Population structure of <i>Gibberella xylarioides</i> Heim and Saccas in Ethiopian forest coffee (<i>Coffea arabica</i> L.) systems

Abstract

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.

Keywords: Aggressiveness, colony growth, forest coffee, Fusarium xylarioides, coffee production systems, host-pathogen interactions

African Journal of Biotechnology Vol. 12(33), pp. 5157-5163