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

F sub(1) hybrids were obtained between two coffee species with the same chromosome number (2n=22) but with different nuclear DNA contents [C. pseudozanguebariae (PSE) 2C=1.13pg and C. liberica var 'dewevrei' (DEW) 2C=1.42pg]. G2 hybrids were obtained by open-pollination of the F sub(1) hybrids. Genomic in situ hybridisation (GISH) and flow cytometry were used on six F sub(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 sub(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.