Assefa Fassil (PhD)Cook Douglas (Professor)Fikre Asnake (PhD)Mohammed Zehara2021-02-052023-11-082021-02-052023-11-082021-01-01http://etd.aau.edu.et/handle/123456789/24999Chickpea is among widely cultivated legumes for human consumption and grown as a rotation crop for the enhancement of soil fertility in succeeding cereal crops. The crop has the ability to fix atmospheric nitrogen in association with symbiotic nitrogen fixing bacteria in the genus Mesorhizobium. Thus, in order to fully realize the potential of nitrogen fixation in the crop and improved soil fertility, it is important to understand symbiont diversity, their eco-physiological competence among strains and to identify elite Mesorhizobium strains for their symbio-agronomic effectiveness. To this end, 138 farmer fields throughout major chickpea production regions were sampled for collection of root nodules, soils and recording of their farming practices. Pure rhizobial isolates (80) were subjected to Illumina whole genome sequencing and characterized using average nucleotide identity analyses. 64 strains occur within the Mesorhizobium genus that were assigned to eleven distinct Mesorhizobium genospecies and 3% of the surveyed diversity (genus) previously observed on chickpea, corresponding to genospecies 7A which is M. ciceri. The largest group of 26 strains belonged to M. genospecies 2A, which is conspecific M. spp. ORS3359, corresponding to unnamed symbiont isolated from Acacia seyal in Senegal. Genospecies 2A is related to but distinct from M. plurifarium. Among the diverse clade, 20 representative isolates were tested in-vitro for their eco-physiological competency and symbiotic efficiency in a greenhouse using Natoli and Arerti chickpea varieties. Most isolates were tolerant to high salinity 35%, high temperature 20%, acidity 25%, antibiotics resistance 67% and heavy metal resistance 83% as well as substrate (Carbon, Nitrogen) utilization and inorganic phosphate solubilization. The strains showed difference in nodule number, nodule dry weight and shoot dry weight of which 85% of the Mesorhizobium strains were either effective or highly effective on Natoli and Arerti varieties. Ten of the best performing symbiont strains were tested at three experimental locations for three consecutive years in split plot design using Natoli and Arerti chickpea varieties. Results from field evaluation indicate that the number of nodule and nodule dry weight showed two-fold difference between the low nodulating and high nodulating strains. Similarly, these strains increased shoot dry weight of Natoli and Arerti varieties (21-40%), above ground biomass accumulation (13-22%) and seed yield (19-31%) compared to uninoculated control irrespective of planting years at three sites. The robust strains comprising of M. loti 45P4S, M. amorphae 80P4S2, M.sp. LSJC280B00 2P3S1-b and M plurifarium 43P2S1 revealed more pronounced response in both nodulation and yield enhancement. These four strains are recommended for future inoculant production after validation with further field trials at different soil conditions. This study demonstrated symbiont diversity, eco-physiological competence and symbio-agronomic potential of selected elite Mesorhizobium strains in soils of chickpea growing regions of Ethiopia.enChickpeaEco-PhysiologicalField EvaluationGenetic DiversityMesorhizobiumPhylogenySymbiotic GenesThesis