Population structure of Gibberella xylarioides Heim and Saccas in Ethiopian forest coffee (Coffea arabica 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.

Status of Forest Coffee (Coffea arabica L.) Diseases in the Afromontane Rainforest Areas of Ethiopia: A review

“…As host-pathogen interaction results reported by Sihen et al, (2013) the accession versus isolate interactions demonstrated differential effects, and thus, seedlings of Harenna accessions (P4, P6 and P11) were horizontally resistant (< 30%) to almost all isolates of G. xylarioides but susceptible to the isolate originated from the same site (H11) which induced 90% seedling death. In contrast, Yayu accessions (P47, P49 and P59) were highly resistant only to Berhane-Kontir isolate (SH21) without expressing any wilt symptoms (0.0%); although, they are susceptible to the other four isolates, namely, 'B23', 'Y21', and 'H11' and 'G11' with varying disease levels.…”

“…Results of greenhouse inoculation experiments proved that there was important diversity in coffee populations (within and among the forest sites) in reaction to G. xylarioides infection (Arega Z., 2006;Sihen et al, 2012 andSihen et al, 2013). However, there is a tendency towards occurrence of higher frequency of susceptibility reactions except in Harenna coffee populations that consistently revealed higher level of resistance in both sets of experiments, even despite the fact that relatively more CWD incidence recorded in the fields.…”

“…Among the four coffee production systems known in the country, forest and semi-forest coffees are believed to possesses the largest coffee genetic resources (gene pool) followed by the 'landraces' with enormous potential to improve the crop (Sylvain, 1958;Meyer, 1965;Van der Graaff, 1981;Mesfin, 1991;Paulos and Demel, 2000;Gole et al, 2002;Tesfaye, 2006;Tadesse et al, 2008).…”

Coffee wilt disease: The forgotten threat to coffee

“…Greater host heterogeneity is thought to reduce susceptibility to CWD and restricts the rapid spread of the disease (Getachew et al, 2012(Getachew et al, , 2013Zeru et al, 2009). CWD is considered to be a minor problem in Ethiopia, and its coffee exports have yet to suffer large drops (Figure 1d).…”

Induction of coffee wilt disease infection using different types of contaminant in field conditions in Democratic Republic of Congo

“…However, its production is experiencing a remarkable decline due to aging plantations, the degeneration of planting materials, use of uncertified plant materials and attacks of pests and diseases (Tshilenge-Djim et al, 2004). Among these, coffee wilt disease (CWD) is one of the most important diseases dramatically limiting coffee production (Coste, 1989;Tshilenge-Djim et al, 2004;Girma et al, 2005;Sihen et al, 2012Sihen et al, , 2013. This fungal disease caused by Fusarium xylarioides Steyaert (teleomorph: Gibberella xylarioides Heim & Saccas) had devastated plantations in West Africa and also in DRC (Tshilenge-Djim et al, 2004).…”