Evaluation of laboratory techniques for creating epiphytotics and bioassay of fungicides against sheath rot of rice

Two inoculation techniques were applied for the development of sheath rot (ShR) of rice on detached sheaths as well as on plants of different growth stages in the growth room. In the first method, 35, 50, 65, 80 and 95 days old rice plants were inoculated using spore suspension and mycelial discs (5mm diameter) of the fungus. In the second technique, the detached sheaths of different plant growth stages were inoculated with fungal discs (5mm). On plants and detached sheaths inoculated with fungal discs, symptoms started appearing within 3 days of inoculation and typical symptoms were produced within 7 days on all the growth stages of rice plants and detached sheaths. Maximum lesion size (9.0 mm) developed on 95 days old and minimum (5.0 mm) on 35 days old plant sheaths. However, in spore suspension inoculation, symptoms develop only on 65 or more days old plants. Ten fungicides were tested against ShR pathogen in the growth room. Tilt proved to be the most effective, which controlled 94.8 per cent disease incidence and 98.5 per cent severity.