Comparative analysis of structural chromosome variability and heterochromatin localization in Passiflora L. (Passifloraceae)

Passiflora is the most diverse genus of the Passifloraceae family, and holds great economic importance. However, cytogenetic information is still limited for most species. This study aimed to analyze the karyotypes of nine Passiflora species, to determine the chromosome number and the distribution of heterochromatic regions by double staining with CMA/DAPI and by fluorescence in situ hybridization (FISH) with 35S and 5S rDNA probes. Eight species presented a karyotype with 2n=18 chromosomes, and in contrast, P. foetida was the only species to exhibit a karyotype with 2n=20. Double staining with CMA and DAPI revealed distinct staining patterns, with four CMA+ blocks located in the terminal regions of the chromosomes of eight species, except in P. foetida, where six CMA+ blocks were observed in the proximal regions. FISH identified four to six 35S rDNA sites in the terminal regions of the chromosomes in P. alata and P. edmundoi, and six sites in interstitial region in P. foetida. In these same species, two 5S rDNA sites were observed, and in P. foetida four sites in the subterminal regions. The observed chromosomal variations suggest significant genetic diversity in the genus, valuable data for studies of diversity, conservation and genetic improvement.