Soybean preference for Bradyrhizobium japonicum for nodulation - Nodulation by Rj(2)Rj(3)Rj(4)-genotypes isolated from the progenies of a cross between soybean cvs. IAC-2 (Rj(2)Rj(3)) and Hill (Rj(4))

For the increase of the occupation ratio of inoculum strain in the competit ion with indigenous rhizobia, the relationship between Rj-genotypes of soyb ean and the preference of Rj-cultivars for various types of rhizobia for no dulation was investigated by using the Rj(2)Rj(4)-genotype of soybean isola ted from the cross between the Rj(2)Rj(3)-cultivar IAC-2 and Rj(4)-one Hill (Ishizuka et al. 1993: Soil Sci. Plant Nutr., 39, 79-86). Firstly, these R j(2)Rj(4)-genotypes were found to harbor the Rj(3)-gene. The Rj(2)Rj(3)Rj(4 )-genotypes of soybean were considered to exhibit a more narrow microsymbio nt range for nodulation than the Rj(2)Rj(3)- and Rj(4)-cultivars. Therefore , rhizobia were isolated from the nodules of various Rj-genotypes of soybea ns grown in soils, and the preference of the Rj(2)Rj(3)Rj(4)-genotype for i ndigenous rhizobia was examined. The nodule occupancy of serotype 110 was s ignificantly higher in the bacteroids of the nodules from the Rj(2)Rj(3)Rj( 4)-genotypes than in those from the other genotypes, non-Rj-, Rj(2)Rj(3)-, and Rj(4)-cultivars. These results demonstrated that the Rj(2)Rj(3)Rj(4)-ge notype prefers more actively serogroup USDA110 to the others of rhizobia. T hus, Rj(2)Rj(3)Rj(4)-genotype is superior to non-Rj-, Rj(2)Rj(3)-, and Rj(4 )-genotypes for the formation of efficient nodules for nitrogen fixation.