Genomic and functional analysis of Pseudomonas protegens CS11 reveals multifaceted biocontrol mechanisms against Sclerotinia sclerotiorum via antifungal metabolites, root colonisation and plant defence induction in tomato

Abstract

Sclerotinia sclerotiorum is one of many fungal pathogens that threaten global crop production. Antagonistic rhizobacteria have emerged as promising eco-friendly alternatives to synthetic pesticides that can be deployed for effective and sustainable management of the fungal disease. From 60 rhizobacterial strains isolated in this study, eight were able to inhibit the in vitro growth of S. sclerotiorum. Among these, strain CS11 exhibited complete (100 %) inhibition and demonstrated multiple plant growth-promoting traits, including siderophore production, nitrogen assimilation, phosphate solubilisation, and lytic enzyme activity. Motility and root colonisation assays confirmed CS11 to have high motility and efficient rhizosphere establishment. Molecular identification using 16S rRNA sequencing and Multi-locus sequence analysis identified CS11 as Pseudomonas protegens. Whole-genome sequencing revealed gene clusters for key antifungal metabolites, including 2,4-diacetylphloroglucinol, pyoluteorin, pyrrolnitrin, hydrogen cyanide, and orfamides, widely associated with Pseudomonas spp. Although closely related to P. protegens CHA0, CS11 has additional coding sequences associated with protease production (thermostable alkaline protease), root colonisation (cyclic di-GMP phosphodiesterase), and rhizosphere fitness (quorum-sensing-related genes), highlighting its novelty and strong biocontrol potential. In greenhouse trials, treatment of S. sclerotiorum-infected tomato plants with CS11 led to complete suppression of disease progression and significantly enhanced plant height and chlorophyll content. Compared to untreated infected plants, CS11-treated plants had elevated GLU, Chi, PAL, and PPO activities, and RT-qPCR analysis demonstrated upregulation of salicylic acid (PR1, PR2, PR5) and jasmonic acid (PR3, PR4, PDF1.2, VSP2) pathway genes. Collectively, these findings establish P. protegens CS11 as a promising candidate for the development of biopesticides to control fungal pathogens and enhance plant defence.