Abstract
The clones of the same anastomosis group of Rhizoctonia solani Kühn in the fields of white potatoes, sugar beets, and rice plants were investigated. R. solani was isolated from diseased potato tubers in 3 fields, from infested soils in 10 sugar beet fields, and from diseased culms of rice plants in a paddy field. The most isolates from potato tubers, sugar beet field soils, and rice culms were AG-3, AG-2-2, and AG-1, respectively. Reactions of anastomosed hyphae among the isolates of each group were observed on water agar. The isolates which fused perfectly without death of fused cells (S reaction) were determined to be the same clone, and the isolates which showed death of fused cells (K reaction) were determined to be distinct clones. In potatoes, the most AG-3 isolates from the same tuber showed S reaction. The most isolates from individual tubers in the same field and all isolates from separate fields showed K reaction, In sugar beets, the most AG-2-2 isolates from the same soil sample showed S reaction and the most isolates from separate soil samples in the same field showed K reaction. The all isolates from separate fields, even in the same district, showed K reaction. In rice plants, the most AG-1 isolates from several lesions on one culm showed S reaction. K reaction increased between the isolates from neighbour culms. The most isolates from distant culms showed K reaction. There were 41 clones in this paddy field of 11 ares. In the paddy field, although the distribution of one clone was usually limited, a few clones distributed widely in the field. These results indicate that one field is occupied by a specific anastomosis group pathogenic to the crop growing in the field, that there are many clones of pathogen in one field, and that the distribution of one clone is limited within only small area in the field.
