Anastomosis group and subgroup identification of Rhizoctonia solani strains deposited in NARO Genebank, Japan

The Rhizoctonia solani species complex is classified by anastomosis groups (AGs)-1–13 based on the hyphal fusion reaction. Most AGs are further divided into subgroups. However, the AG and subgroup designations of many strains of Japanese R. solani, including pathogens isolated from important crops, have not been determined. We thus identified AGs and subgroups of 45 R. solani strains (38 AG unknown and seven subgroup unknown strains), which had been isolated from 30 crops and identified by depositors in the NARO Genebank, Japan, based on the number of nuclei, culture morphology, PCR amplification with specific primers, and sequences of the rDNA-ITS region. Of the 45 strains, 37 were multinucleate, however, eight were binucleate. Of the multinucleate strains, 18 were identified as R. solani AG-4 HG-I, the rest as AG-1 IA (one strain), AG-1 IB (one strain), AG-2-1 (one strain), AG-2-2 IIIB (one strain), AG-2-2 LP (five strains), AG-2-2 hybrid subgroup between IIIB and IV (newly designated in this study; one strain), AG-3 PT (one strain), AG-4 hybrid subgroup between HG-I and HG-II (one strain), AG-4 HG-III (two strains), AG-5 (two strains), and AG-6 (three strains). Six of the eight binucleate strains were identified as binucleate Rhizoctonia AG-R (one strain) and AG-U (five strains). The rDNA-ITS sequences of the other two binucleate strains did not match any from known binucleate Rhizoctonia AGs-A–W. This study revealed new findings of Rhizoctonia diseases in Japan in 28 strains obtained from 21 crops.