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

The genus Passiflora L. (Passifloraceae) is widely distributed, primarily in the Neotropics, and comprises over 500 species divided into four main subgenera. The subgenus Passiflora is the most economically relevant and has a basic chromosome number of x = 9, with P. foetida L. being the sole species in the subgenus having a chromosome number of n = 10. However, P. foetida exhibits substantial morphological variation among its varieties, and recently, two of these varieties were reclassified as Passiflora vesicaria L. and P. vesicaria var. galapagensis. This study aimed to cytogenetically characterise both species 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 three accessions analyzed, varying from 2C = 1.00 {+/-} 0.03 pg for P. vesicaria var. galapagensis to 2C = 1.16 {+/-} 0.01 pg for P. vesicaria, indicating small genomes. All three accessions showed 2n = 20, confirming the count for P. foetida and revealing the chromosome numbers of the two P. vesicaria accessions for the first time. Six CMA+ bands were observed in P. foetida, four in P. vesicaria var. galapagensis, and two in P. vesicaria, all co-localised with the 35S rDNA sites. FISH with 5S and 35S rDNA showed six pericentromeric 35S sites of different intensities in P. foetida and four interstitial 5S sites, with one individual having only two interstitial 5S sites, demonstrating a polymorphism at the intrapopulation level not yet recorded for the genus or the species. Passiflora vesicaria exhibited four 35S sites also pericentromeric, as well as two 5S sites, while P. vesicaria var. galapagensis presented four pericentromeric 35S sites and two 5S sites. Therefore, despite these species having the same chromosome number (n = 10) and similar genome sizes, there are karyotypic variations in the number of CMA+ bands and rDNA sites, allowing their discrimination.