Abstract
Incidence and severity of sheath rot of rice was recorded in five locations during Aus, Aman and Boro season. The seed-borne infection and seed transmission of Sarocladium oryzae, the cause of sheath rot of rice was studied through dry inspection, blotter method, agar plate method, water agar seedling symptom test, slide cassette holder method and tissue planting method. Different plant extracts and nutrients were tested to control the disease. The incidence and severity of sheath rot disease was the highest in BR-11 during Aman season. Seeds collected from more severely infected plants gave more discoloured and spotted seeds. Sarocladiun oryzae was detected from 46% of the discolored (grey) seeds. Seed-borne infection of this pathogen had strong relation with the severity of infection of the mother plants. The seeds harvested from severely infected tillers had highest seed infection and consequently the rate of transmission of Sarocladiun oryzae was also high. Seed dried for long time had less viable inocula of the pathogen. The pathogen (Sarocladiun oryzae) was detected from embryo, endosperm and glumes of the infected seed. The embryo of 86% of the infected seeds showed the presence of Sarocladiun oryzae. Viability of Sarocladium oryzae decreased with the increase of storage duration. Foliar application of lemon grass extract effectively reduced the incidence and severity of sheath rot of rice in the field. It is evident from the studies that Sarocladium oryzae, the cause of sheath rot of rice is transmitted from seed to plant to seed.
Keywords: Sarocladium oryzae, sheath rot, seed-borne infection, transmission.