Genotypic and environmental variation in production of 2n-gametes of oriental x asiatic lily hybrids

It is attractive to use 2n gametes in breeding for three reasons: a) they can overcome the sterility of F1 hybrids between distantly related species, b) facilitate homoeologous recombination between alien chromosomes and c) generate a large number of different genotypes of 2n gametes from a single F1 hybrid. Such genetic variation can be potentially useful for breeding. However, there is one drawback of using 2n gametes in breeding. The frequency of 2n gamete-producing genotypes OA-hybrids, is very low. By producing a large number of interspecific hybrids followed by careful screening, we have selected few 2n gamete producing F1 hybrids between different groups of Lilium species. This screening for 2n pollen production revealed enormous variation in 2n pollen production frequencies between the different genotypes and between the same genotypes grown in different environments. The fluctuations in greenhouse temperature appeared to influence 2n gametes frequency considerably. To study this during several years, four normally complete sterile genotypes were exposed to a heat shock treatment in phytotron. Three out of the four genotypes produced viable 2n pollen. In total 2% of the treated flowers became fertile due to this temperature-induced stimulation of 2n pollen formation.