Genetic variation of Rhizoctonia solani isolates from canola in Alberta, Canada

Seedling blight and root rot caused by Rhizoctonia solani often results in severe reductions in plant stands of canola (Brassica napus), a major oilseed crop in Canada. A total of 98 R. solani isolates were collected from central Alberta in 2009-2011 and analyzed for aggressiveness, anastomosis grouping and genetic variation. Seventy-six isolates (78%) were identified as AG2-1, three (3%) were AG2-2, one (1%) was AG4, one (1%) was AG8, and the anastomosis group of 17 isolates (17%) could not be determined. Isolates of AG2-1 were more aggressive on canola than the other isolates. The genetic variation among the 98 isolates was evaluated by sequence analysis of the ribosomal DNA internal transcribed spacers (ITS) and inter-simple sequence repeat (ISSR) markers. The isolates clustered into four groups based on a neighbor-joining tree of the ITS sequences using PAUP software, and four groups based on ISSR markers using the POPGENE program. The isolate composition of Group A in both clustering approaches was similar, and those isolates were weakly aggressive on canola seedlings. Although the identities of both groups differed, Groups B and C in both analyses included most of the AG2-1 isolates, which were highly aggressive on canola seedlings. Isolates with undetermined anastomosis grouping and isolates classified as AG4, AG8 or AG2-2 were also included in Groups B and C, but were generally less aggressive than the AG2-1 isolates. Group D consisted of only three isolates in both analyses, but their identities also differed. The results indicated that there was no association between Groups from the two molecular approaches.