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

F-1 hybrids were obtained between two coffee species with the same chromosome number (2n = 22) but with different nuclear DNA contents CC. 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 F-1 hybrids. Genomic in situ hybridisation (GISH) and flow cytometry were used on six F-1 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. F-1 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.