The occurrence of phenotypically complementary apomixis-recombinants in crosses between sexual and apomictic dandelions (Taraxacum officinale)

Apomictic seed development in dandelion (Taraxacum officinale) involves (1) restitutional meiosis (diplospory), (2) egg cell parthenogenesis, and (3) autonomous endosperm development. The question is whether these elements of apomixis are controlled by one single gene or by several independent genes. Five triploid non-apomictic hybrids, obtained in diploid sexual x triploid apomict crosses were characterized using cyto-embryological and genetic methods. Nomarski-differential interference contrast microscopy and the transmission of microsatellite markers and ploidy levels indicated that the hybrids combined elements of the apomictic and the sexual developmental pathway. Hybrids form two complementary groups with respect to the presence or absence of parthenogenesis and autonomous endosperm development. The occurrence of complementary apomixis-recombinants suggests that parthenogenesis and autonomous endosperm development in Taraxacum are regulated independently by different genes. This study also indicates that early embryo development is independent of endosperm formation, but that endosperm is essential for later embryo growth.