Co-Inoculation of Arbuscular Mycorrhizal Fungi and Mycorrhiza Helper Bacteria Enhances Growth and Seed Functional Quality in Soybean (Glycine max (L.) Merr.)

Soybean is a widely cultivated leguminous crop valued as a significant source of high-quality protein. Sustainable strategies to improve soybean productivity and seed quality are therefore of increasing interest. Although arbuscular mycorrhizal fungi (AMF) and mycorrhiza helper bacteria (MHB) play important roles in enhancing plant growth and bioactive compound accumulation, information regarding their combined effects on soybean remains limited. This study investigated the combined effects of AMF and MHB on soybean growth and seed quality. A greenhouse experiment was conducted with seven treatments. Soybean plants were inoculated with AMF, MHB, or their combination under greenhouse conditions and compared with uninoculated and chemical fertilizer controls. Among all treatments, co-inoculation with Acaulospora delicata AG-KKU-01 and Acinetobacter baumannii SK-G-3-2 was the most effective, significantly enhancing growth performance and productivity; moreover, this treatment resulted in the highest protein content and maintained high antioxidant activity and phenolic content compared with the chemical fertilizer treatment. Notably, both single and co-inoculation with AMF and MHB significantly improved seed quality, comparable to the chemical fertilizer treatment. Multivariate analyses further confirmed strong positive associations among growth, yield, root morphology, and seed quality traits. These findings provide new evidence for the synergistic interaction between AMF and MHB in soybean. In particular, co-inoculation with A. delicata AG-KKU-01 and Ac. baumannii SK-G-3-2 showed great potential as a sustainable microbial consortium for improving soybean productivity and seed quality.