Symbiotic and Phenotypic Diversity of Rhizobium leguminosarum var viceae Isolates (Vicia faba) from Northern Gondar, Ethiopia
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Date
2006-05
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Addis Ababa Universty
Abstract
Twenty-one strains of Rhizobium leguminosarum var. viceae spp (Vicia faba) from 21 sites of
North Gondar were isolated from a range of pH 5.8-7.5 to induce nodulation on “Degaga"
cultivar of faba bean. Isolates were authenticated as root nodule bacteria by their ability to form
nodules on their host up on re-inoculation, except AUFR13. All of the morphological features
displayed by all isolates were characteristics of fast growing Rhizobium leguminosarum var
viceae, except AUFR13. Almost all of the isolates grew between 150C and 350C and failed to
grow at 400C, except AUFR22 and AUFR28. All isolates failed to grow at 1% NaCl, except
AUFR12 and AUFR28. AUFR18 was the only osmotolerant strain capable of growing at a
concentration of 5%. The isolates also grew on a wide range of moderate acidity and alkalinity
but only 10% of the isolates grew at pH5.5. With the exception of gluconate, citrate, and tartarate,
almost all isolates grew on 14 out of the tested carbohydrates. The Intrinsic Antibiotic Resistance
(IAR) was found to be the best of all tested physiological characters to identify the heterogeneity
of Rhizobium leguminosarum var. viceae, so that 95% of the tested isolate were resist
erythromycin and chloromphenicol, and 14%, 24%, 38%, 38% and 43% of the isolates tolerated
streptomycin, ampicillin, rifampcin, kanamycin and naldixic acid at highest concentration,
respectively. The relative effectiveness expressed as percentage of shoot dry mass of inoculants
over TN control, showed that 24%, 57%, 4.7% and 9.5% of the isolates were found to be highly
effective, effective, lowly effective and ineffective, respectively. The highest scores of 88-100%
effectiveness of symbiotic nitrogen fixation were displayed by AUFR14, AUFR15, AUFR24,
AUFR28 and AUFR32. Selected strains on soil culture were found to accumulate 81-92% on
Holeta soil and 90-103% on Ambagiorgis soil of their shoot dry mass compared to their
respective N-fertilized controls. All isolates were also found to increase shoot dry weight by 0-
43% higher than their respective sand cultures and response of the Holetta soil to inoculation by
selected effective strains was much pronounced (47-67%) than Ambaghiorgis soil (8-25%)
compared to the negative (N-) controls. The lower dry matter accumulation by Holeta soil
indicates that the low pH and other soil-related factors severely affected survival, nodulation and
nitrogen fixation of their indigenous rhizobia and the process can be rectified by inoculation of
effective rhizobia.
Key words: Faba bean, Rhizobia, Phenotypic diversity, Symbiotic effectiveness
Description
Keywords
Faba bean, Rhizobia, Phenotypic diversity, Symbiotic effectiveness