Some Properties of Anastomosis Group 6 and BI in Rhizoctonia solani Kühn

Morphological and physiological properties of AG-6 and AG-BI, new anastomosis groups in R. solani, and anastomosis frequency between AG-BI and other anastomosis groups were investigated.Metabasidia in AG-6 were barrel-shaped or obovate, 7.5-17.0×5.5-10.0μm and without a median constriction. The length of sterigmata was 4.5-18.8μm and numbers of sterigmata per metabasidium 3-(3.9)-5. Basidiospores were obovate to oblong-ellipsoid, hyaline, smooth, flattened on the inner side, with an apiculus, 5.0-10.0×2.8-5.2μm. They sometimes germinated by the repetition. The mean hyphal width was 8.6μm and the number of nuclei per cell was 3-15. Optimum temperature for growth was 25-30C. Thiamine was autotrophic. Metabasidia in AG-BI were barrel-shaped, short clavate or obovate, 8.8-19.0×7.0-11.3μm and without a median constric-tion. The length of sterigmata was 4.0-12.0μm and numbers of sterigmata per meta-basidium 3-(3.9)-5. Basidiospores were obovate to oblong-ellipsoid, hyaline, smooth, flattened on the inner side, with an apiculus, 5.0-10.0×3.7-6.7μm. They sometimes germinated by the repetition. The mean hyphal width was 10.2μm and the number of nuclei per cell was 5-23. Optimum temperature for growth was 23-25C. Thiamine was heterotrophic. Anastomosis frequency of AG-BI was highest with AG-2-2 and lower by degrees with AG-2-1, AG-3, and AG-6. Judging from their morphological properties of perfect stage, AG-6 and AG-BI are classified as Thanatephorus cucumeris (Frank) Donk.