that have cost saving characteristics such as improved tree structure that would require less pruning, improved fruit dry matter content that would decrease drying costs, and increased tolerance to pests and diseases. Introducing new dried plums that differ in flavor or color could also promote a broadening of the consumer base.
The Dried Plum (Prunus domestica) Development and Evaluation program has enlarged its germplasm and bred new generations of progeny through traditional horticultural breeding methods since its conception in 1985. Through thirty years of evaluation and selection, the breeding program has increased the occurrence of desired characteristics in the germplasm. To insure that the germplasm and new cultivars are well adapted to California’s dry, hot climate, the program evaluates elite selections at two locations; the UC Wolfskill Experimental Orchards, near Winters, in the north; and the Kearney Ag Center, near Parlier, in the southern San Joaquin Valley. The breeding program has matured and is now entering what we anticipate to be a very productive period for producing potential new cultivars that are specifically adapted for California growing conditions and markets.
In recent years we have increased our focus on tree and fruit characteristics that will be particularly helpful in reducing grower costs while improving the dried fruit products. To this end we have put a greater emphasis on evaluating tree structure and fresh fruit characteristics that may influence dry-away ratios and ease of dried fruit handling.
In several years during the last decade dried plum orchard yields have been low because of poor weather conditions for fruit set during the bloom period. The consensus is that this has been largely due to high temperatures during bloom. Since the California industry is composed of one cultivar, in some years the whole industry suffered with poor crops during the years of high temperatures during bloom. Because the time of pollination and fruit set is so critical, we have increased the evaluation of our seedlings and selections for
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differences in bloom date. In doing so, new cultivars can potentially introduce greater diversity of bloom timing so that the entire Californian crop will not be dependent on the same set of weather conditions during periods critical for fruit set and retention.
PROGRAM OBJECTIVES
Objectives:
1.) To develop new dried plum varieties, through traditional horticultural breeding methods, with the following characteristics:
Tree characteristics that reduce labor costs involved in producing driedplums.
Increased fruit quality and fruit characteristics that increase efficiencyand quality of drying and processing.
Earlier or later bloom dates and tolerance to high temperatures duringbloom.
Earlier/later fruit maturity dates than “Improved French” dried plum.
Increased tolerance/resistance to disease.
New specialty traits; with the dried product being equal or improved inquality to “Improved French”, but different in taste and/or color.
2.) Test and evaluate advanced selections resulting from the current breeding program at UC and grower locations in the Sacramento and San Joaquin Valleys.
3.) Cooperate Dr. Chris Dardick (USDA Kearneysville WV) and Drs. Hartmann and Neumuller to obtain sources of Plum Pox (Sharka) resistance that can be incorporated into the breeding program.
PROCEDURES
Breeding methods, pollination procedures, seedling cultivation, and selection evaluation have not been substantially modified for several years. They were described in detail in the Dried Plum Cultivar Development and Evaluation annual report in the 2004 Prune Research Reports published by the California Dried Plum Board. The following is a brief description of our testing and evaluation procedures as a reference for the Results section of this report.
Levels of Testing Field testing and evaluation of dried plum selections developed within this program are being carried out at four levels.
Level 1 testing involves evaluations made in the seedling blocks located at UC Davis. The initial fruit evaluation is made on the original self-rooted seedlings in high density seedling blocks. Fresh and dried fruit characteristics are evaluated at this level of testing. If a positive evaluation results, the seedling becomes a “selection” and is then considered for
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re-propagation in dried plum selection blocks located at the Kearney Research and Extension Center in Parlier, CA and at the Wolfskill Experimental Orchards in Winters, CA.
Level 2 testing occurs in the selection blocks at Kearney and Wolfskill. Depending on the perceived potential of the individual selection, two to four trees of any one selection are established on commercial rootstocks. This level of testing is concerned with fruit characteristics and tree growth habit. Variations in fruit size, tree vigor, maturity date and other characteristics may, and often do, occur when the selection is moved onto a rootstock from the original seedling. Individual selections are evaluated using specific criteria that match the goals of the program. These criteria must be achieved before advancing to Level 3. Therefore there are multiple types of Level 2 trees: those that have yet to fruit in the selection block; others that are still being evaluated and have the potential to advance to grower’s orchards and others that are kept for germplasm and breeding purposes.
Level 3 testing involves the establishment of advanced selections in grower orchards in various locations. This level involves items that have been extensively tested in the selection blocks and are ready for more in-depth evaluation. Despite this, testing at this level is still somewhat preliminary since these plantings are the first instance in which selections are established in varying soil types and in varying climatic regions. Again, depending on the perceived value of the individual item, two to one hundred trees of any one selection are established at any one location. Level 3 grower tests are established in counties throughout the Sacramento and San Joaquin Valleys where dried plums are a commercial crop. In recent years we have increased our selectivity of trees advancing to Level 3 status. The specificity of criteria for new advanced selections is quite narrow and we have chosen to not promote trees to this level until we have confidence in the desirability of their structure, production and process-ability.
Level 4 testing involves the planting of extensive test acreage, usually of a single targeted selection. The size of these Level 4 plantings depends on the apparent potential of the individual selection and the level of risk that the cooperating grower is willing to assume. Ideally these plantings would be as large as 20-40 acres. At this level, thorough tests of process-ability and acceptability in the commercial market are conducted. These tests are designed to gauge the commercial value of the item prior to formal release. The promotion of items to Level 4 is based on the industry’s input and feedback. When the California Dried Plum Board decides a selection is ready for such extensive testing, the University and breeders will develop a research agreement with the Dried Plum Board and the grower. Release of the selection for full-scale commercial production will be delayed until a decision by the Dried Plum Board is made concerning the suitability and desirability of the selection for further commercial production.
Dried Plum/Prune Testing Group The Plum/Prune Testing Group incorporates the participation of growers and processors to evaluate and test dried plum selections for their potential as new cultivars before patenting and public release. For the first twenty years of this project the University of California conducted the dried plum/prune breeding and evaluation program with joint support from the Department of Plant Sciences (previously the Department of Pomology) and the California Dried Plum Board. This program was originally initiated at the request of the
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California Dried Plum Board with the primary goal of developing cultivars that would extend the harvest season with quality characteristics that equal or exceed those of the California standard, Improved French. This project made substantial progress toward that goal with the development of Sutter and Muir Beauty, which have the potential to be harvested up to two weeks earlier than Improved French.
The process used in the final evaluation and release of Sutter and Muir Beauty was based on a traditional model that public breeding programs have used for the past 50 years. After identifying selections that appeared promising and evaluating those selections at the University and in limited grower trials, the selections deemed suitable for public use were patented and released. This assumed that there would be enough interest from growers, packers and nurseries to promote the cultivars and allow them to receive the true test of time in the commercial marketplace. While this model is still valid in a general sense, it is now apparent that it may not be the most efficient or effective model for the evaluation and release of dried plum cultivars in the future.
Therefore we have developed a different strategy for the final evaluation and future release of dried plum/prune cultivars derived from the breeding program. In 2005 we organized a Dried Plum/Prune Testing Group that helped to develop a better process for the release of new cultivars and participate in carrying out that strategy. The group has met two times a year since 2005 to develop testing strategies and evaluate advanced plum/prune selections. Participation in the group involves two general meetings a year, one in the summer just before prune harvest to look at fresh fruit and tree characteristics and a second time in the fall or winter, for the evaluation and discussion of dried product characteristics. The objective is to benefit from greater grower and processor input on individual selections as well as increase grower test plot participation so that by the time a selection is identified for release, the industry is well informed about the cultivar and comfortable about committing to plant, process and sell the cultivar commercially.
The Dried Plum/Prune Testing Group is currently the primary group that will make recommendations to the California Dried Plum Board for initiating large-scale Level 4 commercial testing of new selections. The advantage for participation in this testing group is that growers and processors gain first-hand information on all new selections in the program on which to base future planting/marketing strategies, participate in test plantings, have early access to new cultivars slated for release, and help direct the breeding and evaluation program to address germplasm-based issues in the future.
RESULTS
Bloom Data The importance of bloom data has grown in the last decade because of the changing weather patterns that California has experienced. It has become more common to have heat spells in March that often have temperatures near 80°F. If high temperatures occur when Improved French is blooming the biological mechanisms for successful pollination and fertilization are negatively affected. Historically, the result has been low fruit set across
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the state. Variation for time of bloom is naturally found within the breeding program’s germplasm. Introducing new cultivars to the California dried plum industry that have bloom times earlier or later than Improved French could reduce the risk of having the entire crop reliant on good weather conditions occurring during Imp. French bloom. Bloom set was reduced in two of the last four years in specific areas of California due to low chill winters. The 2016 state wide crop is one of the lowest we have seen in years. However, this year’s crop failure was not due to low chill but due to an aggressive storm that limited bee flying time and physically damaged flowers. Despite adverse weather, most selection trees at our Winters and Kearney locations bore fruit. San Joaquin growers had the highest fruit set statewide because bloom occurred before the storm. Therefore our Kearney location (Fresno county) had the highest fruit set of all our blocks.
Bloom data, including date of full bloom (90% flowers open), amount of bloom, and the first and final day of bloom have been recorded for all the Level 2-4 selections since 2003. Table 1 shows the number of days each top selection blooms, days before or after Improved French’s full bloom as well as the number of days in bloom, the 90% full bloom date and the average bloom date relative to Improved French over the last 2-5 years when known.
Table 1. Bloom data at the Winters selection orchard for the 2016 top selections.
Item ID 2016 Full
Bloom Date (90%)
Days in Bloom 2016
Days from Imp. French
2016
Average Days from
Imp. French Fruit Set
F11S- 38 3/7/16 13 -3 -13 Medium
H13S- 65 3/1/16 13 -9 -14 Medium
H13S- 58 3/5/16 9 -5 -4 Light
H8S- 75 3/2/16 11 -8 -7 Medium
G39S-70 3/7/16 11 -3 -4 Medium
H21N- 101 3/2/16 9 -8 -10 Light
H8N-74 3/2/16 8 -8 -7 Medium
G37S- 38 3/2/16 12 -8 -7 Light
H5N- 83 3/4/16 8 -6 -3 Light
G21N- 20 3/8/16 8 -2 2 Medium
H11N- 38 3/4/16 8 -6 -8 Light
I6N- 83 3/8/16 14 -2 -6 Light
G26N- 8 2/29/16 8 -11 -13 Light
G27N-31 3/9/16 11 -1 0 Light
Imp. French 3/10/2016 13 +/-2 Light
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Level 4 Testing As of now, there are no active Level 4 selections. We would however recommend to the industry to look at H13S- 58 for large scale testing in the future. It has a very low dry away ratio, self-pollinates, and harvests with or after Improved French.
Selection G16N- 19 has been a level 4 candidate in the past, but due to post harvest skin splits we can no longer promote this tree. The program will continue to use it for breeding, but will no longer be showing it to growers as a potential cultivar. More information about G16N- 19 is in the 2015 report.
Level 3 Testing Level 3 testing items are selections that are ready for small trials in grower’s orchards. We have chosen to only promote selections to Level 3 status when the tree has proven to meet specific criteria over multiple years. This has limited the number of active Level 3 selections. We only plant trees in grower’s orchards when we are fairly confident in their fruit and tree quality. The top selection at Level 3 is H13S- 58. Previous top items such as G47S- 4 and G47S- 61 were removed from their Level 3 &2 status because their pollen was not self-compatible. H10N- 38 was removed from its Level 3 status because it had disease problems. We will need to determine if this disease problem was an isolated incident before we could promote this tree any further. So after losing those promising items, we have promoted H8S- 75 and H13S-65 to Level 3.
Table 2. Level 3 selection performance for 2016 at university selection blocks. ‘Days from French’ refers to the difference between the Imp. French harvest date and the harvest date of the selection at the same location. The harvest date listed is for our Winters selection block.
Date Days from
French Name
Dry away ratio
Dried Count per lb.
Weight (g/frt)
Pressure Sugar in
Brix Comments
25-Jul -17 F8N- 68 3.2* 30.0* 43.7 3.7 22.8 Not for commercial
use, for gourmet fresh or dried *2015 data
7-Jul -34 F11S- 38 2.4 45.4 26.7 7.1 30.1 Dried on the tree, low dry away ratio. Will dry
in 18 hours or less
8-Aug -4 H13S- 65 2.7 31.1 37.0 2.9 24.3 Promising tree with
medium to large fruit and strong pit
8-Aug -4 H13S- 58 2.3 40.4 27.6 3.1 28.2 Long pit, good dried
qualities for such a low dry away ratio
15-Aug 3 H8S- 75 2.2 41.8 25.7 6.0 35.5 High brix, slight
crescent shape, dark purple fruit
H13S-58: This is a good tasting dried fruit with a low dry away ratio. It is a yellow fresh fruit that can be a little astringent if picked too early. The high sugars are usually due to the fruit starting to dry on the tree before harvest. This was its third year of evaluation. In
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March it was caged to determine the ability to self-pollinate, and despite low flower density, it set fruit, so is likely self-pollinating. Bloom time is typically 4 days before Imp. French. H13S-58 was budded at Fowler Nurseries and will be planted in a few growers orchards in Winter, 2017.
H8S- 75 This is the third year producing fruit in the selection blocks. In 2014 it had a sugar BRIX of 28, 2015 was 30.7 and this year was 35.5. It had a dry away ratio of 2.2, and good dried scores. The fresh fruit has an odd shape, but this is not noticeable in the dried fruit. The pit tends to have a slight neck on the stem end, but this doesn’t seem like it will affect its ability to be pitted. The fruit is harvested around the same time as Improved French. In 2017 this tree will be caged during pollination to determine if it self-pollinates.
H13S- 65 Is a newer selection with good dried evaluations from our Winters block. It had a dry away of 2.8 and a BRIX of 26.4. Fruit is medium-large with low dry away ratios (2.7-2.9), purple fresh skin, and small, free pits. In 2017 this tree will be caged during pollination to determine if it self-pollinates. The tree has an upright and spreading structure that could help reduce pruning as compared to Improved French.
F11S-38 has an extremely low dry away ratio, usually around 2.0-2.5. This item has unusually low fresh moisture content, and thus will need less drying time or lower drying temperatures than Improved French. The industry has stressed the importance of any new cultivar needing to have a low dry away ratio. Despite the fact that the program has increasingly more low dry away ratio plum selections, this tree was the first of many that has good dried characteristics while also having an extremely low dry away ratio. We feel a thorough processing and field trial test of this fruit would be beneficial in establishing a cultivar that would drastically cuts costs for growers. For more information about this selection see reports from 2012 and 2013. This tree was caged in 2012 and was able to pollinate itself.
F8N- 68 is a large purple fruit with excellent fresh and dried scores. It has been tested multiple years and always sets a heavy crop of large fruit. This selection would be recommended only for a grower who desires to develop a diversified market where gourmet type fruit could be sold. This tree was caged in March and was determined to self-pollinate.
Level 2 Testing Level 2 testing evaluates a selection after it has been promoted from the Davis seedling blocks to the advanced selection blocks at Kearney and Wolfskill. Once the tree has matured and has started producing fruit, the whole tree and fruit characteristics are evaluated. Table 3 shows the harvest data of the top Level 2 selections this year. This is a very exciting time in our program where many of our Level 2 trees are starting to bear fruit in the selection block. Since 2012, the increase of selections in Winters and Kearney have made for a lot of evaluations during harvest. These evaluations are important to determine if the promising characteristics observed in Level 1 seedlings transferred over to the grafted Level 2 trees in the selection block. With many of these fruit with low dry away ratios, there
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is a tendency for the fruit to dry on the tree and have dense fruit flesh. These characteristics will likely change how pressure is used as a harvest indicator in the future.
Table 3. 2016 Level 2 selection performance in University blocks. ‘Days from French’ refers to the difference between the Imp. French harvest date and the harvest date of the selection at the same location. The harvest date listed is specific for locations where samples were collected.
Test Date
Days from French
Name Dry Size
ct/lb Dry away
ratio Weight (g/frt)
Pres-sure
Sugar in Brix
7/6 -36 G39S-70 64.3 2.3 16.9 6.7 33.9
7/7 -34 H21N- 101 44.5 2.3 25.4 3.8 32.3
7/18 -26 H8N-74 45.3 2.8 31.6 3.5 26.2
8/8 -4 G37S- 38 42.5 2.7 31.1 4.1 22.8
8/8 -4 H5N- 83 37.9 2.4 30.0 2.9 26.4
8/8 -4 I7N- 7 31.5 2.7 40.1 2.9 26.6
8/10 3 G21N- 20 40.8 3.0 41.0 3.3 26.7
8/15 3 H11N- 38 40.6 2.2 25.7 5.3 28.8
8/15 3 I6N- 83 36.0 2.5 31.6 5.4 29.4
8/23 11 G26N- 8 37.2 2.6 37.0 7.9 25.6
8/23 11 G27N-31 47.4 2.9 26.9 5.5 23.7
G39S- 70: This fruit has one of the best dry away ratios in the program. The low dry away ratio combined with its good dried scores makes it a very promising selection as a future cultivar or to use as a breeding source. Adoption of such a low dry away ratio item would take extra trials and testing on how to best handle and process such a unique item. For example we dried this item for only 18 hours and the fruit dried wonderfully.
H21N- 101: This tree produces fruit that will dry on the tree but is ready for harvest a full month before Improved French. 2016 was the first year this tree had a significant crop in the selection block.
G27N- 31: This fruit was one of the highest ranked items from our in-house dried fruit tasting. The fruit harvests after Improved French, is similar in size and has a dry away ratio of 2.9. The dried fruit texture can be a little gooey, so processors would need to determine if that certain flesh texture would work for the industry.
H11N- 38: has a really low dry away ratio, the pit tends to sink when dried. It has only been evaluated for two years at this point, but looks promising.
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G21N- 20: This item consistently looks good from year to year. The tree is spreading and has great looking round purple fruit. The dry away ratio is acceptable, but with other items so much lower this tree might not get promoted due to the 3.0 dry away.
Level 1 Testing Level 1 testing evaluates the young seedling trees at Davis with fruit quality being the primary selection criteria at this level. The seedlings set medium to light sized crops this year with no need for thinning. Fruit samples of 174 trees were taken from the Level 1 seedling blocks for fresh evaluations. Of those, 112 samples were dried and processed for the rehydrated in-house tasting evaluation in October. Forty of the 112 items were chosen to be grafted into the selection blocks. Table 4 shows the harvest data of the top thirty-three seedlings evaluated at Level 1. All items listed in Table 4 will be grafted into selection orchards for further potential cultivar evaluation. Seven items were selected from the seedling block for breeding, these germplasm selections all contain fruit traits that are comparable or superior to the breeding germplasm currently used in Winters and Kearney. The items selected this year and last, have substantially lower dry away ratios than we have seen in the years prior. This is the result of continued development of an advanced prune germplasm collection that has enabled selection of parent genotypes to create new selections that can substantially improve fruit dry away ratios and potentially impact grower profitability.
Table 4. 2016: Harvest data for advanced selections in Level 1 testing at Davis.
Test Date Item name Days from
French Weight (g/fruit)
Pres-sure Sugar in
BRIX Dry size count/lb
Dry Away Ratio
7/19 H20N-22 -24 28.2 2.8 28.5 46.4 2.6
7/20 I11S- 30 -23 21.2 5.0 25.5 60.5 2.9
7/26 H9N- 36 -17 41.0 26.8 34.8 2.6
7/27 H13S- 86 -17 26.5 4.8 25.4 36.1 2.7
7/27 H18N- 22 -17 22.5 5.1 26.0 52.1 2.4
7/27 I1S- 45 -17 38.8 4.5 25.6 37.3 2.8
7/27 I2N- 32 -17 22.3 4.1 25.3 52.6 2.8
7/27 I2S- 50 -17 24.7 7.2 33.2 46.0 2.5
8/2 I12N- 66 -12 27.9 5.7 29.5 38.6 2.4
8/2 I13S- 58 -12 18.0 5.1 33.8 61.2 2.5
8/3 H18N- 71 -11 19.7 3.1 28.1 61.2 2.6
8/3 H20S- 30 -11 20.6 6.8 34.3 47.5 2.0
8/4 H16S- 42 -10 24.9 3.8 27.9 49.7 2.7
8/9 H11N- 72 -5 19.8 3.2 30.2 53.1 2.5
8/9 H19S- 22 -5 35.7 2.9 31.6 40.3 2.4
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8/10 I11S- 62 -4 32.0 3.6 31.1 31.0 2.3
8/10 I11S- 67 -4 26.6 4.4 27.3 47.2 2.7
8/10 I11N- 43 -4 28.9 5.6 29.3 38.8 2.4
8/10 I12N- 4 -4 28.0 3.7 32.9 38.3 2.2
8/10 I12S- 6 -4 24.5 4.2 30.3 43.6 2.3
8/10 I13N- 59 -4 28.3 33.4 46.5 2.2
8/10 I13N- 64 -4 27.6 24.5 46.2 2.3
8/10 I13N- 65 -4 24.6 2.9 36.0 44.3 2.2
8/10 J2N- 128 -4 26.4 5.8 34.9 37.8 2.0
8/10 J2S- 58 -4 26.6 6.5 32.0 45.0 2.1
8/10 J2S- 83 -4 27.7 4.6 26.3 44.4 2.7
8/12 I6S- 23 -2 48.8 5.1 30.8 23.1 2.2
8/16 H17N- 88 2 40.1 2.2 24.3 33.7 2.9
8/17 I4S-59 3 29.6 2.4 25.0 39.3 2.5
8/17 I5S- 72 3 29.0 1.4 34.6 33.6 1.9
8/17 I8N- 41 3 24.7 3.6 29.4 47.1 2.2
8/18 J2N- 127 4 26.4 5.2 37.5 38.3 1.7
8/18 J2N- 79 4 31.2 6.2 30.2 37.3 2.3
8/19 I14N- 25 5 34.4 2.8 30.7 34.5 2.5
Levels Summary In 2011 the program was challenged to aggressively pursue reducing grower input costs by reducing the dry away ratio and reducing the costs of pruning through new cultivar development. This program has responded to the challenge and nearly all of our top Level 2 and Level 3 items have a dry away ratio of less than 3.0. In doing this, the program has bred new selections that could save California growers money by reducing the cost of dehydration. Items F11S- 38, H11N-38 and G39S- 70, with their dry away ratio of 2.4 or less, are examples of selections that could dramatically reduce the cost of drying however the industry will have to decide if it can handle dealing with such unique items. Extra tests need to be performed to determine the best drying times and temperature for fruit that have already lost a significant portion of their water content by harvest time.
In regards to reduced pruning costs, we have many new items with more spur bearing tree structure and or have an upright growing habit. For example, H13S- 65 and H15N- 56 both have upright growing habits. Additionally, most of our selection items will produce fruit on first year wood. This means the trees will start to bear fruit at a younger age than Improved French.
Program Inventory All the seedling blocks are located in the UC Davis campus research orchards (Table 5). In the summer of 2016, over 400 seedling trees were discarded after evaluation of the seedlings showed negative fruit or tree characteristics, and the entire H block will be cut out after this winter. Crosses were made in spring of 2015, the seeds were germinated in
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January and were planted in the fall in the “J” seedling block. The inventories of selections at each level of testing were re-inventoried and are shown in Table 6.The numbers in this table represent the number of unique selections and not the number of trees. The “breeding population” category was separated into two categories, breeding and germplasm. The breeding trees are actively being used for breeding whereas the germplasm items are old selections or cultivars collected from other programs that have negative characteristics that prevent them from currently being used in breeding. There is value in preserving them in our germplasm collection to keep the species-wide germplasm diversified; they may someday be important parents for future generations. Because of money and space constraints we plan to discard a segment of our germplasm and breeding stock. We have decided to cut out 79 individual selections that do not contribute to the program’s goal of reducing dry away and pruning.
Table 5. Seedling block inventories for 2016 located in the Davis UC research orchards.
Block Acres Year Planted Seedlings Planted
Seedlings Remaining
Advanced Selections
I 3 2008-2012 2,656 2,190 34
J 4 2013-cont. 5,022 5,022 4
Seeds 2016 (2,324)c
Totals 7 7,678 7,212d cnumber of seeds in stratification for 2017 planting d not including seeds
Table 6. Number of unique selections in the dried plum program and their level of testing including the breeding and germplasm population.
Level of Testing Number of
Items Number of new 2016 additions
Level 1 7,212 1,340 (~2,324)
Level 2 109 33
Level 3 & 4 6 3
Fresh Items 11 1
Breeding Items 82 7
Germplasm Items 80 6
Items Removed 79
Disease Screening This year, very little disease pressure was displayed in the orchard. Therefore no statistical data was collected on brown rot. If we saw any hits of brown rot in the seedling block, the individuals with those hits were rogued from the program. There were also very few
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incidences of scab in our orchards this year, nonetheless, a few selections were evaluated for scab. If an item showed either scab or brown rot it was noted and the item was marked as more susceptible than the general population. Any genotypes documented as being more sensitive to scab than Improved French were discarded.
Plum Pox Virus (PPV) This program is taking action in preparation for when plum pox virus might come to California. As mentioned in previous reports, we have been incorporating Stanley and Jojo genetics into the germplasm. We have been contributing to Dr. Chris Dardick’s (formerly Dr. Ralph Scorza’s) research on fast track genetically modified plum pox resistant plums.
This year the program initiated the importation of hypersensitive cultivars from the German breeding program of Dr. Neumuller. These items have the potential to either be good California cultivars or good breeding sources for hypersensitive resistance. We also have recently acquired 5 trees of the ‘Docera 6’ rootstock that has hypersensitive resistance to PPV. We hope to plant Improved French and top items from the program on this rootstock to begin determining it’s adaptability to California conditions.
Dried Plum/Prune Testing Group Evaluations The Dried Plum/Prune Testing Group met in July this year at the Wolfskill Experimental Orchards to discuss strategies for testing and to tour the program’s orchard. The group looked at fresh fruit and tree characteristics of top selections and discussed their potential as cultivars. Starting in 2011, the November meeting was moved to combine with the Dried Plum Research and Workgroup meeting in December. This was done to help reduce travel for those located far from Davis. The workgroup evaluated our top 15 selections and the results of this tasting are located at the end of this document (Table 9). Table 8 provides details on the fresh and dried characteristics of each of the selections chosen for the December taste testing.
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Table 7. Summary table of all the items tasted at the 2016 CDPB meeting in December. All items were grown in the Winters selection block using various rootstocks and different harvest dates. The taste evaluation was an in-house ranking from 1 being bad tasting to 5 being wonderful flavor.
Tasting number
Test date
Name Rootstock days from
French
weight (g/fruit)
Pressure BRIX count per lb
dry away ratio
Avg. taste evaluation
(1=bad, 5=excellent)
1 7/7 H21N-101 29c -34 25.4 3.8 32.3 44.5 2.3 3.8
2 8/8 G37S- 38 M40 -4 31.1 4.1 22.8 42.5 2.7 3.0
3 8/8 H13S- 58 29c -4 27.6 3.1 20.0 40.4 2.3 3.5
4 8/8 H13S- 65 29c -4 37.0 2.9 24.3 31.1 2.7 3.8
5 8/8 H5N- 83 29c -4 30.0 2.9 26.4 37.9 2.4 3.3
6 8/15 H16N- 83 M40 3 39.9 3.1 29.6 33.7 2.4 3.5
7 8/15 H8S- 75 29c 3 25.7 6.0 35.5 41.8 2.2 3.0
8 8/23 G26N- 8 29c 11 37.0 7.9 25.6 37.2 2.6 3.3
9 8/23 G27N-31 M40 11 26.9 5.5 23.7 47.4 2.9 4.0
10 8/23 H15N- 92 M2624 11 31.5 6.7 27.9 36.0 2.6 3.3
8/8 Imp.
French M58 +/-3 34.2 2.9 27.9 35.1 2.5 2.0
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Table 8. Results from the industry tasting conducted by 15 members at the California Dried Plum Board annual meeting in December. Table listed by tasting number, comments are a compilation of responses. Ranking is 1-5, 1 being poorly rated and 5 being the best.
Item Name Flavor Skin
Color Skin
Quality Fruit Size
Pitting Quality
Flesh Color
Flesh Texture
Summary of Comments
H21N- 101 3.7 4.1 3.7 3.5 3.4 3.8 3.5 good flavor, acidic dark flesh, skin slightly thin
G37S- 38 3.6 3.9 3.6 4.1 3.1 3.9 3.8 pit variable, thin skin,
H13S- 58 3.4 3.8 3.8 3.7 4.3 3.5 3.9 good pit size, soft flesh,
great, heavy flavor
H13S- 65 3.6 4.2 4.3 4.3 4.9 4.2 3.9 good pit shape & free,
good flesh
H5N- 83 3.8 4.0 3.8 4.1 2.7 3.4 3.7 pit not free, very sweet,
good pit and shape
H16N- 83 2.6 3.8 3.8 4.0 2.6 2.6 3.3 cling pit, very sweet dark
flesh, some burnt
H8S- 75 3.3 3.7 3.6 4.2 2.9 3.4 3.5 long, semi free pit,
complex flavor large fruit size
G26N- 8 3.0 3.8 3.4 4.0 3.4 3.6 3.6 dark thin skin, large,
sweet, slight spicy notes
G27N- 31 3.5 3.6 3.6 3.5 4.8 3.6 3.5 thick skin, gooey flesh,
free pit
H15N- 92 3.4 3.6 3.8 4.0 4.1 3.8 3.7 good fleshy fruit, pit large,
fruity good flavor and texture
Imp. French
2.5 4.0 3.1 3.9 3.3 2.8 3.1 tough skin, amber to
burnt flesh
DONATIONS
We would like to thank Duarte Nursery Inc, for the donation of nursery care of the program’s seedlings. We would also like to thank Pacific Western Container for donating the tree protectors for the seedling plantings at Davis. Their generosity helps support UC research and the California dried plum industry’s goal in developing new dried plum cultivars for California.
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RESEARCH RESULTS FOR THE YEAR 2016: GENOMIC PROFILING AND
DEVELOPMENT OF A COMPREHENSIVE CATALOGUE OF PLUM GERMPLASM
USING GENOTYPING-BY-SEQUENCING (GBS)
Tetyana Zhebentyayeva2,3, Chris Dardick1, Chris Saski2,3, Ralph Scorza1, Ann Callahan1,
Michael Rovelandro4, and Ted DeJong5
1 USDA Appalachian Fruit Research Laboratory, Kearneysville, WV 25430, USA2 Clemson University Genomics & Computational Biology Laboratory, Clemson, SC 29634 3 Department of Genetics and Biochemistry, Clemson University, Clemson, SC 29634 4 UMR BFP1332 - INRA-Universite Bordeaux II, Villenave d’Ornon, France 5 Department of Plant Sciences, University of California, Davis, CA 95616, USA
OBJECTIVES
The objective of this study was to determine the genetic relationship of the main
industrial US cultivar ‘Improved French’ to other commercial germplasm that is used
worldwide. The d’Ente (Agen) prunes and Improved French are being analyzed in a set
of cultivars from different morphological groups of plums maintained at germplasm
repository at INRA, Bordeaux representing one of the oldest, largest in diversity and best
characterized plum germplasm sources. In addition, wild Prunus relatives were also
included in the study in attempt to determine the genetic relations of hexaploid Prunus
domestica and its potential wild progenitors, diploid Prunus cerasifera and Prunus
spinosa. This information is of great importance in choosing parents and identifying
sources of diversity for breeding programs.
RESULTS AND CONCLUSIONS
Brief Summary of specific accomplishments in 2016:
144 plum samples were genotyped by sequencing in 2016 (Table 1). Plum samples
represented the US germplasm from USDA repository and UC, Davis germplasm
including unknown plum seedlings from the greenhouse and 2 plum samples from
Argentina. Seven diploid Prunus species were included to increase representation of
diploid progenitors in the analysis. Samples from AFRS USDA (Kearneysville, WV)
represented 7 clones of Improved French from different orchards and 26 individuals from
controlled self-pollination of Improved French. Genotyping also included 5 advanced
selections from the prune breeding program at UC, Davis.
Sequences were processed using an in-house bioinformatic pipeline (see details in
Appendix in 2015 report) and combined with sequences of 192 samples genotyped in
2015. The combined dataset totaled 336 samples. To ensure successful genotyping and
provide inter-plate controls, some important prune varieties and plum cultivars were
genotyped several times. Summary of data processing for individual accessions are shown
in Table 2.
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In the first round of data analysis, a total of 235,609 SNP markers across 336 accessions
were used to evaluate genetic relationships of d’Agen prunes and Improved French
within European germplasm (Fig1). Resulting dendrograms generated from combined
dataset in 2016 and a subset of accessions in 2015 were in agreement. The d’Agen
varieties from France and USA as well as Improved French prune were clustered
separately from greengages, damsons, and mirabelles. Extensive datasets including 26
progeny of self-pollinated Improved French increased resolution of genetic relations
among d’Agen prunes. The d’Agen clones could be largely separated from progeny of
Improved French derived from self-pollination and hybridization with other cultivars. In
addition, indirect support for the clonal status of most d’Agen prunes (red color on
dendrogram) comes from similar tight clustering among Reine Claude clones from
France (dark green color on dendrogram).
The relationship of P. domestica cultivars to both P. cerasifera and P. spinosa supports
the conclusion that this species was likely the result of an inter-specific hybridization as
previously reported in the literature. However, additional ongoing analyses will be
conducted to confirm this.
Results regarding individual accessions: re-sequencing of AP1 and AP2 samples from
Argentina indicated relatedness with d’Agen prunes as well as industrial cultivar Erfdeel
from South Africa. Unknown plum from greenhouse at USDA facilities in UC Davis was
grouped on dendrogram with Improved French clones. List of cultivars grouped in
vicinity of d’Agen prunes (magenta color on dendrogram)– Primacotes-INRA,
Primacortes-USA, Hybride INRA, Muir Beauty, Sans-Noyau, Tulaire Giant and hybrid
form G16N-19. These results are largely consistent with the known parentage of these
varieties.
Plum2016 plant material
Table 1. Samples genotyped in 2016
Group ID Pomological group Accessions
1 European plum 85
2 Improved French/dEnte clones 16
2 Improved French selfpollinated 26
5 Reine Claude 11
3 P.cerasifera 2
4 P.spinosa 4
1 P. simonii total 144
Dendrogram
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SNP profiles for samples were compared and used to generate a complete dendrogram on
Fig.1. Plum accessions were separated into 6-7 groups. Noticeable, d’Agen prunes
including Improved French from USA and France were clustered into distinct group on
dendrogram separately from other groups of European plums.
Fig.1 Dendrogram showing the genetic similarity 336 plum accessions estimated over
235,609 polymorphic SNP markers. Colors indicate pomological groups: magenta, red
and dark blue (Prune), light and dark green (Greengage), black (Damson and
Mirabelle), dark red (hexaploid Prunus domestica, European plum) and cyan (diploid
species P. cerasifera and P. spinosa).
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BUDGET NARRATIVE
Funding was partially used for making GBS libraries (144 samples), sequencing and data
analyses. Remaining funds will be used for sequencing of samples from Australia,
Argentina and Chile not delivered yet to USA.
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2016 FIELD EVALUATION OF PRUNE ROOTSTOCKS
Richard Buchner, Joseph Connell, Franz Niederholzer, Katherine Pope, Carolyn DeBuse, Cyndi
Gilles, Ted DeJong, Sarah Castro, Luke Milliron, Chuck Fleck and Allan Fulton
PROBLEM AND ITS SIGNIFICANCE
The California Prune Industry has historically utilized five rootstocks, Myrobalan seedling,
Myrobalan 29C, Marianna 2624, Lovell peach and some M40. The last statewide organized prune
rootstock effort was the “M” series rootstock plots planted in 1987 (Vina Monastery 3/20/87).
Since the conclusion of that experiment many more potential rootstocks for prune have been
identified. HBOK 50, Krymsk1, Krymsk 86, Citation, Rootpac-R, Viking, Atlas and others.
Three rootstock experiments have been planted in Northern California. One at Wolfskill, planted
1/19/11, a second in Yuba County planted 6/3/11 and a third in Butte County planted 4/28/11. All
trees were nursery grafted to the ‘Improved French’ variety.
OBJECTIVES
1) Evaluate 29 rootstocks potential for use in California Prune production.
2) Evaluate trunk cross sectional area (TCSA), yield, dry ratio, bloom date and bloom conditions.
PLANS AND PROCEDURES
Butte County Location
The Butte County location was planted 4/28/11. The wet winter delayed soil preparation resulting
in the late planting date. The Butte County soil survey lists the soil as Farwell Clay Adobe
alternating with a lighter textured soil described as Nord Loam. Nord loam is noted for its higher
pH, low nutrient status and a greater likelihood of having replant disease Test trees followed
almonds on Lovell peach rootstock with no soil treatments prior to planting. Lesion nematodes
were isolated from soil samples. The layout is a randomized complete block design with 14
treatments and 5 replicates. There are 6 trees per plot in the original design. Trees were headed at
40 inches on 5/10/2011 and the test planting is drip irrigated. The HBOK 50 rootstock came as
potted trees and were delivered 5/4/11 and planted by 5/10/11. Instructions were to remove trees
from the pots, do not disturb the root ball, cover with 2 inches of soil and irrigate carefully to keep
the small root ball moist. The HBOK 50 rootstock produced small bush like trees and did not have
sufficient trunk growth to head the first year and were left alone. Viking and Atlas were not
available in 2011 and were added to the experiment in 2012 and are consequently one year
younger. Viking and Atlas were propagated by Dave Wilson nursery, HBOK 50 from Duarte
nursery and the remaining trees were propagated by Fowler nursery. Tree mortality was high
during the 2011 season. Missing tree locations were site fumigated with 0.5 pound of chloropicrin
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on 11/15/11 and replanted 2/10/12. Viking and Atlas were also planted 2/10/12. Many of the
Rootpac-R trees did not survive the initial planting and replacement trees were not available. On
2/10/12 the few remaining Rootpac-R were extracted at Butte and replanted in the Yuba plot. The
goal was to have one complete set of Rootpac-R at one location. Both the Butte and Yuba locations
have mixed tree ages because of the high initial tree mortality. Fumigated replant trees grew well
and growth caught up with trees planted the first year. Trunk Measurements (11/7/16) include
scion circumference measured 12 inches above the graft union. Trunk circumference is used to
calculate trunk cross sectional area in cm2.
Two representative trees per plot were hand harvested 8/17/16. Fresh weight was field measured
and six pound subsamples were commercially dried, compliments of Sunsweet Inc., to calculate
dry ratio and final dry weight. Data is presented as mean individual dry yield per tree.
Yuba County Location
The Yuba County location was planted 6/3/11. The wet winter delayed soil preparation and
subsequently delayed planting. Similar to Butte, the plot is a randomized complete block design
with 14 treatments and 5 replicates. There are 6 trees per plot in the original design. Rootstocks
are the same as the Butte plot with the exception of Rootpac-R which was transplanted from Butte
to Yuba and Empyrean 2 which did not survive in the Yuba location. Tree mortality was high
during the first growing season. The soil is described as Kilga Clay Loam. Replants in 2012
replaced missing trees. The Yuba experiment is complete and trees are growing well. Tree nursery
propagation is the same as Butte.
For 2016, Yuba data collection included trunk circumference measured 12 inches above the soil
surface taken on 12/3/16. The data is presented as trunk cross sectional area in cm2.
Wolfskill Experimental Orchard
A satellite experiment of prune rootstocks was planted at the UC Wolfskill experimental orchard
in Winters, California. The plot contains 15 experimental rootstocks and 3 standard rootstocks
(Marianna 2624, Lovell, and Myrobalan 29C) nursery budded to ‘Improved French.’ This
experiment provides an initial evaluation of possible rootstocks that have previously not been tried
with prune or have had very little field testing.
The experiment is planted with at least 5 trees of each rootstock and is non-replicated, which limits
statistical analysis. The goal was to get a first look at how these rootstocks performed with
‘Improved French’ scions and identify any defects before commercial planting. ‘Improved French’
on its own root differs from the others in that trees were grown in the nursery for two years. Own
rooted trees do have a graft union because ‘Improved French’ was budded on top. Wolfskill
rootstock entries are listed in figure 17. Trees were planted 17 feet across the row and 14 feet down
the row, which results in approximately 183 trees per acre.
The Wolfskill site was previously planted to peaches that were removed in 2008. The field was
planted annually for 3 years to winter wheat. The Yolo County soil survey describes the soil as
Yolo loam. Nematode samples were taken at four locations within the field at approximately an
18 inch depth and combined for nematode evaluation (8/29/11). One liter of soil contained, 50
Lesion (Pratylenchus sp.), 50 Pin (Pratylenchus sp.), and 30 Dagger (Xiphinema americanum)
26
nematodes. There were not enough nematodes to identify the species of either Lesion or Pin
nematodes.
The majority of the trees were planted on January 19, 2011. Bare-root trees were planted directly
after transportation from the nursery’s sawdust box. HBOK 32 and HBOK 10 were planted on
April 25, 2011 as potted trees. At the time of planting, trees were headed at 36 inches. Trees that
had not reached heading height were left alone and allowed to grow through 2011 then headed at
36 inches in the following dormant season. Measurements for 2016 are not available.
RESULTS AND DISCUSSION
Butte County trunk cross sectional area (TCSA) measurements are shown in Figure 1 with Lovell,
M30, Viking, Atlas and 29C having the greater TCSA values. For the Yuba location (Figure 2),
M40, 29C, K86, Lovell, Rootpac-R, HBOK50, M30, Atlas and Viking were the largest in TCSA
and did not differ statistically.
Figure 1. 2016 Trunk cross sectional area (TCSA in cm2) for the Butte County rootstock
experiment. TCSA measured 12 inches above the graft union. K1=Krymsk 1, emp= Empyrean 2,
cit = Citation, k86 = Krymsk 86, lov = lovell, vik = Viking, atl = Atlas 29c = Myro 29c
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Figure 2. 2016 Trunk cross sectional area (TCSA in cm2) for the Yuba County rootstock
experiment. TCSA measured 12 inches above the soil level. K1=Krymsk 1, Rpac-R = Rootpac-
R, cit = Citation, k86 = Krymsk 86, lov = lovell, vik = Viking, atl = Atlas 29c = Myro 29c
Figure 3. Comparison of trunk size between the Butte and Yuba rootstock experiments. TCSA in
Butte TCSA measured 12 inches above the graft union and 12 inches above soil surface in Yuba.
K1=Krymsk 1, emp= Empyrean 2, cit = Citation, k86 = Krymsk 86, Rpac-R = Rootpac-R, lov =
lovell, vik = Viking, atl = Atlas 29c = Myro 29c
0
20
40
60
80
100
120
TCSA
cm
2
Rootstock
2016 Butte and Yuba TCSA cm2 Blue = ButteOrange = Yuba
28
Trees on nearly all rootstocks in the Butte experiment had larger TCSA than the Yuba trees (
Figure 3). The one exception was the Hbok 50 rootstock which was slightly larger at the Yuba
location. Empyrean 2 is not planted at the Yuba site and Rootpac-R is not planted at the Butte site
so those comparisons are not available. TCSA differences between rootstocks statistically separate
out better in the Butte location compared to the Yuba location but there is a great deal of overlap
between groups. Larger trees and more differences between rootstocks may be attributable to
different irrigation management at the two locations. The Butte orchard is drip irrigated compared
to micro sprinkler irrigation at the Yuba site.
Yield, dry ratio and TCSA for the Butte site are shown in Table 1. Dry ratio varied from 2.71 for
M40 to 3.18 for Empyrean 2. Although some values showed statistical separation, there were not
huge differences in the dry ratios suggesting that sugar accumulations were fairly good between
the rootstocks.
2016 TCSA, Yield and Dry Ratio for Butte
Rootstock TCSA cm2 Dry lbs/tree
dry ratio
Krymsk 1 46.01 a 20.74 d 2.88 ab
Hbok 50 56.07 ab 6.62 a 2.93 bc
M58 56.34 ab 16.41 cd 2.81 ab
Empyrean2 58.97 abc 14.78 bc 3.18 d
Citation 66.52 bcd 15.95 cd 3.1 cd
Krymsk 86 73.19 cde 19.14 cd 2.9 abc
Myrobalan 73.37 cde 5.57 a 2.79 ab
M2624 75.22 def 6.87 a 2.78 ab
M40 84.69 efg 5.87 a 2.71 a
Lovell 89.17 fgh 10.04 ab 2.81 ab
M30 92.45 gh 17.5 cd 2.84 ab
Viking 97.39 ghi 10.02 ab 2.93 bc
Atlas 101.38 hi 8.13 a 2.89 ab
Myro 29c 111.55 i 8.55 a 2.76 ab
Table 1. 2016 Trunk cross sectional area (cm2), dry yield (pounds per tree) and dry ratio of the
Butte County rootstock experiment. Harvest data compliments of Sunsweet Inc. TCSA measured
12 inches above the graft union.
Comparing TCSA to dry yield (Table 1), 29c had the largest TCSA at 111.55 cm2 with one of the
lowest individual tree dry yields at 8.55 pounds per tree. In contrast, Krymsk 1 was the smallest
tree with a TCSA at 46.01 cm2 and the largest yield at 20.74 dry pounds per tree. For the 2016
season, bloom dates, weather conditions and/or bee activity at the Butte location are likely
responsible. With the exception of Hbok 50, rootstocks that imparted later full bloom dates
appeared to set better crops. M40 had an 80% full bloom date on 3/9 with a dry crop load of 5.87
29
dry pounds per tree compared to Krymsk 1 with an 80% full bloom date on 3/14 and a crop load
of 20.74 dry pounds per tree. Bee flight activity (Figure 4) was relatively good during late bloom
with 5 hours on March 14 and 5 hours on March 15. Hbok 50 is a weaker rootstock and may not
have set well regardless of bloom conditions.
Figure 4. 2016 Bloom conditions, bloom dates and dry crop yield (lbs./tree) for the Butte County
rootstock experiment.
30
Rootstock Pedigree (scientific) Pedigree (Common) Other names
Trial Interest to CA
Atlas P. persica (Nemaguard) x (Prunusdulcis x Prunus blierianna)
Nemagaurd x(almond x (apricot x plum))
Grower Bac canker resistant?
Viking P.persica x (P. amygdalus x P.blireiana (P.ceresifera x P.Mume)
Nemagaurd x(almond x (apricot x plum))
Grower Bac canker resistant?
Citation Prunus salicina x Prunus persica Red Beaut plum x peach 4-G-816 Grower
Empyrean 2
Prunus domestica European prune (OP seedling of 'Imperial Epineuse')
Penta Grower small tree
HBOK 50 Prunus persica Harrow Blood X Okinawa Grower nematode resistant?
Krymsk 1 Prunus tomentosa x Prunus cerasifera Plum x plum VVA1 Grower grown in Europe
Krymsk 86 Prunus cerasifera x Prunus spersica Plum/peach hybrid Kuban 86 Grower anchorage
M30 Prunus cerasifera x Prunus munsoniana Plum x wild plum Grower
M40 Prunus cerasifera x Prunus munsoniana Plum x wild plum Grower Less suckering
M58 Prunus cerasifera x Prunus munsoniana Plum x wild plum Grower smaller tree?
Myrobalan seedling
Prunus cerasifera Myrobalan seedlings Grower control
Rootpack R
Prunus cerasifera x prunus dulcis Plum/almond hybrid Replantpac Grower
Lovell Prunus persica peach seedling Grower/Wolfskill
control
M2624 Prunus cerasifera x Prunus munsoniana Plum x wild plum Marianna 2624
Grower/Wolfskill
control
Myro 29C Prunus cerasifera Myrobalan clone Grower/Wolfskill
control
Controller 7 Prunus persica Harrow Blood X Okinawa HBOCK 32 Wolfskill
Controller 8 Prunus persica Harrow Blood X Okinawa HBOCK 10 Wolfskill
Controller 9 Prunus salicina X Prunus persica Plum/peach hybrid P30-135 Wolfskill
Empyrean 1
Prunus persica x P. davidana Peach x Chinese wild peach. Venice, Italy
Barrier Wolfskill
Empyrean 3
Prunus domestica European prune (seedling of Regina Claudia Verde)
Tetra Wolfskill sensitive to ORF
Fortuna Prunus cerasifera x Prunus persica Plum/peach hybrid Wolfskill
HBOCK 27 Prunus persica Harrow Blood X Okinawa Wolfskill
Imperial California
Prunus domestica plum R/S Italian Origin Wolfskill
Ishtara (P. cerasifera x P.salicina)X (P. cerasifera x P. persica)
peach/plum hybrid (complex hybrid selected by INRA)
Ferciana Wolfskill
Krymsk 2 Prunus incana x Prunus tomentosa wild cherry x Manchu cherry VSV 1 Wolfskill
Krymsk 99 P. besseyi x P. salicinaPlum/Plum hybrid (Sand cherry x Japanese plum)
Wolfskill
Own rooted French
Prunus domestica European prune Wolfskill
31
Puente Prunus cerasifera Plum (from Spain) Adara Wolfskill
Sharpe Prunus angustifolia x unknown plum Plum x plum Wolfskill
Speaker No idea scientific name Plum/peach hybrid Spicer Wolfskill
WRM #2 Prunus cerasifera Red leaf myrobalan type (found growing in water)
Wolfskill
Figure 5. Scientific and common pedigree for the Butte,Yuba and Wolfskill prune rootstock
experiments.
32
2016 FIELD EVALUATION OF PRUNE ROOTSTOCKS AT WOLFSKILL Katherine Pope, Richard Buchner, Franz Niederholzer, Ted DeJong and Sarah Castro
PROBLEM AND ITS SIGNIFICANCE
The California Prune Industry has historically utilized five rootstocks, Myrobalan seedling, Myro
29C, Marianna 2624, Lovell Peach and some M40. The last statewide organized prune rootstock
effort was the “M” series rootstock plots planted in 1987 (Vina Monastery 3/20/87). Since the
conclusion of that experiment many more potential rootstocks for prune have been identified.
Three trials were planted in 2011 - two replicated experiments and one non-replicated observation
experiment. Maintenance for the replicated trials is paid for by grower trial hosts. The non-
replicated trial is at Wolfskill and requires funding for on-going management.
OBJECTIVES
Evaluate promising rootstocks potentially valuable for California Prune production.
PLANS AND PROCEDURES
A satellite experiment of prune rootstocks was planted at the UC Wolfskill experimental orchard
in Winters, California. The plot contains 15 experimental rootstocks and 3 standard rootstocks
(Marianna 2624, Lovell, and Myro 29C) nursery budded to ‘Improved French’ (Table 1). This
experiment provides an initial evaluation of possible rootstocks that have previously not been tried
with prune or have had very little field testing.
The experiment is planted with at least 5 trees of each rootstock and is non-replicated, which limits
statistical analysis. The goal was to get a first look at how these rootstocks performed with
‘Improved French’ scions and identify any defects before commercial planting. ‘Improved French’
on its own root differs from the others in that trees were grown in the nursery for two years. Own
rooted trees do have a graft union because ‘Improved French’ was budded on top. Trees were
planted 17 feet across the row and 14 feet down the row, which would result in approximately 183
trees per acre.
The Wolfskill site was previously planted to peaches, removed in 2008 and the field left fallow for
3 years with annual winter wheat. The Yolo County soil survey describes the soil as Yolo loam.
Nematode samples were taken at four locations within the field at approximately an 18 inch depth,
and combined for nematode evaluation (8/29/11). One liter of soil contained, 50 Lesion
(Pratylenchus sp.), 50 Pin (Pratylenchus sp.), and 30 Dagger (Xiphinema americanum). There
were not enough nematodes to identify the species of either Lesion or Pin nematodes.
The majority of the trees were planted on January 19, 2011. Bare-root trees were planted directly
after transportation from the nurseries sawdust box. HBOK 32 and HBOK 10 were potted trees
planted on April 25, 2011. At the time of planting, trees were headed at 36 inches. Trees that had
33
not reached heading height were left alone and allowed to grow through 2011 then headed at 36
inches in the following dormant season.
Fruit set in 2016 was too low to justify harvest. An estimate was made of the number of fruit on
each tree on August 19th. Trunk circumference was measured on December 20th at 12” above the
soil line. Anchorage as measured by angle of tree lean (not pushed) was also measured on that
date.
RESULTS AND DISCUSSION
Because this trial is not replicated, mean separation, also referred to as ANOVA, has not been
conducted. Though we cannot say statically how rootstocks differ or rank, we can make initial
observations. Averages given are for five trees.
At Wolfskill, fruit set varied widely by rootstock, ranging from 32 to 157 fruit per tree on average
(Figure 1, Table 2). Controller 7 and Lovell had the lowest fruit set. Krymsk 99, Myro 29C and
Empyrean 1 had the highest fruit set. Bloom timing data for 2016 was collected but lost. Based on
previous years of data and memory of observations, there were differences in bloom timing, and
it is a reasonable to hypothesize that the difference in set was driven by differences in bloom timing
and thus bloom conditions.
Tree vigor, as measured by trunk circumference, ranged widely among rootstocks (Figure 2, Table
2). Note that size of trunk is also given in Table 2 as Trunk Cross-Sectional Area (TCSA), for
comparison with the Yuba and Tehama trials. Krymsk 2 produces the smallest trees so far, with
an average circumference on 10.7” at 12” above the soil line. Fortuna, WRM 2 and Empyrean 1
have produced the largest trees, with circumferences of 18.7”, 19.4” and 20.9”, respectively. A
number of rootstocks are similar in size to M2624. Lovell and Controller 9 have so far produced
similarly sized trees. Myro 29C and Puente have produced similarly sized trees.
Anchorage, as measured by degrees of tree lean, did not vary widely among rootstocks, with two
exceptions (Figure 2, Table 2). Generally, degrees of lean (without pushing) averaged between 0-
7°. The two exceptions were Fortuna, which averaged 10°, and Krymsk 99, which averaged 23°.
Degrees of lean have been overlayed on top of the trunk circumference data to show which trees
may be small because of poor root structure, making them poor candidates as size controlling
rootstocks.
34
Table 1. Rootstock name and pedigree.
Rootstock Species/ Hybrid Pedigree
Controller 7 (HBOK 32) Harrow Blood x Okinawa
Controller 8 (HBOK 10) Harrow Blood x Okinawa
Controller 9 (P30-135) P. salicina x P. persica
Empyrean 3 (Tetra) P. domestica
Empyrean 1 (Barrier) Peach x Chinese wild peach
Fortuna P. cerasifera x P. persica
HBOK 27 Harrow Blood x Okinawa
Imperial California Plum R/S Italian Origin
Ishtara (Ferciana) Peach/Plum hybrid
Krymsk 2 P. incanus x P. tomentosa
Krymsk 99 Plum/Peach hybrid
Lovell Peach seedling
M2624 Marianna 2624
Myro 29C Myrobalan
Own Rooted French Own Rooted
Puente (Adara) P. cerasifera
Speaker (Spicer) Plum/Peach hybrid
WRM 2 Red leaf myroblan type
Table 2. Fruit set, trunk circumference, trunk cross-sectional area and anchorage for 18
rootstocks. Numbers are average of five trees (except Puente, which has four trees).
Rootstock Fruit Set (# of
fruit/tree)
Trunk
Circumference
(inches, 12”
above soil line)
Trunk Cross-
Sectional
Area(TCSA)
(cm, 12" above
soil line)
Anchorage
(Degrees of
Lean from
Upright)
Krymsk 2 122 10.7 58.9 4
Controller 8 (HBOK 10) 99 13.2 89.8 6
HBOK 27 85 13.5 93.1 5
Speaker 86 13.5 93.1 6
Controller 7 (HBOK 32) 43 13.9 99.7 7
Ishtara 120 14.1 102.0 3
Krymsk 99 156 14.1 102.0 23
Empyrean 3 124 14.3 104.3 1
Imperial California 76 14.3 105.4 5
M2624 89 14.6 110.1 2
Own Root 118 14.8 112.5 6
Lovell 32 15.7 126.1 2
Controller 9 99 16.0 131.2 4
Myro 29C 157 16.9 147.1 1
Puente 96 17.3 154.1 4
Fortuna 145 18.7 180.3 10
35
WRM 2 116 19.4 194.2 4
Empyrean 1 156 20.9 223.5 4
Figure 1. Fruit set (average number of fruit per tree) estimated on August 19th, 2016.
020406080
100120140160180
Nu
mb
er o
f Fr
uit
Fruit Set
36
Figure 2. Trunk circumference and degrees of tree leaning measured December 20th, 2016.
0
5
10
15
20
25
0
5
10
15
20
25
Deg
rees
of
Lean
(N
ot
Pu
shed
)
Cir
cum
in In
ches
, 12
" A
bo
ve S
oil
Lin
eTrunk Circumference & Anchorage (Degrees of Leaning)
Trunk Circumference
Degrees of Lean
37
MANAGING HEAT AT BLOOM IN ‘FRENCH’ PRUNE, 2016
F. Niederholzer
R. Buchner
D. Lightle
K. Pope
L. Milliron
PROBLEM AND ITS SIGNIFICANCE
Excessive heat at bloom is linked to significantly reduced prune production in key California
growing regions in four of the last eleven years (2004, 2005, 2007, and 2014). Total grower
economic losses in Sutter and Yuba Counties – with 40% of the prune acres in the state -- were
in the range of $240 million for 2004, 2005, and 2007, based on county ag commissioners’ data.
Overall economic damage to the regional economy was probably 1.5x that loss -- $360 million.
As the probability of heat in March appears to be increasing (Rick Snyder, UCCE microclimate
specialist, personal communication), California prune growers must develop management
strategies to mitigate heat damage at bloom to remain economically viable.
Recent research results show that temperatures >75oF begin to negatively affect pollen tube
growth rate and viability, but research has not identified temperature thresholds for actual crop
damage.
OBJECTIVES
Determine bloom-time temperature thresholds above which crop damage occurs.
PROCEDURES
Sutter, Glenn and Tehama Counties:
In Tehama County, bloom timing and temperature/relative humidity were observed in three
orchards; one in Red Bluff, one in south Red Bluff and one in South Los Molinos. In Glenn
County, bloom and temperatures/relative humidity were tracked in two orchards east and south of
Orland. In Sutter County, bloom and temperature/relative humidity were tracked in three orchards
reaching from just east of the Sutter Buttes to 10 miles south of Yuba City.
Temperature and relative humidity sensors were placed in between trees down the tree row at 6-
8’ above the orchard floor (Figure 1). Sensors were not placed in tree canopies. Temperatures
and relative humidity in each block were continually recorded during bloom at all sites. Average
hourly temperatures are reported, not maximum temperature for the day.
Bloom progression was measured by counting open flowers on short branches at roughly 6’ height
38
around 3 trees in each orchard. Initial set was measured in May.
RESULTS AND DISCUSSION
Weather during the 2016 prune bloom in the Sacramento Valley was wet, windy and cool. Rain
fell for much of the bloom period (Figure 2) across the region. In the 10 days from March 5-14
in the Sutter County orchards, the highest maximum hourly average temperature was 65oF, with
the maximum temperature not reaching 60oF on five of those days. Very similar temperatures
were recorded in Glenn and Tehama Counties for the same time period.
As in the “heat damage” years of 2004, 2005, 2007, and/or 2014, small prune fruit developed and
then turned yellow and fell off the trees within 3-4 weeks of petal fall. Fruit set was very low,
with 2-12% set measured (Table 2).
CONCLUSIONS
It is difficult to determine what specific weather condition(s) – cold temperatures, rain and/or
wind -- caused the very poor prune crop set in the orchard studied this year (2016). The
development of small fruit followed by yellowing and drop is consistent with pollinization but
not fertilization – the flowers received pollen, but the ovule was not fertilized. (Unpollinated
flowers are reported to drop without any fruit development.)
Pollen tube growth is slow under low temperatures (50-65oF) compared to higher temperatures
(65-80oF). Given the extended period of cool weather from March 3-13, that encompassed full
bloom and the timing immediately following full bloom, we speculate that cool weather slowed
pollen tube growth to the degree that the ovule was no longer viable when the pollen tube arrived
at the base of the style.
Financial value of this research: Prune crop loss in the Sacramento Valley in 2016 was at best
estimate, at least 1.5 dry tons/acre across 90% of the acres in the region (37,000 acres using 2015
crop report data). At $2000/dried ton, that loss = $111M in farm gate value before the multiplier
effect on local economies. This research, developing information to allow growers to more
accurately predict crop risk at bloom, will help growers use management tools to minimize
damage from unseasonable weather at bloom.
39
Table 1. Average prune fruit set and full bloom dates for individual orchards plus maximum
orchard temperatures (hourly average of measurements taken every 5 minutes) during bloom in
Sutter, Glenn and Tehama Counties, 2016. Measurable rain fell in each county on each day
where the daily high temperature appears in bold, blue font.
Mar 4 Mar 5 Mar 6 Mar 7 Mar 8 Mar 9 Mar 10 Mar 11 Mar 12 Mar 13 Mar 14 Mar 15 Mar 16
Tehama max
temp
59 61 54 60 60 55 53 55 63 67 59 68 76
Glenn max
temp 63 62 59 60 54 57 57 55 53 57 63 67 76
Sutter max
temp 65 63 61 57 56 62 59 58 56 56 65 67 72
Tehama % set
3 12 6
Glenn % set
2
Sutter % set
3 4,10 3
40
Figure 1. A weather station with radiation shield containing one temperature/relative humidity
sensor (solid circle) and data logger (dashed circle) in the south Yuba City orchard. February,
2016.
41
Figure 2. Bloom time temperatures (hourly average) and daily % bloom progression for three
orchards in Sutter. 2016
0
20
40
60
80
100
120
30
40
50
60
70
80
90
25-Feb 1-Mar 6-Mar 11-Mar 16-Mar 21-Mar 26-Mar
% B
loo
m
Ave
rage
ho
url
y te
mp
(d
eg
F)
Avg: Temp, °F
%bloom southYuba City%bloom just S ofHwy 20%bloom N YubaCity
4-7" of rain in the southSacramento Valley.
42
BLOOM AND POSTBLOOM PRUNE MANAGEMENT PRACTICES FOR MORE
CONSISTENT PRODUCTION OF HIGH QUALITY PRUNES.
F. Niederholzer
L. Milliron
PROBLEM AND ITS SIGNIFICANCE
Inconsistent cropping (yield/acre) is a major challenge facing the dried plum industry in California.
This is a year to year phenomenon, largely due or linked with weather conditions at bloom. Hot
weather for at least two consecutive days at full bloom (83+oF) coincided with or caused state-
wide crop failure in 2004 and regional failures in 2005, 2007, 2014 and 2015. In 2016, more than
a week of consistent wet and cool weather produced a crop failure in the Sacramento Valley. While
under tree sprinkler irrigation can decrease daytime orchard temperatures by 1-2oF and so may
help growers avoid losses under conditions just above the damage threshold (83-84oF), no
materials or practices have been proven to avoid crop loss at bloom when higher temperatures
(>84oF) or extended wet/cold conditions occur.
Warm to moderate temperatures (daytime highs of 60-80oF) at bloom in many years coincided
with excessive set and over production of small, lower quality fruit -- unless growers shaker thin
at reference date. However, this practice can disproportionately remove larger fruit and damage
older trees and occurs after 4-6 weeks of fruit development. The earliest possible thinning – bloom
thinning – has been shown in peach to deliver larger fruit size and total crop at harvest compared
to later thinning. The same results should follow in prune. Field research with GA-3 showed some
promise in reducing flower number the year after application, but research results are not
consistent. This material is also not currently labeled for prunes for this purpose. Flower thinning
by hand is not feasible and chemical blossom thinning with caustic materials remains largely
untested in prunes.
Objectives:
o Determine materials and practices that either improve or reduce fruit set depending
on the bloom temperature in the orchard to allow consistent production of large,
high quality prunes.
PROCEDURES
Spray treatments were applied in a young, vigorous high production site in south Sutter County.
The orchard is planted 16’ x 20’ on M29C rootstock and flood irrigated until the 2016 season,
when a microjet irrigation system was installed.
In March, 2015, a randomized complete block design orchard experiment was established.
Individual trees were blocked by trunk diameter -- measured at 12” above the soil. In 2015, four
trees, one from each block, were treated with one of seven treatments (Table 1). Surround® WP
and oil were applied to delay and accelerate bloom timing, respectively. Solubor®, a soluble boron
43
source that is reported to reduce fruit set when applied at full bloom (Patrick Brown, personal
communication). Thiosulfate, formulated as ammonium thiosulfate (ATS) or potassium
thiosulfate (KTS), is reported to be an effective bloom thinner in trials in pome and stone fruit.
Due to possible variability in ammonia content of fertilizer grade ATS, KTS was selected for use
in this trial.
Table 1. Treatments and timing applied in 2015.
Material Timing
Untreated control ---
35 & 25 lbs. Surround® WP/acre Jan 22 & Feb 12
4 gallons of oil/acre Dormant (Jan 22)
2 lbs Solubor®/acre 80% bloom (March 15)
4 lbs Solubor®/acre 80% bloom (March 15)
1% (v/v) potassium thiosulfate (KTS) 25% bloom & 80% bloom
(March 12 & 15)
2% (v/v) potassium thiosulfate (KTS) 25% bloom & 80% bloom
(March 12 & 15)
Treatments were applied using a gas-powered, backpack sprayer (Stihl® SR420; Stihl USA,
Virginia Beach, VA) at a volume equivalent to 200 gallons per acre. Treatment materials were
weighed out for individual trees to insure uniform application across treatments. Applications
were made in the early morning—6:30-9:30 AM – before bees were active.
At commercial harvest, individual tree dry fruit yields were determined. All fresh fruit per tree
were weighed after shaker harvesting, commercially drying a four pound subsample and using
the dry away ratio to calculate dry fruit yield per tree. Each fruit in the subsample was weighed
dry to determine fruit size distribution and from those data the percentage of A, B, C, and D
screen as well as percent undersized fruit were determined. Treatment differences in dry fruit
yield per tree (multiplied by 136 trees per acre to provide yield in tons/acre) and percent screen
sizes were tested using Statgraphics Centurion XVII (Statpoint Technologies, Inc., Warrenton,
VA) software package using the General Linear Model procedure with mean separation tested by
the Tukey HSD method.
In February, 2016, spur samples were taken from control and KTS treated trees and starch and
total non-structural carbohydrates determined.
In 2016, a fifth block was added to allow five reps per treatment, boron treatments were dropped,
the KTS treatments expanded and a Retain® treatment added (Table 2). Retain®, a commercial
formulation of aviglycine hydrochloride (AVG), is a plant growth regulator that inhibits a
precursor to ethylene, if applied before the ethylene generating process begins.
44
Table 1. Treatments and timing applied in 2016.
Material 2015 season treatment Timing
Untreated control Unthinned ---
Untreated control Thinned with KTS ---
1% (v/v) potassium thiosulfate (KTS) Unthinned 25% bloom & 80% bloom
(March 8 & 14)
1.5% (v/v) potassium thiosulfate (KTS) Unthinned 25% bloom & 80% bloom
(March 8 & 14)
2% (v/v) potassium thiosulfate (KTS) Unthinned 25% bloom & 80% bloom
(March 8 & 14)
1.5% (v/v) potassium thiosulfate (KTS) Thinned with KTS 25% bloom & 80% bloom
(March 8 & 14)
1.5% (v/v) potassium thiosulfate (KTS) Unthinned 25% bloom (March 8)
1.5% (v/v) potassium thiosulfate (KTS) Unthinned 80% bloom (March 14)
Retain® (333 g/acre) Unthinned 25% bloom (March 8)
Application was again by gas-powered, backpack sprayer (Stihl 420) at a volume equivalent to
200 gallons per acre. On both application dates, treatments went out between 3-6 PM.
Yield and statistical analysis were determined as in 2015.
RESULTS AND DISCUSSION
2015
Fresh fruit weight per tree (p=0.028; r2=24.9) and dry fruit weight per tree (p=0.007; r2=34.4)
were both positively correlated with trunk circumference, supporting the use of trunk
circumference as the blocking factor.
Due to an error at harvest dry fruit data from 8 trees out of a total 28 study trees were not taken.
Fortunately, dry fruit data from three treatment trees, from all but one treatment (2 lbs
Solubor®/acre), were sufficient for statistical analysis.
Fresh fruit yield (n=4) of trees treated with either rate of Solubor® at bloom, prebloom sprays
(Surround® or oil) or 1% KTS at bloom were not significantly different from control yield (Table
3). The 2% rate of KTS produced less fresh fruit than the control or the 2 lb/acre rate of
Solubor® (Table 2). For fresh fruit production, blocking by trunk circumference was not a
significant factor (p=0.34).
Total dry fruit yield (n=3) differed significantly between the blocks (p=0.03), but not between
any of the treatments (p=0.13). Due to decreased fruit number and an increase in average fruit
size (data not presented), the 1 or 2% KTS at bloom treatments produced significantly more high
value prunes (<80 ct/lb = A & B screen) than the control, 4 lbs Solubor®, or dormant Surround®
treatment. The dormant oil treated trees produced numerically, but not statistically, less large
45
fruit than the KTS treated trees (Table 3). The oil treated trees bloomed 4-5 days ahead of the
control, Solubor® or Surround® treated trees and slightly different bloom weather between those
dates may have influenced eventual fruit size through a difference in fruit set and final crop load
or other factor.
Neither starch (p=0.88) nor total nonstructural carbohydrate (p=0.45) levels differed significantly
between KTS thinned or control trees in February, 2016. Data not presented.
2016
Wet, cool and windy bloom weather produced a very light crop for all thinning treatments and
the unthinned, untreated control (Table 4).
Both block (p=0.049) and treatment (p=0.0003) effects were a significant influence on fresh fruit
yield per acre, with the major difference between treatments derived from comparing the
untreated control (but thinned the previous year), to all the current year thinning treatments
(Table 4).
Dry weight per acre treatment analyses were split into two groups – 1) thinning treatments plus
unthinned control and 2) both control treatments plus Retain® treatment. Thinning treatments
did not significantly affect crop yield compared to the untreated control that was not thinned in
2015 (Table 4). The control trees thinned in 2015 produced significantly more dried fruit than
the control trees not thinned the previous year (Table 4). At bloom, the trees thinned the
previous year appeared to have more flowers than the trees not thinned the previous year.
Retain® increased yield in some treated trees compared to untreated controls (Figure 1), but
yield varied between treated trees (blocks) and so was not statistically improved compared to
control trees unthinned the previous year – trees that we assume entered 2016 bloom with a
similar flower bud count as the Retain® treated trees. Lower yielding ReTain® treated trees were
larger and may have bloomed earlier than the smaller trees (Niederholzer observation). We
speculate that the uneven yield from the ReTain® treated trees (Figure 1) was due to a range of
bloom conditions at spraying. The ReTain® label for sweet cherries recommends spraying
between popcorn and first bloom. It was raining during the early bloom in the study orchard and
so early sprays were not possible.
CONCLUSIONS
Under good fruit set conditions, bloom sprays of KTS can significantly improve yield of large,
high value prune fruit (Table 3). However, further work is needed to refine the use of KTS at
prune bloom. Research based programs regarding if, when and how to use KTS at prune bloom
are not yet developed.
At the rates used in this study (2 lbs/acre or 4 lbs/acre Solubor®), boron does not appear to hold
promise as a bloom thinner in prunes.
Further work with Retain® at bloom in years with poor fruit set, especially warm bloom weather,
is warranted. Perhaps greenhouse work with FasTrack prunes developed at USDA Kearneysville
46
could be a way to rapidly evaluate the value of this product against high temps at bloom.
This research shows there is potential to improve prune production consistency with active crop
load management.
Table 3. Average fresh fruit yield/tree (n=4), dry fruit yield/acre (n=3), dry fruit yield (larger
than 80 ct/lb) per acre (n=3) by treatment. 2015. Values in each column followed by the same
letter are not statistically different with 95% confidence using the Tukey HSD method of means
separation.
Treatment Fresh fruit
(tons/acre)
Dry fruit
(tons/acre)
Dry fruit
80 ct/lb
(tons/acre)
2% KTS (25 & 80% bloom) 7.88 a 2.92 a 2.79 a
1% KTS (25 & 80% bloom) 9.24 ab 3.18 a 2.26 a
4% oil (dormant) 11.08 ab 3.98 a 1.16 ab
4 lbs Solubor®/acre 11.87 ab 3.92 a 0.11 b
Surround® WP (2x dormant) 12.38 ab 4.21 a 0.21 b
Untreated control 13.27 b 4.56 a 0.04 b
2 lbs Solubor®/acre* 13.50 b 4.82 0.62
*n=2
Table 4. Average fresh fruit yield/acre, dry fruit yield/acre, dry fruit yield (larger than 80 ct/lb)
per acre by treatment. 2016. Values in each column followed by the same letter are not
statistically different with 95% confidence using the Tukey HSD method of means separation.
Treatment (with spray timing 2015 season
treatment
Fresh fruit
(tons/acre)*
Dry fruit
(tons/acre)*
1.5% KTS (25 & 80% bloom) Unthinned 0.52 a a 0.20
2% KTS (25 & 80% bloom) Unthinned 0.52 a a 0.20
1.5% KTS (80% bloom) Unthinned 0.81 ab a 0.29
1.5% KTS (25% bloom) Unthinned 0.82 ab a 0.32
1% KTS (25 & 80% bloom) Unthinned 0.86 ab a 0.32
1.5% KTS (25 & 80% bloom) Thinned with KTS 1.35 ab a 0.45
Untreated control Unthinned 1.15 abc a 0.44 y
Retain® (25% bloom) Unthinned 3.41 bc 1.36 yz
Untreated control Thinned with KTS 4.62 c 1.74 z
*Fresh weight and dry weight (thinned treatments + unthinned, untreated control) results were
log transformed prior to analysis. Untransformed values are presented.
47
Figure 1. Dried fruit yield for all untreated or ReTain® treated trees. 2x white = untreated trees
thinned the year before, white = untreated trees not thinned the year before, and Org= ReTain®
treated trees. Data presented on a dry ton/acre basis.
2x white Org White
Treatment
0
0.4
0.8
1.2
1.6
2
2.4
Yie
ld p
er
acre
(d
ry w
t)
48
USE OF COVER CROPS TO MITIGATE HEAT AT BLOOM
Dani Lightle & Franz Niederholzer
OBJECTIVE
Evaluate potential of cover crops for reduction of orchard temperatures during bloom and
increasing fruit set.
PROCEDURE
Two orchards are being used for this study. One is located near Orland, CA (Glenn Co.) and the
other near Yuba City (Sutter Co.). The study design was replicated in each of these orchards. In
each orchard, there are 4 experimental replicates and 4 control replicates. Each replicate contains
13 trees down the row and spans 4 middles (approximately ½ acre for each experimental unit).
The control treatment in these studies is a short (mowed) resident vegetation ground cover. The
experimental treatment is a tall cover crop. The cover crop mix selected was the Mustard Mix
provided by Project Apis m. The composition of the Mustard Mix is:
35% Canola
20% Daikon Radish
15% Bracco White Mustard
15% Nemfix Mustard
15% Common Yellow Mustard
The cover crop in both orchards was planted during the week of November 14th, 2016. The
Glenn County orchard was planted with a no-till drill at a rate of 10lbs/ac. The Sutter County
orchard was broadcast at 12 lbs/acre after discing, and then lightly cultivated to incorporate the
seed.
Prior to bloom (March 2017), hobo temperature units will be placed at 5 ft. and 12 ft. heights in
the tree row of each replicate to monitor temperature and humidity. The percent fruit set will be
tracked by flagging and monitoring the number of blossoms and fruit on individual branches in
each plot.
RESULTS AND CONCLUSIONS
At the time of this report, the cover crops in both orchards have germinated. Data will be
collected in March 2017.
49
Photo 1. No till drill used to seed the Glenn County prune orchard cover crop.
Photo 2. Cover crop planting, Glenn County, November 2016.
50
Photo 3. Germination of cover crop at the Sutter county site, December 2016.
BUDGET SUMMARY
Very few funds have been spent so far on this project. The bulk of the expenditures will
occur during the prune bloom period in March 2017. The expenses at this time will include
salary for counting blossoms, travel to field sites, and purchase of hobo temperature units.
51
DEVELOPMENT OF NUTRIENT MANAGEMENT TOOLS FOR DRIED PLUMS
(Year 3)
Project No:
Project Leader: Patrick H. Brown, Department of Plant Sciences, UC Davis. MS#2, One
Shields Avenue, Davis CA (530) 752-0929, Fax (530) 752-8502, [email protected]
Project Cooperators: Franz J.A. Niederholzer. University of California Cooperative Extension,
Sutter-Yuba Counties, 142A Garden Highway, Yuba City, CA 95991-5512, (530) 822-7515,
Amber Bullard, MS Student, Department of Plant Sciences, UC Davis. MS#2, One Shields
Avenue, Davis, CA 95616, [email protected]
Objectives:
• To investigate the influence of yield, plant nitrogen status and fruit size on
nitrogen removal by prune fruits.
• To investigate the seasonal pattern of nitrogen accumulation in prune fruit.
• To develop early-season leaf sampling protocols and interpretation methods.
Interpretive Summary
In California, there are 58,000 acres bearing orchards of dried plums. This makes up a
significant area of land, which requires annual addition of nitrogen fertilizers to maintain high
yields and produce quality. Currently, N management in prune is based on leaf sampling and
analysis in summer, which is to late for N adjustment during the season. Further no guidelines
are available to inform growers of the time and rate of fertilizer application. Due to the lack of N
management support tools, there is potential for overuse of N fertilizer that could leach below
root zone to ground water. There is increasing concern for ground water quality and the
California Water Board is working on legislation to reduce ground water nitrate pollution,
which demands environmental stewardship from the farmers. To provide better N management
and monitoring tools to growers to guide the rate and time of fertilizer application and in season
monitoring of tree N status, this experiment was continued during 2015. Influence of yield, tree
nitrogen status and fruit size on nitrogen removal by prune fruits was monitored in the organic
orchard by taking fruit samples at harvest, categorizing the fruits by size and determining N
52
concentration. Seasonal accumulation of N in fruits was developed by monitoring N
concentration and biomass accumulation in fruits. N removal from the orchard was calculated by
monitoring trees for yield and nutrient concentration. Leaf samples were collected to relate N
status with N export in fruit. Leaf samples from orchards at different sites were collected in July
to understand the spatial and temporal variability of tree N status. Perennial trees store a large
quantity of N in the perennial biomass it takes 1-2 years for the treatment effect to establish. The
information from this project will be used to develop N management protocol for prune, based
on N budget and in-season monitoring of leaf N.
Materials and Methods
Fruit load and N status influence on N removal (Objective 1)
There was significant variation between trees in the same orchard studied in 2014. In 2015 a
more uniform organic orchard was selected to carry out this experiment. Thirty trees in the
orchard were randomly selected and labeled in April. Trunk cross-sectional area (TCSA)
measured at one foot above the soil surface. Three nitrogen fertilization treatments were applied
in order to generate a range of leaf nitrogen status. N – treatments were applied in 2015 and 2016
as follows: 1) Low Nitrogen (LN): 0 kg N tree-1, 2) Medium Nitrogen (MN): 0.23 kg N tree-1
equivalent to 104 kg N ha-1 and 3) High Nitrogen (HN): 0.45 kg N tree-1 equivalent to 204 kg N
ha-1. Nitrogen fertilizer was manually applied as organic nitrogen fertilizer. Each treatment was
replicated on 10 trees.
A composite leaf sample was collected in April and individual leaf samples were collected in
2015 and 2016 from every tree at the end of July. Samples consisted of one hundred non–fruiting
spur leaves taken from exposed mid-canopy positions. Leaves were washed with deionized water
and dried at 60°C and then ground to pass a 30-mesh screen using Wiley Mill. The samples were
analyzed for N, P and K in UC ANR Lab.
At harvest (August), yield of individual trees were determined. In 2015 a subsample of 300
fruits was fresh weighted and sized (small fruits (<17 g fruit-1), medium (between 17 and 25 g
fruit-1), and large (> 25 g fruit-1)). 4 lbs. samples were dried in a commercial drying facility to
~18 % moisture content to obtain the fruit hydration ratio. One sub-sample of 20 fruits by size
range was selected on each tree (90 samples), weighted and carried to the laboratory to be
53
processed. These samples were separated and weighed as mesocarp, endocarp, and seed, and
then ground for analysis. Nitrogen concentration was determined both in the mesocarp and in the
endocarp & seed. The methodology changed slightly fro 2016 due o the poor yield. A subsample
of fruits was collected and of this, 40 fruits were used to determine the size distribution on each
tree. Fruits were not separated into small medium and large sized fruits for processing. If there
was not enough fruit for both the 4 lbs. sample and the 40 fruit subsample, the 4 lbs. sample was
not taken.
Seasonal accumulation of nitrogen in fruit (Objective 2)
In the same orchard used on the Objective 1, eight independent trees were sampled nine
times during the 2015 season (approximately 14 day intervals). The experiment was designed
with four subsamples (two trees per subsample). During the first two sampling dates we
harvested 50 fruits, as fruits were small and 20 fruits on the subsequent sampling dates. In 2016,
fruit samples were taken from the RAI orchard, a conventionally managed orchard with higher N
inputs. Due to poor yield, 42 trees were sampled ten times at approximately 14-day intervals.
These trees included 6 subsamples of 8 individual trees and 20 fruit were collected for each
subsample. For analysis at UC ANR, 2 subsamples were combined for a total of 3 samples per
sampling date for budgetary reasons. For example, at each sampling date subsamples 1 and 2, 3
and 4, and 5 and 6 were combined for N concentration analysis. Fruit samples were weighed in
the field and dried in the laboratory. Biomass of the dried fruits was determined after drying in
oven at 60°C. N concentration in fruits in each sample dates were determined in the UC ANR
Lab.
Prediction of July leaf N from early spring leaf N (Objective 3)
Leaf samples were collected from 6 orchards from different sites selected to represent a range
of typical prune production practices in April and July 2014, 2015, and 2016. These orchards
were located in the Yuba City area and are as follows: Everest East, Everest West, Filter Young,
Hops, Organic, and RAI. In 2014 and 2015, orchard leaf samples were taken from 30 individual
trees in 6 orchards. During April a composite sample of the 30 trees was taken for analysis and in
July individual trees were analyzed. In 2016, 30 individual trees were sampled for a composite
sample in both April and July. Leaf samples consisted of taking 8 non-fruiting spurs from each
54
individual tree for the composite sample. If an individual tree was analyzed then 25 individual
non-fruiting spurs were collected. Leaves were washed with deionized water to remove
contaminants and dried at 60oC and then ground to pass a 30-mesh screen using a Wiley Mill.
Samples collected were analyzed for N, P and K in the UC ANR Lab. N was determined by
DUMAS combustion (Bremner & Mulvaney, 1982) and all remaining nutrients were determined
through nitric acid digestion (Zarcinas et al., 1987).
Results
Fruit load and N status influence on N removal (Objective 1)
In 2015, the average N removal from the orchard in harvested fruits ranged from 5.48 to 5.80
kg per ton dry yield, with no significant difference in N export between treatments (LN, MN, or
HN). Nitrogen concentration by the fruit size (S, M, or L) was only significantly different in the
high N treatment where small fruits removed significantly more N compared to large and
medium fruits as a percentage of dry weight (Figure 1). Since there was very low yield in 2016,
we could not confirm these results the second year.
N concentration in the various parts of the fruit varied with fruit size. At harvest, the N
concentration was significantly higher within small sized fruits compared to medium and large (p
value of 0.00044 and 0.00067). The highest total amount of N was accumulated occurred in
medium sized fruits; there was not a significant difference among N treatments with a p value of
0.30564. This is also due to the fact that medium sized fruits constituted 53% of tree yield in
2015.
Further analysis of the N treatments, effects on the fruit revealed that the medium sized fruit
endocarp and seed N concentrations were higher under low N treatment than under High N
treatment. In small sized fruit endocarp and seed N concentrations were lower under High N
treatment than under low N treatment. After accounting for fruit size distribution and tree yield,
there was however no significant difference in the total amount of N accumulated within each
fruit size in the seed plus endocarp.
There were significantly higher concentrations of N in the prune mesocarp in small sized
fruit compared to medium and large. However there was no significant difference between LN
and HN treatments in mesocarp N concentrations. Within the LN treatment, there was a
55
significantly higher concentration of N within the small sized fruit mesocarp relative to medium
and large sized fruits. There were no significant differences in mesocarp N % between medium
and large sized fruits in addition to between LN and HN treatments.
There were no statistical differences in N removal depending on N application rates during
2015 or 2016 at a significance level of 0.05 (Figure 1). The average N removals for 2015 and
2016 were 5.03 and 5.35, 5.44 and 5.30, and 4.80 and 5.39 kg of N per dry ton for LN, MN, and
HN, respectively. In the same orchard, there were no statistical differences between April or July
leaf N percentage among N fertilizer application rates during 2016 (Figure 3).
The relationship between leaf and fruit %N is shown in Figure 4; the trend line accounted for
20% (R squared value) of the variability within all treatments. Within all N treatments, the July
leaf %N varied from 1.61 (Low N) to 1.95% N (High N). Fruit %N varied from 0.39 (Low N) to
0.59% N (Low N).
Figure 1: N % concentration in 2015 for fruit size classes and N fertilizer treatments.
56
Figure 2: N removal for each of the N applications during 2015 and 2016. There were no
statistically significant differences among the treatments at a level of 0.05.
Figure 3: There was no statistical differences among April or July leaf N concentrations in 2016
among N fertilizer rates at significance of 0.05.
57
Figure 4: Data from 2016 illustrating the relationship between leaf %N and fruit %N.
Seasonal accumulation of N in fruit (Objective 2)
N accumulation in fruit was measured throughout the season. Fruit N accumulation in
both 2015 and 2016 (two different orchards) followed a nearly linear accumulation rate with
about 65% and 50% of total seasonal N accumulation accumulated in fruit by the first week
of June (Figure 5 and Table 1). In 2015, an organic low N input orchard was sampled, while
in 2016 a higher N input orchard was sampled. Differences in the pattern of fruit N
accumulation may be a consequence of the orchards or may have arisen due to the poor yield
in 2016. Despite variation between years and orchards, the N accumulation in the fruit was
not significantly different with 5.78 and 5.37 kg N per dry ton of fruit exported from 2015
and 2016, respectively.
58
Figure 5: N accumulation in the fruit until harvest for both 2015 (organic orchard) and 2016
(conventional orchard).
Percent of N Accumulation
2015 2016 Average
4/12 13
4/26 20 24 22
5/10 34 31 33
5/24 47 39 43
6/7 65 50 58
6/21 70 59 64
7/5 82 70 76
7/18 95 85 90
8/2 87 98 92
8/15 100 100 100
Table 1: Percent N accumulation throughout the season. Percent is based upon total N
accumulation at harvest.
Prediction of July leaf N from early spring leaf N (Objective 3)
The project to develop an early leaf sampling model and prediction protocol is still underway
and will be completed in 2017. Here I discuss only the preliminary data from 2014, 2015, and
2016. This data is not adequate to develop the prediction model.
N concentrations significantly varied among the orchards sampled. This was due to a number
of reasons including N fertilization, grower management, seasonal variation, and yield
differences. In combination with subsequent sampling, these data will be used to develop
59
protocols to predict July leaf N status from early season leaf sampling. Figure 6 illustrates the
relationship between April and July leaf % for both 2015 and 2016.
Figure 7 shows the variation of July leaf %N between years and within orchards. Leaf N%
varied from a low of 2.15 to a high of 2.86 % N in the Organic orchard. In this graph, the
variation among years and orchards is visible.
Figure 6: The relationship between April and July leaf samples varies due to various influences
including orchard, season, and N management.
60
Figure 7: The July leaf N percentage across year and orchards.
Discussion
Frit load and N status influence on N removal (Objective 1)
For 2015, the only significant difference in prune fruit % N accumulation was in the high N
treatment (204 kg N ha-1) where small fruits accumulated significantly more N than the medium
or large fruit classes (Figure 1). This may be a consequence of an effect of N on seed and
endocarp N concentrations when N is abundant. This increased concentration of N was evident
in small sized fruits both in the endocarp plus seed in addition to the mesocarp. However, this
may not indicate that more N was exported from the tree since that would be highly dependent
on the size distribution of the fruit in the orchard. Since 53% of the fruit was medium sized, the
majority of N exported came from the high numbers of medium sized fruit. Despite the
differences in fruit size distribution, there were no significant differences in the amount of N
exported per dry ton for each of the N treatments (Figure 2). This may be a consequence of the
abundant residual N and tree N that delayed the occurrence of N deficiency and that the lack of
an N response on yield, leaf, or fruit suggests even the organically managed orchard with
minimal N applications still had sufficient N. These results differ from previous experiments
when it was calculated that 102 kg N ha-1 was exported in a heavy fruited crop, however this was
calculated based on yields (~17 dry tons ha-1) that were approximately 3 times higher than
61
average California prune yields (Weinbaum et al., 1994).
Due to the poor yield in 2016, there was less competition among fruits for nutrients and
resources; therefore the size distribution of fruits was skewed toward larger fruits. Because of the
high percentage of large fruits, the effects of N treatment on fruit size and N% could not be
determined in 2016.
To understand how N applications affects the leaf N in both spring and summer sampling,
leaf samples were collected. Despite annually receiving no N fertilization, there was no
significant difference in leaf %N in either April or July. The lack of a response may be a result of
inadequate N fertilization or inadequate time to establish treatments. This may have occurred
because tree foliar N absorption and high amino acid concentrations in the plant down regulated
N uptake (Youssefi et al., 2000). Additional years of results may be necessary to establish
differential N responses in prunes as was seen in almond (Muhammad et al., 2015). The
relationship between the April and July leaf samples will be subsequently described in Chapter 3.
Seasonal accumulation of nitrogen in fruit (Objective 2)
Knowledge of the seasonal N accumulation in the fruit can be used to guide N applications
and increase NUE. By the end of May, 43% of the total N content of the fruit had been
accumulated, and by the first week of July, 76% of all N had been accumulated (Table 3). The
prune fruit followed the seasonal N accumulation patterns that were previously described in
pear and peach, but N accumulation appeared to slow closer to harvest (Buwalda & Meekings,
1990; Rufat & DeJong, 2001). This may be due to prune fruit remaining on the tree longer
than peach or pear, which are harvested at physiological maturity. The average N exported
in 2015 and 2016 was 5.78 kg of N per dry ton of fruit. Between 2015 and 2016 the N
accumulation varied; this may be due to differences in orchard and N management. Despite
variation between years and orchards, N export was not significantly different between 2015
and 2016. 2015 data was collected from an organic orchard with minimal N applications,
while 2016 data was collected from a conventional orchard with traditionally higher N inputs.
The small variations in N content, yield, and fruit size between years may also be due to yield
differences between the two years. Compared to data collected by Weinbaum et al. (1994),
defruited trees accumulated significantly less N than cropped prune trees with 121 and 250
grams of N, respectively. This may be due to poor management and yield of the organic
62
orchard or the unusually high yielding prune orchard utilized by Weinbaum. Additional
studies may be beneficial if conducted on conventionally managed orchards. Nutrient
accumulation in the fruit is vital to determine nutrient export especially for nitrogen.
Prediction of July leaf N from early spring leaf N (Objective 3)
Overall, leaf sampling results were not as expected which may be due to a number of reasons
including yearly environmental differences, various orchard management practices, and poor
sampling technique. In comparison to previous leaf sampling results on prunes with cropped and
defruited trees, N concentrations did not follow the expected trends. In prior work, there was a
significant difference between leaf N concentrations with 2.4% in cropped trees and 2.23% in
defruited trees (Weinbaum et al., 1994); similar results were expected between 2015 and 2016,
but this was not the case. These results confirm that despite efforts to standardize leaf samples,
variation still remains suggesting the need for additional research or other methods to determine
plant nutrient status (Burns, 1992). Due to inconsistent results, the development of a model
specifically for prunes may be more complicated than previously anticipated.
The results from 2014, 2015, and 2016 will be used as preliminary data for the model
development of a specific early leaf-sampling model for prunes. The current results confirm that
a similar sampling methodology may be used in prunes as in almonds, but more work is needed
on its development. Future leaf sampling will focus on using a pooled sample from each orchard.
These data will also give the model data points from multiple years which will be useful in
determining if tree-to-tree orchard variation will also account for variation that may occur yearly.
In conclusion, this preliminary data will be useful in the development of a model for early leaf
sampling in prunes with hopes of being available in 2017.
63
Works Cited
2016 California Dried Plum (Prune) Forecast. (2016). Sacramento, CA Retrieved from
https://www.nass.usda.gov/Statistics_by_State/California/Publications/Fruits_and_Nuts/2
016/201606prunf.pdf.
Bremner, J. M., & Mulvaney, C. (1982). Nitrogen—total. Methods of soil analysis. Part 2.
Chemical and microbiological properties(methodsofsoilan2), 595-624.
Burns, I. (1992). Influence of plant nutrient concentration on growth rate: Use of a nutrient
interruption technique to determine critical concentrations of N, P and K in young plants.
Plant and Soil, 142(2), 221-233.
Buwalda, J. G., & Meekings, J. S. (1990). Seasonal Accumulation of Mineral Nutrients in
Leaves and Fruit of Japanese Pear Pyrus-Serotina Rehd Scientia Horticulturae
(Amsterdam), 41(3), 209-222. doi:10.1016/0304-4238(90)90004-x
Muhammad, S., Sanden, B. L., Lampinen, B. D., Saa, S., Siddiqui, M. I., Smart, D. R., Olivos,
A., Shackel, K. A., DeJong, T., & Brown, P. H. (2015). Seasonal changes in nutrient
content and concentrations in a mature deciduous tree species: Studies in almond (Prunus
dulcis (Mill.) D. A. Webb). European Journal of Agronomy, 65, 52-68.
doi:10.1016/j.eja.2015.01.004
Rufat, J., & DeJong, T. M. (2001). Estimating seasonal nitrogen dynamics in peach trees in
response to nitrogen availability. Tree Physiology, 21(15), 1133-1140.
Saa, S., Brown, P. H., Muhammad, S., Olivos-Del Rio, A., Sanden, B. L., & Laca, E. A. (2014).
Prediction of leaf nitrogen from early season samples and development of field sampling
protocols for nitrogen management in Almond (Prunus dulcis Mill. DA Webb). Plant and
Soil, 380(1-2), 153-163. doi:10.1007/s11104-014-2062-4
Weinbaum, Niederholzer, F. J. A., Ponchner, S., Rosecrance, R. C., Carlson, R. M., Whittlesey,
A. C., & Muraoka, T. T. (1994). Nutrient uptake by cropping and defruited field-grown
'French' prune trees. Journal of the American Society for Horticultural Science, 119(5),
925-930.
Youssefi, F., Weinbaum, S. A., & Brown, P. H. (2000). Regulation of nitrogen partitioning in
field-grown almond trees: Effects of fruit load and foliar nitrogen applications. Plant and
Soil, 227(1-2), 273-281. doi:10.1023/a:1026572615441
Zarcinas, B., Cartwright, B., & Spouncer, L. (1987). Nitric acid digestion and multi‐ element
analysis of plant material by inductively coupled plasma spectrometry. Communications
in Soil Science & Plant Analysis, 18(1), 131-146.
64
Annual Report - 2016 Prepared for the Dried Plum Board of California
Title: Epidemiology and management of blossom, leaf, and fruit diseases of prune
Status: 2nd Year
Principal Investigator: J. E. Adaskaveg
Department of Plant Pathology, University of California, Riverside 92521
Cooperating: D. Thompson, H. Förster, R. Buchner (UCCE-Tehama Co.), and F. Niederholzer
(UCCE-Sutter-Yuba Co.).
Acknowledgement: SunSweet Growers Cooperative
SUMMARY OF RESEARCH ACCOMPLISHMENTS DURING 2016
1. Brown rot blossom blight. Natural incidence of blossom blight in 2016 was moderate, and data on fungicide
efficacy was obtained in laboratory studies using detached blossoms and in field studies. Among conventional
fungicides, single-active-ingredients (Rhyme, Quash, UC-1, EXP-A, and R-106506), the tank mixture of Quash
and Intuity, and the pre-mixtures (Luna Experience, Luna Sensation, Merivon, Quadris Top, and experimentals
UC-1 and UC-2B) demonstrated excellent activity.
The biocontrol Serenade Opti was moderately effective in laboratory assays; whereas Botector (Aureobasidium
pullulans) and the natural product Fracture (Lupinus alba) were very effective in field trials and significantly
reduced blossom blight from that of the control, similar to conventional fungicides.
2. Bacterial blossom blast. Due to unfavorable environmental conditions (strong winds) and failed experimental
methods (bagging of branches with flowers) during bloom in the spring of 2016, no disease developed.
3. Fruit brown rot. In applications done at 130 gal/A in combination with 1.0% oil, all fungicides evaluated
significantly reduced the incidence of brown rot when harvested fruit were non-wound-inoculated. Treatments
containing FRAC group 3 (i.e., a DMI that has locally systemic activity) as well as EXP-A, -AD, and -AF
resulted in very low levels of brown rot. The contact fungicides Luna Sensation and Merivon, as well as FRAC
Group 9, the experimentals R-106506 and UC-1 were slightly less effective.
4. Rust. In a late-season study on the management of rust, most fungicides were highly effective. Rhyme, Luna
Sensation, Luna Experience Merivon, Quadris Top, and the experimentals UC-2B and IL-54111 were highly
effective; whereas FRAC Group 9 fungicides and the experimentals R-106506 and EXP-A were the least
effective.
5. Contamination of dried plums with Aspergillus species. When dried fruit from 14 lots from the 2015 harvest
were re-hydrated and incubated at high relative humidity, the incidence of fruit contaminated with Aspergillus
spp. ranged from 20 to 100%, but was mostly >75%. Several colony types were observed. Molecular studies
indicated that the majority of isolates belonged to Eurotium repens, the sexual state of A. reptans. Other
species included A. niger, A. carbonarius, A. ochraceus, and A. tamarii. All 22 samples including fruit with
known A. flavus contamination that were submitted to DFA for aflatoxin testing were negative for aflatoxin.
When conidia of eight species of Aspergillus were incubated on dried plums at an average temperature of
71.5C for 18 h, >95% of conidia were inactivated as compared to incubation at 25C. Thus, these species were
all inactivated at temperatures (71-85C or 160-185F) and drying durations used in commercial fruit drying.
The origin of Aspergillus spp. contamination of dried plum fruit is still unclear. As a general strategy to
minimize fungal contamination, fruit storage facilities should be dry and well ventilated, and we still
recommend fruit surface sterilization immediately after harvest and before drying.
INTRODUCTION
Brown rot, caused by Monilinia species is the most important blossom and preharvest disease of prune in
California. In many growing areas of the state, M. laxa is the primary pathogen on blossoms, whereas M.
fructicola is the main pathogen on fruit. Still, both species can be found causing blossom blight and fruit rot
depending on the geographical production areas in California. Currently, fungicide treatments that are properly
timed are the most effective method to control this disease. Highly effective fungicides of different classes
have been identified over the years: the currently registered FRAC group (FG) 2 Rovral/Nevado/Iprodione; FG
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3 Tebucon/ Toledo, Indar, Tilt/Bumper, Quash, and recently registered Rhyme; the FG 7 Fontelis; FG 9 Scala
and Vangard; FG 11 Abound and Gem; FG 17 Elevate, and FG 19 Ph-D or Oso (Table 1). Pre- mixtures also
provide excellent control, and products evaluated include: FG 3/9 (Inspire Super); FG 3/11 (Quadris Top, Quilt
Excel); FG 7/11 (Pristine, Merivon, and the recently registered Luna Sensation), and FG 3/7 (Luna
Experience). A pending registration on dried plum includes FG 7 Kenja. Several experimental pre-mixtures
such as UC-2B, EXP-AD, -AF, IL-54111, and R-106506 are also planned for registration. Pre-mixtures are
highly effective, consistent, and provide resistance management on stone fruit crops because they have two
modes of action.
We also continued our evaluations of the newly registered FG 19 polyoxin-D (Ph-D; Oso), the natural
product Fracture (active ingredient is an extract of Lupinus alba), and the biocontrols Serenade Opti, and
Botector (Aureobasidium pullulans). Results obtained in 2013-2016 demonstrated good to intermediate brown
rot blossom blight control. Polyoxin-D in mixture with Scala was also very effective against fruit brown rot.
Products such as Ph-D and Oso containing the active ingredient polyoxin-D have exempt status in the United
States. Potentially, the National Organic Standards Board and the Organic Materials Review Institute (OMRI)
could certify some formulations for use in the organic production of stone fruit including prune. Thus, these
products could be critical developments for the organic production segment of the dried plum industry, as well
as to conventional growers because preharvest rotation programs need to be designed that prevent the overuse
of any one fungicide mode of action (FG).
Laboratory inoculation and field studies provide information on the protective and local systemic
action of compounds and should help growers and PCAs in the selection of materials and treatment timing to
optimize individual management programs. Fungicides that have post-infection activity (i.e., ‘kick-back
action’) could be applied as a single, delayed bloom application when environmental conditions are not
favorable for disease. Under high disease pressure, a two-spray bloom program should be followed using
protective or locally systemic fungicides. This information can also be applied to preharvest treatments when
unexpected rains delay fungicide applications for 1-2 days and materials with post-infection activity are
needed. Having several highly effective fungicides belonging to different FRAC Groups for managing diseases
of prune allows for rotations and reduces the risk of selecting for resistance. The overall objective is to rotate
products representing different FGs and using any one of the FGs only once (or twice) per season. Rotations of
pre-mixtures that alternate at least one of the FGs in the mixture are part of resistance management strategies.
In our fungicide field programs, we are also demonstrating how to improve the efficacy of preharvest
fungicide treatments. The addition of a summer spray-oil significantly increases the efficacy of most fungicides
in reducing brown rot. We also demonstrated that preharvest fungicide applications at higher water volumes
(i.e., 160 vs. 80 gal/A) in most cases significantly improved fungicide efficacy on fruit developing in clusters
inside the tree canopy.
In some years with spring and summer rainfall, early season (e.g., early summer) epidemics of prune
rust caused by the fungus Tranzschelia discolor can cause defoliation and subsequent direct (e.g., sunburn) and
indirect (e.g., re-foliation of trees and reduced bloom in the subsequent season) crop losses. In the last few
years, we have identified new effective materials in FGs 3, 7, 11 and 19, as well as pre-mixture FGs 3/11, 3/7,
3/19, and 7/11. Fungicides and integrated approaches need to be evaluated in season-long disease management
programs that take into account the control of multiple diseases such as brown rot and prune rust.
Another disease that we are studying is bacterial blast of blossoms and bacterial canker of woody
tissues of prune and other stone fruit crops caused by Pseudomonas syringae pv. syringae and other pathovars.
Bacterial blast and canker are associated with nematode root damage and cold, wet environments. Blossom
blast is associated with cold injury. With bacterial infection, blossoms become dark to black in color, wilt, and
die. Copper treatments have been used with inconsistent results for years. Copper can be phytotoxic to
blossoms, and we have shown that pathogen populations have developed moderate copper resistance. We will
continue experiments to validate or provide “proof of concept” that the new antibiotic kasugamycin is effective
on prune. This product was federally registered in September 2014 on pome fruit for fire blight management,
and registration is pending on almond, cherry, and walnut. Unfortunately, no disease was detected in our field
studies last year. Thus, we are still defining experimental conditions to obtain efficacy data on prune. The
industry has never had a highly effective material available for management of bacterial blossom blast and our
studies could potentially lead to a major advancement for the dried plum industry.
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At the request of farm advisors, another objective of our research in the last several years was the
occurrence and identification of molds on dried plums with an emphasis on Aspergillus species. Prune fruit
were obtained from 14 lots of the 2015 crop after drying, and the presence of fungal contamination was
determined after incubation of fruit at high humidity. We previously determined that conidia of all Aspergillus
species that we have identified from prune fruit to date were killed when incubated as aqueous suspensions at
temperatures of 71-85C (160-185F) and exposure durations used in commercial fruit drying. This indicated that
contamination with Aspergillus species likely originated after fruit drying and during storage in the processing
facility. In 2016, we evaluated the heat sensitivity of these species by incubating conidia directly on the surface
of dried plum fruit. This was done to rule out that the fruit micro-environment affects the heat sensitivity of
conidia. Additionally, fruit samples with known A. flavus contamination were submitted to DFA for aflatoxin
testing.
OBJECTIVES
1. Evaluate the efficacy of new fungicides (e.g., polyoxin-D, EXP-A, UC-1), pre-mixtures (Viathon, EXP-
AD-, -AF, UC-2B), and biocontrols (Botector, Fracture) representing different modes of action for brown
rot blossom blight and brown rot fruit rot in laboratory and field trials, as well as rust in field trials.
a. Pre- and post-infection activity of selected fungicides against brown rot blossom blight and fruit rot.
b. Evaluation of preharvest fungicides in combination with selected spray adjuvants
c. Evaluation of fungicide efficacy against prune rust.
2. Evaluate the efficacy of new products against bacterial blast in flower inoculation studies and/or canker
in stem inoculation studies.
a. Biologicals/natural products (e.g., Actinovate), polyoxin-D, Bacillus-containing products, Blossom
Protect – Aureobasidium sp.).
b. Antibiotics – Kasugamycin and other antibiotics.
3. Continue to develop baseline sensitivity data for SDHI and new fungicides (e.g., EXP-A, UC-1).
4. Survey of Aspergillus species on dried plum, identify the species using molecular methods, and test for
aflatoxin on fruit samples in cooperation with DFA.
a. Evaluate heat tolerance of dry conidia on dried plum fruit surfaces
b. Evaluate surface sterilization with on harvested fruit prior to drying plums
c. Develop a UC-extension bulletin on proper drying and storage of dried plums
MATERIALS AND METHODS
Evaluation of fungicides for management of brown rot blossom blight. Fungicide pre- and post-
infection activity was evaluated in laboratory studies. For post-infection activity, blossoms at popcorn stage were
collected and allowed to open. They were then inoculated with a conidial suspension of M. fructicola (2 x 104
conidia/ml), treated with selected fungicides after 19 h using a hand sprayer, and incubated at 20C. For pre-
infection activity, blossoms were first treated with a fungicide and then inoculated. Three replications of eight
blossoms were used for each fungicide. Treatments were applied using rates suggested by the fungicide
manufacturers. Data were analyzed using analysis of variance and mean separation procedures of SAS 9.4.
Evaluation of bactericides and biocontrols for management of bacterial blast. Flowers at full bloom on
the trees were treated with selected treatments (the antibiotic Kasumin, the biologicals Actinovate, Double
Nickel 55, and Blossom Protect,) using a hand sprayer, inoculated with a suspension of P. syringae (1 x 107
cfu/ml), and covered with a plastic bag overnight. Bags were removed the next morning after 16 h of wetness and
blossoms were evaluated for disease 7 to 10 days after inoculation. Data were analyzed using analysis of variance
and mean separation procedures of SAS 9.4.
Evaluation of fungicides for management of preharvest fruit decay. Field trials to evaluate preharvest
fungicide applications for control of fruit brown rot were done in a commercial orchard in Yuba Co. Treatments
were applied 7 days before harvest using an air-blast sprayer calibrated at 130 gal/A. All fungicides were applied
in combination with 1.0% of a spray oil (i.e., Gavicide). Single fruit (24 fruit from each of four paired
replications, 8 trees in total) were collected at harvest and non-wound inoculated with conidia of M. fructicola (5
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x 105 conidia/ml). After inoculation, fruit were incubated for 7-10 days at 20 C. Data were analyzed using
analysis of variance and mean separation procedures of SAS 9.4.
Evaluation of fungicides for management of prune rust. A field trial was established in a commercial
orchard in Yuba Co. to evaluate the efficacy of new fungicides. Fungicides were applied on 8-9-16 (as a
preharvest application for management of fruit brown rot) and on 9-7-16 specifically for fall season rust
management. Disease was evaluated on 10-28-2016. Disease severity was determined for four quadrants of each
tree using a scale from 0 (= no disease) to 5. Data were analyzed using analysis of variance and mean separation
procedures of SAS 9.4.
Contamination of dried plums in storage with Aspergillus species. Dried prune fruit from 14 lots of the
2015 harvest were obtained between November 2015 and January 2016. Fruit were surface-sterilized in 100 ppm
sodium hypochlorite for 1 min or not surface-sterilized and were then re-hydrated by immersing in sterile water
for 3 to 6 h. Fruit were then placed into fruit trays (1-2 fruit/tray cavity) in plastic boxes. There were between 40
and 160 fruit for each sanitized and non-sanitized sample. Fruit were incubated at 20C, >90% RH for 3-5 weeks,
misted periodically with water to maintain high humidity, and evaluated for the presence of Aspergillus and other
fungal species. For evaluation, the number of Aspergillus spp. were enumerated for each colony pigmentation
(e.g., black, green, olive-green, yellow, yellow-green, orange). Representative isolates were obtained from
different colony types by culturing on potato dextrose agar. The level of Aspergillus contamination was
determined by calculating the average number of Aspergillus spp. colonies per fruit.
For the molecular grouping of isolates, an RFLP analysis of the ITS1 region of rDNA was performed as
described previously (see Annual Report 2012). DNA was amplified using universal primers ITS1 and ITS2 and
amplification products were digested with restriction enzymes AluI, HinfI, MboI, RsaI, TaqI, and BseI. DNA
fragments were separated in agarose gels, and isolates were grouped according to their fragment patterns. For
species identification of representative isolates, a portion of the large sub-unit rDNA region was amplified using
primers ITS5 and D2R, and primers D1 and ITS4 were used in sequencing reactions. Sequences were aligned
using ClustalW and compared to those of isolates of Aspergillus spp. deposited in Genbank and with our own
sequences that were obtained previously. A total of 22 samples including 12 fruit with known A. flavus
contamination, as well as 10 cultures of the fungus were submitted to DFA for aflatoxin testing.
The heat sensitivity of conidia of Aspergillus spp. and Eurotium repens was previously evaluated using
aqueous suspensions. In 2016, we determined the heat sensitivity of conidia on dried plum fruit. For this,
conidial suspensions (107 conidia/ml) were applied to surface-sterilized dried plum fruit, and fruit were incubated
for 18 h at 25C or at an average temperature of 71.5C. Conidia were re-suspended in sterile water, plated onto
agar media, and conidial germination was evaluated after 18 h. As a control, conidia were also evaluated for their
germination on agar medium following incubation at 25C.
RESULTS AND DISCUSSION
Overview. Rainfall occurred in the spring of 2016, and the natural incidence of brown rot blossom
blight was moderate. Data on fungicide efficacy for managing brown rot blossom blight were obtained in
laboratory inoculation studies and in field studies where natural incidence of disease was recorded. Later in the
summer, natural incidence of rust was also higher than in previous years and results were obtained in field
trials. Inoculations with the bacterial blast pathogen, however, were inconsistent due to windy conditions that
injured and removed flowers inside bagged branches. Blast generally is most severe during cold, wet
conditions during bloom that predispose flowers to infection. Overall, fungicide usage was higher than in
previous years, but still there were no new reports of fungicide failures or suspected resistance in pathogen
populations from the industry.
Evaluation of fungicides for management of brown rot blossom blight. In laboratory studies using
detached blossoms, five single-fungicides, one mixture, and five pre-mixtures significantly reduced the
incidence of stamen infections to very low values when applied before or after infection, and thus, were highly
effective (Fig. 1). The new DMI fungicide Rhyme, the experimentals UC-1, R-106506, the experimental tank
mixture of Quash and Intuity, and most of the premixtures such as Quadris Top, Merivon, UC-2B, and IL-54111
were highly effective in these trials. The biocontrol Serenade Opti (Bacillus subtilis) significantly reduced the
incidence of stamen infections from that of the control, but was less effective than conventional fungicides.
Serenade Opti is registered in California on stone fruit crops including prune.
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In a field trial, Fracture and Botector along with most conventional fungicides including single-site modes of
action Rhyme, UC-1, EXP-A, and R106506, as well as the premixtures Luna Sensation, Luna Experience, Quadris
Top, Merivon, and EXP-AF showed excellent performance. IL-54111, Kenja, UC-2B, and EXP-AD had a small
amount of disease (<0.5%) that was still significantly less than in the untreated control (Fig. 2). The biological
controls Serenade Opti, Botector (Aureobasidium pullulans), and Fracture (extract of Lupinus albus) are currently
registered on stone fruit crops in California.
The post-infection activity of the treatments was evaluated in the blossom experiments to assess their
potential efficacy as a single application in a delayed bloom application when recent infections need to be
controlled. This strategy has been successfully used on other tree crops in spring seasons when precipitation is
low to moderate.
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Currently registered fungicides with high pre- and post-infection activity include single active ingredients
such as the FG 2 dicarboximide Rovral (-oil) and generics; the FG 3 DMIs Tilt (and generics), Indar, Rhyme,
Tebucon (and other generics), and Quash; the FG 7 SDHI Fontelis; the FG 9 anilinopyrimidines (APs) Vangard
and Scala; and the FG 17 hydroxyanilide Elevate. Pre-mixtures include the FG 7/11 Pristine and Merivon, the FG
3/11 Quilt Xcel and Quadris Top, the FG 3/9 Inspire Super, and the FG 3/7 Luna Experience (Table 1). These pre-
mixtures provide consistent, broad-spectrum high efficacy with built-in resistance management.
Evaluation of fungicides for management of fruit brown rot. We previously demonstrated that the
efficacy of preharvest fungicides applications to prevent losses from fruit brown rot is considerably improved
when used in combination with 1-1.5% agricultural spray oil (e.g., Gavicide). We also demonstrated that some
fungicides when applied at an increased volume of 130 gal/A provide better protection of fruit inside clusters.
Therefore, all treatments were evaluated using these methods. Preharvest fungicides were applied 7 days PHI in a
commercial orchard and harvested fruit from each tree and fruit were non-wound-inoculated with the brown rot
pathogen.
All fungicides evaluated significantly reduced the incidence of brown rot as compared to the control after
non-wound inoculation (Fig. 3). Most of the fungicides evaluated were highly effective. The most effective
materials with the lowest diseases levels were EXP-A, UC-2B, EXP-AD, EXP-AF, and IL-54111. Fungicides
containing DMIs have locally systemic activity, whereas other fungicides function as contact materials.
Table 1. Efficacy of single mode-of-action fungicides and pre-mixtures against major diseases of prunes (dried plum)
Jacket rot/
Fungicide product Active ingredientsFRAC
Group
Resistance
riskBlossom Fruit rot
Green
fruit rotRust
Topsin-M/T-Methyl/ Incognito* thiophanate methyl 1 high ++++ +++ ++++ ----
Rovral + oil iprodione-oil 2 low ++++ NL^ ++++ ++
Rovral, Iprodione, Nevado iprodione 2 low +++ NL +++ +
Bumper/Tilt/Propiconazole propiconazole 3 high ++++ ++++ ---- ++++
Tebucon/Toledo tebuconazole 3 high ++++ ++++ ++ +++
Indar fenbuconazole 3 high ++++ +++ ---- +++
Quash metconazole 3 high ++++ ++++ ++ +++
Rally myclobutanil 3 high +++ +++ ---- ---
Rhyme flutriafol 3 high +++ +++ ND ++++
Fontelis penthiopyrad 7 high ++++ +++ ++++ +++
Vangard cyprodonil 9 high ++++ +++ +++ ---
Scala pyrimethanil 9 high ++++ +++ +++ ---
Abound azoxystrobin 11 high +++ + ---- +++
Gem trifloxystrobin 11 high +++ ++ ---- +++
Elevate fenhexamid 17 high +++ +++ ++++ ---
Ph-D, Oso polyoxin-D 19 high ++ ++ +++ ++
Luna Experience tebuconazole/fluopyram 3/7 medium ++++ ++++ +++ ++++
Inspire Super difenoconazole/cyprodinil 3/9 medium ++++ ++++ +++ +++
Quadris Top difenoconazole/azoxystrobin 3/11 medium ++++ ++++ ++ ++++
Quilt Xcel propiconazole/azoxystrobin 3/11 medium ++++ ++++ ++ ++++
Viathon tebuconazole/KPO3 3/33 medium ++++ ++++ +++ +++
Luna Sensation fluopyram/trifloxystrobin 7/11 medium ++++ ++++ +++ +++
Pristine boscalid/pyraclostrobin 7/11 medium ++++ ++++ +++ +++
Merivon fluxapyroxad/pyraclostrobin 7/11 medium ++++ ++++ +++ +++
* - Resistant sub-populations have been detected in some pathogens.
Brown rot
-Rating: ++++ = excellent and consistent, +++ = good and reliable, ++ = moderate and variable, + = limited and/or
erratic, +/- = minimal and often ineffective, ---- = ineffective, ND = no data, NL = not on label,
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Thus, several fungicides with high efficacy are available to the industry to protect fruit from brown rot
decay even when applied 14- to 7-days before harvest (PHI). The highest treatment efficacy is obtained when
fungicide-oil mixtures are applied at higher volumes. Spray oil provides improved coverage of fruit (acting as
a spreader on waxy fruit surfaces) and likely also improves penetration of some fungicides into the fruit. Not
all fungicides, however, may be compatible with oils. It is important to prevent fruit injuries during and after
harvest. To reduce brown rot of mechanically harvested fruit in bins, fruit should be processed for drying
within 48 h of harvest.
Evaluation of fungicides for management of prune rust. The severity of rust was moderate in the 2016
growing season. In a late-season study, two applications of several fungicides (the first application was part of the
pre-harvest brown rot fruit decay study and the second one was applied after harvest) all significantly reduced the
incidence and severity of rust developing in the tree canopy as compared to the non-sprayed control trees (Fig. 4).
Scala, R-106506, EXP-A, Ph-D-Scala, and EXP-AF were significantly less effective than the other fungicides
reduce disease severity from the control. The highest efficacy was obtained using Rhyme, Luna Sensation, Luna
Experience, UC-2B, and IL-54111. These data indicate that effective treatments against prune rust are available.
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Over the years, treatments that include FGs 3, 7, or 11 have been the most effective. Prune rust occurs
sporadically and protective treatments are generally not warranted. These fungicides, however, should still be
very effective if applied when the very first rust lesions are detected in an orchard during regular scouting and
monitoring of orchards during April through June.
Contamination of dried plums in storage with Aspergillus species. Samples of dried plums were obtained
from 14 fruit lots of the 2015 harvest. After re-hydrating fruit and incubation for 3 to 5 weeks at high relative
humidity, growth of Aspergillus spp. occurred on all but two samples. The incidence of contaminated fruit ranged
widely from 20 to 100%, but was mostly >75%. Several Aspergillus spp. colony types were often present on
individual fruit, and at least ten colony types were differentiated based on pigmentation. Thus, in contrast to fruit
from the 2014 harvest season, a wider range of species was observed, but contamination levels in both years were
mostly high. Contamination of fruit in the laboratory can be ruled out because fruit were incubated in bagged-up
plastic boxes and were never exposed to open-air circulation. Additionally, cross contamination during re-
hydration can be ruled out because for some lots, fruit were re-hydrated individually. Wallemia sp. was present in
six lots, and few other fungal genera were observed. Colony types on plum fruit often did not match those on agar
media after fungal isolation. Therefore, for grouping of isolates they were placed into molecular groups by RFLP
analysis of a short rDNA region. Sequencing of representative isolates indicated that a majority of cultures
growing on the dried plums belonged to Eurotium repens, the sexual state of Aspergillus reptans. Other species
identified were A. niger, A. carbonarius (both in the Aspergillus Section Nigri), A. ochraceus, and A. tamarii.
These species, except A. ochraceus, as well as A. brasiliensis, A. flavus, A. melleus, A. phoenicis, and A.
tubingensis were identified in our lab previously from dried plum fruit.
When fruit were surface-sterilized before re-hydration and incubation, a high level of contamination was
still present in most lots, and contamination was significantly reduced in only three of the lots (Fig. 5). Therefore,
the majority of fungal contaminants apparently had penetrated the fruit. In contrast, our previous studies on
surface-disinfestation of fruit had indicated that fungal contamination was superficial because little fungal growth
developed on sterilized fruit. As a precautionary procedure, samples were submitted to DFA for aflatoxin testing.
All samples including known samples with A. flavus contamination and cultures of the fungus were negative for
the presence of aflatoxin.
Because the origin of Aspergillus spp. contamination of dried plum fruit is still unclear, we continued to
evaluate the heat sensitivity of eight selected species of Aspergillus. Previously, when conidia in aqueous
suspensions were exposed to heat (wet heat), they were completely inactivated after 14 h at 70C (158F). In this
year’s studies, conidia were placed onto dried plum fruit, and fruit were incubated for 18 h at 25C or at an average
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of 71.5C (dry heat). When conidia where incubated on potato dextrose agar and incubated at 25C (a control
treatment), germination rates were all >95%. Average germination rates of conidia on fruit at 25C, however, were
variable and ranged from 26 to 90% in the two studies conducted (Table 2). When conidia on fruit were incubated
at an average temperature of 71.5C, germination was reduced by >95% as compared to 25C. No germination was
observed for A. phoenicis/tubingensis, A. niger/brasiliensis (these two pairs of species could not be separated by
the methods we used), A. carbonarius, A. melleus, and Eu. repens. Thus, these species of Aspergillus identified
from prune fruit were all inactivated at temperatures (71-85C or 160-185F dry heat) and drying durations used in
commercial fruit drying. This indicates, as in some previous years, that contamination occurs after drying in
storage. Still, last year’s data of 2014 fruit favored the hypothesis that fruit become contaminated before the
drying process because samples were taken shortly after drying, and not after several months of storage. As a
general strategy to minimize fungal contamination, fruit storage facilities should be dry and well ventilated. Any
rehydration of dried fruit in storage is a non-sanctioned practice that risks mold contamination. Thus, we still
recommend surface sterilization procedures immediately after harvest and before drying. A standard method for
surface disinfestation prior to drying fruit is the use of sodium hypochlorite washes. Concentrations of 50 to 100
ppm of the active ingredient hypochlorous acid are commonly used in the fruit industry. Subsequent steam
sanitation before processing of stored, dried fruit further minimizes the risks associated with fungal contamination
of fruit.
Table 2. Heat sensitivity of conidia of Aspergillus spp. and
Eurotium repens on dried plum fruit
Isolate No. Species 18 h 25C 18 h 71.5C
3991 A. brasiliensis 27 0.2
4325 A. flavus 30 1.2
3996 A. phoenicis/tubingensis 50 0.0
4329 A. niger/brasiliensis 90 0.0
4366 A. carbonarius 32 0.0
4356 A. tamarii 34 1.5
4355 A. melleus 26 0
4373 E. repens 72.5 0
% germination
Conidial suspensions (107 conidia/ml) were applied to surface-
sterilized dried plum fruit and fruit were incubated for 18 h at 25C
or an average of 71.5C. Conidia were re-suspended in sterile water,
plated onto agar media, and conidial germination was evaluated
after 18 h. Data presented are the average of two experiments.
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DIAGNOSIS, ETIOLOGY, EPIDEMIOLOGY, AND MANAGEMENT OF CANKER
DISEASES IN DRIED PLUMS
Themis J. Michailides, Yong Luo, Franz Niederholzer, David P. Morgan, Dan Felts,
Ryan Puckett
and
Richard Buchner, Elizabeth Fichtner, and Daniella Lightle
OBJECTIVES
1) To continue the experiment of monthly inoculations to determine the critical period of
pathogen infection and disease development.
2) To investigate the inoculum dynamics during rain events in three commercial orchards
with severe canker disease.
3) To investigate the development of pathogens’ latent infection and their corresponding
endophytic stage in shoot tissues during and over the growing season.
4) Continue to study the efficacy of certain fungicides to control canker disease.
5) Continue to study the putative effects of sunburn of shoots on pathogen infection and
canker disease development.
PROCEDURES
Objective 1: To continue the experiment of monthly inoculations to determine the critical
period of pathogen infection and disease development.
The experiments were conducted in a prune orchard at KARE. Wounds of 1- or 2-year old
shoots were generated by pruning shoots with a pair of sterile pruners. About 30 shoots per tree
were randomly selected and pruned on March 7-9, 2016 and marked for later inoculations. The
inoculation dates of 2016 on the wounded shoots were March 9, April 23, May 11, June 8, July
7, August 9, September 15 and October 10. On each inoculation date, all wounded shoots of each
tree were individually inoculated by spraying about 3 ml of spore suspension (about 105
spores/ml per shoot) of each of the two pathogen species, Lasiodiplodia citricola and Cytospora
spp. The inoculated shoots were covered with a plastic bag for 48 hours to maintain the
humidity. The disease recording was performed in mid-November of 2016 for all the inoculated
shoots except for those inoculated in October 10. The following scoring system was used to
access canker disease severity: 0: no canker symptom; 1: Canker length <=1cm; 2: Canker length
was1-3 cm; 3: Canker length was 3-5 cm; 4: Canker length was >5 cm; 5: the shoot was died
because of canker. Thus, the canker severity was assessed for each of the inoculated shoot for all
inoculation dates for each pathogen. The average canker severity was calculated and used to
compare among different inoculation dates.
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Objective 2: To investigate the inoculum dynamics during rain events in three commercial
orchards showing severe canker disease.
Three prune orchards were identified in Yuba County, designated as Orchard 1, Orchard 2, and
Orchard 3, and rain samples were collected from these orchards. In each orchard, a rain collector
as a 500-ml plastic bottle with a funnel cap was set at canopy height. The rain samples were
collected four times in 2016, on February 9, March 2, March 17 and May 5. For each sample, a
total of 120 ml of rain water was processed using 4 centrifuge tubes. The centrifuge was set at
10,000 rpm for 10 min, and the supernatants were carefully discarded, leaving about 10 µl
precipitates in the tube. The precipitates of the 4 tubes were combined into a 16-ml centrifuge
tube and centrifuged again under the same conditions described above. After carefully removing
the supernatant, 40 µl precipitates were left to extract DNA. The specific primers for each of the
six pathogen groups, Phomopsis spp., Botryosphaeria dothidea, Lasiodiplodia spp., Cytospora
spp., Neofusicoccum spp. and Diploid spp., were used to target the specific pathogen in rain
samples by using real-time PCR. Our previously-developed equations of standard curves (data
not shown) were used to quantify inoculum density for each pathogen in terms of Log10 (number
of spores/ml).
Objective 3: To investigate the development of pathogens’ latent infection and their
corresponding endophytic features in shoot tissues during and over the growing season.
In each of the three orchards mentioned above, periodical shoot samplings were conducted in
March, June and September of 2016, and will be continued every three months during the
dormant period as well. For each sampling, about 10-20 cm-long shoots including the newly-
emerged shoots and part of the old shoot in the proximity of the new shoot (usually 1-year old)
were collected. Thus, each sample contained two parts: new shoots and old shoots. The two age
kind of shoots were numbered and processed separately. For each sampling, 32 such shoots were
randomly collected in each orchard. These shoots were washed twice with regular water, soaked
in 10% commercial bleach for 10 min for surface sterilization, washed three times again, and air
dried for two days. A pencil sharpener was used to grind shoot samples into fine wood pieces
which were used to extract DNA by sing the FastDNA kit (MP Biomedical, CA). Briefly, the
pathogen group-specific primers were used in real-time PCR to obtain the corresponding Ct
values. The published equation of standard curve for each pathogen group (Luo et al., 2017) was
used to calculate the DNA quantity for each pathogen in each sample.
To quantify the infection level of shoots, we introduced the concept of molecular severity
(MS): MS= Log10(P/H), where P is the weight of the pathogen’s DNA in femtograms (fg), which
is calculated by using the equation of the standard curve for the corresponding pathogen (Luo et
al., 2017) based on the Ct value from its reaction with the corresponding primers, and where H is
the shoot weight in grams (g). Thus, if the minimum detectable amount of pathogen DNA in one
gram of shoot is theoretically assigned as 1 fg, the MS would be 0. The maximum of the amount
of pathogen DNA in one gram of shoot tissue could be theoretically one gram (=1015 fg), and the
maximum value of MS should be 15. Thus, the range of MS value is 0 - 15. However, since
when no infection is detected we assign MS = 0, the theoretically detectable amount of pathogen
DNA in one gram of shoot should be >1fg. The concept and calculation of MS were used to
determine the infection level for all the shoot samples used in this study.
75
Incidence of latent infection in terms of proportion of shoots showing positive results over all
detected shoots was obtained for each pathogen on each sampling date. Average MS from 32
shoot samples was obtained for each pathogen and each sampling date. Comparisons in MS
between new and old shoots were conducted for each pathogen and on each sampling date.
Objective 4: Continue to study the efficacy of certain fungicides to control canker disease.
We continued a fungicide trial in a dried plum orchard located in Yuba County showing severe
Cytospora canker disease. Same as used in 2014-2015 trials, six fungicides were used: Topsin,
Quilt Xcell, VitiSeal, Pristine + Pentra Bark, tebuconazole, Pristine + VitiSeal, plus an untreated
control. Regular pruning was conducted in this orchard in December 2015 and fungicide
treatments were conducted on December 9, 2015. A rate of 5g/L for each fungicide was used to
paint on the pruning wounds. For each fungicide treatment, 10 pruned branches were used. The
fungicide treated wounds were maintained on trees for the whole season of 2016 and disease
recording was conducted on 7 December of 2016 for canker incidence for each fungicide
treatment.
Objective 5: Continue to study the putative effects of sunburn of shoots on pathogen
infection and canker disease development.
We continuously conducted an experiment to determine whether the sunburn could affect the
disease development in this year. On August 5, 2016, some trees of the very south row of the
orchard at KARE described above were selected. The shoots were bended at certain degree to
face the sun and tied to a metal stick so that they are exposed to direct sunlight. About 10 shoots
were used for each of the three pathogens. The inoculations were conducted on August 26, 2016.
Each marked shoot was treated by using a sterile cork borer to make the wound, inoculated by
spraying 2 ml of spore suspension (105 spores/ ml) of each pathogen directly on the wound, and
covered with a piece of parafilm for 48 hours to create high humidity. The whole experiment
was replicated twice and disease was recorded in mid-November 2016.
RESULTS AND CONCLUSIONS
Objective 1: To continue the experiment of monthly inoculations to determine the critical
period of pathogen infection and disease development patterns.
Since two trees with inoculated shoots died because of wood decay fungi and pulled out during
this experiment, the results relevant to inoculations with Paecilomyces variotii were excluded in
data analysis. Figure 1 shows the dynamics of mean canker severity for Lasiodiplodia citricola
(7F93) and Cytospora leucostoma (9D71) during 2016. Comparisons in average canker severity
among different inoculation dates demonstrated that for both pathogen species, early inoculations
(from March and May) on wounds generally promoted significantly higher canker severity than
did later inoculations (Figure 1), especially for Cytospora spp. Compared with the non-
inoculated control, all inoculated shoots showed significantly higher canker severities. Thus, we
concluded that the risky period time promoting higher chance of severe canker occurs in early in
the growing season.
76
Figure 1. Dynamics of canker disease severity cause by Cytospora and Lasiodiplodia spp. on wounded shoots in
2016. Inoculations were conducted on wounded shoots periodically. Each dot represents a mean value from 30
wounded shoots. * indicates the mean value from non-inoculated shoots as control.
Objective 2: To investigate the inoculum dynamics during rain events in three commercial
orchards showing severe canker disease.
Four times of rain samples from each of the three prune orchards in Yuba County mentioned
above were analyzed. We did not find any spores of Phomopsis spp. and Diplodia spp. in any of
the rain samples. Cytospora spp. is major pathogen detected in most rain samples in these
orchards. Thus, this species was predominant in the pathogen populations throughout the season
(Figure 2). Lasiodiplodia spp. was found in all the three orchards especially in early season. It
was also major species detected in rain water, although the amounts were not as high as
Cytospora spp. (Figure 2). However, both Botryosphaeria dothidea and Neofusicoccum spp.
were detected from only some rain samples (Figure 2), indicating that these can be considered as
minor species of the pathogen populations in the rain water.
77
Figure 2. Spore densities of four canker-causing species obtained from four times of rain samples collected from
three prune orchards in Yuba County. The real-time PCR assay was applied to quantify these spore densities in
samples of rain water.
Objective 3: To investigate the development of pathogens’ latent infection and their
corresponding endophytic stage in shoot tissues during and over the growing season.
Similar patterns of latent infections in shoots were observed among the three orchards in Yuba
County. Basically, three major species in shoot tissues detected as latent infections were B.
dothidea, Lasiodiplodia spp. and Cytospora spp. The Phomopsis spp. and Neofusicoccum spp.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
February 9 March 2 March 17 May 15
Orchard 1
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
February 9 March 2 March 17 May 15
Orchard 2
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
February 9 March 2 March 17 May 15
Botryosphaeria dothidea Lasiodiplodia spp. Cytospora spp. Neofusicoccum spp.Lasiodiplodia spp. Cytospora spp. Neofusicoccum pp.
Orchard 3
Sampling date of 2016
Log 1
0(n
o. s
po
res/
ml)
78
were detected in some samples with very low level of incidence and MS and high flexibility.
The Diplodia spp. was not detected in all shoot samples in all the three orchards, indicating that
this species seemed not important in prune orchards so far in this area.
In Orchard 1, the high incidences of latent infections (over 60%) caused by B. dothidea in both
new and old shoots were observed in all three samplings (Figure 3). Relatively lower incidences
of infections caused by Lasiodiplodia spp. and Cytospora spp. were observed, which also varied
between new and old shoots (Figure 3).
Figure 3. Incidences of latent infections of new-emerged shoots and old 1-year shoots caused by six canker-
pathogen groups from prune Orchard 1 in Yuba County. The real-time PCR assay was applied to process these shoot
samples collected from 3 time points in 2016.
Comparison in MS between new and old shoots demonstrated that the MSs were significant
higher in old shoots than in new shoots in the first samples for most pathogens when the new
shoots just emerged (Figure 4). While there was no significant difference in MS between the new
and old shoots for most samples in later two samplings (Figure 4). The results showed that even
at the very shoot emergence at least three predominant species could be isolated from new
shoots, implying some endophytic features of pathogen species in shoots.
0.00
0.20
0.40
0.60
0.80
1.00
March June September
Phomopsis spp.
0.00
0.20
0.40
0.60
0.80
1.00
March June September
Botryosphaeria dothidea
0.00
0.20
0.40
0.60
0.80
1.00
March June September
Lasiodiplodia spp.
0.00
0.20
0.40
0.60
0.80
1.00
March June September
Cytospora spp.
0.00
0.20
0.40
0.60
0.80
1.00
March June September
New shoot One-year old shoot
Neofusicoccum spp.
0.00
0.20
0.40
0.60
0.80
1.00
March June SeptemberNew shoot One-year old shoot
Diplodia spp.
Inci
de
nce
of
lan
ten
t in
fect
ion
of
sho
ots
Month of 2016
79
Figure 4. Comparison of mean molecular severities (MS) between new-emerged shoots and the old prune shoots
quantified for each of the six canker-causing pathogens. Three samplings were conducted in prune Orchard 1 in
Yuba County. The real-time PCR was applied to obtain MS data and 32 shoots were processed for each sampling.
In Orchard 2, similar situations were observed that B. dothidea existed in all new and old shoot
samples with high incidences (Figure 5). Following that, Lasiodiplodia spp. and Cytospora spp.
were the second predominant pathogens that were recovered from shoot samples, while the
incidences were lowers than those of B. dothidea. Phomopsis spp. and Neofusicoccum spp. were
infrequently isolated in some samples, indicating less importance of these two species in both
new and old shoots (Figure 5).
0.00
2.00
4.00
6.00
8.00
10.00
March June September
Phomopsis spp.
aa
0.00
2.00
4.00
6.00
8.00
10.00
March June September
Botryosphaeria dothidea
a abbab
0.00
2.00
4.00
6.00
8.00
10.00
March June September
Lasiodiplodia spp.
aab
a a
b
0.00
2.00
4.00
6.00
8.00
10.00
March June September
Cytospora spp.
aaaaa
b
0.00
2.00
4.00
6.00
8.00
10.00
March June September
New shoot One-year old shoot
Neofusicoccum spp.
aab
a
ab
0.00
2.00
4.00
6.00
8.00
10.00
March June September
New shoot One-year old shoot
Diplodia spp.
Month of 2016
Mo
lecu
lar
seve
rity
of l
ante
nt
infe
ctio
n o
f sh
oo
ts
80
Figure 5. Incidences of latent infections of new-emerged shoots and old 1-year shoots caused by six canker-
pathogen groups from Orchard 2 in Yuba County. The real-time PCR assay was applied to process these shoot
samples collected from 3 time points in 2016.
Similarly, the average MSs were significantly higher in old shoots than in new shoots at very
early stage for the three predominant pathogens mentioned above (Figure 6). This significance
appeared also in the second samplings, while, there was no clear patterns in difference in MS
between new and old shoots in the last sampling (Figure 6). The result implied that the
predominant pathogens existed in new-emerged shoots and could develop during the growing
season.
Results from prune Orchard 3 showed higher incidence of shoot latent infection in old than in
new shoots for the three predominant pathogens for the first sampling (Figure 7). The situations
in incidence of latent infection caused by Lasiodiplodia spp. and Cytospora spp. was quite the
same as that in prune Orchard 1.
Comparisons showed that means of MSs in old shoots were significantly higher than in new
shoots at very early stage for Phomopsis spp. B. dothidea, Lasiodiplodia spp. and Cytospora spp.
(Figure 8). However, no such clear difference patterns were observed in latter samplings.
0.00
0.20
0.40
0.60
0.80
1.00
March June September
Phomopsis spp.
0.00
0.20
0.40
0.60
0.80
1.00
March June September
Botryosphaeria dothidea
0.00
0.20
0.40
0.60
0.80
1.00
March June September
Lasiodiplodia spp.
0.00
0.20
0.40
0.60
0.80
1.00
March June September
Cytospora spp.
0.00
0.20
0.40
0.60
0.80
1.00
March June September
New shoot One-year old shoot
Neofusicoccum spp.
0.00
0.20
0.40
0.60
0.80
1.00
March June September
New shoot One-year old shoot
Diplodia spp.
Inci
de
nce
of
lan
ten
t in
fect
ion
of
sho
ots
Month of 2016
81
Figure 6. Comparison in mean molecular severities (MS) between new-emerged shoots and the old shoots
quantified for each of the six canker-causing pathogens. Three samplings were conducted in prune Orchard 2 in
Yuba County. The real-time PCR was applied to obtain MS data, and 32 shoots were processed for each sampling.
0.00
2.00
4.00
6.00
8.00
10.00
March June September
Phomopsis spp.
a a
0.00
2.00
4.00
6.00
8.00
10.00
March June September
Botryosphaeria dothidea
b baa
a a
0.00
2.00
4.00
6.00
8.00
10.00
March June September
Lasiodiplodia spp.
a aba
a
b
0.00
2.00
4.00
6.00
8.00
10.00
March June September
Cytospora spp.
a aab
a
b
0.00
2.00
4.00
6.00
8.00
10.00
March June September
New shoot One-year old shoot
Neofusicoccum spp.
0.00
2.00
4.00
6.00
8.00
10.00
March June September
New shoot One-year old shoot
Diplodia spp.
Mo
lecu
lar
seve
rity
of l
ante
nt
infe
ctio
n o
f sh
oo
ts
Month of 2016
0.00
0.20
0.40
0.60
0.80
1.00
March June September
Phomopsis spp.
0.00
0.20
0.40
0.60
0.80
1.00
March June September
Botryosphaeria dothidea
0.00
0.20
0.40
0.60
0.80
1.00
March June September
Lasiodiplodia spp.
0.00
0.20
0.40
0.60
0.80
1.00
March June September
Cytospora spp.
0.00
0.20
0.40
0.60
0.80
1.00
March June September
New shoot One-year shoot
Neofusicoccum spp.
0.00
0.20
0.40
0.60
0.80
1.00
March June September
New shoot One-year shoot
Diplodia spp.
Inci
de
nce
of
lan
ten
t in
fect
ion
of
sho
ots
Month of 2016
82
Figure 7. Incidences of latent infections of new-emerged shoots and old 1-year shoots caused by six canker-
pathogen groups from prune Orchard 3 in Yuba County. The real-time PCR assay was applied to process these shoot
samples collected from three time points in 2016.
Figure 8. Comparison in mean molecular severities (MS) between new-emerged shoots and 1-year-old shoots
quantified for each of the six canker-causing pathogens. Three samplings were collected and processed in prune
Orchard 3 in Yuba County. The real-time PCR was applied to obtain MS data, and 32 shoots were processed for
each sampling.
Objective 4: Continue to study the efficacy of certain fungicides to control canker disease.
The 2016 experimental results of the fungicide trial in the prune orchard in Yuba County
demonstrated that the fungicides Quilt Xcell and Topsin M (70 WP) were the most significantly
effective in reducing the incidence of infection under natural infection conditions in (Figure 9).
Results showed that compared with control, the incidences of canker on wounds treated with
other fungicides, including Pristine + Pentra Bark, VitiSeal, Tebuconazole and Pristine +
VitiSeal, were not significantly reduced. Thus, this year’s experiment showed that these
fungicides were not effective in reducing canker development. In the 2015 experiment, again the
Topsin M was the most effective fungicide treatment while the efficacy of Quilt Xcell was not
consistent between the two years.
0.00
2.00
4.00
6.00
8.00
10.00
March June September
Phomopsis spp.
ab
0.00
2.00
4.00
6.00
8.00
10.00
March June September
Botryosphaeria dothidea
ba
abb
a
0.00
2.00
4.00
6.00
8.00
10.00
March June September
Lasiodiplodia spp.
a
aaaab
0.00
2.00
4.00
6.00
8.00
10.00
March June September
Cytospora spp.
aaab
a
b
0.00
2.00
4.00
6.00
8.00
10.00
March June SeptemberNew shoot One-year shoot
Neofusicoccum spp.
aa
0.00
2.00
4.00
6.00
8.00
10.00
March June SeptemberNew shoot One-year shoot
Diplodia spp.
Mo
lecu
lar
seve
rity
of l
ante
nt
infe
ctio
n o
f sh
oo
ts
Month of 2016
83
The same experiments using the same fungicide and fungicide combinations had been
repeated in the December 2016 and results will be collected in December 2017. In addition, a
new fungicide trial will be initiated using Topsin as the standard and other different
combinations of fungicides in an orchard in Yuba County.
Figure 9. Efficacy of fungicide treatments applied after pruning dried plum shoots to reduce canker development in
Orchard 1 under infection by natural spore inoculum. The trees were pruned on December 9, 2015, and the pruning
wounds were painted with different fungicides before a rain event. The disease was recorded on December 7, 2016,
and the average value of disease incidence for each fungicide treatment was calculated from the two replicates each
with 10 pruned shoots.
Objective 5: Continue to study on the putative effects of sunburn of shoots on pathogen
infection and canker disease development.
The disease was recorded in late November of 2016. From two replicates, there was no
significant difference in canker incidence between sunburn treatment and non-sunburn treatment
for each of the pathogens Cytospora spp. and L. citricola. However, the canker incidence caused
by Cytospora spp. was significantly lower than the incidence of L. citricola (Figure 10),
demonstrating the higher virulence of Lasiodiplodia than that of Cytospora in causing canker
development.
84
Figure 10. Incidence of canker disease on shoots for two canker-causing pathogens, Cytospora and Lasiodiplodia
spp. Two treatments: sunburn treatment (see text for details) and non-treatment were conducted in a prune orchard at
Kearney Agricultural Research and Extension Center to study the possible effect of sunburn on canker incidence for
each of the two pathogens.
ECONOMIC BENEFITS
Managing canker diseases of dried plum will lead to longer lifespan of the trees. Although it is
difficult to estimate the benefits, the results of treating pruning wounds with Topsin-M show a
significant reduction of infections by Cytospora and one would think that this fungicide could be
sprayed after pruning to protect wounds from infection.
SUMMARY
This study in 2016 focused on 5 objectives. We continuously involved in monthly inoculations
on wounded shoots by pruning in March in a prune orchard at Kearney Agric. Research and
Extension Center. Two canker-causing pathogens, Lasiodiplodia citricola and Cytospora spp.
were used in inoculations. Disease assessments in November showed similar patterns of canker
development for both pathogens. The early inoculations from March to May resulted in
significantly higher incidence and canker severity than did the later inoculations with these fungi.
This implies that after pruning in early spring, infections that occur in spring and early summer
could bring about high risk of canker development. Thus, treating pruning wounds with
fungicides in early season is very important to reduce canker diseases. In 2016, three prune
orchards in Yuba County of California were identified. Rain samples were collected separately
from each of these orchards four times in spring and early summer. Our previously-developed
85
real-time PCR quantification assay was applied to quantify the spore densities of each of six
canker-causing pathogens in each rain sample: Phomopsis spp., Botryosphaeria dothidea,
Lasiodiplodia spp., Cytospora spp., Neofusicoccum spp. and Diplodia spp. We did not find any
spores of Phomopsis or Diplodia spp. in any of the rain samples. Cytospora spp. was major
pathogen detected in most rain samples in these orchards. Lasiodiplodia spp. was found in all the
three orchards especially in early season. Both B. dothidea and Neofusicoccum spp. were
detected from only some rain samples, indicating that they serve as minor species of the
pathogen populations in rain water. Newly emerged shoots and old shoots where the new shoots
emerged from were also sampled in these three orchards in March, June and September 2016.
Our published real-time PCR quantification assay was also applied to quantify the latent
infection level for each of the six canker-causing species mentioned above. We introduced
Molecular Severity (MS) by quantifying the fungal DNA from the latent infections of these
shoots. Similar patterns of latent infections were observed among the three orchards. The overall
results showed that B. dothidea, Lasiodiplodia spp. and Cytospora spp. were the three
predominant species causing latent infection of shoots. Phomopsis spp. and Neofusicoccum spp.
infrequently existed in shoots and they were not consistent. Diplodia spp. did not exist in any of
the shoot samples. In few days after the new shoots developed (early stage samples), the MSs
were significant lower than the MSs in old shoots. However, this difference was reduced later in
season, indicating an increase (accumulation with time) of latent infections in the new shoots.
The results also implied that these pathogens indicate endophytic features in young healthy
shoots that need further investigation. For instance, if an inoculum source of these pathogens
were close to a nursery, it would be possible these infections to establish in the young looking
plants as early as before leaving the nursery and/or even in the field during the first year of
planting. Thus, it is essential to protect the wounds created during the selection of primary
scaffolds of trees. We continuously involved in fungicide trials in 2015 and 2016. The results
demonstrated that the fungicide Topsin M (70 WP) significantly reduced canker incidence as
compared with other fungicides and the results were consistent in both 2015 and 2016 trials. In
contrast, the fungicide Quilt Xcell (propiconazole+azoxystrobin) reduced canker incidence in
2015, had no effect in 2016. In 2015 we showed effect of sunburn increasing the incidence of
canker, but in 2016 did not affect the incidence of cankers. When the two canker pathogens were
compared, it was determined that Lasiodiplodia spp. were more aggressive (virulent) than
Cytospora spp. in causing canker disease.
References
Chen, S. F., Morgan, D. P., Hasey, J. K., Anderson, K., and Michailides, T. J. 2014. Phylogeny,
morphology, distribution, and pathogenicity of Botryosphaeriaceae and Diaporthaceae from
English walnut in California. Plant Disease 98: 636-652.
86
Adams, G. C., and Jacobi, W. R. 2016. Cytospora canker of Hardwoods. USDA Forest Service
RMRS-GTR-335: 91-93.
Luo, Y., Gu, S., Felts, D., Puckett, R. D., Morgan, D. P. and Michailides, T. J. 2017.
Development of qPCR systems to quantify shoot infections by canker-causing pathogens in stone
fruits and nut crops. Journal of Applied Microbiology (in press).
87
INVESTIGATING INCIDENCE AND TYPE OF WOOD DECAY FUNGI IN
CALIFORNIA PRUNE ORCHARDS
Bob Johnson, Franz Neiderholzer, Dave Doll, Florent Trouillas, Matteo Garbelotto, Neil
McRoberts, and Dave Rizzo
Wood decay fungi reduce the structural integrity of trees, leading to wind-driven collapses and
scaffold limb breakage, causing tree loss and reduced production in the prune growing regions of
California. Wood decay is caused by a wide array of fungi that colonize and digest the
heartwood, and sometimes sapwood, in living trees. Heartwood, being composed of dead xylem
cells, serves as an area of “storage” for plant byproducts and provides structural support for the
tree; sapwood conducts water and tends to be more resistant to decay. This group of fungi
colonize the heartwood; cellulose and lignin are degraded leading to a reduction of the structural
integrity of the trees. Limb breakage as a result of decay can have significant impacts on yield,
and loss of multiple trees over several years leads to orchard decline and eventual removal.
OBJECTIVES
1. Identify the principle fungi associated with heart-rot diseases of dried plum in California
2. Determine the infection process in orchards.
3. Design and employ taxonomic-specific molecular primers for early detection of decay fungi on
standing trees.
PROCEDURES
In 2016 we carried out nine whole orchard assessments in Sutter county, and identified an
additional six orchards for assessment in early 2017. Individual decay samples have been
collected from, Yolo, Solano, Tulare, and Fresno counties. A high incidence Phellinus
tuberculosus (formerly P. pomaceus) was found in every sampled orchard older than 12 years in
the Sacramento Valley and was generally associated with major limb breakage. For this reason,
much of our focus has been on understanding the epidemiology and biology of Phellinus sp. in
prune orchards.
Efficient protocols for the isolation of wood-decay fungi from decay samples are being
developed. Samples, approximately 2mm x 2mm, from decayed areas are plated onto Water
Agar (WA) and 1.5% Malt Extract Agar (MEA) both amended with benomyl (4µg a.i./ml) and
streptomycin sulfate (100 µg/ml) and sub-cultured onto 2% MEA after incubation at room
temperature for 7-14 days. When possible, fungal species are first identified to the genus level
based on morphological characteristics of fruiting bodies and growth in culture. DNA is
extracted from pure cultures or directly from fungal tissue using Prepman Ultra Sample
Preparation Reagent followed by PCR amplification of the ITS region. Isolates are sequenced
and identified using BLASTn searches in GenBank.
88
Whole orchard surveys were preceded by an interview with the grower and a tour of the
orchards. Information on each individual block was recorded including: tree age, rootstock
variety, irrigation type, cultural practices, and disease history, among others. Age of orchards
varies from 5 to 25+. In each orchard, measures of tree condition were recorded for at least 40
trees; presence of limb dieback, broken limbs, evident decay, fungal fruiting bodies, crown gall
and gumming were noted. The number of trees assessed per orchard increased when variability
amongst trees in the orchard was high.
Decayed limbs were collected from 10 trees in each orchard. In cases where no decay or limb
breakage were evident 10 stubs left from pruning were collected. In some trees two or three
branches with evidence of decay or a fungal fruiting body were collected. Isolations were carried
out as described from all limb samples. In larger branches and when multiple branches were
collected from the same tree, multiple fungal isolation were made every 15cm along the length of
the branch (Figure 4).
Somatic incompatibility tests are a widely used method within studies of Basidiomycota to
delineate individuals within the same species that arose from unique infection events versus
individuals that spread clonally through the tree. Mycelia from compatible isolates will fuse and
grow as a single colony and are considered the same individual. Mycelia from incompatible
isolates will not fuse, and often form a visible barrage line and are considered unique individuals.
Somatic incompatibility pairings were carried out with multiple isolates from the same tree to
investigate the number of infection events in an individual tree. Pairings from different trees and
different orchards were made to determine the characteristics of an incompatible reaction. A
mycelial plug (2mm x 2mm) of each isolate were placed 1 cm apart on 2% MEA media.
Following incubation at room temperature in the dark for 14 days, incompatibility interactions
were scored as compatible (+) or incompatible (-).
We have begun testing protocols for extraction and amplification of fungal DNA directly from
wood, allowing us to examine early infections before they are noticeable or culturable. Previous
attempts at spore capture and germination from Phellinus spp. fruiting bodies have been
unsuccessful. However, protocol modifications are underway and should allow for spore
monitoring in the future.
RESULTS AND DISCUSSION
In 2015 and 2016 we identified decay fungi from orchards in Sutter, Yolo, Solano, Tulare, and
Fresno Counties (Table 1). Phellinus turberculosus (Figure 1) was the most abundant decay
fungi identified and was often associated with scaffold limb breakage. When present, P.
tuberculosus was widespread and at least 15% of trees contained a fruiting body, with as many
as 97% in older orchards. While these orchard assessments have been limited to Sutter county, a
clearer understanding of Phellinus biology and epidemiology is applicable to other prune
growing regions. In contrast to previous surveys in prune orchards, the prevalence of Fomitopsis
cajanderi was limited and no fruiting bodies were observed, but this fungus was identified by its
characteristic decay. Trametes, Stereum, and Ceriporia were found dead wood or stumps,
associated with limited decay and were limited in their distribution within the orchard. The status
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and pathogenicity of Antrodia spp. are unknown, but in one case it was isolated from old broken
branch. Ganoderma sp. is known to cause root and butt rot in other Prunus, but its distribution in
prune remains unknown at this time.
Table 1. Wood decay fungi identified in prune orchards in California.
Fungal species Number of
orchards
Status in Orchard County
Phellinus tuberculosus 13 Wide Spread Sutter, Yolo, Solano
Trametes versicolor 3 Limited Sutter, Yolo
Fomitopsis cajanderi 1 Limited Sutter
Stereum hirsutum 3 Limited Sutter, Solano
Ceriporia lacerata 1 Unknown Sutter
Antrodia sp. 1 Unknown Tulare
Ganoderma sp. 1 Unknown Fresno
Orchards older than 12 years showed significant signs of P. tuberculosus infection, the
proportion of trees having broken limbs and fruiting bodies generally increased with orchard age
(Figure 1 and 3). When fruiting bodies were present, we were able to isolate P. tuberculosus
from 90% of sampled broken limbs. Infected limbs all contained one or several large pruning
wounds (>5cm in diameter), suggesting this as a site of infection, in agreement with previous
studies.
In two young orchards, planted in 2009 and 2011, showing no signs of P. tuberculosus and few if
any broken limbs, 10 pruning stubs were collected from the crotch of the tree (Figure 3). The
size of the pruning stubs was different in the two orchards. In the 2009 orchard average stub size
was 12cm long and 5cm in diameter, average size in 2011 orchard was 5cm long and 3cm in
diameter. In the 2009 orchard, 8 of the stubs showed signs of decay; of the stubs that showed
signs of decay, P. tuberculosus was isolated from 5, while only Trichoderma sp. was isolated
from the other three. In the 2011 orchard, no decay was evident in pruning stubs and no wood
decay fungi were isolated. The presence of Trichoderma sp. is intriguing, as it has been tested as
a biocontrol in other cropping systems, and is often isolated from decayed tissue when no wood
decay fungi can be recovered. Additionally, in several instances, Trichoderma sp. contamination
of Phellinus spp. and Ganoderma spp. cultures in the lab, rendered those cultures unrecoverable.
Somatic incompatibility pairings revealed that multiple individuals of P. tuberculosus were
present within the same tree and/or the same branch, but also that single individuals can span
multiple scaffold limbs (Table 2, Figure 4). In the case of tree 95A (Table 2A, Figure 2A) the
presence of the same individual in three scaffold limbs suggest that infection took place near or
below the crotch and spread up through the scaffolds. When multiple individuals were found in
the same tree, there were multiple infection events that took place in that tree.
Our findings show that P. tuberculosus is a significant contributor to limb breakage and loss of
yield in prune orchards. It is unclear what role weakening of trees by abiotic stress and other
disease pressures play in facilitating Phellinus infection. The difference in the presence of
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Phellinus in the 2009 versus 2011 orchards cannot be attributed to one factor; but possibly to
several, including inoculum pressure, size and diameter of pruning wound, timing of pruning,
and orchard age and will be the focus of future studies. The high rate of infected pruning stubs in
the 2009 orchard coupled with their position at or near the crotch of the tree and the ability of P.
tuberculosus to move into multiple scaffolds suggests this wounds at this site could be important
in attempts to manage this disease and limit scaffold limb breakage. Future studies will focus on
understanding the rate and direction spread of P. tuberculosus in a tree, as well as exploring
control options to limit its spread to other orchards.
Figure 1. Proportion of missing trees, limbs with evidence of decay, and trees with fungal fruiting bodies in orchards of various age in Sutter County.
0
0.2
0.4
0.6
0.8
1
1990 1991 1994 1994 1995 2001 2007 2009 2011
Pro
po
rtio
n o
f Tr
es
Planting Year
Prune Orchard Surveys for Wood DecayMissing Trees
Decay
Fungal Fruiting Body
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Figure 2. Phellinus tuberculosus. Clockwise from left, fruiting bodies in 12year old prune orchard, white rot in broken scaffold limb, 14day old culture on 2%MEA.
Figure 3. Typical tree condition in prune orchards of different ages infected with P. tuberculosus. From left to right. 1991, 1994, 2001, 2009. Red arrow indicates example of pruning stubs from which P. tuberculosus was isolated in the 2009 orchard.
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Table 2. Somatic Incompatibility Pairings of multiple isolates from same tree. Each table represents a different tree, while numbers represent individual isolates within that tree. Squares with a (+) or (-) indicate a pairing was done, (+) represents a compatible reaction and (-) an incompatible reaction. See also Figure 4.
A 1 2 3 5 6 7 B 1 2 3 4 5 6 C 1 2 3 4 5 6 7
1 + 1 + 1 +
2 + + 2 - + 2 + +
3 + + 3 - + 3 + +
5 + + + 4 - - - + 4 - +
6 + + + 5 + + 5 + +
7 + + 6 - + + + 6 - +
7 + + - - +
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Figure 4. A, B, and C show source of individual isolates, each limb was attached at the crotch below the lowest number. D, Incompatible reaction, note formation of dark line between isolates. E, compatible reaction, not lack of dark line between isolates.
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BUDGET SUMMARY
Grant support from the almond board is being used concurrently to cover salary and other
expenses. Remaining funds will be used to continue this project through spring of 2017 and will
be fully expended by April, 2017.
16-17 available expended remaining
Employee salary and benefits 7250.59 0 7250.59
Supplies and Equipment 2000 0 2000
Travel 1061 0 1061
Total 10311.59 0 10311.59
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CALIFORNIA DRIED PLUM RESEARCH REPORTS DATABASE
Megan Crivelli, Janet Zalom & Carlos H. Crisosto
Fruit & Nut Research and Information Center (FNRIC)
http://fruitsandnuts.ucdavis.edu.
Abstract: A complete database of California Dried Plum Board Annual Research Reports from
1961 to 2015 have been displayed as a unique website, http://ucanr.edu/sites/driedplum, linked to
the Fruit & Nut Research and Information Center (FNRIC) website:
http://fruitsandnuts.ucdavis.edu. These reports, organized by “category” and “year” topics, are
available electronically and can be easily accessed. The FNRIC used Google Analytics to assess
website visits. From January 1 through November 30, 2016, the Dried Plum Research Reports
database website received 3,877 page views. Regarding geographical distribution of the visits,
30.6% of the visits originated with the United States and 66.1% of those originated in California.
The United Kingdom (22.8%), Russia (9.8%) and Chile (3.8%) led the foreign visits.
Objective
The California Dried Plum Research Reports Database is a database of Annual Research Reports
submitted to the California Dried Plum Board from 1961 to the present. Reports encompass
research in various aspects of dried plum/prune production. The reports, in pdf format, are
housed in the Repository of the University of California Division of Agricultural & Natural
Resources. Files may be viewed and downloaded individually. The database is updated and
website visit statistics are summarized annually.
The database is displayed as a unique website: http://ucanr.edu/sites/driedplum/ linked to the
Fruit & Nut Research and Information Center website: http://fruitsandnuts.ucdavis.edu/
Procedure
Reports for 2015 were prepared and added to the Repository in January, integrating these
reports into the “category” and “year” page displays for the Dried Plum Research Reports
Database.
FNRIC used Google Analytics to assess Total Monthly Page Views and Unique Visits as
a measure of webpage visits. In addition, domestic and international page views are
summarized and presented here for January 1 through November 30, 2016 (Tables 2 and
3).
Results and Conclusions
From January 1 through November 30, 2016, the Dried Plum Research Reports database
received 3,877 page views during 945 visits, with 75% of those from new visitors. The highest
usage months were February and November. Regarding geographical distribution of the visits,
30.6% of the visits originated in the United States, with 66.1% of those visits from California
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(Tables 1 – 4). The website has been “live” for the entire year 2014, and we anticipate future
maintenance to maintain this stability.
In 2014, the Fruit & Nut Research and Information Center website and all associated websites,
including this database website, were converted to a mobile-friendly format. During 2015 and
2016, the FNRIC maintained the mobile-friendly version of the Dried Plum Database.
Table 1. Monthly page view summary for
Jan. – Nov. 2016
Month Page views 2016 Users 2016
Jan 463 145
Feb 590 73
Mar 255 62
Apr 338 53
May 202 104
Jun 244 175
Jul 187 91
Aug 422 97
Sep 182 25
Oct 394 40
Nov 600 134
Table 2. Global distribution of database
visitors for Jan. – Nov. 2016
Country % Visits 2016
United States 30.6
United Kingdom 22.8
Russia 9.8
Chile 3.8
Austria 3.1
Germany 2.4
China 2.1
Iraq 1.9
Italy 1.8
Table 3. Distribution of database visitors
within the United States for Jan. – Nov. 2016
State % Visits 2016
California 66.1
New York 5.0
Virginia 3.2
Michigan 1.8
Texas 1.8
Minnesota 1.6
Colorado 1.3
D.C. 1.3
Florida 1.3
Table 4. Distribution of database visitors
within California for Jan. – Nov. 2016
City % Visits 2016
Davis 24.6
Sacramento 7.5
Chico 7.1
SLO 6.4
Fresno 6.0
Yuba City 5.6
San Francisco 4.4
Modesto 4.0
Red Bluff 3.6
Roseville 2.8
Budget Summary: The $1,500 allocated for this project was toward salaries & benefits of FNRIC staff.
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University of California Cooperative Extension
2016 Horticulture Internship
Franz Niederholzer
UCCE Farm Advisor
Colusa/Sutter/Yuba Counties
The University of California Cooperative Extension (UCCE) is in the midst of a major personnel shift.
Experienced advisors are retiring. Talented candidates are being hired and more are needed. New hires
will/do cover more territory than their predecessors -- all will cover multiple counties and multiple
commodities. Many new advisors are coming from outside California and are not familiar with the crops
and communities UCCE serves or how UCCE functions. Tree crop interns will familiarize themselves with
the region, crops and job of extension while helping current advisors do their expanded jobs.
Objectives:
Provide sustained support (60%) for a qualified UC employee to work on prune production
research and education in the Sacramento Valley.
Help existing farm advisors deliver applied research and extension to prune growers.
Plans and Procedures:
Specific tasks and deliverables were determined after discussing with the prune industry. The search and
hiring process will be facilitated by the UC FNRIC. The chosen candidate will work on the following:
crop management strategies that maximize consistent grower return per acre, thinning strategies, pruning
for maximum thinning efficiency, field sizing research and publications to minimize the loss of valuable
fruit, while avoiding the delivery of poor quality fruit, and developing an annual prune almanac calendar
similar to what has been done in the past by the California Canning Peach Association.
Results
The Horticulture Internship Program is being funded by the Almond Board of California and the California
Dried Plum Board, and the position will be advertised at the beginning of 2017 by the University of
California Cooperative Extension. The preferred candidate should be a recent graduate (MS or PhD) or
graduate student in Horticulture, Agriculture, and/or Biological Sciences. This paid internship offers the
successful candidate an opportunity to learn about and assist with cutting edge applied research and
education programs focused on sustainable agriculture, integrated pest management, water use efficiency,
improved water quality, crop quality, and innovative practices to minimize environmental impacts while
ensuring quality and economic viability of tree crop production. The intern will also participate in
educational and outreach efforts to educate farmers, pest control professionals, and the general public
regarding scientific findings and improve methodologies of crop production and environmental protection.
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While working closely with experienced Cooperative Extension Farm Advisors, the intern will learn about
the latest in agricultural practices and technologies pertaining to almonds, dried plums, and other tree crops.
The successful candidate will interact with the individuals and organizations (public and private) that
support California agriculture.
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LIFE CYCLE ASSESSMENT:
A TOOL FOR QUANTIFYING THE ENVIRONMENTAL IMPACTS OF FRESH AND
DRIED PLUM PRODUCTION
Elias Marvinney
Sonja Brodt
Alissa Kendall
OBJECTIVE
Life Cycle Assessment (LCA) is a comprehensive approach for assessing the
environmental impacts and resources used throughout the full life cycle of a system or a product,
such as an orchard crop. LCAs typically account for the energy and environmental impacts of all
stages of a product’s life cycle, such as acquisition of raw materials, the production process,
handling of waste byproducts, and more. To date, this life cycle model of plum/prune production
considers the quantity of irrigation water used specific to orchard location, energy and fuel
required for pumping water, energy required to produce, transport, and apply fertilizers and
pesticides, energy needed for harvest, transport, and post-harvest processing including drying.
By characterizing, quantifying, and interpreting the environmental flows from “cradle-to-
grave,” LCAs can play an important role in assessing the greenhouse gas (GHG) and pollutant
emissions associated with agricultural products, which tend to be more dependent on regionally
specific conditions and factors than industrial products. Importantly, LCAs can also identify
“hot-spots” - opportunities along the production chain for reducing energy consumption and
pollutant/ GHG emissions. The LCA approach can also identify and quantify potential GHG and
pollutant reductions that occur in the production process. This plum/prune model also includes
estimates of carbon sequestration in orchard floor soils as well as avoided emissions from fossil-
fuel based energy production from the use of orchard waste biomass as an electricity feedstock.
The life cycle perspective is also useful in avoiding problem shifting from one phase of
the life cycle to another or from one environmental issue to another. For example, the use of
synthetic nitrogen fertilizer accounts for a relatively modest portion of the total GHG emissions
of field production for many crops when only considering on-farm operations and soil emissions
of nitrous oxide (caused by adding nitrogen to the soil). However, when the energy-intensive
manufacturing of the fertilizer is included as a stage in the analysis, the portion of GHG
emissions attributable to synthetic nitrogen use can increase by 30-150%, typically making it one
of the largest sources of total GHG emissions in the carbon footprint of many crops, and
warranting much more attention in GHG reduction efforts.
Greenhouse gas tracking or “carbon footprint” LCAs have applications for growers, food
manufacturers, and retailers interested in reducing the GHG emissions of their products. Growers
might use LCA models to estimate total emissions and understand where their greatest emissions
are occurring, as well as to estimate the effects of different farming practices. They may also be
used in the future to help focus publicly funded GHG emissions reductions incentive programs
such as farm bill conservation programs or California’s cap-and-trade Greenhouse Gas
Reduction Fund, or to demonstrate eligibility for market-based carbon offsets as these programs
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become available. Manufacturers, retailers, and commodity organizations can use LCAs on a
farm-level or industry-wide basis for marketing, labeling, or certification purposes.
PROCEDURE
Data on plum and prune production were collected from a variety of sources. UC Davis
Economic Cost/ Return Studies as well as some grower interviews provided generalized data on
typical practices, equipment, and agrochemical inputs; the USDA NASS Cropscape dataset
provides orchard location in the Central Valley; the California DWR provided data on surface
water delivery infrastructure and groundwater depth; an orchard clearing company provided data
on biomass removal; GaBi and EcoInvent provided life cycle-based data on resource use and
pollutant emissions for various inputs and manufacturing processes; the CDFA provided yield
and market share (of dried vs fresh plum) data; and the California Biomass Collaborative
provided data on soil carbon accumulation in orchards and California biomass power plant
locations and characteristics. Data on post-harvest processing and other external or contracted
operations (nursery production, transportation, pollination, etc) were obtained from published
literature, questionnaires, and interviews.
The above data were used to develop an LCA model of plum and prune production in
ArcGIS and Microsoft Excel. This model sums the life cycle emission and energy use data for all
inputs and processes occurring in plum/prune production, treating each production year, from
orchard establishment through maturity, separately. Results are calculated on the basis of several
functional units: per acre of orchard, per kilogram of fruit, and per nutritional calorie.
RESULTS AND CONCLUSIONS
Previously reported results indicate that on-site emissions and energy use are dominated
by nutrient management – in particular by the production and application of nitrogen fertilizer,
and that off-site emissions and energy use are dominated by natural gas combustion in drying
operations (Fig. 1). Post-harvest drying and processing accounts for greater emissions annually
than all other orchard inputs and operations put together (Fig 2). When considered from nursery
tree production through harvest on a per acre basis, plum/prune production environmental
impacts compare favorably to other major California orchard crops. However, post-harvest
drying drives the impacts of production significantly higher than other orchard crops. In the
charts below, GHG impacts are shown because A) this impact category relates directly to
financial implications for the plum industry via California carbon markets, and B) most other air
pollutant emissions are roughly similar in pattern (but not magnitude) in industrial processes.
Quantification of temporary carbon storage in standing biomass of plum/prune orchards
and estimates of soil carbon accumulation indicate some potential for offset of these GHG
impacts. In previous versions of this orchard LCA model, the use of biomass from orchard
removal provides a significant offset of total on-farm GHG emissions (Fig. 3). Results from
almond and walnut orchard models indicate that adoption of certain biomass management
practices such as the use of processing byproducts for on-site energy generation and the use of
orchard clearing biomass for off-site energy generation can increase such offsets to the point
where net orchard greenhouse gas impacts are close to zero or even negative (representing a net
reduction in GHG emission for plum production).
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Organic walnut production is an example of an orchard production system analyzed using
this LCA modeling procedure where post-harvest energy use (here, for refrigeration of nuts used
in lieu of fumigation) represents the major driver of system impacts. In this case study, use of
walnut shell in on-site energy generation using a Biomax100 modular gasification system
resulted in significant offset of fossil-fuel based energy and natural gas use, from on-site
production of electricity and producer gas respectively. Given the importance of natural gas
burning in plum drying operations, this indicates potential for a similar system operating on a
plum pit feedstock to offset the impacts of plum post-harvest operations. The implications and
benefits of such a scenario will be analyzed in future iterations of the plum orchard LCA model.
Greenhouse gas and pollutant offsets from use of orchard clearing biomass for energy
production have changed significantly since this model was first developed. The original
iteration of this model assumed that about 95% of cleared orchard biomass was directed to
biomass energy facilities and resulted in avoided fossil fuel-based emissions. Given plant
closures and updated orchard location information (Fig. 4), this estimate has been reduced to
74%, with a corresponding increase in burning (for firewood or in-field) and mulching biomass
fates. As biomass energy facilities close, the distance for transport and likelihood of alternative
biomass fates increase while the total potential for biomass energy generation from orchard
wastes decreases (Fig. 5).
Calculation of these changes in potential biomass energy credits to prune production is
based on a number of assumptions. First, the exact location and size of any given prune block
affects the net impacts and probability of the use of orchard clearing biomass for energy
production and fossil fuel displacement credits – thus, the more accurate the orchard map the
more accurate the estimates. Recent work by LandIQ on orchard spatial mapping and age
distribution has indicated that the USDA NASS Cropscape Data Layer (CDL), on which this
analysis is based, is only about 75% accurate, which will have a proportional effect on the
accuracy of the plum biomass energy credit calculations.
Second, the production of clearing biomass from plum orchards is estimated based on
orchard clearing data from a collaborating agriservices company as well as the assumed orchard
productive lifespan of 30 years from UC Davis Cost and Return Studies. This generalized
assessment assumes an equal distribution of orchard ages over every plum block mapped in the
CDL. In reality, the specific demographics of plum orchards will determine when clearing
biomass is available and how much “competition” from other perennial crop biomass sources
exists in any given year – thus, orchard age data are needed to go from the current
chronologically generalized model to a year-specific model that can make accurate predictions of
plum production impacts going forward, on a year to year basis. These concerns will be
addressed in the next iteration of this model.
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Figure 1. “Nursery to orchard gate” environmental impacts of major California tree crops as
GWP100 greenhouse gas emissions (kilograms carbon dioxide equivalent over a 100 year
timeframe). Impacts are labeled by management category, NOT including post-harvest
processing.
Figure 2. “Nursery to post-harvest facility gate” environmental impacts of prune production
under drip irrigation as GWP100 greenhouse gas emissions (kilograms carbon dioxide equivalent
over a 100 year timeframe). Impacts are labeled by management category (including post-
harvest processing and drying) and production stage (on farm, off farm, or transport).
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Figure 3. Change in biomass co-product credits for “nursery to post-harvest facility gate”
environmental impacts of prune production under drip irrigation as GWP100 greenhouse gas
emissions (kilograms carbon dioxide equivalent over a 100 year timeframe). The reduction is
caused by biomass power plant closures in the Central Valley and a corresponding assumed
increase in burning and other biomass fates.
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Figure 4. California biomass energy infrastructure and plum orchard distribution as of spring
2016.
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Figure 5. California biomass energy infrastructure as a determinant of the available biomass-to-
energy “sink”. Plum acreage is color coded according to the quantity of orchard clearing
biomass that could potentially go to energy production, based on power plant distance and
ability to accept biomass feedstock and accounting for ‘competition’ from other perennial crops.
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2016 Prune Research tour
Location : Yuba ,Butte, Tehama and UC Davis .
Time : 8:30 am Wednesday May 11 to 1:00 pm May 12.
Motel : Granzella’s Inn 391 6th street Williams California 95987. Phone 530-473-3310 or
http://www.granzellasinn.com/
Contact: Richard P. Buchner 530-527-3101 or cell 530-941-8177 Franz Niederholzer 530-822-7515 or cell
530-218-2359.
Directions to the first stop: The Miki orchard is at 801 Boyer Road, north of Marysville about 8 miles on
the east side of Hwy 70. Follow Boyer Rd to the east into the prune orchards and Franz will have a sign
up to show where to turn off.
Sponsors: California Dried Plum Board and Sunsweet Growers.
Day 1 Wednesday May 11
2016 Prune Research Tour starts 8:30 am at the MIKI prune Rootstock experiment in Yuba county (see
directions above)
1) 8:30 to 9:30 am Yuba Rootstock experiment – Franz Niederholzer
9:30 to 10:30 travel to Deseret Rootstock experiment.
2) 10:30 to 11:30 Butte rootstock experiment – Rich Buchner
11:30 to 12:15 travel to the Corning Sun sweet dryer
12:15 to 1:15 Lunch compliments of Mark Gilles , Sunsweet, Corning dryer , lunch presentation TBA by
Sunsweet growers.
1:15 to 1:45 travel to Vina Monastary .
3) 1:45 to 2:45 Tour the 16th century chapter house with the monastary
2:45 to 4:00 travel to hotel, Granzella’s in Williams (reservations on your own)
4:00 to 5:00 Beer and wine social at the motel.
5:00 Dinner at Louis Cairos in Williams
Day 2 Thursday May 12
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7:00 to 8:00 Breakfast at the motel or Granzella’s restaurant
8:00 to 9:00 travel to UC Davis
4) 9:00 to 9:30 Prune seedling block at Davis-Ted DeJong and Sarah Castro
5) 9:30 to 10:00 Prune vegetation management - Brad Hanson
6) 10:00 to 10:30 Prune nutrition work - Patrick Brown
10:30 to 11:00 travel to Wolfskill research orchards
7) 11:00 to 11:30 Rootstock experiment -Katherine Pope
8) 11:30 to 12:00 Cold/wet at bloom - Franz Niederholzer and Rich Buchner
12:00 to 12:15 travel to winters
12:15 to 1:00 lunch in winters
1:00 adjourn and head home
