Impact of grafting and different strains of plant growth promoting rhizobacteria on tomato plants grown hydroponically under combined drought and nutrient stress

Root inoculation with plant growth promoting rhizobacteria (PGPR) can be beneficial to plants in many ways. Furthermore, grafting has proven to be an efficient practice in controlling soilborne diseases and enhancing plant tolerance to abiotic stress. The combination of the above techniques could potentially enhance plant growth under stress conditions imposed by a shortage of water and nutrient supply. In the present study, the commercial tomato hybrid 'Belladonna', self-grafted or grafted onto the rootstock M82, was hydroponically grown on perlite under non-stress or stress conditions imposed by water and nutrient (N, P) deficit. The roots of both self-grafted and hetero-grafted tomato plants were inoculated with four selected PGPR strains aiming to enhance stress tolerance in terms of crop yield and product quality. The results of this study indicated that PGPR inoculation in roots indeed enhanced plant growth but had no impact on total fruit yield. On the other hand, grafting onto M82 increased fresh biomass and total yield under both stress and non-stress conditions. In conclusion, both grafting and PGPR inoculation proved to be beneficial to tomato crops faced with limitations in water and/or nutrient supply. However, further research is needed for the appropriate selection of rootstock genotypes and PGPR strains with enhanced stress tolerance.