Chromosome constitution and nuclear DNA content of Phalaenopsis hybrids

Phalaenopsis is one of the most popular potted plants in the horticultural market because of the colorful and long-lasting flowers. In Phalaenopsis, interspecific hybridization between sections or subgenera has long been used for breeding cultivars with novel traits. Considering the diverse genome size and karyomorphology in Phalaenopsis species used in breeding, a study of genome size and chromosome composition would be crucial to provide fundamental knowledge for Phalaenopsis breeding. In this study, we characterized the chromosome composition of 60 representative Phalaenopsis cultivars of various colors and types commonly used in breeding programs. Our genome size analyses indicated that calculating the ploidy of Phalaenopsis cultivars based on their C-value data is difficult because of the diverse genome sizes of the parental species and different genome introgression of the parental species used for hybrids. Most Phalaenopsis cultivars are polyploid, and a few cultivars possess hyperand hypoploid chromosome numbers. Analysis of chromosome composition of these cultivars suggested that the occurrence of unreduced gametes played a significant role in polyploidization of Phalaenopsis cultivars during breeding. Chromosomal data also demonstrated different chromosome introgression of parental species in novelty and harlequin types of cultivars. The genome size and chromosomal data provided in this study are important for breeders to assist in planning efficient Phalaenopsis breeding programs.