Effect of soybean root exudates on Bradyrhizobium japonicum

Abstract

Effects of soybean root exudates on the growth and survival of Bradyrhizobium japonicum (USDA 110) in artificial medium as well as in a Chester silt loam soil were studied. Exudates were added to a yeast extract‐mannitol medium at concentrations of 0.00, 0.01, 0.02, and 0.04% (w/v). Results showed that the lowest exudate concentration did not affect the growth of B. japonicum, while the highest level (0.04%) reduced the population in the medium. Exudates at a concentration of 0.02% enhanced the. population of B. japonicum in the medium.

A study of the survival of B. japonicum in soil amended with exudates at 0.0, 0.1, 0.2, and 0.4% (w/w) was also conducted. Results indicated that exudates at 0.1 and 0.2% did not affect the population of rhizobia during the first week of incubation. The 0.4% concentration exhibited a rapid reduction in the population of B. japonicum during this time. After the first week, the population of B. japonicum declined for all treatments. By the end of the study, the soil amended with 0.4% exudates exhibited the lowest soil population.

Key words:

• Antagonism
• nitrogen fixation
• symbiosis