COMPARISON OF PECTIC ZYMOGRAMS PRODUCED BY DIFFERENT CLONES OF SCLEROTINIA-SCLEROTIORUM IN CULTURE

The isozymes of polygalacturonase (PG) and pectinmethylesterase (PME), produced in vitro by 35 isolates belonging to 15 clones of Sclerotinia sclerotiorum, were detected by isoelectric focusing on polyacrylamide gels and activity staining of agarose overlays containing the appropriate substrate. Analysis of the PG isozyme banding patterns (zymograms) identified two distinct phenotypes among the isolates from canola, S. sclerotiorum zymogram group-1 (SSZG-1) and SSZG-2. Of the 11 clones tested, nine clones had the SSZG-1 phenotype, two clones had the SSZG-2 phenotype, and one clone had both SSZG-1 and -2 phenotypes. Therefore, in this sample, there were fewer PG phenotypes than clonal genotypes. One frequently sampled clone with wide geographic distribution included two isolates of SSZG-1 and eight of SSZG-2. Two isolates, one from cultivated sunflower and one from a wild plant, Ranunculus ficaria, showed isozyme patterns different from the isolates obtained from canola. The isolate from sunflower had the SSZG-3 phenotype, and the isolate from R. ficaria had the SSZG-4 phenotype. There was no apparent correspondence between isozyme phenotype and either the pathogenicity or aggressiveness of the clones on canola. The isozyme analysis of PME showed no variation among the isolates collected from canola.