Identification of Pythium spp. from the rhizosphere of soybeans in Ontario, Canada

Production of soybean in short-season areas of Canada is affected by Pythium species causing seed rot, seedling damping-off and root rot under the cool, moist conditions prevalent early in the growing season. To determine which Pythium species infect soybean plants under these conditions, soil samples were collected in 2010, 2011 and 2012 from soybean fields in Ontario where symptoms of damping-off or root rot were observed. Pythium spp. were isolated from soil using a seed baiting approach and selective media. PCR amplification and sequencing of the internal transcribed spacer of the nuclear ribosomal DNA allowed for identification of six different Pythium species (out of a total of 104 strains). Pythium ultimum var. ultimum (56.7%) and P. sylvaticum (29.8%) were the most frequently isolated species over all sampling years. Other species isolated included P. dissotocum (6.7%), P. ultimum var. sporangiiferum (3.8%), P. irregulare (1.9%), and P. hypogynum (1.0%).