CHARACTERIZATION OF A NEW CULTURAL TYPE (LP) OF RHIZOCTONIA-SOLANI AG2-2 ISOLATED FROM WARM-SEASON TURFGRASSES, AND ITS GENETIC DIFFERENTIATION FROM OTHER CULTURAL TYPES

Isolates of Rhizoctonia solani AG2-2 obtained from turf with symptoms of large-patch disease of warm-season turfgrasses were compared with k nown AG2-2 isolates belonging to cultural types IIIB and IV Some isola tes that were previously identified as type IV have been separated her e and named LP isolates. Comparisons among isolates were based on cult ural morphology, hyphal growth rate, pathogenicity and restriction fra gment length polymorphism (RFLP) analysis in the nuclear encoded ribos omal DNA (rDNA) genes. The cultural characteristics of LP isolates var ied from those of types IIIB and IV. LP isolates did not show distinct sclerotial formation and zonation, and the colour of their mycelia an d pigment deposition was dark brown. LP isolates had slower hyphal gro wth rates than types IIIB and IV with an optimum temperature of 25 deg rees C compared with 28 degrees C for types IIIB and IV. LP isolates w ere less virulent on radish but highly virulent on zoysia grass when c ompared with isolates of types IIIB and IV. Genomic DNA was digested s eparately with Eco RI, Ban III, Xba I and Sal I, and probed with clone d rDNA from Alternaria alternata in Southern hybridizations. LP isolat es had one RFLP pattern, while both IIIB and IV possessed four differe nt patterns each. Cluster analysis of RFLPs showed that R. solani AG2- 2 is divided into three genetic subgroups, consisting of the IIIB, IV and LP isolates, respectively. The polymerase chain reaction (PCR) amp lified rDNA internally transcribed spacer (ITS) regions of the IIIB, I V and LP isolates had the same length but produced different restricti on patterns when digested with Msp I and Taq I. These results indicate that there are three cultural types in R. solani AG2-2, namely IIIB, IV and LP.