ORIGINAL ARTICLE Expressivity of apomixis in 2n + n hybrids from an apomictic and a sexual parent: insights into variation detected in Pilosella (Asteraceae: Lactuceae) Anna Krahulcova ´ • Frantis ˇek Krahulec • Radka Rosenbaumova ´ Received: 25 May 2010 / Accepted: 1 October 2010 / Published online: 27 October 2010 Ó Springer-Verlag 2010 Abstract Reproductive variation was studied in the tet- raploid Pilosella aurantiaca, hexaploid P. rubra (both species with facultative autonomous apospory) and in their 2n ? n hybrids, which were obtained by crossing with a sexual pollen parent (tetraploid P. officinarum). The dif- ferent DNA content in P. aurantiaca and P. officinarum demonstrated the actual 2n ? n origin, both spontaneous from the field and through experimental crosses, of their hexaploid hybrids. The octoploid 2n ? n progeny were recovered from an experimental cross of P. rubra and P. officinarum. The reproductive pathways operating in two maternal facultatively apomictic species and in the hybrids were quantified using a flow cytometric analysis of seeds obtained from either open-pollinated or emasculated plants. Whereas both maternal species displayed a high penetrance of apomixis, the level of apomixis among the majority of 2n ? n hybrids was much lower and variable. Some of the hexaploid hybrids had a reduced seed set. Compared to the respective maternal parents, the decrease in apomixis due to haploid parthenogenesis and/or n ? n mating was evident in almost all unreduced hybrids, irrespective of their field/experimental origin and ploidy. Hence, the reproductive behaviour in the apomictic maternal parent was profoundly different from that of the 2n ? n hybrids with a sexual parent in spite of the preservation of the complete maternal genome in the hybrids. The regulatory interactions in hybrid genomes, such as effects of modifi- ers, heterochrony, and epigenetic control, may be consis- tent with the different expressivity of apomixis observed under different genetic backgrounds. Keywords Apospory Á Facultative apomixis Á Inheritance of apomixis Á Residual sexuality Á Unreduced hybrids Introduction Apomixis results in the autonomous formation of seed progeny in flowering plants by circumventing meiosis and fertilisation (Bicknell and Koltunow 2004; Tucker and Koltunow 2009). Only in pseudogamous apomicts, how- ever, fertilisation is necessary for endosperm development; in contrast, the embryo develops autonomously. Faculta- tive apomictic reproduction allows the formation of non- maternal (termed aberrant) progeny besides the usually dominant apomictic progeny, which replicate the maternal genome (Bicknell and Koltunow 2004). Such aberrant progeny are comprised of polyhaploids generated by haploid parthenogenesis and/or the products of sexual reproduction. For a relatively long time, studies of the genetic control of apomixis have been attractive both from a scientific and an applied point of view. Finding the genes responsible for apomixis has been the subject of much research during the last 10 years (e.g., Matzk 2000; Dresselhaus et al. 2001; Koltunow and Grossniklaus 2003; Spielman et al. 2003; Communicated by Thomas Dresselhaus. Electronic supplementary material The online version of this article (doi:10.1007/s00497-010-0152-x) contains supplementary material, which is available to authorized users. A. Krahulcova ´(&) Á F. Krahulec Institute of Botany, Academy of Sciences of the Czech Republic, Pru ˚honice CZ-252 43, Czech Republic e-mail: anna.krahulcova@ibot.cas.cz R. Rosenbaumova ´ Department of Botany, National Museum, Praha—Hornı ´ Poc ˇernice CZ-19300, Czech Republic 123 Sex Plant Reprod (2011) 24:63–74 DOI 10.1007/s00497-010-0152-x