Browsing by Author "Gashu Minbale"

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    Antifungal Natural Products Against two Plant Diseases: Root Rot/Wilt of Faba Bean and Late Blight of Potato
    (Addis Ababa University, 2018-08-04) Gashu Minbale; Dagne Ermias (Professor); Alemu Melaku (PhD)
    In Ethiopiafaba bean and potato are two important crops for food security and nutrition. Root rot/wilt is a notorious fungal disease of faba bean caused by Fusarium spp., while late blight is a potato disease due to attack by the fungus Phytophtra infestans. These two diseases cause from time to time severe crop losses. Hence it is important to control growth and spread of these fungal diseases.It is well known that although the use of synthetic fungicides contributes to enhance crop yield, toxic residues in treated crops cause environmental and health problems. Therefore, the search for eco-friendly plant-based antifungal agents is a worthwhile strategy. In this work, thetwo pathogenic fungi were isolated from diseased parts of crops, identified and maintained with periodic sub-culturing in Potato Dextrose Agar.In this studyfifty seven ethanol extracts of different plants were screened for their antifungal activity using optimized food poisoning technique. Dimethylsulfoxide (5% aq) and 0.5% Mancolaxyl were used as vehicle and standard, respectively. The standard fungicide showed respective growth inhibition percentage (%GI) of 68 and 88 against F. spp.and P. infestans at a concentration of 5 mg/mL. Bioactivity of screened plant extractswas classified into high, moderate and inactive by taking the minimum %GI of the standard (68%) as reference. Of these extracts, Inula confertiflora (69/78%), Echinops kebericho(73/80%) and Artemisia annua(71/73%) showed higher %GI in the control of F. spp./ P. infestans, respectively. The nonpolar portions were found comparable with that of the reference in inhibiting mycelial growth of tested fungi relative to their polar counterparts. The active compounds were isolated and characterized. In the bioassay study dehydrocostus lactone, carabrone, graveolide, carpesiolin and artemisinin demonstrated significant inhibition on the growth of tested fungi.
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    Determination of Caffeine level in Coffee and Artemisinin in Artemisia annua
    (Addis Ababa Universty, 2009-07) Gashu Minbale; Dagne Ermias (Professor)
    Coffee is the second important raw material within the international trade, the most important foreign exchange supplier for many agricultural oriented countries, and the most popular drink. Assessment of the caffeine level is crucial to coffee quality. An HPLC-UV method with microwave assisted extraction was developed, which allowed the determination of caffeine in green, roasted, home-and coffee-house brewed coffee samples. The chromatographic separation was achieved on reversed-phase C-18 pre-packed analytical column (RP-18 Lichrospher®, Waters, 5μm, 4.6 X 150 mm i.d.) using water: Acetonitrile (70:30, v/v) as isocratic mobile phase at 0.8 mL/min flow rate. The method has been applied to samples to afford average caffeine contents (0.8-1.0%) green and roasted, (48-102 mg) home- brewed, (24-56%) coffee-house brewed. The overall procedure had percent recoveries of 93%. The within day and between day percent RSD in coffee samples ranged from 2.4-6 and 0.8-14%, respectively. HPLC-UV is a method used for caffeine routine analysis. Artemisia annua is the only commercial source of artemisinin. Due to the absence of appropriate UV absorption, artemisinin should be converted into UV active compound before HPLC analysis. It can be analyzed using Quantitative TLC method with anisaldehyde visualization reagent