WALNUT IMPROVEMENT PROGRAM

Gale McGranahan, John Hansen, Ben Iwakiri, and Ron Snyder

ABSTRACT

This report covers the progress made in the USDA-funded WalnutImprovement Program in 1984. Two Juglans regia rootstock trialsdesigned to assess variation in seedling vigor in the first growingseason are summarized. The results indicate that seedlings fromIAmigo I and 'Eureka' are the most vigorous. 'Waterloo' seedlingsare the most uniform. No J. regia family approached J. hindsiiin vigor. A comparison of 'Manregian' seedlings obtained fromOregon with 'Manregian' seedlings from California (UCD varietyblock) indicated that there are no significant differences betweenthe two sources in vigor. A trial of J. hindsil and J. californicaseedlings showed that the source of J. hindsii is a significantfactor ln vigor. This trial is a long-term study designed tocharacterize variation in a number of traits including Phytophthorasusceptibility in California black walnuts. Other aspects ofthe Walnut Improvement Program aimed at improving rootstock areoutlined.

Seedling selection evaluation was continued. ApproXlmately 200seedlings derived from controlled pollinations prior to 1978 wereheld for additional evaluations. These include 150 which havehad less than 2 years evaluation, and 56 which are potential selec-tions or are being saved as representative genotypes. The majorityof the seedlings leaf out after 'Hartley', are laterally fruitful,and have high quality nuts. Several of these are ready to harvestat, 'Payne' time0 A list of selections (potential releases) willbe . made available to farm advisors along with instructions forcompleting the test agreement later this year. Those wishingto participate in selection evaluation in their counties are encour-aged to do so. A summary of 1983 cultlvar and selection evaluationsis included in this report.

OBJECTIVE

The goal of the Walnut Improvement Program is to develop germplasmwhich will provide the walnut industry with a means to overcomethe major problems limiting walnut production in the United States.These problems, as identifled by farm advisors through their grow-ers, industry representatives, and scientists involved in walnutresearch, are the blackline virus disease caused by the cherryleafroll virus and Phytophthora root and crown rots. Our programis also involved in the development of new sources of germplasm(see Tulecke & McGranahan), micropropagatlon, and in the evaluationof seedlings and selections developed through controlled crossingprior to 1978.

SPECIFIC OBJECTIVES AND PROCEDURES

A. Blackline.

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Several genetic approaches are available for reducing theimpact of the blackline virus on the walnut industry. Oneis the development of superior rootstocks which will tolerateinfection by the cherry leafroll virus; another is the incorpor-ation of hypersensitivity into scion varieties. The latteris a long term project whose feasibility will be unknown untilthe genetics of the host reaction is understood.

Juglans regia L., the Persian walnut, is currently the onlyspecies known to tolerate the virus strains present in Cali-fornia. J. hindsii (Northern California black), J. nigra(Eastern black), J. californica (Southern California black),'Paradox', and pterocarya stenoptera ('Wingnut') all resistvirus infection to some extent by a hypersensitive reaction.This reaction causes a lethal girdle between an infected scionand a hypersensitive rootstock. Therefore, the source oftolerant rootstocks appears to be limited to Persian walnutsor, if only a few genes are responsible for the hypersensitivereaction, to a segregating backcross generation (e.g. 'Paradox'x J. regia).

Persian walnut rootstocks are understood to have many drawbacksincluding poor vigor and sensi tivity to di seases, nematodes,and adverse soil conditions. To determine whether there isvariation in seedling vigor, a study designed to compare firstyear growth in seedlings from six potential J. regia rootstocksources. was undertaken in 1983. At the end of the firstgrowing season a subset from this trial was replanted in arootknot nematode block under the direction of Mike McKenry.Because 'Manregian' had not been included in the initial study,a separate trial comparing 'Manregian' from Oregon (HarryLagerstedt) and 'Manregian' from California (UCD variety block)with J. hindsii, J. regia India, and 'Amigo' seedlings wasundertaken in 1984.

To determine whether superior tolerant rootstocks can be ob-tained in the first backcross generation, a replicated trialof 70 'Paradox' x J. regia were grafted onto J. hindsii andJ. regia rootstock for evaluation of their reaction to theblackline virus. This study also involves seedlings fromthe 'Paradox' x J. hindsii backcross, 'Paradox', J. regia,and J. hindsii to determine whether hypersensitivity is governedby one, two, or many genes. Additional 'Paradox' x J. ri::!giaseedlings were created this year by pollinating an isolated'Paradox' tree with J. regia pollen using bags of dehiscingcatkins as a pollen source. More than 1000 nuts resultedfrom this effort. From these studies it is expected thatthe feasibility of selecting rootstocks from among the 'Pardox'x J. regia population as well as the potential for breedingfor hypersensitivity in the scion will be determined. Prelimi-nary results from evaluations will be available in 1985.

A project aimed at assessing the effect of the blackline viruson own-rooted J. regia cuItivars is in the initial stages.Before evaluation is possible, methods for propagating matureJ. regia cultivars must be developed. Seven cultivars havebeen targeted for research in methods of micropropagation

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of mature J. regia cultivars.

B. Phytophthora.

Three approaches to the development of Phytophthora resistantor tolerant rootstock are being employed. The first is aimedat determining whether individual trees which have survivedin orchards that are severely infested with Phytophthora haverootstocks with genetic resistance. The first step has beento identify surviving individuals in the field and propagatethem through tissue culture. They will then be evaluatedfor their response to Phytophthora. The second approach in-volves interspecific hybridization between species with dif-ferent levels of resistance. Controlled crosses were madebetween J. ailantifolia (Japanese walnut), J. nigra, J. hindsii,and J. regia. The resulting seedlings will also be evaluatedfor their response to Phythophthora. The final approach isdesigned to provide additional information regarding the varia-tion within J. hindsii because it is a commonly used rootstockas well as a-parent of 'Paradox'. To assess the within speciesvariation, seed from J. hindsii trees in 17 locations wasfield planted together -with five sources of J. californica,one of J. regia, and one of a J. nigra which produces 'Royals'(J. nigra x J. hindsii). Data on germination, height, diameter,and number of branches was recorded. A subset of this collec-tion is being tested for its reaction to Phytophthora in artifi-cially infested soil in the greenhouse.

C. Evaluation and selection of seedlinqs for cultivar development.

The specific goal of this part of the Walnut Improvement Programis to evaluate and select promising individuals from amongprogeny of controlled crosses undertaken by Serr and Forde1973 to 1977. Data is collected annually on the followingtraits: dates of leafing, pollen shedding, female fertilrtyand harvest, lateral bud fruitfulness, yield, blight incidence,shell characteristics and seal, nut and kernel weight, kernelcolor, and frequency of blanks. Compiled data is reviewedby a panel which recommends action (select, save, or discard)on each seedling.

RESULTS AND DISCUSSION

A. Blackline

In both J. regia rootstock trials, J. hindsii was superiorto all the Persian walnut families in height, diameter, anduniformity at the end of the first growing season (Table 1).The most vigorous J. regia families in the 1983. trial were'Amigo' and 'Eureka'. The most uniform family determinedby the coefficient of variation (standard deviation/mean)was 'Waterloo'. 'Paradox' derived from J. hindsii SCN hadthe greatest mean diameter. In the 1984- trial 'Amigo' wasagain the most vigorous J. regia source. The two sourcesof 'MaIiregian'were almost identical in vigor which suggeststhat growers interested in using 'Manregian' will not improveperformance by obtaining seed from Oregon. (It had been sug-

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gested that the male parent of Oregon 'Manregian' might contri-bute substantially to the progeny's performance which couldaccount for the recommendation 'Manregian' in Orgeon). Ourresults confirm earlier studies that in terms of early vigor,'Manregian' is not superior to other sources of J. regia.Whether the superiority of 'Eureka' and 'Amigo' will be main-tained beyond the first year is unknown. .

Results from the rootknot nematode trials suggest that J.regia is more susceptible to rootknot infection than J. hindslior 'Paradox'. There was considerable variation, however,within all familities. This variation indicates that selectionwithin vigorous families followed by clonal propagation maybe the most promising method of obtaining rooknot nematoderesistant rootstock. It should be noted that rootknot nematodeis a potential problem only in sandy soils.

I

Micropropagated plantlets of mature J. regia cultivars('Chandler', 'Sunland', 'Chico', 67-11, 'Scharsh-Franquette','Vina', and 'Eureka') have been established and are in themultiplication phase in culture. These will be used to assessthe impact of blackline on own-rooted cultivars. Techniquesfor micropropagation will be reviewed in a chapter on tissuecuIture of Juglans in volume II of Tissue Culture in Forestry(Martinus Nijhoff publishers).

B. Phytophthora.

Micropropagated plantlets from seven surviving trees in Phytoph-thora infested orchards (Hagus, Wray, Mapco) are multiplying'in culture. A 'Wingnut' (resistant) and the rootstock ofa dying J. regia tree (susceptible) are included as controls.Rooting trials have been unsatisfactory and only a few individ-uals have been transferred to pots. Techniques for micropropa-gation of J. hindsii will be included in the previously men-tioned book-chapter.

Interspecific controlled pollinationsyielded .the following numbers:

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for PhY!.£J2hthora studies

% SET SEED

9 22

21 22

27 21

75 6

8 17

6 9

38 3

0 0

19 45

27 30

CROSS

J. nigra x J. regia

J. nis.ra x J. ailantifolia

J. nis.ra x J. hindsii

J. nigra x J. nigra

J. hindsii x J. res.iaJ. hindsii x J. ailantifolia

J. hindsii x J. hjindsiiJ. ailantifolia x J. res.iaJ. ailantifolia x J. ailantifolia

J. res.ia x J. ailantifolia

J. regia x J. hindsii

J. regia x J. regia

34

57

30

44

The resulting hybrid seed will be evaluated for Phytophthoraresistance in infested soil in the greenhouse.

The results of the black walnut rootstock study are shownin Table 2 for mean height, diameter, and the ratio of numberof growing tips to height. There were significant differencesin each trait which were due to family source. The two tallestfamilies were seedlings of J. californica. The least vigorousfamilies included one J. hindsii source, J. regia, and J.nigra. J. californica had significantly more growing tipsthan J. hindsii, J. regia, or J. nigra giving ita bushyappearance. For example an average J. californica, 50 cmtall, would have nine growing tips, one at the apical meristem,and eight branches over 5 cm long, while a typical J. hindsiiof the same height would have only one branch. -

This study on variation in black walnut is a long term study.Traits such as date of leaf abscission and bud break, ageat first flowering, crossability with J. regia as well asvigor and response to Phytophthora will all be used tocharacterize the species. From this information it will bepossible to eventually answer questions such as whether aprecocious rootstock has an affect on the precocity of thescion, whether there is variation in Phytophthora susceptibilityinn J. hindsii and how this affects the response of the'Paradox' offspring.

c. Evaluation and selection of seedlinqs for cultivar development.

After evaluation of data collected in 1983 on 15 traits relatedto yield and quality, approximately 206 seedlings derivedfrom controlled crosses 1973-1977 were saved for further evalua-tion. The majority of these (150) are part of the "78" serieswhich have not had the minimum of 2 years evaluation. Ofthe remainder two leaf out near 'Payne' time, but have yieldand quality characteristics which make them valuable for areaswithout blight problems, and 15 leaf out between 1 and 2 weeksafter 'Payne'. 'Hartley' would have been in this group thisyear, having leafed out 10 days after 'Payne'. The majorityof the seedlings selected (28) leaf out between 2 weeks after'Payne' and 'Franquette' time. A small population (9) leafout a month or more after 'Franquette'. These are not expectedto have any commercial value (yield is low, nuts are of poorquality) but they may be important in germplasm collectionsrepresenting the diversity present in leafing dates in Juglansregia.

Although harvest time is well correlated with leafing date,several individuals leafed out more than 1 week after 'Hartley',but were ready to harvest near 'Payne' time. Since late leafingcombined with early harvest would be desirable for the walnutindustry, the most promising of these individuals (76-131)will be made available for evaluation to nurseries or growers

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through their farm advisors if 1983 crack out confirms itspreviously excellent size and quality. In April 1985 a listof promising selections will be made available to farm advisorsalong with test agreements. If they have plots or growerswho would be willing to participate in selection evaluationthey should contact Gale McGranahan.

In addition to seedling evaluation, cultivar and selectionevaluations are also undertaken in this part of the program.The results from 1983 are presented in Tables 3 and 4. Thenumbered selections are those that may be released if fieldevaluations indicate that they are equal or superior to culti-vars commercially available. These also are available undertest agreement.

Several changes have been made in seedling selection and inevaluation procedures this year. One is aimed at clarifyingthe difference between seal and shell strength. Previously,a poor seal rating (three or higher) could represent eithera weak shell or a poor (open) seal. This year shell strengthwill be graded separately from seal.

CONCLUSION

We are often asked why we are not at present continuing to makecrosses between the best cultivars as was done by Serr and Forde.There are several reasons. First the manpower, time, and spacerequirements of a breeding program limit the number of areas whichcan be targeted for improvement. Blackline and Phytophthora prob-lems which can be approached through rootstock breeding have thehighest priority and therefore, our major emphasis is in thisarea. Secondly, the major gains in cultivar improvement for late-leafing, light-colored, laterally fruitful individuals have beenmade. Unless we have a new focus such as precocity or increasednuts per shoot and new germplasm to work with, the gains willbe minimal. With additional space and manpower our program wouldcontinue conventional cuItivar development, but with our limitedresources we have chosen to focus on the traits which will havethe most effect in increasing overall yields and decreasing costsfor the walnut industry.

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TABLE 1. Canparison of first year growth (English 83,84).

ROOTKNaI'HEIGHT DI1\ME'I'ER NEMATODE

5CXJRCE SPECIES 1 n mean (an) cv mean (urn) cv per gm roots

1983

J. hindsii PC hi 115 92.20a2 28.68 14.85ab 26.54 11

J. hindsii 5CN3 hi x re ('Paradox') 37 53.00 b 47.69 15.26a 36.50 11

'Amigo, re 102 48.59 be 50.67 11. 66 be 34.98 40

'Eureka' re 95 41.03 bed 55.15 11.57 be 37.71 20

'Paradox' (hi x re)x hi 129 37.74 bed 61.13 11.04 c 39.09

64-57 re 116 35.68 cd 55.52 10.64 c 42.72 63

I 'Waterloo' re 115 33.39 cd 44.79 10.33 c 36.28 7-...J 67-11 123 30.02 d 61.33 9.92 37.38 90I re c

'Serr' re 99 27.03 d 58.70 10.95 c 43.95 58

1984

J. hindsii P.c. hi 24 52.58a 33.30 10.83a 29.53

,li..nigo, re 65 34.74 b 47.08 8.80a 38.91

'India' (a) re 96 23.48 b 42.86 7.48a 33.21

'Manregian' re 40 22.20 b 37.59 7.a8a 33.31(Oregon)

'Manregian' re 34 22.00 b 46.60 6.97a 39.40(California)

'India' (b) re 96 19.10 b 32.51 7.47a 27.88

1 hi= hindsii re= regia2 Mean separation in colunms by Tukey' s HSD, 5% level.3 hindsii SCN,a 'Paradox' producer was provided by Driver Nurse...ry.

TABLJ:2. Comparison of first year growth (Blacks, 1984).

HEIGlrr DIAMETER BR1\NCHES/HTSOURCE SPECIESl n rrean(an) cv rrean (mn) cv mean CV

84-12 ca 48 64.21a2 36.50 12.79a2 37.09 .14 b2 44.6584-9 ea 8 61.13a 43.99 12.88ab 54.52 .22a 48.5383-84 hi 24 58.04ab 36.01 12.13ab 33.02 .04 e 75.0084-8 ea 44 57.98ab 31.22 13.46a 44.78 .18ab 42.5883-91 hi 5 57.46ab 29.45 12.80ab 25.55 .04 e 47.0383-93 hi 25 57.24ab 36.01 11.88ab 32.63 .03 e 65.0283-95 hi 47 56.83ab 41. 42 13.17ab 39.40 .05 e 60.9583-104 h' 82 55.20ab 43.18 12.57ab 32.18 .03 57.94. J. e83-133 hi 50 53.88abc 30.75 11.40ab 26.52 .03 e 77.6983-106 hi 61 55.12abc 43.58 11. 51ab 37.66 .04 e 78.1584-103 hi 26 52.58abc 37.32 11.35ab 31. 33 .04 e 60.0883-11 ea 22 50.86abc 38.55 11. 68a 43.82 .18ab 65.28

I 83-107 hi 59 50.51abc 39.64 ] o. 81ab 34.12 .05 e 81.3200I 83-86 hi 23 50.21abc 31.22 10.70ab 24.16 .04 e 60.78

83-85 hi 30 48.63abc 43.97 10.63ab 42.60 .06 e 60.2284-10 ea 27 48.33abc 33.12 12.78a 35.69 .16ab 46.2983-102 hi 26 48.04abc 37.90 11.19ab 31. 97 .04 e 57.0683-147 ni x hi 18 48.00abe 31.00 9.44ab 32.99 .03 e 44.9583-89 hi 38 45. 55abe 46.96 10.63ab 43.54 .06 e 57.5483-101 hi 26 45.04abc 57.17 9.54ab 48.20 .05 e 58.7783-83 ni 13 38.38abc 49.37 9.62ab 32.21 .04 e 71.3183-96 hi 12 37.17abc 37.84 10.5ab 35.05 .04 e 33.4783-128 re 49 24.43 be 47.78 7.69ab 37.91 .06 e 97.7683-147 ni 36 23.17 be 35.32 5.69 b 38.43 .05 e 54.5583-135 hi 9 18.56 e 21.06 6.78ab 20.57 .06 e 25.87

1 ca = J. ealifomica hi= J. hindsii ni= nigra ni x hi= 'Royal'

2 Meanseparation in columnsby Tukey' s HSD, 5% level.

TABLE 3. Diarrond walnut growers crack test 1983 U.C. orchards, Davis.

KERNEL GRADES (PERCENT IN SHELL WEIGIITSI DISTRIBUTION OF D1I1-1AGEBY NUHBEROF NUTS

INl'ERNAL EXTERNAL

Age Percent Relative Edibleof Nuts in Large Light Light Total off Total Harvest

Variety Tree Sanple Size Intensity Light limber A-ooer yield Grade yield Mold Insects Shrivel Black Rate

Old Cultivars

'Payne' 15 100 61 52.2 35 4 3 42 4 46 2 8 4 0 2b 9/29'Hartley , 15 100 98 56.3 34 5 5 44 2 46 2 0 7 0 4a Ib 9/29'Scharsh' 15 100 86 57.8 46 0 2 48 0 48 0 0 2 0 2b 10/17New CUltivars

'Serr' 11 100 96 51.5 24 24 4 52 2 54 5 2 2 0 Ib 10/5'Ashley' 15 100 89 52.2 33 4 3 40 6 46 5 11 5 0 b"

9/292'Westside'13 100 67 51.5 24 6 4 34 7 41 3 12 10 1 18 Ib 1014I'Trinta ' 14 100 100 54.2 30 5 3 39 6 44 0 9 14 1

°b 10/4I.D'Chico' 10 100 12 55.5 35 5 4 44 1 45 0 0 8 0 1014I 2,SUnland' 11 100 93 56.1 36 31 0 67 1 68 0 2 1 1 0 10/5'Vina' 11 100 81 52.6 48 1 0 49 1 50 2 2 0 0 0 1014'Tehama ' 11 100 97 54.8 46 2 0 48 2 50 0 0 9 0 0 1014,lImigo , 11 100 74 52.7 36 6 1 43 6 49 5 4 1 0 0 1014'Pedro' 10 100 98 54.2 41 G 1 48 0 48 0 0 2 0 0 1014'Howard I 13 100 98 56.0 44 3 2 49 0 49 0 0 2 0 0 10/5'Chandler' 13 100 88 60.0 48 2 0 50 0 50 0 0 1 0 0 10/566-178 11 100 100 56.8 46 2 1 49 0 49 0 0 2 0 °b 10/1768-104 9 100 68 53.5 52 2 0 54 1 55 0 1 2 0 Ib 101467-11 10 100 100 56.9 50 3 2 55 1 56 0 0 3 0 1 1014New AddiHons

67-13 11 100 98 57.2 51 2 2 55 0 55 0 0 1 0 Ib 10/463-378 13 100 100 53.9 43 4 1 48 2 50 0 2 11 0 0 10/7

a Mheringhull.b Stained.

TABLE 4. 19B3 Calparison of old and new walnut varieties, U.C. orchard, Davis.

Lateral Buds

Time of Leafing Producing Average Keme1 Average Kernel Number of Shell Seal

Tree (Days after Payne) Pistillate weight (g) percent light kernels Gradeb Crop Estimate c

VarietY Age 19B3 5yr F1CMerS (%) 19B3 5 yr 19B3 5 yr 19B3 5 yr 19B3 5yr 19B3 5yr

Old CUltivars

'Payne' 15 0 0 - 5.1 5.1 45 47 6 5 2 2 2 2.9'Hartley , 15 15 15 - 5.9 5.9 47 46 B 9 2 2 4 2.B'Scharsh' 15 2B 29 - 5.2 5.2 48 46 9 B 2 2 3 2

NewCUIti vars

'Serr' 11 -2 -1 50 7.4 7.6 5B 59 6 6 2 2.2 3 2.5'Ashley, 15 -1 -1 - 5.5 5.4 46 49 3 4 2 2 2 2.7'\>1estside' 13 0 0 - 4.9 5.3 45 43 7 6 2 loB 3 2.4

I 'Trinta' 14 1 3 50 7.5 7.1 46 45 7 6 2 1.B 3 2.4I-' 'Chico ' 10 0 2 70 4.3 4.7 44 46 10 7 1 2 5 40I 'Sun1and' 11 -2 1 90 B.7 9.7 57 5B 9 7 2 1.B 5 3.1

'Vina' 11 2 6 50 5.3 5.7 51 49 9 6 2 2.1 5 3.6'Tehama' 11 B 11 70 6.5 6.B 51 51 7 7 2 2.2 3 1.B'Amigo' 11 11 12 60 5.9 6.0 46 50 7 9 2 2 4 3.7'Pedro' 10 12 17 60 4.0 6.0 45 47 5 5 3 2.4 5 2.9I HCMardI 13 16 15 90 5.2 6.1 52 50 10 9 2 2.2 5 3.B'Chandler' 13 17 19 90 4.7 6.1 52 49 10 9 2-3 2.5 5 3.766-17B 11 30 31 60 6.0 6.4 4B 47 10 7 2 2 4 1.96B-104 9 7 11 BO 4.6 6.2 56 56 9 B 2-3 2.3 5 3.367-11 10 12 16 90 6.9 7.3 56 55 9 B 2-3 2.5 5 3.7

New Additions

67-13 11 1 4 90 8.0 B.O 55 55 10 7 2 2 4 2.B63-376 13 6 B 70 5.2 6.9 50 52 5 5 2 2.1 5 3.9

a Based on ten nuts or four tree samples.b

(2) Well sealed (3) Moderately well sealed (4) Poor (5) Very poor.Shell Seal = (1) Very well sealed

c Crop estimate = (1) Poor (2) Fair (3) Good (4) Heavy (5) Very heavy.