Dual Benefits of Opuntia dillenii (Ker Gawl.) Haw. (Cactaceae) Microbiota: Tomato Growth Promotion and Ralstonia solanacearum Mitigation

Tomato production is severely affected by bacterial wilt caused by Ralstonia solanacearum. This study assessed the biocontrol potential of bacterial strains isolated from the cladodes, roots, and rhizosphere of Opuntia dillenii for the sustainable management of bacterial wilt in tomato. An in vitro screening identified antagonistic strains, which were subsequently assessed under greenhouse conditions. Among the isolates, Priestia flexa C10 and Bacillus subtilis R6 showed the strongest antagonistic activity against R. solanacearum, with inhibition zones of 22.5 and 20.0 mm, respectively. Under pathogen pressure, the inoculated control exhibited a wilt incidence of 47.5%, whereas B. subtilis R6 and P. flexa C10 reduced disease incidence to 40% and 45%, respectively. Both strains also improved plant growth. Under non-inoculated conditions, B. subtilis R6 showed the greatest growth-promoting effect, increasing plant height (35.9%), leaf number (24.6%), root biomass (94.5%), and root length (59.4%). Under pathogen pressure, P. flexa C10 notably enhanced root biomass (49.8%) and root length (30.6%), while B. subtilis R6 increased root biomass by 80.4%. These findings indicate that while P. flexa C10 and B. subtilis R6 offer limited direct suppression of bacterial wilt, they significantly promote tomato vegetative growth and could serve as valuable plant growth-promoting inoculants to mitigate disease-induced stress.