Low-Density Co-Inoculation of Myanmar Bradyrhizobium yuanmingense MAS34 and Streptomyces griseoflavus P4 to Enhance Symbiosis and Seed Yield in Soybean Varieties

Abstract

This study examined whether low-density co-inoculation of Myanmar Bradyrhizobium yuanmingense strain MAS34 and Streptomyces griseoflavus P4 would enhance nodulation, N2 fixation, and seed yield in two soybean varieties. A field experiment was conducted during the July to November 2012 growing season at Kyushu University Farm, Japan, using a split-plot design with three replications and the following four treatments: T1, an uninoculated treatment with peat moss (uninoculated); T2, a single inoculation with S. griseoflavus P4 (P4); T3, a single inoculation of Bradyrhizobium yuanmingense MAS34 (MAS34); and T4, a dual inoculation of P4 with MAS34. Two varieties of soybean, Yezin-3 and Yezin-6, were used. The N2 fixation activity of soybean was evaluated by the relative ureide method using xylem solute from root bled sap at the early pod-fill stage (R3.5). Dry matter production, N2 fixation, and seed yield were significantly different between the inoculated treatments. These results indicate that low inoculum concentrations increase N2 fixation and seed yield in these soybean varieties under open field conditions.