DNA-BASE SEQUENCE HOMOLOGY IN RHIZOCTONIA-SOLANI KUHN - INTERGROUP AND INTRAGROUP RELATEDNESS OF ANASTOMOSIS GROUP-9

Isolates of anastomosis group-9 (AG-9) of Rhizoctonia solani are approximately 81% thiamine prototrophic and approximately 19% thiamine auxotrophic. These subgroups, or intraspecific groups (ISG), can be distinguished from one another by DNA hybridization techniques but not by hyphal anastomosis. DNA hybridization among isolates belonging within either group is 94% or higher, whereas hybridization among thiamine prototrophic and thiamine auxotrophic isolates ranges from 78 to 87%. Isolates of AG-9, regardless of thiamine requirement, show low DNA hybridization (15% or less) with isolates representing 10 AG and 15 ISG of R. solani, indicating the genetic isolation of AG-9. We propose that the two ISGs of AG-9 be designated AG-9 TP (thiamine prototrophic) and AG-9 TX (thiamine auxotrophic).