Nodulation pattern and biodiversity of rhizobia of some important leguminous trees and shrubs of Ethiopia

Abstract

A collection of 20 root nodule bacteria were isolated from the hitherto unexplored indigenous woody legumes from Ethiopia. Their diversity was evaluated using numerical analyses on different morphological and physiological characteristics. Most of the isolates were found to be slow-growing, sensitive to high concentration of NaCl, sterptomycin sulphate, but able to utilize a wide range of carbon sources, to grow at different temperatures and pH ranges implying that they can be good candidates for inoculation under varied conditions. They were grouped into one major cluster with a 20% average similarity level representing all but 2 isolates, and into four clusters representing a 60% average similarity level, except six isolates. In order to show the existence of cross-inoculation pattern between woody isolates and grain legume hosts, four selected isolates fromErythrina brucei, Crotalaria, Indigofera, and Tephrosia spp were inoculated into common bean (Phaseolus vulgaris) and cowpea (Vigna unguiculata) All, but one isolate from Indigofera (AURI30) elicited nodulation on both grain hosts with symbiotic effectiveness ranging from 41% to 100% against the Nitrogen-inoculated control. This suggests that the grain legumes can be cultivated in close association of the woody legumes in agroforestry systems without requiring their specific endosymbionts.

Keywords/phrases: Cross-inoculation, Endosymbionts, Indigenous trees, Nodule bacteria

Ethiop. J. Biol. Sci., 9(2): 153-171, 2010