Screening of multifunctional PGPB from the Qinghai-Tibet Plateau and their effects on tomato growth and quality

The identification of indigenous plant growth-promoting bacteria (PGPB) from the Qinghai-Tibet Plateau is vital for developing region-specific microbial inoculants to improve crop productivity in high-altitude agricultural ecosystems. The solubilizing strains were isolated from faba bean leaves and roots collected in alpine farmlands of Qinghai using selective media. Following this, multifunctional PGPB with plant growth-promoting traits and biocontrol activities were identified. Selected PGPB strains were introduced into the rhizosphere of tomato plants to assess their impact on growth promotion. Results revealed that strain H18 displayed nitrogen fixation, phosphorus and potassium solubilization, IAA production and ACC deaminase activity. Additionally, it also exhibited antagonistic effects against eight fungal plant pathogens. Physiological and molecular analyses identified strain H18 belongs as Bacillus atrophaeus. This strain significantly improved tomato seed germination and enhanced growth during seedling and flowering stages, including parameters such as plant height, crown width, and stem diameter. Furthermore, during the fruiting stage, it increased yield and improved fruit quality. In conclusion, strain H18 is a multifunctional PGPB with excellent biocontrol and growth-promoting effects.