Coffee wilt caused by Gibberella xylarioides (Fusarium xylarioides) is a troublesome soil borne disease of Arabica coffee (Coffea arabica L.) in Ethiopia. It has been known to be prevalent and severe in plantation, garden and semi-forest coffee production systems in that order of importance. A number of recent reports have also indicated that the disease is equally damaging coffee trees with varying intensities thereby endangering the conservation of wild coffee genetic resources in forest coffee systems of the country. However, the reasons for the disease upsurge in the forest remain speculative. Thus, population structure of coffee wilt pathogen was studied by cross inoculating 12 accessions with four isolates collected in the four forest sites, namely, Bonga, Berhane-Kontir and Yayu (southwest) and Harenna (southeast) of Ethiopia. A pathogenic isolate 'Gx11' and a moderately resistant coffee cultivar cv. 7440, both from plantation were included as respective standard checks. The cultural and morphological characteristics of 24 isolates from the forests were compared with six strains collected from semi-forest and plantation coffee. The cultural appearance of most isolates from southwest was generally similar in pigments, aerial and radial growths but relatively different from those isolates collected in the Southeast forest site (Harenna). The result of coffee accession by isolate interactions showed that accessions of Harenna (P4, P6 and P11) were resistant to almost all isolates (except to its isolate) with low mean percent seedling deaths (< 31%) while Bonga (P27) and Berhane-Kontir accessions (P34 and P38) were highly susceptible to all isolates with higher seedling deaths of 79.2 to 85.7%. The Harenna isolate was most aggressive (78.7%) followed by Bonga 'B23' and Yayu 'Y21' isolates which were as aggressive as the one from plantation coffee 'G11'. In conclusion, the fungus population structure in the forest coffee sites have basically similar cultural and morphological characteristics of the species G. xylarioides (F. xylarioides) with certain differences between southwest and southeast in colony growth nature, pigmentation and aggressiveness. The study evidenced that the pathogen strains in the forest coffee are equally or even more aggressive than those strains in other coffee production systems, thus rapidly threatening Arabica coffee gene pool of Ethiopia.
Ethiopia, as the center of origin for Coffea arabica, hosts a large diversity of germplasm. Besides drastic reduction in the forest cover and low average yield, the crop is attacked by several diseases, among that coffee leaf rust; coffee berry disease and coffee wilt disease are the major fungal diseases contributing to reduced yield in the country. In this article, the main objective is to provide an overview on current status of major forest coffee diseases prevalence and distributions recorded in afromontane rain forest area of Ethiopia; and to indicate the incidence and severity of forest coffee diseases in the forest coffee populations and elucidates some basic management studies and efforts made to manage those diseases occurred over the past 10 years. The incidences of diseases are reviewed based on different research out puts that was conducted in the afromontane rainforests of the southeast (Harenna) and southwest (Bonga, Berhane-Kontir, Yayu) of Ethiopia. CLR incidences in Ethiopia were present in all forest coffee areas with highest between January and March and lows between June and October with incidence varied from 0.36 to 18.5% in Bonga, 1.8 to 49% in Berhane-Kontir, and 11.8 to 62.6% in Yayu forest coffee populations. The corresponding severity ranged from 0.08 -1.2%, 0.24 -1.7% and 0.91 -3.3% whereas the Sporulation Lesion density varied from 0.08 -1.9, 0.33 -3.65 and 1.5 -5.9% in that order. Leaf rust was low (18.5%) in July 2007 and high (62.6%) in January 2008. CBD was present mostly in Bonga (40.0%) and Yayu (26.3%), but less frequent in Harenna (18.6%) and Berhane-Kontir (6.0%). CWD as a recently developed disease in Arabica coffee could be detected ranging from during the dry season of 2012, the incidence ranged respectively from 0 to 15.4%, 7.3 to 37.6%, 0 to 22.3%, and 26.4 to 28.3% in Bonga, Berhane-Kontir, Yayu and Harenna. During the wet season of 2012, the average disease incidence was 11.9, 29.2, 13.2 and 27.7% at the respective forest sites. Significant variation also observed among each coffee tree within a location and season significantly interacted with both location and coffee trees within a location. As researcher indicated in 2010 heterogeneity of forest coffee populations to those diseases in the field under native agro-ecology provides an opportunity to develop resistant varieties among the enormous forest coffee genetic resources and at the same time calls for strategic multi-site in situ conservation to rescue and maintain the present genetic variation and enhance co-evolutionary processes. From this review, in the case of CBD and CWD selections of tolerant Arabica accessions are being pursued from local landraces in afromountan rain forest areas of Ethiopia that undoubtedly needs detailed research work on screening tolerant variety against to the major diseases.
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