Detection of plasmid-like DNA and double-stranded RNA elements in some Canadian isolates of the oilseed rape pathogen Leptosphaeria maculans

Abstract

Nine Canadian isolates of Leptosphaeria maculans were examined for the presence of plasmid-like elements. A single extrachromosomal DNA element, with an estimated size of 9 kb, was detected in undigested genomic DNA of a virulent isolate, Fairview 1. This element was susceptible to hydrolysis by DNAse I and exonuclease III, and it was shown to hybridize to DNA of all virulent isolates. In addition, another virulent strain, Saskatoon 8, was observed to contain four double-stranded RNA (dsRNA) segments, ranging from approximately 500 bp to 2.4 kb. The latter segments (dsRNA) were resistant to DNAse I and exonuclease III treatment, and to RNAse A in high-ionic-strength buffer, but were susceptible to RNAse A in the presence of low-ionic-strength buffer.Key words: Leptosphaeria maculans, Canola, double-stranded RNA, plasmids.