Coffee wilt disease (CWD), caused by Gibberella xylarioides (Fusarium xylarioides) causes major damage to Coffea canephora grown by smallholder farmers in the Democratic Republic of Congo and Uganda and threatens the crop in Rwanda and Tanzania; it is also present on Coffea arabica in Ethiopia and causes substantial losses in some areas. This project provided an important research element that is directly linked with a larger regional coffee rehabilitation and disease management programme (the Regional Coffee Wilt programme, RCWP), led by the Common Fund for Commodities (CFC). Associated funding for complementary scientific studies was also made available under the European Union (EU) INCO-DEV programme.
Through acquisition of a comprehensive collection of F. xylarioides isolates from CWD affected areas in Ethiopia, Tanzania, Uganda and other parts of Africa, application of a broad range of approaches to study genetic and pathogenic variability and initiation of a range of relatively simple on-farm and on-station field studies, new knowledge on the variability and epidemiology of the CWD pathogen was gained. The project research has revealed, for example, that very little genetic variability exists within the CWD pathogen and suggests that two populations, possibly clonal, are currently responsible for the disease in these countries. Host specificity would also appear to be operating within the pathogen, in that isolates obtained since re-emergence of the disease on C. canephora are pathogenic either to C. arabica or to C. canephora, but not to both coffee species, and clearly relates to the two genetic groups. Given the occurrence of the two coffee species within Eastern Africa, the two variants are also therefore geographically separated. Field studies, while still in their infancy, have helped to clarify the mechanisms of survival and transmission of the CWD pathogen in confirming that, for example, the disease can be spread from plant to plant through use of a machete. However, no evidence was acquired to indicate that the pathogen survives on plants other than coffee, or that insects are involved in disease transmission. The various findings have major implications with regard to future management of CWD through cultural approaches, by providing information of relevance to the current search for durable resistance in particular.
CABI Bioscience, UK, 55 pp.