Project Details:

Identifying factors that influence genetic diversity in endemic Phytophthora sojae populations

Parent Project: This is the first year of this project.
Checkoff Organization:Iowa Soybean Association
Categories:Soybean diseases
Organization Project Code:
Project Year:2009
Lead Principal Investigator:Alison Robertson (Iowa State University)
Co-Principal Investigators:
Anne Dorrance (The Ohio State University)

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Project Summary

Phytophthora root and stem rot (PRR), caused by Phytophthora sojae, is an economically important disease of soybean in the United States. In 2005, yield suppression by PRR in the US was estimated to cost over $250 million. Currently, the disease is primarily managed by planting varieties with genes that confer resistance (Rps genes) to the pathogen. Fourteen Rps genes have been identified, and three (Rps1c, 1k and 3a) are currently deployed in commercial varieties. The problem is P. sojae has the ability to develop new races that overcome these Rps genes. More than 70 races of P. sojae have been identified, and this number continues to increase. Thus, when a Rps gene is deployed, it has a limited life span (usually 8-15 years).

What factors are responsible for these changes in the pathogen population? The goal of this proposal is to identify factors that shape the genetic diversity of endemic P. sojae populations in Iowa and Ohio using microsatellite analysis (SSR). These molecular markers enable the biology and ecology of a plant pathogen and the mechanisms and tempo of variation within its population to be better understood. An improvement in our understanding of the basic biology of this important pathogen will enable us to achieve our long-term goal to improve management systems and minimize losses due to PRR.

Phytophthora seedling blight and stem rot was especially severe in 2008 in both Iowa and Ohio due to the very wet weather that occurred from May through July. Approximately 170 new isolates of P. sojae were collected in Iowa and additional 50 isolates of the pathogen were added to the Ohio collection. The majority of the isolates have been purified and DNA extracted in preparation for SSR analysis in late fall. Plants with symptoms of Phytophthora damping off were also collected from 12 fields across Iowa. Isolations for P. sojae from each of six plants per field were collected and purified. Race testing of the isolates will begin in the fall.

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Benefit to Soybean Farmers

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