Multi-stress Tolerant Biocontrol Formulation Against Soil-borne Pathogen of Cotton

Cotton production is negatively affected by both biotic and abiotic factors. Thus, we aimed to isolate and identify multi-stress tolerant bacterial biocontrol agents (BCAs) against two major soil-borne pathogens, Macrophomina phaseolina and Fusarium oxysporum. A dual culture plate and broth assay confirmed the antagonistic activity of the isolates against these phytopathogens. Four isolates were regarded as multi-stress tolerant BCAs based on their biocontrol and abiotic stress (salt, temperature, osmotic, and acidity/alkalinity) tolerating abilities and were identified as: Bacillus siamensis SSVP1 (18), Bacillus halotolerans SSVP2 (34), Pseudomonas aeruginosa SSVP3 (62), and Bacillus tequilensis SSVP4 (S46-7). HPLC-MS identification of metabolites revealed several antifungal compounds like iturins, surfactins, bacillibactin, fengycin, phenazine, and pyocyanin, and headspace GC-MS showed several VOCs production involved in antifungal activity of these BCAs. In-planta efficacy evaluation showed that the BCA inoculation activated induced systemic resistance (ISR) in cotton plants, leading to increased levels of two defense enzymes, polyphenol oxidase (110-180%) and phenyl ammonia lyase (22-58%), and three antioxidant enzymes, catalase (36- 98%), peroxidase (44-71%), and superoxide dismutase (72-145%). Further, two selected isolates B. siamensis SSVP1 and P. aeruginosa SSVP3, were chosen for bioformulation investigations and results showed that 2% gum arabic is a suitable additive for their liquid formulations. The results indicated that these BCA bioformulations are reliable and sustainable options for enhancing crop growth.