A Survey on Relatedness among Field Isolates of Sclerotium fumigatum Nakata and S. oryzae-sativae Sawada Causing Rice Sclerotial Diseases

Abstract

Many isolates of Sclerotium fumigatum Nakata and S. oryzae-sativae Sawada from sheath blight-like lesions of rice plants in the paddy field were used for grouping by the hyphal anastomosis. Isolates from different lesions of the same sclerotial disease on a single rice hill were quite similar in the cultural characteristics. Perfect fusion without death of the cell was commonly observed when the hyphae of these isolates came into contact with each other on the plain agar medium. Therefore, single perfect fusion group (p-group), in which the perfect fusion was observed in the pairing test between two isolates, appeared to be dominant in a hill. When the disease caused by S. fumigatum or S. oryzae-sativae occurred widely in the field, 22-71 isolates of the respective fungus obtained from diseased plants in 30-35 plots (4.5-5.0m interval between plots) in the field were assigned to at least 9-34 p-groups. In many cases, single p-group tended to distribute in a limited part of the field.