Clonal lineages of Sclerotinia sclerotiorum previously known from other crops predominate in 1999-2000 samples from Ontario and Quebec soybean

Abstract

Twenty-one mycelial compatibility groups (MCGs) and 41 DNA fingerprints were identified from 213 isolates of Sclerotinia sclerotiorum from 10 fields and three performance trials of soybean, and one test plot and one field of edible bean sampled in eastern Ontario and Quebec (1999) and western Ontario (2000). Population structure was predominantly clonal as evidenced by repeated recovery of MCGs and fingerprints in the sample and the association of fingerprint with MCG. Evolution of new fingerprint phenotypes within some clones was indicated by differences of one to three hybridizing fragments from the most frequently sampled fingerprint associated with an MCG. A single MCG represented 46% of the isolates; this was clonal lineage 1, a frequently sampled clone from Ontario canola in 1989, also sampled previously from cabbage in New York State. Five of the 21 MCGs represented 84% of the total sample. Sixty percent of the isolates had fingerprints identical to or differing by one or two hybridizing fragments to fingerprints archived from previous samples from canola, cabbage, edible bean, and other crops. Results indicate that soybean is infected mainly by pathogen genotypes residual from other crop or weed hosts and that a few pathogen genotypes are responsible for a large proportion of infections.

Keywords:

• clonality
• sclerotinia stem rot
• white mold