Bradyrhizobium strains from Brazilian tropical soils promote increases in nodulation, growth and nitrogen fixation in mung bean
2022
Favero, Vinício Oliosi | de Carvalho, Rita Hilário | Leite, Ana Beatriz Carneiro | dos Santos, Dieini Melissa Teles | de Freitas, Karine Moura | Boddey, Robert Michael | Xavier, Gustavo Ribeiro | Rumjanek, Norma Gouvêa | Urquiaga, Segundo
Mung bean [Vigna radiata (L.) Wilczek] is a legume of Asian origin cultivated in several countries, including Brazil, where its commercial cultivation has expanded in recent years. It has a promiscuous N₂-fixing association with rhizobia, but nodulation in Brazilian soils has been highly variable. To achieve satisfactory yields with low production costs, studies are being carried out to select rhizobia from soils in Brazil that result in efficient symbiotic associations with mung bean. Previous studies indicate that only Bradyrhizobium strains were able to nodulate mung bean in Brazilian soils. The objective of this study was to evaluate the effect of 31 Bradyrhizobium strains and increasing levels of N fertilizer on nodulation, plant growth and N₂ fixation. Bradyrhizobium strains resulted in increases of up to 71, 79, 43, 66, 40 and 55%, respectively, in nodule number and nodule, root and shoot biomasses, accumulated N and biological nitrogen fixation (BNF) contribution compared to the uninoculated control, however, there was no increase in grain yield. Compared to the control with N fertilizer, inoculated plants had lower biomass and accumulated N, despite the high BNF contribution. In general, strains of Bradyrhizobium japonicum superclade, especially those close to B. yuanmingense B071, showed greater efficiency compared to those of the superclade of B. elkanii. The application of N fertilizer increased root and shoot biomasses, however, significantly reduced nodulation. Bradyrhizobium strains isolated from Brazilian tropical soils showed potential for mung bean inoculation, however, the BNF contribution was not sufficient to meet the plant's N demand.
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