Competition between three bradyrhizobium japonicum strains as affected by strain proportion in inocula

ABSTRACT

Double strain combinations of Bradyrhizobium japonicum strain USDA 110 with strains USDA 138 or TAL 379 mixed in different ratios [1 1. 1 5, 1 10, 1 25. 1 50, and 1 100] were used as inocula for soybean Crowford. Modulation of soybean plants were not affected by changes in ratios of inoculant strains. Increasing the ratio of inocularil strains 138 or 379 to strain 110 resulted in a gradual decrease in plant dry weight, N content and seed yield. A significant decrease in plant dry weight, N content and seed yield was obtained when the ratio exceeded 25 1. Strain USDA 110 was more competitive than strain USDA 138 or TAL 379. Strains, USDA 138 or TAL 379 from nodules, reached the same level of USDA 110 nodule occupancy at ratio 25 1 for both strains