Myrmecridium schulzeri B-4 promotes the growth of Bletilla striata (Thunb.) Reichb. f. through the production of IAA

The Plant growth-promoting rhizofungus (PGPR) enhances plant growth and improves plant health by secreting plant hormones. In our study, we investigated the PGPR of Bletilla striata (Thunb.) Reichb. f. ( B. striata ) and elucidated its underlying mechanism. We found that introducing sterile B. striata seedlings into soil inoculated with sandy loam rhizosphere soil microbiome significantly enhanced the biomass, height, tuber weight, root weight, root number, and leaf length of B. striata , suggesting modulation of B. striata growth by rhizosphere soil microbiome. A total of 117 fungal strains were extracted from the rhizosphere soil of B. striata , five potential PGPRs were identified, and the growth-promoting effects on B. striata seedlings were evaluated. The inoculation of the cell-free fermentation broth (CFB) of Myrmecridium schulzeri B-4 ( M. schulzeri B-4) significantly enhanced plant height, leaf length, and tuber thickness in B. striata seedlings, suggesting that M. schulzeri B-4 is a PGPR of B. striata . Transcriptome sequencing showed that co-culturing the CFB of M. schulzeri B-4 with B. striata seedlings increased the expression of genes related to Indole-3-acetic acid (IAA) and brassinosteroid (BRs) in B. striata tubers. Additionally, we found that M. schulzeri B-4 produces IAA. Overall, this study demonstrates that M. schulzeri B-4 is a PGPR associated with B. striata , and its growth-promoting effect on B. striata is attributed to its ability to produce IAA, and is involve in the IAA and BRs signaling pathways.The findings have significant implications for developing microbial fertilizer or inoculants using M. schulzeri B-4 to enhance the stability and productivity of B. striata and other crops. • Microbiome in sandy loam can promote the growth of B. striata . • Myrmecridium Schulzeri B-4 exhibited significant growth-promoting effects on B. striata . • Myrmecridium schulzeri B-4 promotes the growth of B. striata through the production of IAA.