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Rhizobiophage effects on Bradyrhizobium japonicum, nodulation and soybean growth

1988; Elsevier BV; Volume: 20; Issue: 1 Linguagem: Inglês

10.1016/0038-0717(88)90128-9

1879-3428

Fawzy Hashem,

Bacteriophages and microbial interactions

Rhizobiophage may potentially alter the ecological balance of competing rhizobial strains in soil. We determined the effect of a phage specific for Bradyrhizobium japonicum USDA 117 on the survival of two strains of B. japonicum (USDA 117 and 110) in soil. The phage was initially added to a sterile silt loam soil amended with the homologous (USDA 117) or the nonhomologus (USDA 110) rhizobia. The soil was assayed for the survival of both the phage and the rhizobia. The phage reduced the population of homologous rhizobia. This reduction was accompanied by a concurrent increase in phage titer. The phage had no significant effect on the soil population of the nonhomologous rhizobia. To examine the effects of the phage on nodulation and soybean [Glycine max (L.) Merr.) growth, inoculated (B. japonicum USDA 117) and noninoculated soybeans were grown in a sterile silt loam soil amended with two different concentrations of the phage. The phage significantly reduced nodule number, nodule weight and acetylene reduction. In soil inoculated with greater numbers of phage, the nodule number, nodule fresh weight and acetylene reduction were 10 nodules, 40 mg and 2340 nmol C2 H4 g−1 nodule h−1, respectively. The control plants inoculated with B. japonicum USDA 117, but without phage, had a nodule number of 44, a nodule weight of 144 mg, and an acetylene reduction rate of 7145 nmol C2H4 g−1 nodule h−1. To assay the selective effect of the phage on B. japonicum USDA 117, the phage was also inoculated into a nonsterile, phage- and rhizobia-free silt loam soil amended with B. japonicum USDA 117 and the nonhomologous B. japonicum USDA 110. The phage significantly reduced nodulation and N2 fixation by soybeans inoculated with only B. japonicum USDA 117. No significant phage effect on these qualities was observed on plants inoculated with B. japonicum USDA 110 or a combination of B. japonicum USDA 110 and USDA 117. The phage also significantly decreased nodule occupancy by B. japonicum USDA 117 with a corresponding increase in occupancy by B. japonicum USDA 110.