Abstract
Endoreduplication refers to reduplication of chromosomes in the absence of chromatin segregation and cytokinesis. It is a common process for plants and particularly among angiosperms. Phalaenopsis is among the most beautiful of all orchids. Taiwan Sugar Research Institute (TSRI) has collected 27 wild species for the improvement of Phalaenopsis culture and for the production on a commercial scale. The techniques of interspecific hybridization and chromosome doubling are often applied for breeding in Phalaenopsis. Accurate estimations of nuclear genomic sizes are important for plant genome analysis and understanding the relationship of nuclear DNA content to plant physiology and ecology. Our studies showed that the 2C-values of Phalaenopsis species correlate with their chromosome numbers. Most Phalaenopsis species have 38 chromosomes with large, medium, and small sizes in length. Genome size of Phalaenopsis is related to its chromosome size. Phalaenopsis containing all or a portion of large size chromosomes usually possesses large genome size. Polyploidy was observed in all Phalaenopsis we examined, although the distribution in tissues varied. In most species, 8C is the major population and maintained at a constant level during leaf development. The ploidy levels in different leaf proportions of W09-51 seem to have a pattern. The distal portions of a leaf tend to have small proportion of 16C nuclei and larger proportion of 8C nuclei than the proximal portions. The population of 4C nuclei is the major proportion of flowers and roots, however, the population of 8C nuclei is the major proportion of leaves.