Development of a long term strategy based on genetic resistance and agroecological approaches against Coffee Wilth Disease in Africa : Third intermediate report: Covering period 1/11/2003 to 30/04/2004

Over this period (1/11/2003 to 31/04/2004), with the exchange of strains between partners, it was possible to complete the study of biomolecular pathogen diversity. The results will be compared at the end of year 3. Particular attention was paid to screening tests by artificial inoculations on open pollinated seedlings and cuttings. The surviving plants will be installed in a hot spot in the field to confirm their resistance. The production of crosses to study the inheritance of resistance is starting in Uganda. New results: - Introduction of F. xylarioides isolates collected on C. arabica in Ethiopia. (obtained through a joint UK DFID funded project R8188). - "Historical strains" are exchanged between all the partners. - Three biomolecular approaches, ISSR, AFLP, IGS, to study the genetic diversity of F. xylarioides indicate that there is significant polymorphism which differentiates between strains collected on C. Arabica and other strains collected on C. canephora. These results confirm the data obtained with the microsatellite approach. - Cross inoculation between strains collected on C. canephora and C. liberica inoculated on the threee species C. canephora, C. liberica and C. deweivrï, seems to indicate a specific reaction. - Representative isolates stored for long-term storage at both CABI and BCCM:UCL. - Artificial inoculation by injection and wounding has been mastered by all the partners. A strain-cross trial has been conducted on artificial media. Perithecial formation is observed, but there is some variation between trials. - Hypothesis of the partly homothallic nature of G. xylarioides. - The aggressiveness of different Fusarium spp, (F. falciforme, F. solani, F. stilboides, F. equiseti) present on wilted coffee does not appear to be directly implicated in in the pathogenesis due to F. xylarioides. - Identification of resistant plants by artificial inoculation at CORI, UNIKIN, CIRAD. Resistant trait should be confirmed. - Field resistance evaluation of healthy inoculated plants in progress at CORI. - First description of the fungal life cycle in the field (CORI). - First survey with a statistical design of coffee wilt disease in 6 farmer's fields in 4 districts (CORI). - Collection of wild canephora coffee from Kibale forest for genetic diversity analysis (CORI). Priorities for the next 6 months: - Complete and compare genetic analyses of F. xylarioides with the different molecular approaches. - Pursue the analysis of the life cycle, both the lab experiments and the field observations. - Assess coffee germplasm resistance with reference isolates. - Analyse the genetic diversity of wild coffee germplasm. - Confirm the response of survivors to artificial inoculation, and their field resistance. (Résumé d'auteur