HETEROGENEITY IN ELECTROPHORETIC KARYOTYPE WITHIN AND BETWEEN ANASTOMOSIS GROUPS OF RHIZOCTONIA-SOLANI

Isolates of the soil-borne basidiomycete Rhizoctonia solani vary in cu ltural appearance, in growth characteristics and in pathogenicity towa rds plants. Isolates of R. solani can be divided into anastomosis grou ps (AGs) and this division accommodates part of the observed diversity . However, a clear link between AGs and relevant phytopathological cha racters is missing and a well-described genetic basis for AGs is lacki ng. To provide genetic information, we examined polymorphism of the in ternal transcribed spacer (TTS) of the ribosomal RNA genes and determi ned the electrophoretic karyotype by means of pulsed field gel electro phoresis (PFGE). ITS polymorphism confirmed the genetic isolation of A Gs and indicated that genetically isolated subgroups exist within AGs. PFGE showed that X. solani isolates have at least II chromosomes rang ing in size from 0.6 to 6 Mb. The X. solani genome size is estimated t o be between 37 and 46 Mb. The karyotype of R. solani is highly variab le and although the observed heterogeneity in karyotype within an AG i s smaller than between AGs, karyotype and AG are not obviously correla ted. Rather it can be concluded that the variation in electrophoretic karyotype is reflected in the phenotypical variation of R. solani, wit h generally less diversity within an AG than between AGs.