Bacillus spp. Mediated Growth Enhancement and Antioxidative Defence Activation in Peppermint (Mentha piperita L.)

Peppermint (Mentha piperita L.) is a valuable medicinal and aromatic herb cultivated globally for its essential oil, prized for its therapeutic and flavouring properties. The productivity and essential oil quality of peppermint is strongly influenced by the intervention of biotic and abiotic elicitors, which eventually induces plant growth dynamics, redox homeostasis, and secondary metabolite biosynthesis. This study evaluates the effect of five plant growth promoting rhizobacteria (PGPRs): Bacillus tequilensis (T1), Bacillus subtilis (T2), Bacterium strain (T3), Bacillus thuringiensis (T4), and Bacillus cereus (T5), to access the modulation efficiency of these plant probionts over morphological, physiological, and biochemical parameters of peppermint variety CIM-Suras. The surface sterilized, uniform sized suckers of a menthol-rich peppermint variety CIM-Suras were inoculated with five aforementioned Bacillus spp., endowed with phosphate solubilization, ammonia production, siderophore production, and Indole Acetic Acid production efficiencies, in triplicate. The results of the study revealed that T2 (Bacillus subtilis) has significantly enhanced the photosynthetic process, contents of chlorophyll (64.71%), accumulation of proline (43.17%), SOD (24.89%), and catalase (56.33%), over the control, followed by T1 (Bacillus tequilensis), and T4 (Bacillus thuringiensis). Treatment with Bacillus subtilis (T2) showing maximum improvement in studied morphological, physiological and biochemical parameters in peppermint suggests the potential of the isolate to abate the oxidative damage of the cells during altering environmental conditions. These findings underscore the efficiency of peppermint-native Bacillus-based PGPRs, especially B. subtilis, for improving crop growth, stress resilience, and essential oil yield in a menthol-rich cultivar. This approach offers a sustainable alternative to synthetic fertilizers to improve peppermint productivity.