DEVELOPMENT AND EVALUATION OF MICROENCAPSULATED BIOFORMULATIONS OF BIOCONTROL AGENTS AGAINST BIPOLARIS ORYZAE CAUSING BROWN SPOT OF RICE

Abstract

Brown spot of rice, caused by Bipolaris oryzae, is a major disease that adversely affects rice production. This study evaluated selected microbial biocontrol agents against B. oryzae, developed microencapsulated bioformulations, and assessed their efficacy under in vitro and greenhouse conditions. Trichoderma asperellum TAIK1, Bacillus cabrialesii BIK3, and Pseudomonas putida PIK1 were evaluated for antagonistic activity and plant growth-promoting ability. TAIK1 exhibited the highest antagonistic activity (81.85%), followed by BIK3 (67.54%) and PIK1 (57.85%), and also showed superior plant growth-promoting effects. Among the carrier materials, rice bran supported the highest viable population, followed by peat, whereas cellulose recorded comparatively lower viability. The bioagents were encapsulated using cellulose, peat, and rice bran with gelatin through emulsification. Stable microcapsules ranging from 23.31 to 97.50 µm were obtained. Maximum release occurred at 48 h for BIK3 and 96 h for TAIK1, with peat-based formulations showing the highest release efficiency. In in vitro assays, Peat-TAIK1 showed the highest inhibition of B. oryzae in agar disc diffusion (83.26%) and dual culture (84.01%). The peat-based formulations MET (microencapsulated Peat-TAIK1) and MEB (microencapsulated Peat-BIK3) were further evaluated under greenhouse conditions. The combined MET + MEB treatment applied by seed and foliar routes produced the greatest improvement in plant growth and yield attributes under B. oryzae challenge, reducing disease severity by 81.48% and increasing grain yield per hill by 73.01% over the pathogen-inoculated control. Overall, Peat-TAIK1 showed the highest in vitro efficacy; seed and foliar application of MET + MEB resulted in significantly greater plant growth, disease suppression, and yield benefits under greenhouse conditions, supporting further evaluation under field conditions.