Optimized Endospore Production and Carrier Formulations of Endophytic Bacillus Species to Enhance Field Control of Wheat Blast

Abstract

Harnessing endophytic bacteria for plant disease management offers a promising sustainable strategy. We previously demonstrated that endophytic Bacillus spp. significantly suppress wheat blast disease under field conditions. Despite their promising biocontrol potential, the successful commercialization of microbial biopesticides depends on economical mass production, high microbial viability, prolonged shelf-life, and consistent field performance. This study optimized fermentation conditions, endospore production and carrier formulations of three endophytic Bacillus strains (B. subtilis BTS-3 and B. velezensis BTS-4 and BTLK6A) for the sustainable management of wheat blast caused by Magnaporthe oryzae pathotype Triticum (MoT). Sugarcane molasses was evaluated as a low-cost alternative to commercial nutrient broth, while supplementation with 500 ppm MnCl2·4H2O enhanced growth and endospore production for Bacillus spp. Talc- and molasses-based liquid formulations were subsequently developed and evaluated for storage stability. A talc formulation containing 1% (w/w) carboxymethyl cellulose and 1.5% (w/w) calcium carbonate (CaCO3) provided the highest survival up to 180 days, maintaining a population density of 1 × 105–106 CFU g−1, whereas liquid formulations exhibited a faster decline in cell viability. Despite these differences, both formulation types significantly reduced blast disease severity by 48.78–75.98% compared to the only MoT- inoculated control in the field. Seed priming consistently outperformed foliar application and enhanced tiller production (9.40–16.62%), thousand-grain weight (13.47–32.41%), and grain yield (up to 321 g/m2), achieving up to 38.58% higher yield than the MoT-inoculated control. Taken together, these findings establish a cost-effective approach for developing stable talc- and molasses-based formulations, thereby enhancing the commercial viability and large-scale deployment of biological control strategies for sustainable wheat blast management.