Grafting and Inoculation of Grafted Plants With Bacillus amyloliquefaciens Enhances Biotic and Abiotic Stress Tolerance in Organic Tomato

Biotic and abiotic stress factors pose significant challenges to organic tomato production in Alabama and the southeastern United States. High temperature, drought, soil, and foliar-borne diseases have rendered it exceedingly difficult for organic tomato growers in Alabama to produce profitable crops. Our objective was to evaluate plant response to imposed biotic (Verticillium dahliae) and abiotic (drought) stress in the popular tomato variety ‘Roma’ through grafting unto the resistant rootstock ‘Maxifort’, and the incorporation of the plant growth-promoting rhizobacterium (PGPR) B. amyloliquefaciens, to mitigate challenges posed by these stress factors. The research was conducted in a greenhouse in north Alabama where both soilborne pathogens (V. dahliae) and drought stress treatments were applied. The experimental design was a split plot with 4 main plots (Grafting, PGPR, Grafting + PGPR, and Control) and 3 subplots (drought, pathogen, and control) treatments with 4 replications. B. amyloliquefaciens was applied in the rhizosphere of grafted and non-grafted plants at 1 × 108 CFU/ml/plant. Pathogen-treated plants were also inoculated with V. dahliae at 1 × 105 propagules/ml. The study revealed that grafting, and grafting + B. amyloliquefaciens caused a significant increase in stem girth, plant biomass, early flowering, and fruiting of tomatoes compared to the non-grafted and control treatments. Integrating grafting and PGPR could be beneficial in enhancing plant resilience and performance under biotic and abiotic stress conditions.