Update on Soybean Rust Daren Mueller

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

Survival of the fungus

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

Distribution in March – 2005/2006

Distribution in March – 2007 Easter freeze could chill development of Asian soybean rust By Gary Wulf, Dow Jones Newswires 4/17/2007 10 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

Other sources of spores? ALERT: Asian soybean rust found on yam beans in Veracruz, Mexico By Marilyn Cummins, Editor StopSoybeanRust.com 7/23/2007 10:15 a.m. CDT -- Mexican officials have confirmed the presence of Asian soybean rust on yam bean leaves in the state of Veracruz in January, 2007. 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

Other sources of spores?

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

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

Build up of inoculum – 2006

Build up of inoculum – 2007

Wind Patterns Dr. Pan, St. Louis University

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.

National Atmospheric Deposition Program Percentage of sites with measurable precipitation

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

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

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

Detached leaf study O hour 4 hour 8 hour 12 hour

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

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

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

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).

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

Local environment – 2006

When they all come together – 2006

Local environment – 2007

When they all come together – 2007

Texas as an early season source of inoculum

Predictive models for soybean rust Indicator disease Simple soybean rust model

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

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

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

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

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

Soybean rust for 2008 Keep an eye on rust development throughout the season www.sbrusa.net