Distribution and survival of sclerotia of rice sheath blight fungus, Thanate phorus cucumeris, in Taiwan.

Abstract

The number of sclerotia of rice sheath blight fungus, Thanatephorus cucumeris (Rhizoctonia solani AG 1, Sasakii type), from single sampling spot (50×50×20cm), varied from 561 to 13 with an average of 156.5 after harvest of the first rice crop from 13 sampling locations in Taiwan in 1979. Sclerotia were most densely distributed on the surface layer (0-1cm) which contained 36.1 per kg dry soil. As the soil depth increased, the numbers of sclerotia decreased to 3.2, 3.3, 2.6, and 0.9 per kg dry soil, respectively, from 1-5, 5-10, 10-15 and 15-20cm depth. Per cent germination of the recovered sclerotia on 2 per cent water agar, in average, was 45.4, 19, 14.8, 8.5, and 5.5, respectively, from the surface to 20cm soil depth. The buoyant sclerotia in the paddy showed 14-40 per cent germination with average of 36.4 during 120 days growing period of the first rice crop in 1979. Sclerotia collected from the rice plants began to decrease in germination after being buried in soil for 4-6 months without regard to the cover crops. However, one year after burial, the sclerotia still showed 50-80 per cent germination. The germination of sclerotia kept at room temperature in the laboratory for 6 months declined to half and ceased 8-12 months later. The number of smaller sclerotia (those captured on 40 mesh screens after passing through 20 mesh screens) was 78.2% in average of those captured in the 20 mesh screen from the same sample while per cent germination from 40 mesh ones was almost half of those in the 20 mesh ones.