Meiotic recombination in sexual diploid and apomictic triploid dandelions (Taraxacum officinale L.)

Taraxacum officinale L. (dandelion) is a vigorous weed in Europe with diplo id sexual populations in the southern regions and partially overlapping pop ulations of diploid sexuals and triploid or tetraploid apomicts in the cent ral and northern regions. Previous studies have demonstrated unexpectedly h igh levels of genetic variation in the apomictic populations, suggesting th e occurrence of genetic segregation in the apomicts and (or) hybridization between sexual and apomictic individuals. In this study we analysed meiosis in both sexual diploid and apomictic triploid plants to find mechanisms th at could account for the high levels of genetic variation in the apomicts. Microscopic study of microsporocytes in the triploid apomicts revealed that the levels of chromosome pairing and chiasma formation at meiotic prophase I were lower than in that of the sexual diploids, but still sufficient to assume recombination between the homologues. Nomarski DIC (differential int erference contrast) microscopy of optically cleared megasporocytes in the a pomicts demonstrated incidental formation of tetrads, which suggests that h ybridization can occur in triploid apomicts.