Soybean Rust Teleconference

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Soybean Rust Teleconference

• Disease Cycle Epidemiology

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Pathogen
Disease Triangle
Environment
Host
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Soybean Rust Pathogen Wind Transported
90 years for wind to transport spores of soybean
rust pathogen from Eastern Hemisphere to the
United States
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Soybean Rust Pathogen in USA

• Survival of Rust Fungus
• Must have living green leaf tissue
• Soybean
• Common bean (snapbean and etc)
• Pea
• Kudzu (introduced legume weed in S.E. USA)
• Yellow sweetclover (WI)
• White clover (WI)
• Lupine (WI)
• Purple crownvetch (WI)
• Ticktrefoil (WI)

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KudzuPotential Survival of Rust Fungus
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Assumption

• Kudzu will be major winter
• survival host
• Soybean rust pathogen will not
• survive in Wisconsin or Upper
• Midwest
• - Foliage of perennial hosts will freeze
• and die each winter
• Soybean rust pathogen must be
• reintroduced into Northern States
• each growing season

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Projected Survival of Kudzu
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Soybean Asian Rust
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Over-winter in Gulf Coast StatesSouth-North
spread of inoculum each growing seasonThe
earlier spores arrive, the greater the severity
of rust
Projected movement of soybean rust pathogen in
the USA
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Soybean Rust Infection Cycle
Urediniospores

• Spore germination
• 80 in 1 hr
• 90 in 2 hr

Spores germinate
Penetration Infection
10 to 12 hr
Pustules
5 to 10 days
Urediniospores
Spores form within 10 to 21 days Pustule forms
spores for 10- 14 days
Multi-cyclic Disease
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(Poppler, 2004)
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Response of Soybean Rust Pathogen to Environment

• Spore Germination
• Temp. Range 46 to 97o F
• Temp. Optimum 60 to 75o F
• 8 hrs or more of continuous leaf wetness
• gt75 to 80 relative humidy or precipitation
• Penetration and Infection
• Range 50 to 82o F
• Optimum 65 to 75o F
• Minimum of 6 hrs or more of continuous leaf
  wetness
• Hot temperatures, gt 86 F may significantly slow
  development of soybean rust

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Response of Soybean Rust Pathogen to Environment

• Under optimum conditions
• Pustules form in 5-10 days after infection
• Spores are produced in 10-21 days
• Spores continually produced as long as
  environmental conditions are conducive
• Soybean rust pathogen will go through many cycles
  of spore production, spore release and new
  infections in a growing season.
• Within optimal conditions, a soybean plant can go
  from initial symptoms to complete defoliation in
  1-2 weeks.

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Environmental impact on soybean rust

• Prolong leaf wetness
• 8-12 Hours
• Temperatures between 59 F to 86 F
• Relative humidity between 75-80 required for
  spore germination and infection

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Soybean Rust China USA
34o N --------------------------------------
24o N_________________________________
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Rust epidemic and rain (Sept only), Hubei, China
Year Rainfall (inches) Rainy days Epidemic Severity
1973 6.8 22 Severe
1974 2.2 10 light
1975 3.3 10 light
1976 2.0 13 light
1977 5.1 12 moderate
1978 0.4 4 very light
1979 2.0 12 light

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Hubei, China USA Comparison
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Environmental impact on soybean rust

• Prolong leaf wetness
• 8-12 Hours
• Temperatures between 59 F to 86 F
• Relative humidity between 75-80 required for
  spore germination and infection

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Epidemiology r factor
Rust Progress rate 2001/2002)
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Yield Loss Potential

• Potential loss 0-80
• Rust severity in Gulf Coast area
• Crop growth stage at initial infection
• July-August weather conditions
• Northward movement of inoculum
• Weather systems
• green-bridging
• Many unknowns varieties, planting date

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Information on Soybean Rust

• University of Wisconsin Extension
• Soybean Plant Health Website
• www.plantpath.wisc.edu/soyhealth
• Soybean Plant Health Initiative North Central
  Soybean Research Program http//www.ncrsp.com/plan
  thealth
• Each website links to many other sites