Meiotic polyploidization in five different interspecific lilium hybrids

With the aim of transferring important horticultural and disease resistance characters that are available in different Lilium species (2n=2x=24) into the cultivars of lilies, an extensive interspecific hybridization program is in progress at the Plant Research International, Wageningen. In this context, we have made thousands of interspecific hybrids, and investigated them for the occurrence of 2n gametes. These sexual polyploid progenies that were produced were cytologically analyzed through genomic in situ hybridization (GISH). Out of the five different sets of interspecific hybrids that produce 2n-gametes, the following four hybrids involved species that belonged to different taxonomic sections: L. longiflorum×Asiatic hybrids; L. longiflorum×L. henryi; Oriental×Asiatic hybrids and L. auratum×L. henryi. One was an intra-sectional species hybrid involving the cultivar 'Enchantment'×L. pumilum. In all the four intersectional hybrids meiosis was highly irregular during meiosis and produced almost exclusively first division restitution (FDR) gametes. On the contrary, the single hybrid, 'Enchantment'×L. pumilum had normal chromosome pairing and produced only second division restitution (SDR) gametes. Although the frequency of 2n-gamete production in all cases was greatly influenced by the environment, it was possible to produce backcross progenies in all cases. Analyses of backcross progenies through GISH proved that intergenomic recombination occurred in the case of FDR gametes that were produced in all the four interspecific hybrids. Furthermore, analyses of BC2 and BC3 progenies in some cases proved that recombinant chromosomes were transmitted normally. These investigations have shown that meiotic polyploidization is highly promising for lily breeding.