Genetic relatedness among anastomosis groups in Rhizoctonia as measured by DNA/DNA hybridization.

Genetic relationships of 44 multinucleate and binucleate isolates of Rhizoctonia were investigated by the technique of heterologous DNA/DNA hybridization. Genomic DNA was isolated from representative isolates of eight different anastomosis groups (AG) in Rhizoctonia solani, five different anastomosis groups (CAG) of binucleate Rhizoctonia, and several isolates of uncertain anastomosis affinity. Results of more than 200 pairwise DNA hybridization experiments strongly support previous intraspecific groupings based on anastomosis. Isolates belonging to different AG show little DNA sequence complementarity, usually less than 25%. DNA hybridization values within each AG range considerably (30–100%) and indicate that substantial genetic variation is present within some AG. Within AG, reduced DNA hybridization values (< 60%) indicate the presence of genetically divergent subgroups, some of which had previously been recognized on the basis of colony morphology, pathogenicity, or anastomosis behavior. The lowest DNA hybridization values from this study were observed between the multinucleate R. solani reference isolates and isolates representing five CAG of binucleate Rhizoctonia. Highly reduced levels of DNA hybridization indicate that multinucleate and binucleate Rhizoctonia spp. are unrelated and provide genetic evidence to support the taxonomic separation of the teleomorph genera Thanatephorus and Ceratobasidium.

Duke Scholars

Author Rytas J. Vilgalys Biology