Co-inoculation with Pantoea ananatis D1-28 and Bacillus aryabhattai F promotes the growth of sweet cherry rootstock Gisela 6 under salt stress

Soil salinization, caused by the extensive use of inorganic fertilizers, has restricted the development of the sweet cherry industry. Plant growth-promoting rhizobacteria (PGPR) are beneficial bacteria that colonize the area around the roots, playing a crucial role in promoting plant growth, alleviating salt stress, and enhancing crop productivity. However, few studies have investigated whether PGPR can alleviate salt stress in sweet cherry. This study aimed to investigate whether co-inoculation (MIX) of Pantoea ananatis D1-28 and Bacillus aryabhattai F isolated from the rhizosphere of Zea mays L. could improve salt tolerance in seedlings of the common cherry (Prunus avium) rootstock Gisela 6. The results indicated that MIX inoculation alleviated salt stress and enhanced plant height and biomass. Under 100 mM salt stress, the MIX strain inoculant treatment significantly increased the net photosynthetic rate (14.38%), transpiration rate (22.61%), stomatal conductance (15.63%), total soluble sugar content (18.72%), free proline content (23.79%), superoxide dismutase activity (19.53%), and peroxidase activity (21.96%) but reduced the O₂•^- (16.99%) and H₂O₂ contents (17.59%) in Gisela 6 compared to CK without PGPR inoculation. After the MIX treatment, multiple indices showed strong correlations and improved salt stress resistance. In addition, principal component analysis showed that under 100 mM salt concentration, the MIX strain exhibited the largest separation from CK and had the strongest alleviating effect on plant salt stress. These results suggest that co-inoculation with the strains P. ananatis D1-28 and B. aryabhattai F effectively alleviated salt stress, improved plant photosynthetic capacity, and increased plant biomass by regulating antioxidant defense system and osmotic adjustment substances.