Antimicrobial Use in Plant Agriculture - Dr. George Sundin, Michigan State University, from the 2012 NIAA One Health Approach to Antimicrobial Resistance and Use Symposium, October 26-27, 2012, Columbus, OH, USA. More presentations at: http://www.trufflemedia.com/agmedia/conference/2012-one-health-to-approach-antimicrobial-resistance-and-use

1. Antimicrobial Use in Plant Agriculture
George W. Sundin
NIAA Sympsium;
November 13, 2012

2. 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

3. Citrus canker
Bacterial spot on pepper

4. Pseudomonas syringae–
bacterial brown spot of
bean

5. Symptoms
Soft rot

6. 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 106cfu/g on leaves
– As high as 1011cfu/g in xylem
• Copper bactericides
– Rapid re-establishment of populations
after control treatment
– Other control agents needed

7. 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

8. Streptomycin
• Discovered by Selman Waksman
in 1943
• Activity against gram-negative
and gram-positive bacteria

9. Antibiotics examined for plant
disease control (1940s)
• Penicillin
• Streptomycin
• Aureomycin
• Chloramphenicol
• Oxytetracycline

10. 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

11. 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

12. Streptomycin Usage on Apples in the
USA
Streptomycin usage (1,000s of pounds) 25
20
15
10
5
0
1991 1993 1995 1997 1999 2001 2003

13. 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)

14. 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

15. Fire Blight Disease
• Reduces fruit yields
• Kills branches
• Kills roots (tree death)

16. 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

17. 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

18. stigma
ca. 105 to 106 cells / stigma

19. stigma
ca. 105 to 106 cells / stigma

20. Blossom blight infection

21. Management of Blossom Blight with
Streptomycin
90
80
70
60
50
40
30
20
10
0
Trial data, East Lansing, MI

22. 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

23. Problem: shoot blight could occur on
highly-susceptible apple cultivars
throughout the growing season

24. Problem: shoot blight could occur on
highly-susceptible apple cultivars
throughout the growing season
Solution: increase applications of
streptomycin to control shoot blight

25. 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

26. Oxytetracycline
• Structure identified by Robert
Woodward in 1953
• Produced by Streptomyces rimosus
• Medical uses, animal husbandry,
plant pathology
• Bacteriostatic

27. Oxytetracycline
• Degradation by sunlight:

28. Oxytetracycline Usage on Plants in the
USA
Oxytetracycline usage (1,000s of pounds)
30
25
20
15
10
5
0
1991 1993 1995 1997 1999 2001 2003
Oxytc: more use on peaches (bacterial spot) than on apples and pears

29. Oxytetracycline and Blossom Blight
Control Under Higher Pressure
80
% Blossom Blight
70
60
50
40
30
20
10
0
Agrimycin Oxytetracycline Control

30. 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

31. Evaluation of Kasumin for fire blight
control in East Lansing, MI field trials
70 Streptomycin
Kasumin
Nontreated control
60
50
40
30
20
10
0
2006 -- 2007 – 2007 – 2008 – 2008 – 2009 –
Gala Jonathan Jonathan Gala Jonathan Jonathan
#1 #2

32. 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

33. 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

34. 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

35. Funding sources:
USDA – NIFA
USDA -- SCRI
MSU Project GREEEN
MI Apple Committee