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Lychnis (Caryophyllaceae) consists of about 30 species distributed throughout the temperate regions of the Northern Hemisphere, from East Asia to Europe. Many Lychnis spp. have high ornamental value and cultivated as pot or garden plants. In the present study, in vitro chromosome doubling of several Lychnis spp. was examined in order to widen their variability in horticultural traits. Initially effect of various spindle toxin treatments [100, 500 or 1000 mg l−1 colchicine (COL), 10, 20 or 50 mg l−1 oryzalin (ORY), or 1, 5, 10 mg l−1 amiprophos-methyl (APM)] of nodal segments of a triploid genotype of L. senno (3x) was investigated on survival of nodal segments and chromosome doubling in nodal segment-derived plantlets. Significantly higher percentage (75.0%) of surviving segments after spindle toxin treatment was obtained in 10 mg l−1 ORY treatment. Flow cytometry (FCM) analysis of leaf tissues showed that 9.4–13.8% of plantlets, which were derived from 10 to 20 mg l−1 ORY, or 5 mg l−1 APM treatments, were hexaploid (6x) or ploidy chimera (3x + 6x, 4x + 6x, 5x + 6x, 3x + 4x + 6x). The results obtained by FCM analysis were confirmed by chromosome observation in root tip cells. Thus 10 mg l−1 ORY treatment of nodal segments is suitable for in vitro chromosome doubling of triploid L. senno. Efficient chromosome doubling was also achieved in diploid L. fulgens (2x) and L. sieboldii (2x) by treating nodal segments with 10 mg l−1 ORY: 68.9–88.7% of nodal segments survived after ORY treatment, and 24.7–26.5% of plantlets derived from ORY-treated nodal segments were tetraploid (4x) or ploidy chimera (2x + 4x) in both species. These results indicate that the in vitro chromosome doubling method established for triploid L. senno may be applicable to a wide range of Lychnis spp. Tetraploid L. fulgens and L. sieboldii showed a compact plant form, and had thick stems and deep green leaves compared with the diploid mother plants. On the other hand, hexaploid L. senno showed very poor growth and died before flowering.

The Liliaceous perennial Tricyrtis hirta, sometimes called ‘Japanese toad lily’, has recently become popular as an ornamental for pot and garden uses. Highly embryogenic callus cultures of this plant predominately consisted of diploid cells but also contained tetraploid cells after 1 year of establishment. In the present study, plans regenerated from the 1-year-old embryogenic callus cultures were subjected to ploidy level analysis and morphological characterization following 3 years of cultivation. Among 37 plants examined, 28 kept the diploid level (2n = 2x = 26) but nine were tetraploid (2n = 4x = 52) as indicated by FCM analysis and chromosome observation. Although no morphological alterations were detected in 26 out of 28 diploid regenerants, the remaining two showed noticeable variations: both were severely dwarf and had crimped leaves and many malformed flowers. The tetraploid regenerants had several horticulturally attractive characteristics compared with the diploid controls, such as longer shoots, thicker stems, and larger flowers. Thus regeneration of tetraploid plants from 1-year-old embryogenic callus cultures offers a possibility to improve the horticultural value of T. hirta, although regeneration of trueness-to-type plants is essential for utilizing the cultures for micropropagation and genetic transformation.