Browsing by Author "Adugna, Girma (PhD)"

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    Diversity of Arabica Coffee Populations in Afromontane Rainforests of Ethiopia in Relation to Colletotrichum Kahawae and Gibberella Xylarioides
    (Addis Ababa University, 2006-07) Zeru, Arega; Asefa, Fasil (PhD); Adugna, Girma (PhD)
    Coffee berry disease (CBD), caused by Colletotrichum kahawae and coffee wilt disease (CWD), which is caused by Gibberella xylarioides, are the major coffee diseases in Ethiopia. Assessment of CBD and CWD was conducted in Harena, Bonga, Birhan-Kontir and Yayu from July to September 2005. These diseases were prevalent in all surveyed forest coffee areas of Ethiopia. The mean percent incidence and intensity of CBD varied from 6.0-40.0% and 2.0-17.9% across forest coffee areas. The mean incidence of CWD varied from 2.4 to 16.9% across forest coffee areas. Seedling inoculation tests conducted on indigenous forest coffee selections from 4 different forest coffee areas revealed significant variations (P < 0.05) among the selections both in percent seedling CBD infection, inoculated with C. kahawae and in percent wilt seedlings, inoculated with G. xylarioides. Selections from Yayu, Bonga, Berhan-Kontir and Harena showed mean seedling CBD infection rate from 69.0-100%, 57.5-100%, 75.3-100% and 23.3-100% where as percent wilt seedlings varied from 58.0-97.2%, 26.2-97.3%, 72.7-100% and 0-94%, respectively. This indicated that in the course of resistant coffee variety development it is possible to get wider alternative resistant gene pool from Harena and Bonga, followed by Yayu indigenous forest coffee germplasms. These observations allow first remarks on possible CBD and CWD tolerant or resistant selections in the indigenous forest coffee of Ethiopia, which increase the value of afromontane rainforest coffee. Hence it is important to conserve and use sustainably the indigenous coffee germplasms both insitu, and exsitu, by conducting intensive selection from more diverse coffee population and evaluation for diseases resistant (priority on CBD and CWD), high yield, better quality and other characteristics. 15 representative C. kahawae isolates were obtained from forest coffee areas of Ethiopia and 2 isolates from Gera were studied based on their cultural and morphological characters. Isolates could be grouped into 3 based on their colony color manifestation on the obverse side of potato dextrose agar (PDA) and malt extract agar (MEA). The cultures exhibited lightgray, darkgray and gray mycelia forms. Mean radial colony growth rate of C. kahawae isolates ranged between 0.6 and 5.5 millimeter (mm)/24 hour (hr), and between 1.2 and 6.1mm/24 hr on PDA and MEA, respectively. Conidia width and length ranged as 3.6–4.8 μm and 12.7–15.5 μm, respectively. Highly significant (P < 0.05) variation was observed among C. kahawae isolates in their sporulation capacity, and varied between 25.93 x 104 and 253.22 x 104 conidia/ml. No race difference was observed within C. kahawae isolates; however, certain cultural, morphological variations as well as significant variation in aggressiveness were detected among them. Pathogenicity test of 12 isolates on seedlings of 4 Coffea arabica L. cultivars indicated that there was a highly significant difference (P < 0.05) among cultivars, isolates, and cultivar x isolate interactions. The resistance manifested by cultivars was horizontal or non-biotype specific. The difference in virulence and aggressiveness implies that care should be taken in while developing resistant varieties. Aggressive isolates should be used for successful screening of resistant coffee germplasms before releasing any newly developed coffee cultivar(s). Key words/phrases: Afromontane rainforest indigenous coffee, Coffea arabica, Colletotrichum kahawae, Gibberella xylarioides