Behavior and control of Pyricularia oryzae in brown rice seed as inoculum source of rice seedling blast.

Abstract

This study investigated Pyricularia oryzae infection of seeds harvested from seed production fields, the role of infected seeds in seedling blast occurrence, and effective methods for disinfecting infected seeds for the purpose of developing control methods for seedling blast caused by infected seeds. Infection intensity in fungus-infected seeds was tested with the Brotter method. About 20% of seeds, in which sporulation was observed with a stereomicroscope, showed invasion by the fungus into the rice husk. From results of periodical observation on fungus-infected seeds from the heading to late reaping the stage of infection in brown rice and the invasion process within rice seeds was determined. Blast-infected seeds harvested at the late reaping were neither removed by specific gravity with salt, nor disinfected with some seed disinfectant agents. The heavily infected seeds developed seedling damping-off and abundant sporulation at the base of the seedling stem 40 days after sowing. Two methods were able to disinfect the pathogen in infected brown rice seeds: the vacuum method with disinfectant chemicals, and hot water immersion.