Abstract
The species-mixed Pilosella populations comprising diploid sexual and polyploid facultatively apomictic biotypes were studied in Bulgaria. Parentage of co-occurring recent hybrids was inferred from a combination of morphology and ploidy level that corresponded to simple/multiple crosses of basic species via either reduced or unreduced gametes. The flow cytometric seed screening illustrated the capacity for heteroploid hybridization both in open-pollinated plants in the mixed-ploidy populations and in crossing experiments. The diploid sexual species in Bulgaria have a limited impact on interspecific hybridization, and simple inter-cytotype hybrids are only sporadically formed. The origin of the most common hybrids in Bulgaria that are apomictic and retain the pentaploid/hexaploid ploidy level of a co-occurring putative apomictic parent remains unclear. The absence of stabilized hybridogeneous species and scarcity of commonly hybridizing polyploid sexual biotypes are crucial attributes that distinguish the Pilosella populations in Bulgaria from those in the Czech Republic and Germany. No recent high-polyploid hybrids of 2n + n origin that would potentially become drivers of ongoing hybridization in the mixed sexual-apomictic Pilosella populations similar to those in Central Europe have been recorded in Bulgaria. The pattern of co-occurring cytotypes in Bulgaria likely limits interspecific hybridization due to stronger ploidy barriers.
Highlights
The genus Pilosella Hill. has a complicated taxonomy due to polyploidy, ongoing hybridization, and diversity in modes of reproduction (Fehrer & al. 2007b)
The diploid fully sexual species of Pilosella, which are common in Bulgaria, hybridize only exceptionally as maternal parents with facultatively apomictic polyploids cooccurring in mixed populations in Bulgaria
The crucial difference between the two regions involves the occurrence of the high-polyploid 2n + n hybrids from an apomictic and a sexual parent that are occasionally and repeatedly formed in the mixed sexual-apomictic populations in Central Europe (Czech Republic and Germany), whereas they are exceptionally rare in Bulgaria
Summary
The genus Pilosella Hill. has a complicated taxonomy due to polyploidy, ongoing hybridization (the crosses are both homoploid and across ploidy level), and diversity in modes of reproduction (Fehrer & al. 2007b). Has a complicated taxonomy due to polyploidy, ongoing hybridization (the crosses are both homoploid and across ploidy level), and diversity in modes of reproduction Both the fully sexual biotypes (diploid and polyploid) and facultatively apomictic biotypes (exclusively polyploid) form this agamic complex Apomixis of the aposporous type is autonomous in Pilosella; the development of both embryo and endosperm occurs independently of pollination (Bicknell & Koltunow 2004). Population-based approaches reveal relationships among coexisting biotypes, i.e. the intercytotype mating interactions in a mixed-ploidy and exclusively sexual population of P. echioides (Lumn.) F.
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