A Molecular Cytogenetic Analysis of Introgression in Backcross Progenies of Intersectional Lilium Hybrids

The genus Lilium is comprised of about 100 species and has been divided into seven taxonomic sections. The abundance and diversity of species within the genus Lilium offers numerous and rewarding possibilities to lily breeders. Species within the same section can be crossed by conventional hybridization and this has led to different hybrid groups of great commercial importance such as Longiflorum, Asiatic and Oriental lilies. On the other hand, the divergence of species between various taxonomic sections causes considerable difficulties for intersectional crosses. Such difficulties include crossing incompatibility barriers, embryo abortion, sterility and reduced fertility in intersectional hybrids. For these reasons, various pollination techniques followed by in vitro embryo (sac) rescue and ovary culture, chromosome doubling, and 2n gametes are used frequently to obtain progeny between parents from different sections. Being the largest genome in the plant kingdom, lily is used as a model plant for cytogenetic analysis. The genome composition of the hybrids and backcross progenies were monitored through genomic in situ hybridization (GISH). The progress in molecular cytogenetic studies has been associated with the analysis of introgression of chromosomal segments in backcross progenies of various interspecific hybrids, contribution of individual genome in the resultant progenies, and the mechanism of 2n gamete formation. Based on the cytological analysis of progenies derived from the use of both haploid and 2n gametes, cytological maps of three different genomes have been constructed and the relevance of these analyses for introgression in Lilium is demonstrated