Abstract
Survival and pathogenicity of sclerotia produced by sugarbeet root rot fungus (Rhizoctonia solani AG-2 Type-2) were compared among fields with different degree of disease incidence (DI). In the Hombetsu area with high DI, sclerotial formation (SF) was not abundant, but sclerotial germination (SG) in the next spring was high. In the Kiyokawa area with low DI, SF was abundant, but SG was low. It can therefore be seen that the number of overwintered viable sclerotia (NVS) was almost same between the Hombetsu and Kiyokawa areas. There are quite high positive correlations between NVS and the DI of sugarbeet root rot. And there is a tendency for the DI in the Hombetsu area to be rather higher than in the Kiyokawa area. As there is a high positive correlation between the percentage of SG and that of sclerotia with 5 or more emerged hyphae, the difference of the DI in different areas is due to the difference of activity of sclerotia as inoculum.
