Characterization of the antifungal activity of three rhizobacterial strains against Rhizoctonia solani

In this study, three rhizobacterial strains were characterized by their ability to inhibit Rhizoctonia solani and tested in chili (Capsicum annuum L.) seedlings. Strains A46 and P61 were identified as Pseudomonas tolaasii, and S108 as Rhanella aquatilis. In the dual culture tests, all the strains inhibited the radial growth of R. solani. None of the three strains produced chitinases or volatile compounds, but they were found to produce siderophores. However, this last characteristic was not responsible for the rhizobacterial inhibitory effect on the growth of R. solani, other bacterial metabolites were possibly involved. The bacterial filtrates added to the potato dextrose agar medium (PDA) in a 3:7 ratio had significant antifungal activity, being the filtrate from strain S108 the one that showed the highest effect, with 56% fungal inhibition. The co-culture of strain A46 with the phytopathogenic fungi in potato dextrose broth (PDB) increased the antifungal activity of the rhizobacterial filtrate. The application of the rhizobacterial strains to Serrano chili decreased the R. solani-related mortality rate in seedlings; particularly, S108 had the greatest effect, which was similar to the fungicide effect. This study showed that the S108 strain has potential as a biofungicide to control R. solani in chili seedlings.