Comparative karyotype analysis of threePassifloraL. species and cytogenetic characterization of somatic hybrids

Abstract

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 be- tween 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 A3. FISH sig- nals 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 A3 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 hy- brids, 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.