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Searching for Myanmar indigenous Bradyrhizobium type C strains that best identify Rj₄ genotypes in soybean

Htwe, Aung Zaw, Taira, Kenjirou, Yamakawa, Takeo
Soil science and plant nutrition 2019 v.65 no.3 pp. 228-233
Bradyrhizobium elkanii, Bradyrhizobium japonicum, bacteria, cultivars, genotype, roots, soybeans, Myanmar
Bradyrhizobium species are symbiotic partners of soybean plants. However, some Bradyrhizobium bacteria do not form functional nodules on the roots of Rj₄ genotype soybean cultivars. Our objective was to identify the strains of Bradyrhizobium (i.e., type C strains) that are least competent to form nodules on the roots of this plant genotype. We checked (i) previously isolated type C strains of Myanmar Bradyrhizobium elkanii (MMY6-1, MMY6-2, and MMY6-5), (ii) previously isolated type C strains of Myanmarese Bradyrhizobium spp. (MMY3-5 and MMY3-7), and (iii) strain Is-34 of B. japonicum, for nodule formation when associated with Rj₄ and other Rj genotype soybeans. Strains in groups (i), (ii), and (iii) are known to be incompatible with Rj₄ soybean genotypes. MMY3-5 and MMY3-7 produced functional nodules when associated with Rj₄ and other Rj genotype soybean cultivars, except Hill (Rj₄) cultivar. The ratios of ineffective nodule numbers/total nodule numbers (I/T ratios) for MMY6-1, MMY6-2, MMY6-5, and Is-34 in association with Rj₄ soybean cultivars were > 0.5, demonstrating incompatibility between these bacterial strains and the Rj₄ genotype. Interestingly, the I/T ratios of MMY6-1 and MMY6-2 were higher than that of Is-34 in almost all Rj₄ soybean cultivars. Thus, the nodule-forming abilities of the B. elkanii strains MMY6-1 and MMY6-2 were strongly suppressed in Rj₄ soybean cultivars; these strains may therefore be useful to identify the Rj₄ genotype in soybean cultivars.