Karyotypic analyses and genomic affinity among Argentinean species of Passiflora

Abstract

The genus Passiflora (Passifloraceae) has more than 500 species, nineteen are native to Argentina. By their austral distribution, these species were included in breeding programs to obtain ornamental varieties tolerant to low temperatures. The aim of this work was to know the cytogenetic characteristics of Passiflora genotypes present in a working collection, as an indispensable knowledge for the development of a breeding plan. Chromosomal preparations were performed and karyotypic characteristics, rDNA sites by FISH and affinity among subgenera by GISH were studied. Chromosome counts in fourteen Argentinean species confirmed the basic chromosome numbers previously published: x = 6 for subgenus Decaloba, x = 9 for subgenus Passiflora and x = 10 for Dysosmia. The karyotypic parameters (karyotype, haploid chromosome length and asymmetry indices) and genomic affinities among the subgenera, clarify most of the chromosomal evolution of the genus. The results obtained strongly suggest that the basic number x = 6 would be the original one and that x = 9 was originated by processes of polyploidy and descendent dysploidy. Since subgenus Passiflora possesses the largest genomes, it is postulated that evolutionary process leading to x = 9 was accompanied by unequal distribution of non-coding repetitive DNA, mainly transposable elements. These processes could explain the asymmetrical karyotypes of species of subgenus Passiflora.

Genome size in Argentinean species of Passiflora genus: cytological and phenotypical correlates

“…This similarity in genome size between both subgenera is in coincidence with an evolutionary closeness, supported by karyotype analysis and in the haploid chromosome length (HCL) and karyotypical symmetry indices. Nonetheless, results of GISH analysis showed that there is greater homology between the genomes of the Passiflora and Dysosmia subgenera (Bugallo et al 2020), agreeing with the molecular phylogenies of Muschner et al (2003) and Sader et al (2019). However, the hypothesis made by Sader et al (2019), asserting that the species of the subgenus Dysosmia derives from the subgenus Passiflora also assumes that there would be an intermediary between the subgenera Decaloba and Passiflora with a basic number x = 8, an unknown number within species of the genus.…”

“…A linear regression was performed between the total length of the genome, estimated by measuring the chromosomes in the genotypes of the collection (Bugallo et al 2020), and the amount of DNA per haploid genome estimated in this work. The results showed that the two variables were closely correlated, with a coefficient of determination R 2 = 0.95 (Fig.…”

“…The comparisons between the genomic size and the phenotypic characters obtained in this work, as well as with previously published cytological characters (Bugallo et al 2020;Kew 2021), were made through regressions to establish correlations.…”

“…For subgenus Dysosmia x = 10 (2n = 20) and x = 6 (2n = 12 and 24) for Decaloba (Tab. S1, available on supplementary material <https://doi.org/10.6084/ m9.figshare.23905617.v1>) (Souza et al 2008;Melo et al 2001;Bugallo et al 2020). Polyploidy is not frequently seen in the Argentinean species of Passiflora, being found only in P. suberosa (2n = 24 and 36), P. misera (2n = 12 and 36), both from subgenus Decaloba, and in P. mooreana (2n = 18 and 36) from subgenus Passiflora (Ferreira et al 2020;Bugallo et al 2020).…”

“…S1, available on supplementary material <https://doi.org/10.6084/ m9.figshare.23905617.v1>) (Souza et al 2008;Melo et al 2001;Bugallo et al 2020). Polyploidy is not frequently seen in the Argentinean species of Passiflora, being found only in P. suberosa (2n = 24 and 36), P. misera (2n = 12 and 36), both from subgenus Decaloba, and in P. mooreana (2n = 18 and 36) from subgenus Passiflora (Ferreira et al 2020;Bugallo et al 2020). Interestingly, in recent years, many studies have been published exposing the origin of the variation in the genomic size of some Passiflora species.…”