Growth, nodulation, and nitrogen fixation of soybean plants with seeds treated with kasugamycin

For the purpose of using kasugamycin resistant rhizobium as an inoculum, the effects of kasugamycin on growth, nodulation, and nitrogen fixation of soybean were investigated. Differences in the kasugamycin tolerance among rhizobial strains were also studied. Seed treatment with kasugamycin at 2,500 ppm brought about a change of the leaf shape and also induced the growth suppression of plants semi-aseptically cultured in vermiculite sterilized by autoclave. On the contrary, the growth of the plants cultured in soil was not appreciably suppressed by the kasugamycin treatment. However, kasugamycin markedly affected the nodulation process. That is, the number of nodules formed on the treated plants (more than 500 ppm kasugamycin) decreased by about 50% of that of the non-treated plants. However kasugamycin did not affect significantly the nitrogen fixation of soybean plants. Nineteen Bradyrhizobium japonicum strains out of the 21 strains tested were sensitive to 1,000 ppm kasugamycin. On the contrary, strain A1017kas + (mutant of A1017: with kasugamycin resistance and high ability of nitrogen fixation) was tolerant to 16,000 ppm of kasugamycin. Consequently, it is considered that the inoculation of A1017kas + to soybean seeds treated with kasugamycin may enhance the nitrogen fixation of soybean plants.