ISOZYME VARIATION AND GENETIC RELATEDNESS IN BINUCLEATE RHIZOCTONIA SPECIES

Fifty isolates of binucleate Rhizoctonia representing 12 Japanese and five North American anastomosis groups (AGs) were characterized by isozyme electrophoretic patterns. Of the 23 enzyme systems screened, eight enzymes with a total of 63 phenotypes were applied to study the genetic relationship among the AGs. Hexokinase and malate dehydrogenase displayed the most polymorphic banding patterns. Cluster analysis of isozyme bands generated four distinct groups (I, II, III, and IV). Group I was represented by all AG-G isolates. Group II was subdivided into two subgroups (IIA and IIB). Subgroup IIA was made up of the cross-anastomosing groups AG-D/CAG-1 and AG-E/CAG-3, and subgroup IIB was made up of groups AG-F/CAG-4, AG-I, and CAG-5. Group III included isolates belonging to AG-K and CAG-2 with one isolate each of AG-A and AG-B(o). Group IV consisted mainly of AG-Bb isolates. AG-A, AG-Ba, AG-C, and AG-O isolates were placed in different groups and were considered genetically diverse. Isozyme groups of binucleate Rhizoctonia were consistent with prior groupings determined by hyphal anastomosis and by DNA restriction pattern analysis. The present study provides evidence that isozyme phenotypes are good indicators of genetic diversity among anastomosis groups of binucleate Rhizoctonia species.