GENETIC-VARIABILITY IN PECTIC ENZYMES OF RHIZOCTONIA-SOLANI ISOLATES CAUSING BARE-PATCH DISEASE OF CEREALS

Field isolates of Rhizoctonia solani obtained from three discrete bare patches in a wheat field in Western Australia were characterized by p ectic zymogram grouping. The genetic background of pectic enzymes was analysed by comparing the zymograms of asexual homokaryons and sexual progenies derived from field isolates. The 170 field isolates obtained from the field site produced indistinguishable pectic zymograms. Howe ver, variations among field isolates of the same zymogram group were d etected on the basis of zymograms of their resultant protoplast-regene rated cultures. Asexual sibling homokaryons derived from each of the f ield isolates were heterogeneous for their pectic enzymes. Homokaryons with a common heterokaryon incompatibility factor obtained from a fie ld isolate were homogeneous for pectic enzymes. Basidiospore progenies of a field isolate segregated widely in pectic zymograms. It appeared that the expression of pectic enzymes by field isolates involved mult iple genetic factors. The variation of zymograms among homokaryotic st rains suggests that each field isolate of R. solani contains two types of nuclei, although cells of vegetative hyphae are multinucleate.