Plant diseases are among the major factors affecting plant productivity. Biological control of plant diseases is preferred over chemical control as it is environment-friendly, cost-effective, and sustainable. Among many microbes capable of providing biological control of plant diseases, probiotic Bacillus species are most promising as they can survive in adverse conditions, provide plants with a wide range of benefits including protection from phytopathogens. Wheat blast caused by Magnaporthe oryzae Triticum pathotype (MoT) has emerged as a potential threat to global wheat production. Due to unreliability of fungicides and limited cultivar resistance, we aimed to screen and identify potential antagonist bacteria collected from internal tissues of rice and wheat seeds to determine their in vitro and in vivo inhibitory effects against MoT. Dual culture and seedling assays were performed to evaluate the efficacy of probiotic bacteria. Out of 170 bacterial isolates, three bacteria (BTS-3, BTS-4, and BTLK6A) were screened as potential antagonists against MoT in vitro. Artificial inoculation at the seedling stage showed that the isolates BTS-4, BTS–3, and BTLK6A reduced 89, 88, and 85% of wheat blast disease severity, respectively, compared to mock-inoculated control. The bacterial isolates were identified as Bacillus subtilis (BTS-3) and B. velezensis (BTS-4 and BTLK6A) through genome phylogeny. The whole genome sequence of these three bacterial strains decoded a number of orthologs to intrinsic genes of antimicrobial peptides, antioxidant defense enzymes, cell wall degrading enzymes, compounds involved in the induction of systemic resistance (ISR) in host plants, and volatile compounds to make them promising biologicals to control MoT in wheat. Combined data of in vitro and in vivo along with genome analysis suggest that Bacillus spp. suppress the destructive wheat blast disease likely through antibiosis and ISR in the host plants. Further field evaluation and characterization of antimicrobial compounds are needed for a better understanding of the mode of action and practical recommendation of these bacteria for wheat blast control in the farmers’ fields.

Application of chemical pesticides to protect agricultural crops from pests and diseases is discouraged due to their harmful effects on human and environment. Therefore, alternative approaches for crop pro-tection through microbial or microbe originated pesticides have been gaining momentum. Wheat blast is a destructive fungal disease caused by Magnaporthe oryzae Triticum (MoT) pathotype, which poses a seri-ous threat to global food security. Screening of secondary metabolites against MoT revealed that antimy-cin A isolated from a marine Streptomyces sp. had significant inhibitory effect on mycelial growth in vitro. This study aimed to investigate the inhibitory effects of antimycin A on some critical life stages of MoT and evaluate the efficacy of wheat blast disease control by this natural product. Bioassay indicated that antimycin A suppressed mycelial growth, conidiogenesis, germination of conidia and formation of ap-pressoria in germinated conidia of MoT in a dose-dependent manner with minimum inhibitory concen-tration 0.005 μg/disk. If germinated, antimycin A induced abnormal germ tubes (4.8%) and suppressed the formation of appressoria. Interestingly, application of antimycin A significantly suppressed wheat blast disease in both seedling and heading stages of wheat supporting the results from invitro study. This is the first report on inhibition of mycelial growth, conidiogenesis, conidia germination, detrimental morphological alterations in germinated conidia, and suppression of wheat blast disease caused by a Triticum pathotype of M. Oryzae. Further study is required to unravel the precise mode of action of this promising natural compound for considering it as a biopesticide to combat wheat blast.