Nodule formation and distribution of Rj₂Rj₃-genotype soybean infected with Bradyrhizobium japonicum

Nodulation and nodule distribution of Rj₂Rj₃-genotype soybean cultivar CNS infected with Bradyrhizobium japonicum strain Is-34 which is a compatible strain with this genotype cultivar or B. japonicum Is-1 which is an incompatible strain were investigated. Nodule formation and distribution were quite different patterns between two type strains. On 28-day-old roots, the number of ineffective nodules of roots inoculated with Is-1 was more than five times of that of effective nodules of roots with Is-34. Although nodules on the single inoculation of Is-1 were almost ineffective, a small number of effective nodules were observed. However, this strange phenomenon was not observed on mixed inoculation of Is-34 and Is-1. Many root hairs curled on the epidermis of roots inoculated with either Is-34 or Is-1. Cortical cell division, however, initiated only in roots inoculated with Is-34, but did not in those with Is-1 at seven days after inoculation. These results show the first step of discrimination of ineffective nodule formation from effective nodule formation may be the initiation of induction of root cortical cell division on roots inoculated with Is-1.