Coculture with two Bacillus velezensis strains enhances the growth of Anoectochilus plants via promoting nutrient assimilation and regulating rhizosphere microbial community

The potentiality of PGPR and biocontrol bacteria in agriculture is steadily increased as it offers an attractive way to replace the use of chemical fertilizers, pesticides and other supplements. This study aimed to investigate the effects and potential mechanism of inoculation with two Bacillus velezensis strains on the growth and quality improvement of Anoectochilus roxburghii (Wall.) Lindl. (MRH) and Anoectochilus formosanus (Wall.) Lindl. (YYB). The control treatment was non-inoculated (CK) and the coculture treatments were inoculated with Bacillus yelezensis D2WM (D2), Bacillus velezensis ZJ-11 (ZJ-11), Bacillus velezensis D2WM and Bacillus velezensis ZJ-11 (D2 + ZJ-11). The fresh weight, plant length, amount of active compounds, as well as chlorophyll content were significantly increased under D2, ZJ-11, and D2 + ZJ-11 treatments compared with MRH and YYB plants in CK. In particular, D2 + ZJ-11 treatment resulted in the greatest growth promotion. In MRH and YYB plants, the fresh weight increased by 82.6 % and 106.6 %, the kinsenoside content increased by 9.33 % and 21.65 % per gram, and the flavonoid content increased by 44.70 % and 21.07 % per gram, respectively. D2WM and ZJ-11 were capable of secreting siderophore, phytase, indole-3-acetic acid (IAA), and zeatin to promote plant nutrient assimilation and growth. Moreover, when D2WM and ZJ-11 were both inoculated with Anoectochilus roxburghii, the rhizosphere soil enzyme activities of urease, phosphatase, and invertase were significantly higher than control, thus helped to provide more nutrients to Anoectochilus. Further, the analysis of microbial community diversity indicated the increase of abundance of beneficial microorganisms, such as nitrogen-fixing bacteria, Basidiomycota and Ascomycota both of which are known to fuel their plant partners with mineral nutrients from the soil. Additionally, the abundance of pathogens belonging to Xanthobacteraceae as well as Cladophialophora and Penicillium were reduced. Hence, coculture with beneficial microorganisms can improve the growth and quality of Anoectochilus plants via promoting nutrient assimilation and regulating rhizosphere microbial community. This technique is of great application value in promoting the efficient cultivation and production of high-quality plant materials.