Browsing by Author "Assefa Fassil"

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    Isolation and Characterization of Aerobic Cellulose-Degrading Microorganisns
    (Addis Ababa University, 1983-06) Assefa Fassil
    Seventeen species of cellulose-degrading fungi that fall into fifteen genera were isolated from decomposing plant matter, p;arden soil, arable soil and manure. They were Alternaria sp., Aspergillus ilayus, ~. niger, Cephalospor:ul!', sp., Chaetomium sp., Curvularia sp., Fusarium sp., Geotrichum sp., Helminthosporium sp., Penicillium sp., Pythium sp" Rhizopus sp., Stachbotrys sp., Trichoderml.!. sp. 1, Trichoderma sp. 2, Verticillium sp. and Zygorrhynchus sp. Gr01,th rate determination on filter 1)aper showed that A. niger, Chaetomium sp., ~urvularia sp., Helminthosporium sp., Rhizopu~ sp., Stachybotr12 sp., Trichoderma. sp. I and 2 and Zygorrhynchus sp., displayed abundant growth within 7-21 da~at pH 4.5, 7.2 and B.S. Out of the fungi tested, only eight isolates namely Cephalosporium sp., Curvularia sp., HelminthosporiuJ!l: sp., Pythium sp., Stachybotrys sp., Trichoderma sp. 2., Verticillium sp., and Zygorrhynchu~ sp., were found to elaborate free cellulase in the culture medium. High cellulase activity was found in Zygorrhynchus sp. at pH 7,2 and Stachybotrys sp., at pH 4.5. Low cellulase activity was shown by Cephalosporium sp., at pH 7.2 and Pythium sf., at pH II,S The effect of different cellulosic substrates on cellulase elaboration was tested on these organisms. The influence of cellobiose and glucose on the in vitro cellulase activity of ~ygorrhynchus sp., was tested. The type and concentrations of reducing sugars released in the enzyme hydrolysates of the eight species were evaluated.
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    Symbiotic and Phenotypic Diversity of Rhizobium Leguminosarum Var Viceae Lsolates (Vicia Faba) from Northern Gondar, Ethiopia
    (Addis Ababa University, 2006-05) Belay Zerihun; Assefa Fassil
    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