Anti-fungal activity of bacterial endophytes associated with legumes against Fusarium solani: Assessment of fungi soil suppressiveness and plant protection induction

Legumes (Fabacea) plants are mainly known for their symbiotic relationship with soil nitrogen-fixing bacteria (rhizobia). This symbiosis requires the formation of new root structures called nodules. Besides rhizobia, nodules host several microbial species that may serve to enhance plant growth and disease resistance. In this study, we demonstrate that several endophytic bacteria isolated from nodules harbour plant growth promotion and biocontrol traits. A collection of 120 bacterial strains isolated from Faba bean (Vicia faba) and chickpea (Cicer arietinum) nodules were screened for their ability to inhibit phytopathogenic Fusarium solani on “In vitro” antibiosis tests. Sixteen best effective isolates were selected, identified and sequences were deposited in Genbank. These strains were all isolated from Faba bean nodules. These have the characteristics to produce siderophores and auxin as well as expression of some genes coding the production of the antibiotic compounds as Pyrrolnitrin (PRN), Phenazine (PHZ)… Based on the former PGPR and biocontrol characteristics, three strains; Rahnella aquatilis B16C, Pseudomonas yamanorum B12 and Pseudomonas fluorescens B8P were analyzed for their “In vivo” biocontrol potential in suppressing F. solani root rot of three cultivars of Faba bean under greenhouse conditions. The three strains significantly reduced the pathogen symptom severity. R. aquatilis B16C showed the best protecting potentiality with the three Faba bean cultivars and it is consequently, suggested as biocontrol agent for field application. Then again, our study confirms previous suggestion of legume nodules as untapped suitable source of beneficial microorganisms that can be used to control pathogens in a sustainable way.