Nodulation Interaction of the Soybean Allele Rj2 with Asiatic Isolates of Bradyrhizobium japonicum

Abstract

The dominant allele Rj2 in soybean, Glycine max (L.) Merr., restricts nodulation with Bradyrhizobium japonicum (Jordan) strains USDA 7, USDA 14, and USDA 122, while the recessive allele rj2 permits normal nodulation. To determine the frequency of nodulation restriction by the Rj2 allele of soybean, 89 bradyrhizobial isolates from Asia were tested in Leonard jar culture for nodulation response with near isogenic plant lines differing at the Rj2 locus. Fifty‐one percent of the isolates tested elicited the nodulation restriction of the Rj2 allele. No geographic pattern in the occurrence of Rj2‐restricted strains was discerned. Nearly half (47%) of the isolates restricted by the Rj2 allele were from Serogroup 6. Twenty‐one of 25 Serogroup 6 strains were restricted by the Rj2 allele. Since some strains in Serogroup 6 were not restricted by the Rj2 allele and some strains not in Serogroup 6 were restricted, specific serological reaction per se is not essential or necessary for eliciting the action of the Rj2 allele. It appears that the Rj2 rejection is not as related to serotype as had been assumed.