Ecology of Hup+ Rhizobium strains of cow pea miscellany: native frequency and competence

Rhizobium strains nodulating summer legumes cow pea Vigna unguiculata (L.)], green gram V. radiata (L.) (Wilczek)], black gram V. mungo (L.) (Hepper)] and cluster bean Cyamopsis tetragonoloba (L.) (Taub)] and a winter legume chick pea Cicer arietinum (L.)] were surveyed in the Northern Plains of India and screened for hydrogenase activity to determine distribution of Hup character in the native ecosystem. It was observed that 56% of the Rhizobium strains of summer legumes were Hup⁺ whereas that of the winter legume, chick pea, were all Hup^-. Ex planta acetylene reduction activity was observed in most of the Hup⁺ but not in the Hup^- strains of any of the host species. In summer legume, mixed inoculation of Hup⁺ and Hup^- strains, under sterilized as well as unsterilized soil conditions, showed that the host species were predominantly nodulated with Hup⁺ strain.