Mitigating maize stalk rot disease: harnessing Bacillus subtilis PM57 and Bacillus cereus PM38 as biocontrol allies against Erwiniacarotovora.

Maize bacterial stalk rot, caused by Erwinia carotovora pv. zeae (EC) is a significant threat to maize production, and applicable biocontrol measures are lacking. This study aims to identify a potent biocontrol agent against Erwinia carotovora and enhance plant growth under stress conditions. Thirty strains were screened using the agar plate well diffusion method. Strains PM57 and PM38 exhibited the highest antagonistic activity, forming inhibition zones of 5.0 and 4.51 mm, while distilled water served as a control with no inhibition. Their cell-free supernatants (CFSs) also demonstrated strong antagonistic activity with the maximum inhibition zones of 7.0 and 5.5 mm. The minimum inhibitory concentration of cell-free supernatants from both strains was 50 μg/ml. PM57 was identified as Bacillus subtilis via 16S rRNA gene sequencing. FTIR analysis revealed functional groups, including sulfonates, carbohydrates, proteins, and polyphenols in PM38, while PM57 exhibited peaks related to C-N stretching and aliphatic primary amine. GC-MS analysis identified twenty-six bioactive compounds known for their biological and medicinal properties, including tert-butyl phenol compounds, hydrocarbons, aldehydes, benzoquinones, pyrroles, and terpenes. Both inoculants produced volatile metabolites that effectively inhibited Erwinia carotovora growth in vitro. A greenhouse study revealed that PM57 reduced stalk rot disease incidence by 76.83 %, while PM38 reduced it by 74.94 %. The application of both inoculants enhanced chlorophyll activity; PM57 increased plant-growth by 11 %, and PM38 by 6 % and improved pathogen stress tolerance in maize seedlings compared to the positive control. These results demonstrate the potential of PM57 and PM38 as effective biocontrol agents for sustainable maize cultivation.