Antimicrobial peptides (AMP)-producing Bacillus spp. for the management of Fusarium infection and alfalfa growth promotion.

Alfalfa is the most extensively cultivated forage legume worldwide. Its yield and quality may be affected by various pests and pathogens. Among them, fungal pathogen Fusarium oxysporum, the causal agent of Fusarium wilt, is considered as the main threat. The aim of the present study was to investigate the potential of the Bacillus spp. isolated from alfalfa rhizosphere to be used as biocontrol agents against F. oxysporum, as well as plant-growth promoting agents. A total of six isolates were identified as B. halotolerans LA1K3 and LA1NK3, B. toyonensis LA1K2, B. thuringiensis LA1K4, B. megaterium LA2K1, and B. safensis LA1NK1. Suppression of F. oxysporum was recorded in a range from 2.86% (LA2K1) to 31.43% (LA1NK3), except for LA1K2. The presence of antimicrobial peptide biosynthetic genes was detected: bacyllomicin and fengycin (LA1NK1); subtilin and fengycin (LA1K2); subtilin (LA1K4 and LA2K1), and bacyllomicin (LA1NK3 and LA1K3) by PCR method. Bacillus halotolerans LA1NK3 showed six PGP traits (production of indole-3-acetic acid, siderophores, HCN, protease, cellulase and amylase). Bacterial inoculation increased the germination percentage of infected seeds from 42.85% (LA2K1) to 85.71% (LA1NK1, LA1NK3), as well as the yield of infected alfalfa plants of 186.07% (LANK1), compared to the infected control. The results of this study highlight the potential of rhizosphere soil to harbor beneficial bacterial strains that could be exploited for disease control and plant growth promoting. Bacillus safensis LANK1 stood out as the most effective strain in promoting the growth of alfalfa infected by F. oxysporum under controlled conditions. © 2025 Society of Chemical Industry.