An integrated approach to Rhizoctonia taxonomy: cultural, biochemical and numerical techniques

Twenty-five isolates of Rhizoctonia, comprising 12 anastomosis group strains belonging to R. solani and 13 isolates from orchids, were compared on the basis of cultural characteristics on a variety of media, of effects on growth to varying pH and carbon and nitrogen sources, and enzymic abilities. Data were coded and analysed using the computer programs taxmap, taxpac and numipac. The orchid isolates, although exhibiting significant variation among themselves, were distinct from the R. solani anastomosis groups. Results support recognizing AG4 as a distinct species, Thanatephorus praticola, but do not support recognizing T. sasakii or Corticium microsclerotium as taxa distinct from T. cucumeris. Orchid isolates were separated among three diverse groups representing T. pennatus, R. repens, and a final large and diverse group consisting of R. anaticula, Ceratobasidium obscurum and several unidentified isolates.