Selection of bioantagonistic bacteria to be used in biological control of Rhizoctonia solani in tomato

Bacteria from the rhizoplane and surrounding soil of healthy and Rhizoctonia solani diseased tomato plants, cropped in greenhouse of the V Region of Chile, were collected. The best bacterial strains, based on their ability to control development of three R. solani isolates (identified as belonging to the anastomosis groups AG-2-1, AG-4), were identified as B. subtilis (one isolate) and B. lentimorbus (two different isolates). All bacterial isolates resulted effective for the in vitro control of growth of all R. solani isolates, where the control mechanisms used by the bacteria do not involve the secretion of fungal cell wall hydrolytic enzymes. R. solani AG-2-1 was more sensitive than R. solani AG-4. On the other hand, all bacteria grew well in conditions similar to those that can be found at the field level (considering pH, salinity, Fe ³⁺ and temperature) and showed a good capacity of tomato root colonization. These results suggest that the B. subtilis and B. lentimorbus isolates studied have an excellent potential to be used as biocontrol agents of R. solani in tomato greenhouses at the field level.