ORIGINAL ARTICLE The intriguing complexity of parthenogenesis inheritance in Pilosella rubra (Asteraceae, Lactuceae) Radka Rosenbaumova´ • Anna Krahulcova´ • Frantisˇek Krahulec Received: 4 January 2012 / Accepted: 3 June 2012 / Published online: 19 June 2012 Ó Springer-Verlag 2012 Abstract Neither the genetic basis nor the inheritance of apomixis is fully understood in plants. The present study is focused on the inheritance of parthenogenesis, one of the basic elements of apomixis, in Pilosella (Asteraceae). A complex pattern of inheritance was recorded in the segre- gating F 1 progeny recovered from reciprocal crosses between the facultatively apomictic hexaploid P. rubra and the sexual tetraploid P. officinarum. Although both female and male reduced gametes of P. rubra transmitted parthe- nogenesis at the same rate in the reciprocal crosses, the resulting segregating F 1 progeny inherited parthenogenesis at different rates. The actual transmission rates of parthe- nogenesis were significantly correlated with the mode of origin of the respective F 1 progeny class. The inheritance of parthenogenesis was significantly reduced in F 1 n ? n hybrid progeny from the cross where parthenogenesis was transmitted by female gametes. In F 1 n ? 0 polyhaploid progeny from the same cross, however, the transmission rate of parthenogenesis was high; all fertile polyhaploids were parthenogenetic. It appeared that reduced female gametes transmitting parthenogenesis preferentially developed par- thenogenetically and only rarely were fertilized in P. rubra. The fact that the determinant for parthenogenesis acts gametophytically in Pilosella and the precocious embryo- genesis in parthenogenesis-transmitting megagametophytes was suggested as the most probable explanations for this observation. Furthermore, we observed the different expression of complete apomixis in the non-segregating F 1 2n ? n hybrids as compared to their apomictic maternal parent P. rubra. We suggest that this difference is a result of unspecified interactions between the parental genomes. Keywords Apomixis Á Inheritance of parthenogenesis Á Haploid parthenogenesis Á Pilosella rubra Á Pilosella officinarum Introduction Apomixis is asexual reproduction through seeds in flow- ering plants (Asker and Jerling 1992; Nogler 1984a). Apomixis omits both meiosis and fusion of the gametes and thus produces progeny that are genetically identical to the maternal plant (Koltunow 1993). Plants reproducing exclusively through apomixis (obligate apomicts) are quite rare in nature (Asker and Jerling 1992). Most apomictic plants are facultative apomicts and retain some level of residual sexuality. Inheritance studies suggest that apo- mixis is a heritable trait that is controlled by one or only a few dominant loci. One apomixis locus has been reported in Brachiaria, Cenchrus, Panicum, Paspalum, Pennisetum, Tripsacum, and Ranunculus; several loci have been reported in Erigeron, Hypericum, Poa, and Taraxacum (reviewed in Bicknell and Koltunow 2004; Grossniklaus et al. 2001; Ozias-Akins and van Dijk 2007). The genus Pilosella, formerly classified as Hieracium subgenus Pilosella, within the Asteraceae family, repre- sents an established model system for studying apomixis (Bicknell 1994; Bicknell and Koltunow 2004; Catanach et al. 2006; Koltunow et al. 1995, 2011a, b). Apomixis in Communicated by Thomas Dresselhaus. R. Rosenbaumova´(&) Department of Botany, National Museum, Cirkusova´ 1740, Praha 9, Hornı ´ Pocˇernice 193 00, Czech Republic e-mail: radka.rosenbaumova@seznam.cz A. Krahulcova´ Á F. Krahulec Institute of Botany, Academy of Sciences, Za´mek 1, Pru˚honice 252 43, Czech Republic 123 Sex Plant Reprod (2012) 25:185–196 DOI 10.1007/s00497-012-0190-7