Abstract
The time and location of isolation of the sclerotial fungi causing a group of sclerotial diseases called “pseudo-sheath blight of rice plant” was surveyed. Rhizoctonia oryzae, Sclerotium oryzae-sativae and S. fumigatum were isolated from rice seedlings growing in nursery boxes. R. oryzae, R. solani AG 2-2, S. orvzae-sativae, S. fumigatum and S. hydrophilum were also isolated from the rice seedlings which had been left for complementary planting in paddy fields. The isolation frequencies of S. hydrophilum, S. fumigatum and S. oryzae-sativae were higher than those of other sclerotial fungi. These fungi were isolated from dead or weakened leaves of lower plant parts immediately after transplanting. The isolation frequencies of R. oryzae and R. solani AG 2-2 increased from the tillering or heading stage onwards. These results suggest that the rice seedlings were immediately infected with the sclerotial fungi at an early stage after transplanting, with the fungi growing predominantly on lower leaves.
