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Breeding for host resistance to coVee berry disease (CBD) in arabica coVee (CoVea arabica) was initiated some 35-40 years ago in Kenya, Ethiopia and Tanzania in response to severe CBD epidemics. The release of CBD resistant cultivars to the coVee growers has been in progress since 1985. The resistance of cultivars like Ruiru 11 (Kenya) and Ababuna (and other cvs in Ethiopia) appears to be of a durable nature, since conWrmed cases of a breakdown of host resistance under Weld conditions have not been reported over the past 20 years. Host resistance to the hemibiotrophic fungus Colletotrichum kahawae is of a quantitative nature, but nevertheless can be practically complete in some genotypes of arabica coVee. There is still no consensus on the genetics of CBD resistance, some claiming convincing evidence for oligogenes (1-3 major genes) and others for polygenes determining CBD resistance. Results from genetic studies with germplasm from the centre of genetic diversity for C. arabica in Ethiopia are presented here. These together with the recent identiWcation of molecular markers associated with and the mapping of one major gene, provides additional evidence for oligogenic inheritance of CBD resistance. The development of cultivars combining yield and quality with durable host resistance to CBD has contributed greatly to increased sustainability of arabica coVee production in Africa. It has also considerable relevance to arabica coVee in Latin America and Asia, where CBD is still a quarantine disease but with a risk of becoming endemic one day, just as has happened earlier with coVee leaf rust (Hemileia vastatrix).

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Understanding the genetic diversity existing in a germplasm collection is important to identify parental combinations with distinct gene sets that can be used in crossing to obtain superior hybrids. This study was carried out to evaluate the genetic diversity in the Rwandan coffee germplasm using both RAPD and SSR markers and to determine any relationship between these two markers. Varieties with resistance to coffee leaf rust and coffee berry disease as well as local cultivars in Rwanda were used for DNA extraction and subjected to PCR amplification. The highest values for genetic distances were obtained between BM 139 and HDT and between Harar and Catimor implying that these varieties were genetically quite distinct. The lowest values for genetic distance were recorded between BM 139 and BM 71 and between Matinho and Rume Sudan implying that these varieties were genetically fairly similar. A Pearson correlation of 55.52% was obtained between the two markers indicating a moderate association between these two analytical procedures. It is recommended that crosses should be made between genetically distant susceptible and resistant varieties to derive hybrids that combine resistance with marked levels of heterosis particularly for yield.