Identity and host specificity of root rot pathogens of pea, wheat and canola colonizing standing pea stubble from the Canadian Prairies.

The composition and host specificity of pathogenic fungal communities colonizing pea residues from Alberta and Manitoba was studied. Standing pea stubble was sampled from diseased and healthy patches of 16 commercial fields in 2013–2015 after harvest and in the following year prior to crop seeding. In a series of greenhouse bioassays, canola, wheat and pea were grown in pots filled with ground pea stubble mixed with sterile Cornell potting mix. Root rot severity of the three hosts was evaluated and sections from diseased roots were plated on agar media. Fungal communities isolated from roots were characterized using characteristics in culture and PCR-based identification. Approximately 2700 fungal isolates, belonging to 60 species, were identified. Fusarium avenaceum was the most prevalent species in all hosts; F. avenaceum and F. culmorum were most prevalent in wheat, and F. avenaceum, F. solani and F. oxysporum were most abundant in pea, and F. avenaceum was most abundant on canola. Aphanomyces euteiches was isolated only from one Manitoba field, and only on pea. Fungal communities of healthy and diseased patches of fields were similar, but the fungi isolated from post-harvest stubble were different from that of pre-plant stage. Root rot incidence and severity were lower on canola than on pea or wheat, which indicates that canola is less susceptible to the fungal root pathogens of pea than either pea or wheat.