Assembly of Tomato Rhizobacteria from Different Functional Groups Improves Seedling Photosynthesis and Growth

The rhizosphere harbors abundant plant growth-promoting rhizobacteria (PGPR) that are vital for plant health. In this study, we screened growth-promoting bacteria from tomato rhizosphere soil, verified their functions, and constructed the optimal combination of growth-promoting bacteria for promoting tomato growth. Furthermore, the effects of these bacteria on various physiological and biochemical parameters of tomato plants were evaluated. A total of 36 strains of rhizobacteria were isolated from tomato rhizosphere soil and their abilities to produce indole-3-acetic acid (IAA), solubilize phosphate and iron carriers were assessed. The bacterial strains with the highest capacities for IAA production (R62, R317), phosphate solubilization (R41, R219), and siderophore production (R25, R325) were selected to form three bacterial combinations: R62 + R219 + R317 + R325 (T1), R62 + R325 (T5), and R317 + R325 (T8). Fifteen days after inoculation, all three combinations showed a stimulatory effect on seedling growth compared to the un-inoculated control. Inoculation with T1, T5 and T8 increased the seedling vigor index by 173.7%, 204.1%, and 168.7%, respectively. Compared to the un-inoculated control, the T1 combination increased the activities of polyphenol oxidase, peroxidase, and the net photosynthetic rate by 132.7%, 18.7%, 58.5%, and upregulated the relative expression levels of the photosynthetic assimilation-related genes RbcL, RbcS, FBPase and FDA by 22.2-, 6.6-, 1.95-, and 2.0-fold, respectively. Our findings provide a potential for constructing rhizobacterial combinations of different functional groups for improving crop growth.