heterogeneity of the rDNA-ITS sequence and its phylogeny in Rhizoctonia cerealis, the cause of sharp eyespot in wheat

The sequence heterogeneity of the ribosomal internal transcribed spacer (ITS) region was investigated for Rhizoctonia cerealis isolates from the anastomosis group AG-DI. Although sequence variability of the ITS has been reported in a few multinucleate R. solani isolates, it has very rarely been reported in binucleate Rhizoctonia spp. isolates and has never been described in R. cerealis, the pathogen of wheat sharp eyespot. In this study, the ITS regions of 15 R. cerealis isolates were cloned and sequenced. The results revealed more than one different ITS sequence within each isolate. This is the first evidence of ITS sequence heterogeneity in R. cerealis. Based on these ITS sequences, different sequences of one isolate did not cluster in one clade, but all of the sequences of the 15 isolates were clustered in the anastomosis subgroup AG-DI, suggesting that the heterogeneity of the ITS did not affect the molecular identification of their anastomosis group. Haplotype analyses indicated that there might be three evolutionary origins of R. cerealis, or a recombination event could be the cause of different ITS sequences in one genome. This study demonstrates the variability and the evolution of Rhizoctonia, especially binucleate R. cerealis. These findings will help design disease control strategies.