Characterization, Symbiotic Effectiveness and Host range of Alfalfa Nodulating Rhizobia Isolated from Soils of Selected Kebele‘s in Hawella District, Sidama Regional State, Ethiopia.

Abstract

Feed shortage, low quality and seasonal fluctuations have constrained livestock production in Ethiopia. Using high-yielding, good quality and drought-tolerant forage legumes like alfalfa (Medicago sativa L.) has been suggested to overcome the feed constraints. Alfalfa is an important forage crop, which forms a symbiotic relationship with nodule-forming bacteria Sinorhizobum meliloti. The aim of this study was to characterize and evaluate the symbiotic effectiveness and host range of rhizobia isolated from smallholder farmers’ fields in Hawella District, Sidama Regional State of Ethiopia using Alfalfa as a trap plant. To this end, a total of 12 bacterial isolates were trapped from different soil samples. The isolates showed differences in various presumptive, cultural, biochemical characteristics and physiological tolerances. Six (50 %) of the isolates( ANR 9, ANR 8, ANR 2, ANR 1, ANR 5 and ANR 11) could nodulate alfalfa with significant difference (P<0.05) in their capacity to infect and effectively fix nitrogen as evidenced from variations in nodulation parameters, shoot dry weights and shoot length. Accordingly, the isolates induced nodulation with nodule number ranging from 25.67 (ANR 9) to 9.00 (ANR 11) nodule per plant; nodule dry weight of 0.07 mg per plant (ANR 9) to 0.03 mg per plant (ANR 11); shoot dry weight ranging between 0.96 (ANR 9) and 0.17 (ANR 4) mg per plant and shoot length ranging from 30.50 (ANR 9) cm -11.47 (ANR 4) cm per plant. Using shoot dry weight as an indicator of the relative effectiveness, it was found that 33.3% of the isolates were highly effective (SE > 85 %) and 8.3 % were effective (SE ranging from 55 to 85 %) on alfalfa. Furthermore, the isolates showed broad host ranges on three legume species, namely, faba bean (Vicia faba), common bean (Phaseolus vulgaris), and lentil (Lens culinaris). All the six isolates (100 %) formed nodules with effective nitrogen fixation in faba bean, common bean and lentils exhibiting varying levels of effectiveness. Five of the six rhizobial isolates, ANR 9, ANR 8, ANR 2, ANR 1 and ANR 5 exhibited high N2-fixation efficiency and are recommended for further evaluation to use them as inoculants for different legumes. We also recommend these isolates for molecular characterization to determine their phylogeny and taxonomic classes.