Characterization of Diversity Among Isolates of Rhizoctonia oryzae-sativae from California Rice Fields.

Thirty-one California isolates of Rhizoctonia oryzae-sativae, the cause of aggregate sheath spot of rice, were characterized by culture morphology, pathogenicity tests, somatic compatibility groups (SCGs), single-locus microsatellites (SLMs), and multilocus microsatellites (MLMs). The highest level of diversity (individual isolates) was described by MLMs whereas pathogenicity tests exhibited the lowest resolution. In general, a high degree of diversity was revealed (diversity from 51.6 to 100%) within the California population. Several lines of evidence indicated sexual reproduction in the population of R. oryzae-sativae. Genetic analyses of SLMs and MLMs revealed high genetic diversity and gametic equilibrium of all SLMs and most MLMs. Furthermore, unique individuals were recovered by MLMs and there was no correlation of phenotypes to either SCGs or genetic markers. In addition, incongruence of parsimonious trees generated from each of five primers of MLMs and a poorly resolved consensus tree inferred from the combined data set were demonstrated. Accordingly, sexual reproduction of R. oryzae-sativae is probably more prevalent in California than previously assumed.