Résumé
F1 and backcross hybrids were obtained between two diploid coffee species (2n = 22) differing by their nuclear DNA contents (C. pseudozanguebariae (PSE) 2C = 1.13 pg and C. liberica var. dewevrei (DEW) 2C = 1.42 pg). Genomic in situ hybridisation (GISH) and flow cytometry were used on 6 F1 hybrids and 7 backcross hybrids in order to determine their parental chromosomic contribution and their nuclear DNA content (qDNA), respectively. GISH and flow cytometry results in the two species and their interspecific hybrids: 1. GISH efficiently identified chromosomes from both species. 2. In PSE and DEW, two 18S-5.8S-25S rDNA sites were localised on terminal segments of two chromosomes. 3. F1 hybrids had DNA content intermediate between the parental species and contained 11 chromosomes from each species as expected. 4. There was a linear relationship between the number of PSE chromosomes and the nuclear DNA content. Conclusiosn: Flow cytometry allows to sort hybrids with nuclear DNA content and DEW chromosome number close to the cultivated species. In introgression programmes, the aim is to produce plants with the interesting wild trait, but conserving the back-ground of the cultivated species. This is usually done by backcrossing the hybrids having the favourable trait on the cultivated species and this process have to be carried out on about ten generations. This is time-consuming, especially for coffee trees which yield after four years. The use of molecular markers and flow cytometry for early selection could accelerate this pro-cess. (Résumé d'auteur)