First report of Phytophthora sansomeana causing root rot in field pea in Alberta, Canada

Root rot is a major constraint on field pea (Pisum sativum L.) production. Species of Phytophthora can cause seed rot, pre- and post-emergence damping-off, and stem and root rot in many legume crops, but have not been reported in association with pea root rot in Canada. Following a survey of pea fields in Alberta, Canada, in 2015, root tissue with typical symptoms of root rot was plated onto a growth medium, and one isolate was identified as a putative Phytophthora spp. based on its colony characteristics. The isolate was homothallic, producing smooth, thick-walled oospores and both paragynous and amphigynous antheridia on lima bean agar. The sporangia were ovoid or elliptical, non-papillate, and had internal proliferations. Based on these criteria, the isolate was tentatively identified as Phytophthora sansomeana. Sequencing of the internal transcribed spacer (ITS) and Cox II regions revealed 100% identity with the ITS and Cox II sequences of P. sansomeana available in GenBank, confirming this identification. A pathogenicity test indicated that the isolate was pathogenic and caused pre-emergence damping-off, root discoloration, and root rot with brown to dark brown lesions on pea cultivars. This is the first report of P. sansomeana causing root rot in pea in North America.