Symbiotic And Phenotypic Characteristics Of Rhizobia Nodulating Faba Bean (Vicia Faba) From Tahtay Koraro, Northwestern Zone Of Tigray Regional State, Ethiopia

The ability of indigenous rhizobia to nodulate a legume crop effectively was critical to successful establishment and growth of legumes. This study was aimed to evaluate the symbiotic effectiveness along with growth responses to varied conditionslike pH, salt, temperature, antibiotics, and carbon and nitrogen sourcesfor rhizobial isolates nodulating faba bean from Tahtay Koraro, northwestern Zone of Tigray. For this matter, a total of thirtysix isolates of Rhizobium were isolated from as many sampling sites of Tahtay Koraro using plant infection method in Addis Ababa University, Applied Microbiology greenhouse.The isolates were characterized morphologically and physiologically and tested on sand to evaluate their symbiotic effectiveness.Results indicates that culturally almost all of them displayed large colonies with diameters of 2 to 4.5 mm, generation time of >3.91 hrs and showed characteristics of fast growing rhizobia.The symbiotic effectiveness results on sand culture indicated that, the isolates showed shoot dry matter ranging from 0.47 (AUFR-9) to 1.5 g/plant (AUFR-17), with negative control of 0.43 g/plant and positive control of 1.3 g/plant. All the tested isolates were able to grow well within the ranges of 6-9.5 and 15 0 C-35 0 C for pH and temperature, respectively. The highest and lowest nodule number score was 91 (AUFR-5) and 17 (AUFR-36), respectively. The preliminary screening of the authenticated isolates for symbiotic effectiveness on sand culture showed 74% of the isolates were found to be effective, whereAUFR-8, AUFR-13, AUFR-14, AUFR-17 and AUFR-25, were rated highly effective, of these AUFR-25 was found to be phosphate solubilizer. The numerical analysis on phenotypic features revealed the existence of diversity among the test isolates and categorized all isolates into six groups.Generally, the present work shows the physiological and symbiotic diversity of the isolates in the traditional agricultural areas of the study site and the potential of these rhizobia to be used as effective commercial inoculants in areas where the indigenous rhizobia fail to do so.