Abstract:[Background] Dark septate endophytes (DSEs) are representatives of endophytic fungi capable of enhancing the disease resistance and promoting the growth of plants. With wide distribution, culturability, and non-host specificity, DSEs demonstrate broad application prospects in agricultural production as well as environmental protection and restoration. [Objective] To screen the DSE strain(s) capable of controlling powdery mildew in bitter gourd (Momordica charantia) out of seven strains and investigate the effects of the strain(s) screened out on the phyllosphere bacterial community of M. charantia plants. [Methods] We carried out pot experiments with the seed soaking+soil spraying+root irrigation methods to study the effects of seven DSE strains on powdery mildew of M. charantia. The effects of the strain screened out on the seed germination and plant growth of M. charantia were studied by the seed soaking method. The 16S rRNA gene high-throughput sequencing was employed to reveal the structure of phyllosphere bacterial community in the early, middle, and late stages of powdery mildew in M. charantia inoculated with the strain screened out. [Results] The strain X22 (Ochroconis guangxiensis) was screened out as a potential biocontrol agent, with the control efficacy of 56.58% on powdery mildew of M. charantia. Compared with the non-inoculated control (O-), inoculation with X22 (O+) increased the seed germination rate and led to uniform seedlings. The inoculation increased the leaf number, stem diameter, SPAD, and plant height by 3.18%, 6.08%, 7.88%, and 22.59% (P<0.05), respectively. Compared with O-, O+ showcased increased alpha diversity of phyllosphere bacteria in the early, middle, and late stages of powdery mildew, while the abundance of phyllosphere bacteria in the O+ group presented an increase-decrease-increase trend. In all the stages of powdery mildew, neither the dominant phyla nor their relative abundance there were no significant differences between O- and O+ groups. In the early and middle stages of powdery mildew, the dominant genera and their relative abundance showed significant differences between the two groups. Specifically, beneficial bacterial genera such as Sideroxydans, Saccharomonospora, and Natronincola involved in the nitrogen cycle or with antimicrobial activity were enriched in the O+ group. [Conclusion] The DSE strain X22 exhibited good biocontrol effect on powdery mildew and promoted the seed germination and plant growth of M. charantia. It may regulate the community structure to maintain the diversity and stability of phyllosphere bacteria. Meanwhile, this strain can recruit beneficial bacteria with antimicrobial activity and nitrogen-fixing ability to inhibit pathogens and provide nitrogen sources for hosts to promote host growth, thereby improving host disease resistance. The strain X22 is a biocontrol agent with great potential for development and application.
