Two species and two karyotypes? Cytogenetic differentiation between Passiflora foetida L. and P. vesicaria L. (Passifloraceae)

Within the Passiflora L. (Passifloraceae) genus, subgenus Passiflora L. is the most economically important. It is reported to have a basic chromosome number of x = 9, with the exception of P. foetida L., which has n = 10. Passiflora foetida, however, exhibits substantial morphological variation, and recently, P. foetida var. versicaria was re-established at the species level, along with related varieties such as P. versicaria var. galapagensis. This study aimed to cytogenetically characterise two P. foetida accessions and two P. vesicaria varieties by estimating genome sizes using flow cytometry, mapping heterochromatic regions by CMA/DAPI staining, and identifying 5S and 35S ribosomal DNA sites using fluorescent in situ hybridization (FISH). The genome sizes were similar across the analysed species, varying from 2C = 1.00 ± 0.03 pg for P. vesicaria var. galapagensis to 2C = 1.16 ± 0.01 pg for P. vesicaria var. vesicaria, indicating small genomes. All P. foetida accessions and P. vesicaria varieties showed 2n = 20, confirming previous counts for P. foetida and revealing the chromosome numbers of the two P. vesicaria taxa for the first time. Six CMA+ bands were observed in P. foetida, compared to four in P. vesicaria var. galapagensis, and two in P. vesicaria var. vesicaria, all co-localised with the 35S rDNA sites. A second, weaker pair of 35S rDNA sites was observed in P. vesicaria var. vesicaria but these did not correspond to CMA+ bands. Passiflora foetida showed four interstitial 5S rDNA sites, but one accession exhibited only two interstitial 5S sites, indicating an intra-specific polymorphism not previously documented for either the genus or the species. Both P. vesicaria varieties exhibited two 5S sites. Thus, although the taxa share the same chromosome number (n = 10) and have comparable genome sizes, they exhibit karyotypic variation in the number of CMA bands and rDNA sites, enabling their cytogenetic differentiation.