Diversity Of Arabica Coffee Populations In Afromontane Rainforests Of Ethiopia In Relation To Colletotrichum Kahawae And Gibberella Xylarioides

Coffee berry disease (CBD), caused by Colletotrichum kahawae and coffee wilt disease (CWD),rnwhich is caused by Gibberella xylarioides, are the major coffee diseases in Ethiopia. Assessmentrnof CBD and CWD was conducted in Harena, Bonga, Birhan-Kontir and Yayu from July tornSeptember 2005. These diseases were prevalent in all surveyed forest coffee areas of Ethiopia.rnThe mean percent incidence and intensity of CBD varied from 6.0-40.0% and 2.0-17.9% acrossrnforest coffee areas. The mean incidence of CWD varied from 2.4 to 16.9% across forest coffeernareas.rnSeedling inoculation tests conducted on indigenous forest coffee selections from 4 different forestrncoffee areas revealed significant variations (P < 0.05) among the selections both in percentrnseedling CBD infection, inoculated with C. kahawae and in percent wilt seedlings, inoculatedrnwith G. xylarioides. Selections from Yayu, Bonga, Berhan-Kontir and Harena showed meanrnseedling CBD infection rate from 69.0-100%, 57.5-100%, 75.3-100% and 23.3-100% where asrnpercent wilt seedlings varied from 58.0-97.2%, 26.2-97.3%, 72.7-100% and 0-94%, respectively.rnThis indicated that in the course of resistant coffee variety development it is possible to get widerrnalternative resistant gene pool from Harena and Bonga, followed by Yayu indigenous forestrncoffee germplasms. These observations allow first remarks on possible CBD and CWD tolerantrnor resistant selections in the indigenous forest coffee of Ethiopia, which increase the value ofrnafromontane rainforest coffee. Hence it is important to conserve and use sustainably thernindigenous coffee germplasms both insitu, and exsitu, by conducting intensive selection fromrnmore diverse coffee population and evaluation for diseases resistant (priority on CBD and CWD),rnhigh yield, better quality and other characteristics.rn15 representative C. kahawae isolates were obtained from forest coffee areas of Ethiopia and 2rnisolates from Gera were studied based on their cultural and morphological characters. Isolatesrncould be grouped into 3 based on their colony color manifestation on the obverse side of potatorndextrose agar (PDA) and malt extract agar (MEA). The cultures exhibited lightgray, darkgray andrngray mycelia forms. Mean radial colony growth rate of C. kahawae isolates ranged between 0.6rnand 5.5 millimeter (mm)/24 hour (hr), and between 1.2 and 6.1mm/24 hr on PDA and MEA,rnrespectively. Conidia width and length ranged as 3.6–4.8 μm and 12.7–15.5 μm, respectively.rnHighly significant (P < 0.05) variation was observed among C. kahawae isolates in theirrnsporulation capacity, and varied between 25.93 x 104 and 253.22 x 104 conidia/ml.rnNo race difference was observed within C. kahawae isolates; however, certain cultural,rnmorphological variations as well as significant variation in aggressiveness were detected amongrnthem. Pathogenicity test of 12 isolates on seedlings of 4 Coffea arabica L. cultivars indicated thatrnthere was a highly significant difference (P < 0.05) among cultivars, isolates, and cultivar xrnisolate interactions. The resistance manifested by cultivars was horizontal or non-biotypernspecific. The difference in virulence and aggressiveness implies that care should be taken inrnwhile developing resistant varieties. Aggressive isolates should be used for successful screeningrnof resistant coffee germplasms before releasing any newly developed coffee cultivar(s).rnKey words/phrases: Afromontane rainforest indigenous coffee, Coffea arabica,rnColletotrichum kahawae, Gibberella xylarioides

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