antimicrobial use in plant agriculture - national … - symp...bacterial diseases are exceedingly...
TRANSCRIPT
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
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
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
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 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