A Comparative Study of the Physiology of Symbioses Formed by Rhizobium japonicum with Glycine max, Vigna unguiculata, and Macroptilium atropurpurem

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Abstract
Although R. japonicum nodulates V. unguiculata [cultivars Cardinal, Black Eye-5, Pinkeye Purple Hull, Queen Anne and Suneto] and M. atropurpurem, little is known about the physiology of these symbioses. Strains of R. japonicum of varying effectiveness on soybean [cultivars Bragg, Clark, Hood, Kent, Lee and Roanoke] were examined. The nonhomologous hosts were nodulated by all strains tested, but effectiveness was not related to that of the homologous host. On siratro, compared to soybean, many strains reversed their relative effectiveness ranking. Both siratro and cowpea produced more dry matter with standard cowpea rhizobia CB756 and 176A22 than with the strains of R. japonicum. Strains USDA33 and USDA74 were more effective with siratro and cowpea than with soybean. The strain USDA122 expressed high rates of hydrogenase activity in symbiosis with the cowpea as well as the soybean host. The strains USDA61 and USDA74 expressed low levels of hydrogenase activity in symbiosis with cowpea, but no activity was found with soybean. Host influence for the expression of hydrogenase activity was indicated and the possibility of host influence of nitrogenase for the allocation of electrons to N2 and H+ was suggested.