Comparative karyotype analysis of three Passiflora L. species and cytogenetic characterization of somatic hybrids

- The present study was carried out to analyze the karyotypes of three Passiflora species with 2n = 18 (the yellow passion fruit P. edulis f. flavicarpa and the wild species P. amethystina and P. cincinnata) previously used to obtain somatic hybrids by protoplast fusion. A biometrical analysis of Feulgen stained metaphases showed that the karyotypes of these species were quite similar with subtle differences in the morphology of some chromosomes between the species. These data were integrated with the physical mapping of the 45S rDNA (18S-5.8S-26S rRNA genes) and 5S rDNA loci using FISH, and with the pattern of fluorescent staining with chromomycin A 3. FISH signals of 45S rDNA were localized on the secondary constriction and satellite of two chromosome pairs, identified as 8 and 9, in the three species. An additional site was observed on the long arm of chromosome 1 in P. amethystina. Chromomycin A 3 staining revealed highly fluorescent bands corresponding to 45S rDNA loci. One 5S rDNA site was detected on the long arm of chromosome pair 4 in the three species. Silver staining showed four positive signals on the small satellited chromosomes, and the locus on chromosome 1 of P. amethystina seemed to be inactive. Soma-clones derived from four somatic hybrid plants (P. edulis + P. amethystina) had 2n = 4x = 36, but in samples of two hybrids, 2n = 35 was observed. Variability in the number of 45S rDNA sites (10 or 12) was detected among the hybrids, and the FISH signals were smaller than in the parental species. These findings suggest that DNA sequence loss and transposition occurred in these newly formed polyploids.