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A Modified Method to Screen for Partial Resistance to Phytophthora sojae in Soybean

Stewart, Silvina, Robertson, Alison E.
Crop science 2012 v.52 no.3 pp. 1181-1186
Glycine max, Oryza sativa, Phytophthora sojae, agar, disease resistance, disease severity, genes, germplasm, greenhouses, pathogens, pathotypes, rice, root rot, roots, screening, soybeans, stem rot, United States
Phytophthora root and stem rot, caused by Kauf and Gerd, is one of the most damaging diseases of soybean [ (L.) Merr.] in the United States. Partial resistance (PR), which is defined as the relative ability of a soybean plant to survive root infection without showing severe symptoms, is an effective way to manage this disease. A modification of the layer test method used to screen for PR to in soybean was evaluated. Instead of the -colonized agar layer, which is used in the current greenhouse cup assay, -infested rice (L.) grains were used. In addition, a dry root weight (Drw) measurement was compared to a disease severity root rot score, which uses a 1 to 10 visual scale. The rice method was not statistically different from the layer test for the variables evaluated. Advantages of the rice method include reduced cost and the ability to screen soybean germplasm with more than one pathotype of the pathogen in a single assay. A mixture of several pathotypes of ensures compatible interactions between isolates used and all known genes, thus avoiding genes that could go undetected and mask PR during screening. Although collecting and handling of roots for Drw data may require more time, it is a more objective variable, which assures precise scoring, it is not rater dependent, and less training of personnel is required.