To date, much of the genetics of the basidiomycete Thanatephorus cucumeris (anamorph = Rhizoctonia solani) remains unknown. Here, we present a population genetics study using codominant markers to augment laboratory analyses. Seven single-copy nuclear RFLP markers were used to examine 182 isolates of Rhizoctonia solani AG-1 LA collected from six commercial rice fields in Texas. Thirty-six multilocus RFLP genotypes were identified. Population subdivision analyses indicated a high degree of gene flow/migration between the six geographic populations. Tests for Hardy-Weinberg equilibrium (HWE) among the 36 multilocus RFLP genotypes revealed that four of the seven loci did not significantly differ from HWE. Subsequent analysis demonstrated that departures from HWE at the three remaining loci were due to an excess of heterozygotes. 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 Academic Press.
Bibliographical noteFunding Information:
We thank N. K. van Alfen for initiating this project; N. G. Whitney for collecting the R. solani strains from Texas rice fields; D. Hedgecock, S. B. Goodwin, K. J. Leonard, and A. P. Roelfs for helpful discussions on heterozygote excess; M. A. Cubeta, R. Vilgalys, and J. Xu for comments and encouragement; and L. M. Kohn and two anonymous reviewers for their efforts to improve this article. This project was partly supported by the Texas Agricultural Experiment Station and Grant 402108 to B.A.M. from the Texas Rice Research Foundation.
- Gene flow
- Hardy-Weinberg equilibrium
- Heterozygote excess
- Rhizoctonia solani
- Sheath blight
- Thanatephorus cucumeris