The Significance of Polyploidy for Bulbous Ornamentals: A Molecular Cytogenetic Assessment

Most of the bulbous crops, viz., Crocus, Narcissus, Tulipa, Alstroemeria and Lilium that are commercially important, share certain common characteristics. The present day cultivars are all derived from hybrids between distantly related species, and in almost all cases spontaneous polyploidization has played a prominent role and there is a tendency to replace diploids by polyploid cultivars. Molecular cytogenetic techniques such as genomic in situ hybridization (GISH) and fluorescence in situ hybridization (FISH), along with other techniques, have greatly facilitated our understanding of the modes of origins of polyploids. Because the bulbous crops generally have large chromosomes, the parental genomes, individual chromosomes, as well as intergenomic recombinant chromosomes, can be accurately identified in the interspecific hybrids and their backcross progenies. This enables an assessment of the potential genetic variation that might occur in the progenies as well as the extent of introgression. Although the superiority of polyploids as compared to their diploid parents is beyond doubt, the actual explanation for their superiority is still elusive. Of the several explanations, chromosome dosage, optimal amounts of 4C DNA values of the complements, heterozygosity and favourable gene interactions transmitted by the 2n gametes to polyploid progenies are some of the factors that might be considered at present. Undoubtedly, more studies on the bulbous ornamental crops using molecular techniques might be rewarding.