Abstract
The number of nodules formed by the soybean cv. Bonminori in combination with Bradyrhizobium japonicum strain A1017 was very low compared with other cultivars, Enrei, Nanbushirome, Okushirome and Suzukari. In the current experiment, attempts were made to determine the mechanism underlying low capacity of nodule development in the soybean cv. Bonminori which possesses the Rj gene. The attachment of the bacteria to the root hairs, curling of root hairs, infection thread formation and cortical cell divisions were investigated by comparing these characteristics in the soybean cv. Bonminori and Enrei in combination with the B. japonicum strains A1017 and IRj2101. 1. The number of nodules formed by Bonminori inoculated with the strain A1017 was less than two per plant, although the acetylene reduction activity of the individual nodules was almost identical with that of the control. 2. There was no difference in the attachment of the strain A1017 to root hairs between Bonminori andEnrei. 3. The frequencies of root hair curling and infection thread formation in Bonminori induced by the strain A1017 did not differ from those by the strain IRj2101. 4. The number of primary nodule meristems in the tap roots of Bonminori inoculated with the strain A1017 was lower than that of the strain IRj2101. 5. The results of the observations suggest that the low compatibility of Bonminori with the B. japonicum strain A1017 is due to an abnormality in the development at a relatively early stage of cell division prior to the formation of nodule meristems rather than to the inhibition of the attachment of the rhizobia to the root hair and induction of root hair curling.
