Abstract
Hybridization associated with polyploidization and apomixis is a frequent mechanism of speciation.Sorbusis a genus with ongoing hybridization resulting in a polyploid complex with different parental lineage.Triparensis the smallest hybridogenous subgenus ofSorbusso far known to comprise only two taxa,S. intermediaandS. x liljeforsiithat combine the genomes of three taxa (S. ariaagg.,S. aucupariaandS. torminalis). To elucidate the origins ofS. dacica,S. paxianaandS. tauricola, three new trigenomic candidates formerly believed to be of biparental origin with eitherS. ariaagg. x S. aucupariaorS. ariaagg. x S. torminalislineage we combined data from HPLC and chloroplast DNA analysing additional 33 related taxa as well.
We concluded that the 'torminalis-type' flavonoid profile and the 'aucuparia-type' plastid indicate the participation of bothS. torminalisandS. aucupariaresulting in the formation ofS. dacica,S. paxianaandS. tauricola.Sorbus ariaagg. as the third ancestor and as a necessary link to meet genes ofS. torminalisandS. aucupariain one genome is obvious from morphological features (densely tomentose undersides of leaves). The tetraploid cytotypes and obligate pseudogamy ofS. dacicaandS. paxianawere determined by flow cytometry and are published here for the first time.
The most probable evolutionary scenario forTriparensspecies is: 1. a diploid sexualS. aucupariaas pollen acceptor hybridized with a tetraploid apomictic taxon from theS. ariaagg. producing a triploid apomictic taxon with 'aucuparia-type' plastid inherited maternally; 2. during a second crossing event this subgenusSorariahybrid as maternal progenitor hybridized with the sexual diploidS. torminalis(providing gene(s) of apigenin O-glucuronide synthesis) forming a tetraploidTriparenshybrid with 'aucuparia-type' plastid and 'torminalis-type' flavonoids.