Use of 2n gametes for inducing intergenomic recombination in lily hybrids

Genetic recombination is an important pre-requisite for transferring specific genetic traits across distantly related plant species. With a view to transfer some of the desirable characters like resistances against viruses, Fusarium and Botrytis, besides many horticultural traits, we have made interspecific hybrids between different species of lilies (Lilium, 2n=2x=24). The F1 hybrids in all these cases are totally sterile because of the lack of chromosome pairing. Traditional method of somatic chromosome doubling (mitotic polyploidization) can produce fertile allotetraploids. But, because of strict autosyndetic pairing in allotetraploids, no genetic recombination occurs in the progenies. In order to overcome this difficulty, we have selected 2n gamete producing F1 hybrids of different Lilium species and used them successfully for sexual polyploidization (meiotic polyploidization). An important feature of meiosis in the F1 hybrids is that a certain amount of homoeologous chromosome pairing does occur in them. When 2n gametes originate from such F1 hybrids through first division restitution (FDR) they are expected to possess recombinant chromosomes. Cytological analyses, using genomic in situ hybridization (GISH), of the sexual polyploid progenies have proved that considerable amount of intergenomic recombinant chromosomes can be recovered in the chromosome complements. One example of the sexual polyploid progenies from Oriental×Asiatic hybrid lilies possessing intergenomic recombinant chromosomes will be illustrated and discussed.