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Aerial Dispersal of Soybean Rust Spores: An Aerobiological Model to Forecast the Spread of Phakopsora Pachyrhizi


To develop a Soybean Rust Aerobiology Modeling System (SRAMS) to quantify, integrate, and predict the impact of biological, meteorological, geographical, and anthropogenic processes on P. pachyrhizi spore movement at global, continental, and regional scales. The work involved is organized around the processes affecting the movement of fungal spores.

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NON-TECHNICAL SUMMARY: The goal of the team is to develop and operate a Soybean Rust Aerobiology Modeling System to forecast aerial transport of P. pachyrhizi. These daily forecasts displaying the risk of P. pachyrhizi dispersing to U.S. soybean fields will be deliver to growers and government agencies through the Internet as easy to read, color maps.
<P> APPROACH: The task of providing U.S. soybean producers with accurate, timely, and easy to use daily forecasts of the risk from aerial movement of P. pachyrhizi spores to their fields can be divided into three tasks. 1) Develop a spatial and temporal database on soybean rust by collecting information from researchers, producers, and government agencies in soybean-growing regions worldwide who are monitoring the disease. Special emphasis will be given to the Western Hemisphere and Africa, likely source areas for pathogens transported to the U.S. In the event that soybean rust enters the U.S., Mexico, or the Caribbean Islands, the spatial and temporal resolution of this data set will increase. Maps depicting where and when P. pachyrhizi spores are being released in these regions will be uploaded to the Internet for public viewing and used to drive the aerobiology modeling system. Data on the expansion of soybean rust into new areas will be used to evaluate spore transport forecasts. 2) Conduct an intensive field, greenhouse, and laboratory measurement program in Brazil to investigate the poorly understood P. pachyrhizi canopy escape and survival processes. These experiments require an "off-shore" soybean rust infected cropping system. Findings will be integrated into the modeling system. 3) Construct and operate a state-of-the-art system to generate daily forecasts of the risk of soybean rust infecting U.S. soybean fields. Color maps depicting the risk of P. pachyrhizi spore dispersal to U.S. growers? fields will be uploaded daily to the Internet during the growing season.
PROGRESS: 2004/07 TO 2007/06 <BR>
OUTPUTS: Temporal dimensions of P. pachyrhizi spore escape from soybean canopies were the focus of field studies conducted in Quincy, Florida. Scott Isard and Jeremy Zidek, a Masters student in the Ecology graduate program at Pennsylvania State University completed this research in 2007. We gained an understanding of the influence of environmental factors (e.g., wind, temperature, atmospheric stability, and canopy structure) on the quantity of released spores that escape the soybean canopy. The results of this research can be found in Zidek 2007. Studies of wet and dry deposition of soybean rust urediniospores were conducted by Nick Dufault (Ph.D. student in Plant Pathology at PSU) and Scott Isard at the University of Florida, North Florida Research and Education Center in Quincy, Florida. We determined the percentage of wet and dry deposited spores that are retained in the lower, mid, and upper soybean canopy levels. We also examined the effects of environmental factors (rain intensity, and wind) and cultural practices (row spacing) on the distribution and retention of spores throughout the soybean canopy. The results of this research can be found in Dufault 2008. Research on the adhesion of Phakopsora pachyrhizi urediniospores to soybean was conducted by Maria Velez (PSU graduate student) and Scott Isard. We constructed a timeline of Phakopsora pachyrhizi spore adhesion to soybean leaves and determined the nature of the adhesion process and its chemical components. The research was conducted in collaboration with Dr. Doug Luster (ARS) under strict quarantine conditions within a USDA-ARS containment facility located at Fort Detrick, Maryland and at the University of Florida North Florida Research and Education Center. The results of this research can be found in Velez 2008. Many of the results of these epidemiology studies have been incorporated into our Integrated Aerobiology Model System that was developed by project participants to forecast the movement of P. pachyrhizi spores and the spread of soybean rust in North America. Outputs from this model are the cornerstone of the IPM PIPE ensemble soybean rust forecasting effort, and are disseminated on the restricted access IPM PIPE platform and are used by State Extension Specialists in their weekly soybean rust management commentaries. <BR> <BR>

IMPACT: 2004/07 TO 2007/06<BR>
In 2006, the USDA Economic Research Service published a report that indicated that millions of U.S. soybean acres that would have received at least one fungicide application remained untreated for soybean rust in 2005 due to information disseminated through the U.S. Department of Agriculture Soybean Rust Information System website. The information provided by the system increased U.S. producers' profits by between $11 to $299 million at a low cost of between $2.6 and $5 million (Roberts et al. 2006 This savings and the positive environmental implications of not spraying millions of acres with fungicides demonstrated the value of a coordinated national pest management framework and stimulated the development of the 2006-2008 Pest Information Platform for Extension and Education (IPM PIPE). The platform is operated by the PIs of this project and has expanded to take on soybean aphid and viruses of legumes. Three project members were part of the Asian Soybean Rust Team that received the Secretary of Agriculture's Group Honor Award for Excellence in 2006. Estimates of saving by U.S. soybean growers due to the soybean rust effort for 2007 were approximately $200 million (Giesler and Hershman 2007). The Integrated Aerobiology Modeling System was an important component for the success of the USDA Soybean Rust Information System during 2005 and the IPM PIPE from 2006 to 2008. This model which incorporates the new knowledge gained from the project's epidemiology field studies simulates the local development of soybean rust infections based on weather-driven transport of spores from infected geographic regions to downwind areas with potential host vegetation. The maps of spore movement and infection development both in the present and the future are valuable in guiding extension specialists as to the likelihood, location, and timing of soybean rust in their states. The work of the project PIs was featured in the "The Rust Invation", part of the USDA CSREES CD entitled "Feeding America-Partners 17".

Isard, Scott
University of Illinois - Urbana-Champaign
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