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Addis Ababa University Libraries Electronic Thesis and Dissertations: AAU-ETD! >
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| Title: | DIVERSITY OF ARABICA COFFEE POPULATIONS IN AFROMONTANE RAINFORESTS OF ETHIOPIA IN RELATION TO COLLETOTRICHUM KAHAWAE AND GIBBERELLA XYLARIOIDES |
| Authors: | Arega, Zeru |
| Keywords: | Afromontane rainforest indigenous coffee
Coffea arabica
Colletotrichum kahawae
Gibberella xylarioides |
| Date Added: | 31-Aug-2007 |
| Abstract: | 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). |
| Description: | In Partial Fulfillment of the Requirements of the Degree of Master’s of Science in
Biology, Applied Microbiology |
| URI: | http://hdl.handle.net/123456789/23 |
| Appears in: | Thesis - Biology
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