Plant growth-promoting properties and anti-fungal activity of endophytic bacterial strains isolated from Thymus altaicus and Salvia deserta in arid lands

Endophytes, as crucial components of plant microbial communities, significantly contribute to enhancing the absorption of nutrients such as nitrogen and phosphorus by their hosts, promote plant growth, and degrade pathogenic fungal mycelia. In this study, an experiment was conducted in August 2022 to explore the growth-promoting potential of endophytic bacterial strains isolated from two medical plant species, Thymus altaicus and Salvia deserta, using a series of screening media. Plant samples of Thymus altaicus and Salvia deserta were collected from Zhaosu County and Habahe County in Xinjiang Uygur Autonomous Region, China, in July 2021. Additionally, the inhibitory effects of endophytic bacterial strains on the four pathogenic fungi (Fusarium oxysporum, Fulvia fulva, Alternaria solani, and Valsa mali) were determined through the plate confrontation method. A total of 80 endophytic bacterial strains were isolated from Thymus altaicus, while a total of 60 endophytic bacterial strains were isolated from Salvia deserta. The endophytic bacterial strains from both Thymus altaicus and Salvia deserta exhibited plant growth-promoting properties. Specifically, the strains of Bacillus sp. TR002, Bacillus sp. TR005, Microbacterium sp. TSB5, and Rhodococcus sp. TR013 demonstrated strong cellulase-producing activity, siderophore-producing activity, phosphate solubilization activity, and nitrogen-fixing activity, respectively. Out of 140 endophytic bacterial strains isolated from Thymus altaicus and Salvia deserta, 104 strains displayed anti-fungal activity against Fulvia fulva, Alternaria solani, Fusarium oxysporum, and Valsa mali. Furthermore, the strains of Bacillus sp. TR005, Bacillus sp. TS003, and Bacillus sp. TSB7 exhibited robust inhibition rates against all the four pathogenic fungi. In conclusion, the endophytic bacterial strains from Thymus altaicus and Salvia deserta possess both plant growth-promoting and anti-fungal properties, making them promising candidates for future development as growth-promoting agents and biocontrol tools for plant diseases.