Biocontrol of rhizoctonia root rot in tomato and enhancement of plant growth using rhizobacteria naturally associated to tomato

In the present study, 25 rhizobacterial isolates, obtained from rhizosphere of healthy tomato plants collected from various tomato-growing sites in Tunisia, were tested in vitro and in vivo against Rhizoctonia solani. This bacterial collection, composed of isolates belonging to Bacillus spp., Enterobacter cloacae, Chryseobacterium jejuense, and Klebsiella pneumoniae, was assessed for its antifungal potential against R. solani the causative agent of Rhizoctonia Root Rot disease in various crops including tomato. Antifungal activity of diffusible and volatile metabolites derived from these isolates was tested against target pathogen using dual and distance culture bioassays, respectively. Growth inhibition rates, recorded after 5 days of incubation at 25°C, depended significantly upon tested bacterial isolates and screening methods and reached 34-59% and 18-45% for diffusible and volatile metabolites, respectively. The screening of disease-suppressive and plant growth-promoting abilities of these tomato-associated rhizobacteria showed 47-100% decrease in disease severity and significant increments in plant height by 62-76%, roots fresh weight by 53-86%, and aerial parts fresh weight by 34-67% compared to pathogen-inoculated and untreated control. B. thuringiensis B2 (KU158884), B. subtilis B10 (KT921327) and E. cloacae B16 (KT921429) were found to be the most efficient isolates in decreasing R. solani radial growth, suppressing disease severity, and enhancing plant growth