The Detection, Rate and Manifestation of Residual Sexuality in Apomictic Populations of Pilosella (Asteraceae, Lactuceae)

Abstract

The effect of maternal, facultatively apomictic plants on population diversity was evaluated in seven hybridizing polyploid Pilosella populations, where apomictic (P. bauhini orP. aurantiaca)andsexual(P. officinarum) biotypes coexist. The ploidy level, reproductive system, morphology, clonal structure and chloroplast DNA haplotypes were used to characterize these plants and their hybrids. The reproductive origins of the progeny were assessed through either a flow cytometric seed screen and/or a comparison between the ploidy level of progeny embryos/seedlings and the maternal ploidy level. The cultivated progeny derived from residual sexuality in maternal apomicts were also identified based on their morphology and reproductive behaviour. The progeny different from their maternal parents (0.6�92.3 % of progeny embryos and 0�100 % of progeny seedlings) originated either sexually or via haploid parthenogenesis. Comparing the facultatively apomictic and sexual mothers, the progeny arrays generated in the field showed that apomictic mothers produce progeny that is more variable in ploidy level. This effect was demonstrated at both the embryonic and seedling stages of progeny development. Residual sexuality in apomicts was also effective in experimental crosses, generating progeny similar to spontaneous hybrids in the field. The 2n + n hybrids produced from an apomictic and a sexual parent displayed similar reproductive behaviour, producing polyhaploid, sexual and apomictic progeny in variable ratios. Repeated hybridizations between parental species and/or multi- step crosses can result in hybrid swarms rich in cytotypes and morphotypes. The variation recorded in these populations suggests prevailing introgressive hybridization towards the sexual species P. officinarum.