Production and regulation of polygalacturonase isozymes in Canadian isolates of Leptosphaeria maculans differing in virulence

The polygalacturonase (PG) isozymes produced by weakly virulent and highly virulent Canadian isolates of Leptosphaeria maculans that cause blackleg on canola, were examined. PG zymograms as determined by isoelectric point and molecular weight were distinctive between the highly virulent and weakly virulent types and could be used to differentiate the geographic origin of isolates within both virulence types. Highly virulent isolates produced PG isozymes of greater mobility in polyacrylamide gels than those of the weakly virulent isolates. Highly virulent isolates produced fewer PG isozymes with only acidic isoelectric points compared to weakly virulent isolates which produced many isozymes with either acidic or basic isoelectric points. Production of most PC isozymes was induced by polygalacturonic acid and was not repressed by glucose, and some isozymes were produced at basal levels without induction, suggesting that regulation of isozymes may have an effect on their activity in plant tissue. The characteristics of specific PG isozymes may affect their activity in the plant and the virulence of L. maculans isolates to their host. PG zymograms also will be useful as characteristics for analyzing the diversity of L. maculans populations.