Reduction of initial occurrence of rice blast (Pyricularia oryzae) inocula on seeds by microbial and hot water seed treatments.

Abstract

Rice blast disease resulting from infected rice seed can be avoided by using treated seeds. Seed treatment using chemical fungicide has many limitations such as development of resistance to pathogens, damage to the natural environment and the health of farmers and consumers. Such limitations have raised the need for alternative non-chemical seed treatment methods such as antagonist microbial agents and hot water. Laboratory and the screen house experiments were carried out with the aim of evaluating the efficacy of 'Trichoderma asperellum', 'Bacillus subtilis' and hot water (50 degreesC/15 min) seed treatments against rice blast disease inocula on rice seeds. The results showed that, seeds treated with microbial agents ('T. asperellum', 'B. subtilis') and hot water reduced the percentage of infected rice seeds by 4.3 to 52.7% relative to non-treated seeds. The germination percent and seedling vigour index increased from 12.3 % to 17.1 % . Rice seeds treated with 'B. subtilis' reduced the incidence and severity of rice blast disease from 10% to 72.4 %. Seed treatment using 'B. subtilis' followed by 'T. asperellum' were the best in reducing the number of infected seeds and rice blast disease incidence and severity on rice seedlings. Therefore, the use of these microbial agents has a potential for effective management of rice blast disease.