High levels of gene flow and heterozygote excess characterize Rhizoctonia solani AG-1 IA (Thanatephorus cucumeris) from Texas

To date, much of the genetics of the basidiomycete Thanatephorus cucumeris (anamorph = Rhizoctonia solani) remains unknown. Here, we present a populat ion genetics study using codominant markers to augment laboratory analyses. Seven single-copy nuclear RFLP markers were used to examine 182 isolates o f Rhizoctonia solani AG-1 IA collected from six commercial rice fields in T exas, Thirty-six multilocus RFLP genotypes were identified. Population subd ivision analyses indicated a high degree of gene flow/migration between the six geographic populations. Tests for Hardy-Weinberg equilibrium (HWE) amo ng the 36 multilocus RFLP genotypes revealed that four of the seven loci di d not significantly differ from HWE, Subsequent analysis demonstrated that departures from HWE at the three remaining loci were due to an excess of he terozygotes, Data presented here suggest that R. solani AG-1 IA is actively outbreeding (heterothallic), Possible explanations for heterozygote excess , which was observed at all seven RFLP loci, are discussed. (C) 1999 Academ ic Press.