Orcein, C- and NOR-banding on mitotic chromosomes of some wild diploid coffee species (Coffea L.)

The mitotic chromosomes of four diploid and auto-incompatible coffee species - Coffea congensis, C. eugenioides, C. liberica and C. stenophylla have been comparatively analyzed by acetic orcein, C-banding and nucleolar organizer region (NOR)-banding techniques in order to complete the chromosome characterization in the Coffea genus, by determining morphometric parameters and heterochromatin localization, and to establish karyotype traits, including the degree of symmetry/asymmetry of the karyotypes of the four studied species. The subject is of practical interest because botanical classification of coffee species is still controversial and the reported results can contribute to a better comprehension of interspecific relationships as well as of the evolutionary trends in Coffea. Some species differed from others based on some karyomorphometric parameters. The karyotype formula obtained was the same for all coffee species analyzed, 3m + 6sm + 2sm(s). All species displayed a moderate karyotype asymmetry and according to the Stebbins system, C. congensis and C. liberica were classified as 2A while C. eugenioides and C. stenophylla, classified as 2B, were more asymmetrical than the two former ones. Among the four indices used to assess karyotype asymmetry, Stebbins and Paszko AI indices were the best suited to individualize the species. C-bands occurred preferentially at pericentromeric/centromeric position. Two pairs of chromosomes with secondary constriction and satellite segments were observed in the species following acetic orcein staining. C. congensis, C. eugenioides and C. liberica displayed one pair of chromosomes with the NOR-band after silver staining procedure, while C. stenophylla showed two pairs. Data on morphometric chromosome and NOR-banding results were suitable for the characterization of the species.