Races of Phytophthora sojae in Ontario, Canada, 2010-2012


Xue, A.G., Marchand, G., Chen, Y., Zhang, S., Cober, E.R., Tenuta, A. (2015). Races of Phytophthora sojae in Ontario, Canada, 2010-2012, 37(3), 376-383. http://dx.doi.org/10.1080/07060661.2015.1052562


Phytophthora root rot (PRR), caused by the oomycete Phytophthora sojae, is a devastating disease of soybean worldwide, and has been present in Canada since the 1950s. Major resistance to P. sojae (Rps) genes have been deployed by soybean breeders to mitigate yield losses, which has caused shifts in the pathogen population to more complex pathotypes and the emergence of new races. This study reports on a survey of races and pathotypes of P. sojae throughout 203 commercial soybean fields and two PRR nurseries in the province of Ontario, Canada, and is the first extensive survey to be conducted in Canada since the late 1980s. A total of 22 races and one intermediate reaction type (IRT) were detected from 262 isolates from commercial soybean fields. Race 25 was the predominant race, comprising 43 isolates and representing 16% of the pathogen population. Races 3, 4, 5, 6, 7, 9, 28 and 45 were frequently detected, each representing 5-11% of the pathogen population. A total of 16 races and two IRTs were detected in 96 isolates from the two PRR nurseries. Race 3 was the most abundant, representing 23% of isolates, while races 5, 6, 7, 8, 9, 14, 25 and 28 each represented 5-10% of total isolates. New races and more complex pathotypes have emerged since the last Canadian survey, and this will have implications for the future deployment of Rps genes or other forms of resistance to P. sojae.