A Simplified Synthetic Community of Indigenous Rhizobacteria Enhances Tomato Growth, Fruit Yield and Quality, and Suppresses Bacterial Wilt Under Continuous Cropping in Northwest China

Continuous cropping obstacles (CCOs) seriously constrain tomato yield and quality in facility agriculture, primarily due to rhizosphere microbial imbalance. Indigenous synthetic microbial communities (SynCom) offer superior colonization and stability compared to single strains. This study aimed at constructing a simplified SynCom from indigenous rhizobacteria in Northwest China to alleviate tomato CCOs. A total of 155 rhizobacterial strains (29 genera) were isolated. Sixteen strains with significant growth-promoting effects were selected through seedling assays. Based on the carbon source niche overlap index (NOI > 70%) with Ralstonia solanacearum QL-Rs1115, eight candidate strains were retained. Using the broken-stick model, 29 simplified SynComs were constructed. SynCom28, composed of six functionally complementary strains (Azospirillum brasilense, Massilia niabensis, Enterobacter hormaechei, Chryseobacterium sp., Priestia megaterium and Pseudomonas brassicacearum), showed the best performance. Pot experiments revealed that SynCom28 reduced the bacterial wilt disease index to 32.41, with a biocontrol efficacy of 41.72%. Greenhouse trials under continuous cropping demonstrated that SynCom28 significantly increased seedling Dickson quality index (DQI), stem diameter and biomass. Fruit yield increased by 12.98–15.30% across the 2nd to 4th cropping cycles (p < 0.05). Fruit quality parameters were also enhanced, with soluble sugar, lycopene, and vitamin C contents increasing by 47.22–65.07%, 33.07–81.71% and 80.56–166.67%, respectively. In conclusion, the indigenous simplified SynCom28 effectively alleviates tomato CCOs, enhancing growth, yield, and quality while suppressing bacterial wilt, providing a promising strategy for sustainable facility agriculture.