Phenotypic and genome size changes (variation) in synthetic tetraploids of daylily (Hemerocallis) in relation to their diploid counterparts

Tetraploids of daylily have taken a leading position among the daylily cultivars due to desirable traits such as vigorous growth and flowers with more intense colour. In our previous studies, several tetraploids of daylily cultivars 'Blink of an Eye' and 'Berlin Multi' were obtained using in vitro techniques with different antimitotic agents (colchicine, oryzalin, trifluralin, and amiprophos methyl). The purposes of this study were to evaluate changes in daylily tetraploids in relation to their diploid counterparts and to assess variation among diploids and tetraploids derived from genetically homogenous plant material treated with antimitotic agents. In the first year of the ex vitro cultivation, growth of tetraploids was poorer in comparison with diploids, but in the second year, tetraploid growth was much more vigorous. Compared to diploids, in tetraploids of both cultivars percentage of flowering plants was lower, flowering was delayed by 8 days and 1 month in 'Blink of an Eye' and 'Berlin Multi', respectively, and bud number per scape was lower by approximately 20 and 40 %, respectively. Tetraploid leaves and flowers of both cultivars were significantly larger, chlorophyll concentration index was higher by approximately 40 %, and stomata were longer by 35 %. In 'Berlin Multi' tetraploids, inflorescence stems were shorter by 20 %. In 'Blink of an Eye', variation in flower colour tone and shape and stamen malformation rate was detected both within the unconverted diploids and tetraploids but was more evident in tetraploids. In both cultivars, variation was also found in the nuclear DNA content, which ranged in diploids and tetraploids, respectively, 8.02-8.53 and 16.01-17.13 pg in 'Berlin Multi' and 8.28-8.71 and 15.93-17.36 pg in 'Blink of an Eye'. Since the variation, while less evident, also occurred in the diploids (regenerated from the antimitotic treated material), we suppose that these variations could be due to antimitotic agents that can induce not only chromosome doubling but also chromosomal and gene mutations. The extent and character of these changes can be related to parental genotype and/or antimitotic agent. Further research is required at the cytological and molecular level to explain the character of changes, epigenetic and/or genetic.