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 B. yuanmingense MAS34 (MAS34); and T4, a dual inoculation of P4 with MAS34 (P4 + MAS34). Two varieties of soybean, Yezin-3 (Rj4) and Yezin-6 (non-Rj), 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 (P 0.01) different between the inoculated treatments. The effect of variety was also significant (P 0.05) for nodule dry weight at the V6 stage, percentage of N derived from the atmosphere at the R3.5 stage, and seed yield at the maturity stage. The number of nodules on the tap roots was significantly higher in Yezin-3 than in Yezin-6. The single inoculation of P4 did not have a significant effect on dry matter production, N2 fixation, and seed yield in either soybean variety. The dry matter production, relative ureide index, percentage of N derived from the atmosphere, and seed yield were significantly (P 0.01) enhanced by a single inoculation of MAS34 in Yezin-3 and by dual inoculation of P4 + MAS34 in Yezin-6. These results indicate that low inoculum concentrations (105 cells seed-1) increase N2 fixation and seed yield in these soybean varieties under open field conditions. Myanmar B. yuanmingense MAS34 and S. griseoflavus P4 are expected to be useful biofertilizers for soybean production.
Highlights
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
The density of indigenous rhizobia from cultivated soil was estimated by the most probable number (MPN) method
A single inoculation of MAS34 resulted in a significantly (P < 0.01) higher number of nodules on the tap roots of the Yeizn-3 soybean variety compared to the uninoculated control at the V6 and R3.5 stages
Summary
In Myanmar, soybean has been cultivated for centuries, providing a nutritious food, and helping to increase the soil fertility [2]. With demands for this legume increasing domestically and abroad, soybean has become the second largest crop cultivated in Myanmar [3]. Soybean helps to maintain soil fertility by assimilating nitrogen from the atmosphere through symbiotic bio-. BNF is of agronomic importance because it reduces the need for chemical nitrogen fertilizer [5], and nitrogen fixation in the root nodule is an important area of study. The level of nitrogen fixation varies by cultivar in many legume crop species. Several studies have reported differences between Bradyrhizobium strains regarding their effectiveness with different soybean genotypes [7,8,9]
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