Bacillus amyloliquefaciensHN11 enhances cowpea growth and systemic resistance to Spodoptera litura viaJA/SA pathways and growth‐mediated tolerance

Abstract BACKGROUND Plant growth and development benefit from the contribution of plant growth‐promoting rhizobacteria (PGPR), which have a positive effect on plants by breaking down organic matter and synthesizing growth hormones. In addition, PGPR can stimulate plants to produce secondary metabolites, thereby enhancing its defense against pathogens and pests. To study the effects of Bacillus amyloliquefaciens 8421 (HN11) on the promotion and induction of defense against pests in cowpea, the effects and mechanisms were determined on the basis of phenotypic traits and changes in the levels of defense enzymes and phytohormones in cowpea after application of HN11. RESULTS The results showed that HN11 effectively colonized the cowpea root system, and at 15 days, 10 7 CFU mL −1 HN11 significantly improved cowpea agronomic traits and root morphology, especially promoting an increase in nodule weight (47.6%). Furthermore, when challenged by Spodoptera litura larvae, plants inoculated with HN11 exhibited significantly less damage and displayed a greater ability to recover their growth. It was found that HN11 treatment increased both defense enzyme activities and phytohormone levels in cowpea. Notably, HN11 indirectly affected the induced defense against S. litura by promoting plant growth and enhancing tolerance. CONCLUSIONS This study opens up new avenues for biological control using PGPR, which is of far‐reaching significance for enhancing crop yields, reducing chemical pesticide dependence, and preserving the ecological environment. © 2025 Society of Chemical Industry.