Nitrogen fixation and hydrogen evolution by the pigeon-pea- Rhizobium symbiosis

Abstract

Thirty-seven strains of rhizobia primarily from Panama, were evaluated for N2-fixing ability as determined by shoot-N accumulation of nodulated pigeon peas (Cajanus cajan (L.) Millsp.) grown in a N-free system. Acetylene reduction activity and H2 evolution were measured on whole root systems in order to determine relative N2-fixing efficiency and the presence of hydrogenase activity (Hup+). Thirty strains were found to be Hup-. As a group, plants nodulated with Hup+ strains accumulated 42 mg N shoot-1, and Hup plants accumulated 36 mg N shoot-1, a non-significant difference. N2-fixation ability was not correlated with the relative efficiency of a strain, but with nodule mass.