Biocontrol of Wheat Blast by Seed-Associated Bacillus Strains: Three-Year Field Evaluation and Comparison with Chemical Fungicide for Disease Control and Yield Optimization

Wheat blast, caused by Magnaporthe oryzae pathotype Triticum (MoT), poses a major, escalating threat to global wheat production, particularly in South Asia. This study systematically evaluated the biocontrol and yield-enhancing potential of three seed-associated Bacillus strains, Bacillus subtilis BTS-3, B. velezensis BTS-4, and BTLK6A, against MoT under both greenhouse (seed priming, preventive, and curative foliar application) and field conditions (seed priming and foliar spray). Seed priming with BTS-4 demonstrated significant disease suppression, reducing leaf blast severity by up to 89.88%. Synergistic seed priming treatment further enhanced protection, with the BTS-3 + BTS-4 consortium achieving 93.38% reduction of the disease in the seedling assay. Notably, preventive foliar application of BTS-4 also resulted in complete leaf blast suppression (0% severity), demonstrating its prophylactic efficacy, whereas curative treatments were comparatively less effective. Three years of rigorous field trial data confirmed the high efficacy of the Bacillus treatments, with BTS-4 and the bacterial consortium consistently reducing blast severity by more than 50% compared with the negative control. More importantly, the biocontrol treatments significantly improved yield attributes, with the consortium achieving the highest grain yield. These results clearly demonstrated that biological control treatments, alone or combined with fungicide, outperformed the negative control by 86.2% and the standard chemical fungicide (Nativo) treatment by 47.3%, respectively. These findings highlight the strong potential of these Bacillus strains, particularly the BTS-4 and consortium treatments, as sustainable, superior biocontrol agents for the integrated management of wheat blast and field-scale crop productivity enhancement.