1. Update on Soybean Rust
Daren Mueller

2. Factors Affecting Severity of Soybean Rust in U.S.
Survival of the fungus
Movement of viable spores
Local temperature and moisture when spores arrive

3. Survival of the fungus

4. Surviving kudzu patch with soybean rust in Alabama, January 2006
Survival of the fungus
Ed Sikora
Surviving kudzu patch with soybean rust in Alabama, January 2006

5. Distribution in March – 2005/2006

6. Distribution in March – 2007
Easter freeze could chill development of Asian soybean rust
By Gary Wulf, Dow Jones Newswires 4/17/ a.m. CENTRAL CITY, Neb. -- Record cold that struck the U.S. this Easter could ultimately wind up benefiting U.S. soybean growers by reducing the threat posed by the Asian soybean rust fungus. The cold weather likely killed the fungus in parts of the Southeast, according to plant pathologists. "We had a record-breaking frost Easter morning, with temperatures in the panhandle below freezing for several hours," University of Florida plant pathologist James Marois told the USDA last week.
StopSoybeanRust.com

7. Other sources of spores?
ALERT: Asian soybean rust found on yam beans in Veracruz, Mexico
By Marilyn Cummins, Editor StopSoybeanRust.com 7/23/ :15 a.m. CDT -- Mexican officials have confirmed the presence of Asian soybean rust on yam bean leaves in the state of Veracruz in January, According to a report posted July 12, 2007, on the North American Plant Protection Organization's Phytosanitary Alert System, "by the middle of January 2007, the Plant Health General Directorate received samples of yam bean (Pachyrhizus erosus) crop foliage from the communities of Agua Dulce and Pajapan, in Papantla township, in the state of Veracruz. These samples showed signs and symptoms of Asian soybean rust (Phakopsora pachyrhizi)."
StopSoybeanRust.com

8. Other sources of spores?

9. Factors Affecting Severity of Soybean Rust in U.S.
Survival of the fungus
Movement of viable spores
Local temperature and moisture when spores arrive

10. Movement of Viable Spores
Build up of inoculum
Light affects spore survival
Wind patterns – movement of majority of spores

11. Build up of inoculum – 2006

12. Build up of inoculum – 2007

13. Wind Patterns
Dr. Pan, St. Louis University

14. National Atmospheric Deposition Program
124 rainwater collectors across Corn Belt
Weekly samples from mid-May to early November
Rainwater samples collected, filtered, dried and tested for DNA of soybean rust spores
250 rainwater collectors across the US that was set up in the 1970s to monitor air pollution. “NADP analyzes filtered rainwater for dissolved pollutants in rain samples and thus allowed us to analyze the filtered particulate matter for fungal spores," he said. In 2005, scientists collected spores in rainwater and looked at them with a microscope. “This was a tedious process and very difficult to differentiate Asian soybean rust from other rust spores,” Szabo said. "They just can’t confirm their identity.” Szabo and his colleagues last year received funding to do a national survey to further develop the molecular assay and monitor 124 sites across the Corn Belt. “We covered all states south from North Dakota to Texas and east to the Atlantic coast, except New England states,” he said. “We selected 124 sites to represent all of the soybean growing areas in the central and eastern part of the U.S. All the states contained more than one collection sites, however since the network was established to monitor air pollution several key soybean states had only a few sites.” The NADP program took weekly samples, Szabo said. “Sites are sampled weekly, every Tuesday morning," he said. "We have samples from the mid-May through early November.” Rainwater samples were collected and then filtered by the NADP staff, Szabo said. Filter papers with particular matter containing the rust spores was dried and then tested for DNA of Asian soybean rust spores. Unfortunately there is not a good molecular method to test for viability and it is unlikely spores survived collection and transport. One important aspect of the project was developing a molecular method to detect the Asian soybean rust spores, Szabo said, so they modified a real-time polymerase chain reaction assay developed by scientists at Fort Detrick, Md. Polymerase chain reaction is a method for amplifying DNA. This is important because a few spores do not contain enough DNA for identification. But if you amplify the DNA by making many copies, it is easier to confirm the identity with the necessary degree of accuracy.

15. National Atmospheric Deposition Program
Percentage of sites with measurable precipitation

16. National Atmospheric Deposition Program
Spore detection and rust detection in 2007 season
We know spores can move, but are they viable?

17. Is light a limiting factor for movement of rust?
Why is the disease more severe in shaded kudzu than in open ground?

18. Effect of light on spore germination
Isard et al., 2006

19. Detached leaf study
O hour
4 hour
8 hour
12 hour

20. Light effects on number of pustules (infection)
Detached leaf study
Light effects on number of pustules (infection)
Hours of darkness
Pustules/leaflet
4.3 2
7.6 4
9.5 8
27.0 12
74.9 16
97.8

21. Light intensity study
Inoculated plants were placed under shade cloth with different mesh sizes to obtain 4 light intensity levels
100%
20%
50%
70%
A. P. Dias and X.B. Yang, 2007

22. Light intensity study
Incidence of soybean rust under four light intensity levels: 100% sunshine all time (L1), shade all time (L4), L4 for 1 day then L1 (L4 – 24h), L4 for 2 days then L1 (L4 – 48h). Statistical at 5%.
A. P. Dias and X.B. Yang, 2007

23. Movement of spores - summary
Build up of soybean rust depends on weather in south
Spores are found in most sampled places in the rain trap study; no information on spore viability
Light will affect spores, limiting movement of viable spores to specific situations (heavy cloud cover, close source of spores).

24. Factors Affecting Severity of Soybean Rust in U.S.
Survival of the fungus
Movement of viable spores
Local temperature and moisture when spores arrive

25. Local environment – 2006

26. When they all come together – 2006

27. Local environment – 2007

28. When they all come together – 2007

29. Texas as an early season source of inoculum

30. Predictive models for soybean rust
Indicator disease
Simple soybean rust model

31. Identify other rust diseases as an indicator
Indicator Disease
Identify other rust diseases as an indicator
WHICH ONE?
common corn rust
wheat leaf rust
southern corn rust
peanut rust

32. Comparison of development among different rust diseases in July, Indianapolis, IN
Indicator Disease
Southern corn rust biology similar to soybean rust
If southern corn rust starts showing up, this may be an indicator that conditions are ideal for soybean rust
Overwintering of pathogens will differ in south
Infection

33. Comparison of development among different rust diseases in July, Indianapolis, IN
Simple model
Source of inoculum
Rainfall
Temperature

34. Summary
Soybean rust movement in the U.S. may be limited by slow early-season inoculum build-up and inhibitory solar radiation levels in the summer.
Amount of rainfall is critical to occurrence of soybean rust
The western route is faster than eastern route in the U.S. – but early establishment of rust is key

35. Summary
Rust can get to Iowa
Rust had no impact on soybean yield in Iowa in 2007
Rust pathogen will not survive the winter in Iowa
2007 findings will not impact the chances of rust getting to Iowa in 2008

36. Soybean rust for 2008
Keep an eye on rust development throughout the season