Nuclear DNA content in the subgenus Coffea (Rubiaceae): inter- and intra-specific variation in African species

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Abstract
Flow cytometry has been used to estimate nuclear DNA content of 13 Coffea species (Rubiaceae) native to Africa. Twelve diploid (2n = 22) and one tetraploid (C. arabica, 2n = 44) species were investigated. Isolated nuclei from 77 genotypes were stained with propidium iodide (PI; not base specific). Thirty-nine genotypes were stained with 4′,6-diamidino-2-phenylindole (DAPI; AT specific). Nuclear DNA content (2C values), estimated with PI, ranged from 0.95 to 1.78 pg. By aggregative clustering, three groups of accessions with increasing DNA content were identified. Three species, namely C. sessiliflora, C. racemosa, and C. pseudozanguebariae, had a low DNA content (0.90 – 1.30 pg). Three species, namely C. eugenioides, C. stenophylla, and C. sp. F, were exclusively found in the intermediate group (1.31 – 1.60 pg). The remaining species were distributed between the intermediate group and the last group (1.61 – 1.80 pg). The values determined for the Coffea species are compared, inter- and intra-specifically, to those of other angiosperm species. The observed differences are discussed according to the ecogeographic origin of the species, their phenological characteristics, and the fertility of the F1 interspecific hybrids. Key words: Africa, Coffea, flow cytometry, nuclear DNA content, genome evolution.