Antimicrobial Use in Plant Agriculture

George W. SundinNIAA Sympsium; November 13, 2012

Bacterial Plant Diseases

• Occur on most crop plants, fruits, vegetables etc.

• Major effects of diseases are spots and rots on fruit or lesions on leaves that lead to reductions in yield

• Wilting diseases can kill plants

Citrus canker

Bacterial spot on pepper

Pseudomonas syringae – bacterial brown spot of bean

Symptoms

Soft rot

Bacterial Diseases are Exceedingly Difficult to Control

• Bacterial disease is a population-driven process• Large populations can develop on plant surfaces

under optimal environmental conditions– 105 to 106 cfu/g on leaves– As high as 1011 cfu/g in xylem

• Copper bactericides– Rapid re-establishment of populations after

control treatment– Other control agents needed

Bacterial Diseases are Exceedingly Difficult to Control

• Lack of host resistance is a critical issue• Most popular varieties are typically the

most disease susceptible

‘Gala’ ‘Golden Delicious’

Streptomycin• Discovered by Selman Waksman in

1943• Activity against gram-negative and

gram-positive bacteria

Antibiotics examined for plant disease control (1940s)

• Penicillin• Streptomycin• Aureomycin• Chloramphenicol• Oxytetracycline

Problems with antibiotic use for plant disease control (1940s-50s)

• Lack of efficacy at lower doses• Phytotoxicity issues at higher doses• Expense compared to other existing methods of

disease control

Streptomycin• Utilized in plant disease management

since the early 1950’s• 100 ppm solution–Targets: –Fire blight of apple and pear–Bacterial blight of celery–Shoot tip dieback of nursery trees–Bacterial spot of tomato and pepper

Streptomycin Usage on Apples in the USA

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5

10

15

20

25St

rept

omyc

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1991 1993 1995 1997 1999 2001 2003

Streptomycin Usage on Plants

• Avg. 20,200 lbs streptomycin/yr on apple• 1991-2003 data USDA NASS• Treated acreage -- ~ 15%(1-3

applications)

• Avg. 10,000 lbs streptomycin/yr on pears• Treated acreage -- ~ 37%(1-3

applications)

Antibiotic Usage on Plants

• Total annual usage on plants -- ~ 20,000 kg to 65,000 kg (1990s data)

• Lower estimate from NASS• Higher estimate from US Geological

Survey• By either estimate, plant use is less than

0.5% of 22.6 million kg of annual US production of antibiotics

Fire Blight Disease

• Reduces fruit yields

• Kills branches

• Kills roots (tree death)

2000 Fire Blight Epidemic, Southwest Michigan

• Tree losses -- approximately 450,000 trees killed• Acreage -- approximately 2,300 acres lost in five

counties• 35% overall yield reduction statewide• $42 million direct economic loss

Fire blight: match between a plant disease system and an antibiotic for control

• High economic value crop• Focused time frame of use– Need is during bloom (~ 2-3 weeks)– Significant population reduction necessary for

disease control on flowers

• System amenable to use of streptomycin• Development of disease

forecasting/warning systems

stigmaca. 105 to 106 cells / stigma

stigmaca. 105 to 106 cells / stigma

Blossom blight infection

Management of Blossom Blight with Streptomycin

Strep treated

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90

2004

‘Jon

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2006

‘Gal

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2007

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Control

% B

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Trial data, East Lansing, MI

Use of streptomycin for fire blight management

• Highly effective control measure for blossom blight in affected states:

• West, PNW – CA, OR, WA• Midwest – MI, WI, IN, OH• East – NY, PA, VA, MA

• 1-3 applications of streptomycin @ 100 ppm during bloom

Problem: shoot blight could occur on highly-susceptible apple cultivars

throughout the growing season

Problem: shoot blight could occur on highly-susceptible apple cultivars

throughout the growing season

Solution: increase applications of streptomycin to control shoot blight

Streptomycin Resistance in E. amylovora in Michigan

• Early-mid 1990’s -- Southwest Michigan

• 2004 -- Fruit Ridge area

• 2005 -- Fruit Ridge area (further spread), Ionia cty.

• 2006 -- Oceana county

• 2010 – Grand Traverse county

• 2012 – Leelanau, Antrim counties

Oxytetracycline• Structure identified by Robert Woodward

in 1953• Produced by Streptomyces rimosus• Medical uses, animal husbandry, plant

pathology

• Bacteriostatic

Oxytetracycline• Degradation by sunlight:

Oxytetracycline Usage on Plants in the USA

Oxy

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acyc

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usa

ge (

1,00

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f po

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)

1991 1993 1995 1997 1999 2001 20030

5

10

15

20

25

30

Oxytc: more use on peaches (bacterial spot) than on apples and pears

Oxytetracycline and Blossom Blight Control Under Higher Pressure

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Agrimycin Oxytetracycline Control

% B

loss

om B

ligh

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Kasugamycin

• Kasugamycin – aminoglycoside antibiotic in the same class as streptomycin

• Produced by Streptomyces kasugaensis• Targets the bacterial ribosome – target site

is different from that of streptomycin• No cross resistance between streptomycin

and kasugamycin• No medical uses, no animal agriculture uses

Evaluation of Kasumin for fire blight control in East Lansing, MI field trials

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% B

lossom

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2006 -- Gala

2007 – Jonatha

n #1

2007 – Jonatha

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2008 – Jonatha

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2009 – Jonathan

2008 – Gala

StreptomycinKasuminNontreated control

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Kasugamycin

• Kasumin – use in Michigan through a Section 18 specific exemption from the EPA (2009-2011)

• Label requirements:– Can only be used in counties where

streptomycin resistance has been reported– Can only be used when fire blight disease

model predicts epidemic conditions– Can only be used during bloom– No more than two consecutive applications,

three maximum

Non-antibiotic methods of plant disease control

• Plant disease resistance• Copper spray materials– Cu(OH)2; CuSO4

• Biological controls– Antagonistic bacteria; Bacteriophage; Antimicrobial

peptides

• Plant growth regulators• Plant resistance inducers

Summary – Antibiotic use in plant agriculture

• Streptomycin, oxytetracycline, kasugamycin• Targets are diseases on high-value crops• The nature of bacterial plant diseases and the

economic necessity of growing highly disease-susceptible cultivars contributes to antibiotic use

• Use of disease forecasting systems helps to limit the number of antibiotic applications

• Growers are more aware of resistance management strategies and of not overusing antibiotics

Funding sources:

USDA – NIFAUSDA -- SCRIMSU Project GREEENMI Apple Committee