Host specificity and phenotypic diversity of Rhizobium strains nodulating Leucaena, Acacia, and Sesbania in Egypt

Abstract

Phenotypic diversity was studied among 13 Rhizobium strains selected from a total of 160 Rhizobium isolates from root nodules of Leucaena leucocephala. Two strains from Acacia saligna and two strains from Sesbania sesban plants were included in the examination for host range in the greenhouse. The Rhizobium sp. (Leucaena) strains were different from the reference strains and fell into three distinct groups for the utilization of 95 different carbon sources. Four of the best symbionts constituted a group, the majority of the strains fell into a second group, and strain DS 91 was the only member of the third group. Strains were effective symbionts for their original hosts. Nine strains were tolerant to elevated temperature (>42°C), and three strains were resistant to high salinity (>3% NaCl). All Rhizobium sp. (Leucaena) strains effectively nodulated L. leucocephala and L. culensii, but nitrogen fixation was greater with L. leucocephala than with L. culensii. These strains failed to form effective symbioses with two other species of Leucaena (L. retusa and L. divursiflora) or with alfalfa, Medicago sativa. Rhizobium sp. (Leucaena) strains DS 65, DS 78, and DS 158 nodulated and efficiently fixed nitrogen with Phaseolus vulgaris, with DS 65 showing the highest symbiotic capability. Strain DS 65 also nodulated and fixed nitrogen with Glycine max and Vigna sinensis. Nodulation of Leucaena by two Bradyrhizobium sp. (Acacia) strains was sparse. Strain DS 101 from Sesbania formed nodules on Leucaena, whereas the other strain from Sesbania, DS 110, failed to nodulate this genus.