Poster Session: Biology of Pathogens - Oomycetes

291-P

Races of Phytophthora sojae causing root rot of soybean in Ontario.
A. XUE (1), Y. Chen (1), G. Marchand (1), S. Zhang (2), y. Meng (1), E. Cober (1), A. Tenuta (3)
(1) Agriculture and Agri-Food Canada, Ottawa, ON, Canada; (2) Soybean Research Institute, Northeast Agricultural University, Harbin, China; (3) Ontario Ministry of Agriculture, Guleph, ON, Canada

Phytophthora sojae is the causal agent of Phytophthora root and stem rot (PRSR), an economically important disease of soybean worldwide. To determine the pathogenic variation of P. sojae in Ontario, where most Canadian soybean is grown , a total of 359 single-zoospore P. sojae isolates were obtained from plant and soil samples collected from 207 soybean fields and two PRSR nurseries during 2010-2012. Twenty-four races and 17 pathotypes of P. sojae were identified from the 359 isolates on a set of eight soybean differentials, each containing a single resistance (Rps) gene. Races 25, 3, and 9 were the predominant races, comprising 49, 43, and 34 isolates and representing 13.6, 12.0, and 9.5% of the pathogen population, respectively. Of the 41 races and pathotypes, 33, including the predominant race 25, were identified for the first time in Ontario. These results suggest that the race profile of P. sojae in Ontario has changed and new sources of resistance are needed for the development of resistant cultivars. Eleven races and four pathotypes were identified from 52 P. sojae isolates obtained from the PRSR nursery in Woodslee, and 13 races and two pathotypes identified from 44 isolates from the PRSR nursery in Ottawa. The common races in these nurseries were similar to what was found in commercial soybean fields, suggesting that both PRSR nurseries are appropriate and effective for screening soybean germplasm for cultivar development for Ontario.