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Symbiotic effectiveness of rhizobia from chickpea (Cicer arietinum L.) and phenotypic characteristics of faba bean (Vicia faba L.) nodulating rhizobia

Chickpea (Cicer arietinum L.) and faba bean (Vicia faba L.) are the most important food legumes grown in Ethiopia. Their growth and yield are mainly affected by available soil nitrogen, while they symbiotically associate with soil bacteria known as rhizobia and fix atmospheric nitrogen to supplement their nitrogen requirements. However, effectiveness of this symbiosis depends on rhizobium strains, host legumes and other biotic and abiotic factors. seventeen rhizobial strains nodulating chickpea were evaluated for their symbiotic effectiveness to screen high nitrogen fixers and thirty-three faba bean nodulating isolates were characterized to determine their phenotypic and symbioti identity. For symbiotic effectiveness test total shoot nitrogen content was dertermined using Kejdhal method; phenotypic identity was determined following numerical taxonomic approach. There was a signinficant difference (p<0.05) in nodule number, nodule & shoot dry weights among rhizobia nodulating chickpea. The preliminary symbiotic effectiveness (PSE) of fababean isolates ranged from 10.65% to 130.5%.. Isolate FBM11 was found symbiotically effective than controls and reference strain 35. While in chickpea case strain CA10 was found to be the best at Damot Gale, Strain ICRE18 on the other hand was found to be the best effective at Eastbawawacho and Damotpullasa soils suggesting that inoculation is needed for these sites. Nodule dry weight significantly and strongly correlated with nodule number and shoot dry weight both in pot filled field soil samples and sterilized sand pot experiments, and plant total nitrogen was strongly correlated with shoot dry weight. Based on on the total nitrogen analysis,plants inoculated with ICRE18 EAL029 and CA10 strains were found to accumulate higher shoot nitrogen than plants inoculated with other tested strains. Faba bean isolates exhibited diverse and interesting features such as ability to grow on wide range of carbon and nitrogen sources, tolerance to higher and lower temperatures, salt concentration as high as 2.5%, pH ranging between 4.0 and 10.0 Most isolates were resistant to neomycin and novobiocin (5μg/ml). All of them failed to solublize phosphate and most were resistant to heavy metals. These showed that the tested isolates were fastidious in their physiological requirements, thus can be considered as enabling factors for isolates to grow and survive in diverse soil conditions. The numerical analysis revealed the existence of diversity among the test isolates and grouped them into three clusters (designated as Cluster I-III) and unclustered (designated as U) at 65% relative similarity. Nineteen of the isolates were clustered with reference strain 35. Taken together, the study identified diverse and better nitrogen fixing rhizobia in biobank. Based on the study findings it is recommend that further screening under field condition but also their identity using molecular methods should be determined in the future.

Thursday, November 23, 2017

MSc and Bcs thesis, internship reports

Tadele Ereso
Biological nitrogen fixation, Numerical taxonomy, Rhizobia, Symbiotic effectiveness