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

Abstract

Plant growth-promoting rhizobacteria (PGPR) represent a sustainable alternative to reduce excessive agrochemical use and strengthen environmentally responsible agricultural practices. This study aimed to isolate, identify, and molecularly characterize endophytic bacteria associated with jalapeño pepper (Capsicum annuum L.) to evaluate their potential as PGPR and their antagonistic activity against phytopathogenic fungi. In vitro assays were conducted to determine functional traits related to plant growth promotion and biocontrol. Phylogenetic analysis identified the genera Stenotrophomonas, Pseudomonas, Paenibacillus, Klebsiella, Aeromonas, and Enterobacter. Among these isolates, Klebsiella sp. IR6 exhibited the most notable agronomic performance, increasing seedling leaf area (57%), fruit production (89%), and fruit size (15% in length and 31% in diameter) under field conditions. Additionally, IR6 was non-hemolytic, suggesting low risk to human health. This strain demonstrated antagonistic activity against Fusarium oxysporum (15-34%), siderophore production, and phosphate solubilization, confirming its potential as a biocontrol agent and PGPR. Transformation with plasmid pAD4325 carrying the GFP gene, followed by confocal microscopy, revealed its endophytic colonization within root tissues. Further evaluations using different jalapeño hybrids are necessary to validate the biotechnological potential of IR6 for sustainable agriculture.