Browsing by Author "Alemu, Tesfaye(PhD)"

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    Evaluation of Antifungal Activity of Plant Extracts Against Chocolate Spot Disease (Botrytis Fabae) on Faba Bean
    (Addis Ababa University, 2010-06) Mesfin, Roman; Alemu, Tesfaye(PhD)
    Aqueous, ethanol, methanol, chloroform and ethyl acetate extracts of seven plants were screened for antifungal activity against Botrytis fabae at different concentrations using poisoned food techniques. The phytopathogenic fungi were isolated from diseased faba baen plants. Four effective plant extracts were selected in vivo test on the infection of B. fabae on faba baen plants, were evaluated and measured in comparison with sterile distilled water which was used as control. The result revealed that aqueous extracts of immature and matured leaf extracts of C. macrostchyus completely inhibited mycelial growth at 30mg/ml and 50mg/ml respectively. C. aurea extract also inhibited fungal growth at 50mg/ml concentration. Most of the selected plants were highly extractable with ethanol especially, the immature and mature leaf extracts of S. marginatum and immature leaf extracts of S. incunum siginificantly inhibited the growth of B. fabae at a concentration of 30mg/ml, followed by immature leaf extracts of D. stramonium and mature leaf extracts of S. incunum at 40mg/ml concentration. From the methanol extracts D. stramonium and C. aurea showed the highest inhibition. It was observed that the chloroform extracts of most selected plants do not show significant effect but, C. macrostchyus at 40mg/ml inhibit 62%. The ethyl acetate extracts of all selected plants do not show effectiveness on the inhibition of the selected isolate. It was observed that ethanol extracts showed highly significant antifungal activity followed by aqueous and methanol extracts. The chloroform and ethyl acetate extracts were inferior on inhibition of the fungal isolate. Methanol extracts of D. stramonium, C. aurea, ethanol extracts of S. marginatum and aqueous extracts of C. macrostchyus were selected from the in vitro evaluation and tested in vivo on faba bean plants and at 20% show significant inhibition. Mixture of plant extracts and bioagents Trychoderma harzianum show significant inhibition on the growth of B. fabae on faba bean in vivo test. The semi purified fraction of chloroform and ethyl acetate extracts of the selected plants did not exhibit effective antifungal activity, but the aqueous solubilized fraction of all plants show significant inhibition. Key words: Antifungal compounds, Biocontrol, Botrytis fabae,MIC, Plant extracts, Solvent
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    Isolation and Characterization of Ethanol, Sugar and Thermo Tolerant Yeast Isolates for Biomass and Bio-Ethanol Production
    (Addis Ababa University, 2014-12) Negera, Taye; Alemu, Tesfaye(PhD); Beyene, Dereje(PhD); Asfaw, Araya(PhD)
    The aim of the study was to isolate and characterize ethanol, sugar and thermo tolerant yeast to optimize maximal ethanol production from coffee husk. The yeasts were isolated from (Psidium guajava), grapefruit (Citrus paradise), avocado (Persea americana), papaya (Carica papaya) and gishita (Annona senegalensis pers.). All the yeast isolates were first tested for carbohydrate fermentation using Durham tube fermentation method in yeast extract peptone dextrose broth. Four isolates which were relatively high fermentative in Durham tube fermentation method were selected for testing of the isolates for ethanol, sugar and thermo tolerance. Further, the optimum conditions for isolation and characterization of yeast isolates were determined. The investigation revealed that the optimum conditions are 37°C temperature, 30% sugar concentration, 15% ethanol concentration, pH 5 and 15% diammonium hydrogen phosphate ((NH4)2HPO4) were used as nitrogen source in M9 minimal medium. According to the morphological and biochemical characterization, the selected yeast isolates were belonged to the genus saccharomyces. The results showed that the content of sugars increased as the acid (H2SO4) was increased from 0.25M - 3 M and decreased as the acid concentrations increased beyond 3 M. At the optimal acid concentration (3M; H2SO4), the sugar yield obtained was 85% from the coffee husk. The optimum condition for acid hydrolysis was 3M H2SO4, 10 min hydrolysis time, pH 5 and 30°C temperature at 48 hrs fermentation time. Under the optimum conditions the maximum yield of ethanol (5.56% v/v) was obtained using AAUP1 yeast isolate. The results indicated that locally available cheap substrate which occurs in excess and non-edible material, coffee husk will be a potential feedstock for bio-ethanol production. Keywords: Fermentation parameters, fruits, optical density and S. cerevisiae