Role of B. velezensis RaSh2 inoculation on enhancing cowpea (Vigna unguiculata L.) plants grown under drought conditions

Drought stress poses a danger to global agriculture, significantly reducing crop productivity in arid and semi-arid regions. The application of Bacillus velezensis RaSh2 has been evaluated as a promising approach to enhance cowpea’s resilience to drought stress. Initially, B. velezensis RaSh2 was isolated from Solanum lycopersicum leaves then its plant growth-promoting traits were assessed, including siderophore production, nitrate reduction, protease, cellulase, and the solubilization of zinc, calcium and phosphorus. The mechanisms through which B. velezensis RaSh2 mitigates this stress in cowpea plants were assessed through in vivo and in vitro experiments. In the in vivo study, cowpea seeds were mixed with B. velezensis RaSh2, and after a week of sowing, 40% of water field capacity (WFC) was withheld. Exposure to drought altered the morphological, physio-biochemical attributes, osmolytes, secondary metabolites, and scavenging antioxidant enzymes. Specifically, drought reduced growth, chlorophyll, leaf water content, and membrane stability, while a rise in oxidative stress markers was observed. However, relative water content, chlorophyll, and both shoot and root lengths increased in B. velezensis inoculated plants. The RaSh2 inoculation significantly decreased membrane leakage by 28.6% by reducing malondialdehyde levels by 20.9% and hydrogen peroxide content by 22.7% under drought stress. Along with the reduction in oxidative stress, bacterial inoculation positively influenced glycine betaine and proline contents, enzymatic and non-enzymatic activities, illustrating its role in alleviating stress. Collectively, the evaluation of cowpea’s response to drought stress after inoculation with B. velezensis RaSh2 has provided critical insights to its potential use to enhance plant stress tolerance.