Development of a long term strategy based on genetic resistance and agroecological approaches against Coffee Wilth Disease in Africa : Second annual report : covering period 1/11/2002 to 31/10/2003

Bieysse Daniel. 2004. Development of a long term strategy based on genetic resistance and agroecological approaches against Coffee Wilth Disease in Africa : Second annual report : covering period 1/11/2002 to 31/10/2003. s.l. : s.n., 107 p. N° de rapport : CIRAD-AMIS N° 07/2004

Technical and research document
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Additional Information : INCO : International Scientific Cooperation Projects. Contract number ICA-CT-2001-10006

Abstract : Coffee Wilt Disease due to Fusarium xylarioides is currently a major problem, especially for Canephora coffee in DRC, Uganda, Tanzania, and on C. Arabica in Ethiopia. This vascular disease leads to coffee tree death within 9 to 15 months, depending on susceptibility and agro-ecological conditions. Replanting is impossible. due to the soil being infested for several years. Genetic resistance seems to be the only solution for fighting the disease and is being investigated by the COWIDI INCO DEV Project. In year 2, emphasis was placed on: 1- Studying genetic diversity, 2- Assessing the aggressiveness of isolates, 3- Identifying coffee trees with resistance factors, 4- Establishing a breeding scheme, 5- Analysing disease distribution in the field, 6- Assessing correlations between field resistance and artificial inoculation tests. During this year, the collection of strains from all the geographical zones affected by Coffee Wilt (DRC, Uganda, Tanzania, Ethiopia), and from different coffee species (C. canephora, C. arabica, C. excelsa), was completed. In addition, historical strains collected before the re-emergence of the disease were studied. An analysis of molecular variability at CABI, using IGS, demonstrated some degree of variability between isolates collected from C. canephora in Uganda and DRC, and isolates collected from C. arabica in Ethiopia. This result was confirmed at CIRAD, with the analysis of 150 isolates by the microsatellite method. However, the historical strains (CBS 258.52 and 749.79, ATCC 156.64 and DsMZ 624.57) revealed a degree of genetic variability within the species F. xylarioides. These strains were collected from coffee trees of the C. canephora and C. excelsa types in the 1960s during the first wave of infections and differed from C. canephora / C. excelsa and C. arabica. These historical strains also displayed diversity between themselves. The CBS strains collected in West Africa (Guinea, Ivory Coast) differed from strain DsMZ 624.57 collected in the Central African Republic. Current data is insufficient to reach any conclusion as to the origin of the diversity observed, or to possible evolution of the species. The hypothesis of selection pressure generated by the massive eradication of the disease in the 1950s and the use of resistant C.canephora var. robusta may explain the low diversity observed within current strains, whereas diversity does exist within historical strains. The low genetic diversity found within the species F. xylarioides suggests clonal multiplication of the pathogen since the re-emergence of the disease. However, the teleomorphic form Gibberella xylarioides that has been described (Heim, 1954) suggests that K is involved in genetic recombination phenomena. Moreover, perithecia formation in the field is very often seen. Given that these phenomena are part of the mechanisms responsible for the introduction of high genetic diversity within a species, it seems essential to take a closer look at the sexual cycle of F. xylarioides. These results also suggest that host specialization (C. canephora / C. arabica) may be operating, at least within the isolates investigated. CABI has developed an Excel electronic data base with information on collected strains, available for all the partners. If in vitro perithecia production was mastered (UCL), R would be possible to carry out directed crosses, and an indepth study of the pathogen's sexual cycle. A study on tissue invasion by the pathogen was launched at UNIKIN and is being continued at UCL. At CIRAD, variability has been found in the aggressiveness of strains collected from C. canephora in Uganda, along with a ranking of mortality rates on homogeneous progenies of C. canephora. Similar results have been reported at UNIKIN. At CORI, the study of coffee tree resistance by artificial inoculations is continuing. The expression of field resistance in J/1/1 and Q/3/4 was observed under artificial inoculation with a field isolate. These varieti

Mots-clés Agrovoc : Coffea canephora, Coffea arabica, Coffea excelsa, Fusarium, Résistance aux maladies, Variation génétique, Épidémiologie, Pouvoir pathogène, Amélioration des plantes

Mots-clés géographiques Agrovoc : Ouganda, République-Unie de Tanzanie, Éthiopie

Mots-clés complémentaires : Fusarium xylarioides

Classification Agris : H20 - Plant diseases
F30 - Plant genetics and breeding

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