Klebsiella sp. IR6, an endophytic rhizobacteria with potential as a plant growth-promoting agent for jalapeño pepper (Capsicum annum L.) production.

Plant growth-promoting rhizobacteria (PGPR) offer a sustainable alternative to mitigate the excessive use of synthetic agrochemicals in modern agriculture. This study focused on the isolation and molecular characterization of endophytic bacteria from jalapeño pepper (Capsicum annuum L.) to evaluate their multi-functional PGPR traits and antagonistic activity against phytopathogenic fungi. Phylogenetic analysis identified several genera, including Stenotrophomonas, Pseudomonas, Paenibacillus, Klebsiella, Aeromonas, and Enterobacter. Among these, Klebsiella IR6 and Enterobacter IR9 significantly enhanced vegetative vigor under greenhouse conditions compared to the untreated control. These isolates demonstrated robust phosphate solubilization, siderophore production, and in vitro antagonism against Fusarium oxysporum (15%-34% growth inhibition). Furthermore, endophytic colonization of the root tissues by Klebsiella IR6 was successfully validated via confocal scanning microscopy using green fluorescent protein-tagged cells transformed with the pAD4325 plasmid. These findings suggest that Enterobacter and Klebsiella isolates are promising biotechnological tools for optimizing horticultural yields, while reducing chemical dependence. Nevertheless, further field evaluations across diverse jalapeño hybrids are essential to validate the consistency and stability of both as reliable bio-inoculants for sustainable agriculture.