Abstract
Healthy melon seedlings transplanted in the soil artificially infested with two isolates (CH 83-14 and CH 83-15) of Monosporascus cannonballus, collapsed about 50 days after inoculation, and the fungus was recovered from roots. Young seedlings did not show any symptoms, but the fungus was detected in the recovery tests. The affected roots were rotted and brown colored, and slender roots disappeared, together with numerous scattered, small, round, black peritheicia. These symptoms were similar to those of the collapses of matured melon plants found in Chiba and other prefectures in Japan.
