Antimicrobial Use in Plant Agriculture

George W. Sundin NIAA 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

0

5

10

15

20

25 S

trep

tom

yci

n u

sage

(1,0

00s

of

pou

nd

s)

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

stigma

ca. 105 to 106 cells / stigma

stigma

ca. 105 to 106 cells / stigma

Blossom blight infection

Management of Blossom Blight with

Streptomycin

0

10

20

30

40

50

60

70

80

90

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

tetr

acy

clin

e u

sage

(1,0

00s

of

pou

nd

s)

1991 1993 1995 1997 1999 2001 2003 0

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

0

10

20

30

40

50

60

70

80

Agrimycin Oxytetracycline Control

% B

loss

om

Bli

gh

t

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

0

10

20

30

40

50

60

70

2006 -- Gala

2007 – Jonathan

#1

2007 –

Jonathan #2

2008 – Jonathan

2009 – Jonathan

2008 – Gala

Streptomycin Kasumin Nontreated control

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 – NIFA

USDA -- SCRI

MSU Project GREEEN

MI Apple Committee