Relationship between parental chromosomic contribution and nuclear DNA content in the coffee interspecific hybrid C. pseudozanguebariae x C. liberica var 'dewevrei'

F1 hybrids were obtained between two coffee species with the same chromosome number (2n = 22) but with different nuclear DNA contents [C. pseudozanguebariae (PSE) 2C = 1.13 pg and C. liberica var 'dewevrei' (DEW) 2C = 1.42 pg]. G2 hybrids were obtained by open-pollination of the F1 hybrids. Genomic in situ hybridisation (GISH) and flow cytometry were used on six F1 hybrids and seven G2 hybrids to determine their parental chromosomic contribution and their nuclear DNA content (qDNA), respectively. GISH efficiently identified chromosomes from both species. F1 hybrids had a qDNA intermediate between that of the parental species and contained the expected 11 chromosomes from each species. There was a linear relationship between the number of PSE chromosomes and the nuclear DNA content, which indicates that flow cytometry can be used to give a rough estimate of the parental chromosomic contribution in G2 hybrids.