Assessing the Potential Role of Compost, PGPR, and AMF in Improving Tomato Plant Growth, Yield, Fruit Quality, and Water Stress Tolerance

Among abiotic stresses, drought is considered the most important growth-limiting factor, particularly in arid and semiarid regions. Therefore, new management strategies are needed to resolve and mitigate these negative consequences, improve soil quality and plant growth, and rationalize water use. In this context, we investigated the role of beneficial plant growth–promoting rhizobacteria (PGPR), arbuscular mycorrhizal fungi (AMF) consortium, and compost (Comp) in improving tomato growth and yield, and drought tolerance. A completely randomized design was used in this experiment with the water stress as the main factor consisting of two treatments: (1) control well-watered (WW) plants (75% field capacity (FC)) and (2) water-stressed (WS) plants (35% FC), and the fertilization as a subfactor consisting of eight treatments. Growth parameters (shoot and root dry weight, leaf number, and area), productivity (fruit number and weight), mineral content (Ca2+, Na+, K+, and P), biochemical parameters (sugar, protein, and polyphenols), and antioxidant enzyme activities (polyphenoloxidase, peroxidase, catalase, and superoxide dismutase) were evaluated to investigate the effect of both factor. Soil physicochemical and microbial properties were examined after the experiment to assess the impact of water stress and applied biofertilizers on these parameters. Water stress affected negatively plant growth traits and yield and unbalanced the antioxidant enzymes. However, application of biofertilizers attenuated the negative effect of drought stress. For instance, a significant increase in shoot biomass of 160%, 120%, and 156% was obtained by Comp, PGPR + Comp, and AMF + Comp treatments compared to the control, respectively. Indeed, all treatments (except AMF under both conditions and PGPR + AMF + Comp under WS conditions) significantly increased the fruit number per plant. Concerning fruit yield, Comp, PGPR + Comp, AMF + Comp, PGPR, and PGPR + AMF treatments were the most effective treatments resulting in 179%, 149%, 111%, 203%, and 181% of the increment, respectively. Concerning the fruit quality, our finding showed a positive effect on sugar content and a significant decrease in the amount of polyphenol content was recorded by the different applied treatments compared to control plants under WW conditions. Under WS conditions, the PGPR significantly enhanced sugar and protein by 24% and 177%, respectively. However, they significantly decreased the polyphenol content under WS conditions by 42%. According to the antioxidant enzymes, a significant decrease in polyphenoloxidase, peroxidase, catalase, and superoxide dismutase activities in roots was recorded by the different applied treatment plants than WS control plants. In the shoot part, treatments with PGPR increased the catalase activity under WS conditions. PGPR + Comp, AMF + Comp, PGPR, and PGPR + AMF treatments significantly decreased the polyphenoloxidase activity and increased the peroxidase activity under WS conditions. In light of these findings, the use of compost alone or in combinations with the beneficial microorganisms (PGPR and AMF) enhanced the water stress tolerance of tomato plants by improving plant growth, osmolyte accumulation, and mineral accumulation and by decreasing the amount of antioxidant enzyme activity. This strategy could be vital to resolve and mitigate the negative consequences of drought stress and rationalize water use.