Interspecific hybridization in lily (Lilium): Interploidy crosses involving interspecific F1 hybrids and their progenies

Despite a long history of cultivation, a large number of lily (Lilium) cultivars were still diploid (2n=2x=24) till recently. But polyploid cultivars are rapidly increasing. In addition to having robust stems, large flowers, thicker and larger leaves, polyploids can also serve to combine desirable characters from species of different taxonomic sections; not only from the cultivated groups, viz., Sinomartagon, Archelirion and Leucolirion, but also from sections that include non-cultivated species. Because the F1 hybrids between the species of different taxonomic sections are highly sterile, it is imperative that breeding has to be carried out at the polyploidy level. This chapter is based on our results on using intersectional interspecific hybrids of Longiflorum x Asiatic (LA) and Oriental x Asiatic (OA) groups of lilies and their polyploid backcross progenies BC1, BC2 and BC3). In order to cross genotypes of different ploidy levels, i.e., interploidy crosses, a knowledge of embryo and endosperm ploidy levels is valuable because, unlike in most other plant species, lily has very large chromosomes and the embryo sac formation is of tetrasporic 8-nucleate type. In order to highlight the differences, a comparison is made with the most commonly occurring, monosporic 8-nucleate type of diploid potato, with 24 chromosomes (same as lily). Some of the limitations and constraints associated with interploidy crossing are considered