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

Harnessing endophytic bacteria for disease management offers a promising sustainable strategy owing to their biocontrol activity in agriculture. Our previous research has shown that endophytic Bacillus spp. significantly suppressed wheat blast disease in field. 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 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. Talc formulation containing 1% (w/w) carboxymethyl cellulose and 1.5% calcium carbonate (CaCO₃) provided the highest survival up to 180 days, maintaining a population density of approximately ~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 infected control in the field. Seed priming consistently outperformed foliar application and also enhanced tiller production (9.40–16.62%), thousand-grain weight (13.47-32.41%), and highest grain yield (321 g/plot), achieving up to 38.58% higher yield than the MoT-inoculated control. These findings established an effective approach for developing stable talc- and molasses-based formulations capable of maintaining bacterial viability and supporting the field efficacy for sustainable wheat blast management.