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Daylilies (Hemerocallis hybrids) are one of the most important ornamental perennial plants nowadays used in gardens and parks. Flower forcing of daylily hybrids in early spring or autumn could broaden their application and marketing possibilities. There is very limited data available on this topic. In our early flower forcing experiment ‘Moonlit Masquerade’, for late flowering ‘Mary Todd’ were used. During the study we have sought answer for the following questions: the amount of growing degree-day required for flower stalk induction and for flowering and whether the day length has an effect on these values or not. In the early flower forcing experiment 4 treatment groups were established: plants of the first treatment group were placed in a moderately heated greenhouse without assimilation lighting. The second treatment group were placed in the same greenhouse but artificial light was used to extend the day length for 15 h. The examination of the third group happened in a plant growth chamber with 15 h day length and a daily average temperature of 20°C was provided for the plants, and there was also a control group in open field environment. For late flowering the bare rooted dormant plants were stored in refrigerator and were planted to open-field in late spring and summer. During the experiments temperature data were logged and plant morphology characteristics were measured in two following year. According to the results it can be stated that the differentiation of inflorescence is not depending on the day length rather on the leaf surface area. Growing degree-day is the main factor which influences the speed of inflorescence development once it has already differentiated, so temperature is the key factor in flower bud opening and it also defines the number of the developing flower buds. The data from late flowering experiment show that bare-rooted daylily plants are suitable for long-term cold storage and this method offers late season flower forcing.

Daylilies are very valuable ornamental plants. Their various colors and resistance to undesirable conditions make them useful in perennial landscapes such as flower borders, gardens and road green belts. The natural distribution of daylilies covers East and Southeast Asia and mainly China. The nocturnal blooming species Hemerocallis citrina is not only used as Chinese traditional edible food but has also fragrance and produces large amount of flowers. Every year many new cultivars are released with different flower colors, shapes and sizes. However, the lack of knowledge on the heritability of traits limits the efficiency for the selection of cultivars with desirable characteristics. This study aimed to estimate genetic parameters and genetic correlations among diurnal and nocturnal daylily parents and their hybrids and to select new cultivars with fragrance and large amount of flowers. Crosses were performed among 3 nocturnal blooming (NB) species or cultivars (H. lilio-asphodelus, H. citrina, H. ‘April flower’) and 4 diurnal blooming (DB) cultivars. In total 386 F1 hybrids were obtained. In the third and fourth year, plant height, leaf length and width, number of flower buds per stem, stem length and the opening and closing times were recorded. High heritability estimates were obtained for plant height, leaf length and width and stem length. A new nocturnally flowering hybrid with fragrance has been selected and registered. The results indicated that the estimates of average heritability of families were superior to the estimates of individual heritability for most characteristics evaluated. The flower opening and closing time are regulated by different nucleus genes. This research will provide guidance for further hybridization in daylily.

Introduction of new cultivars of daylilies (Hemerocallis spp.) into commercial production requires effective methods of propagation. The quality of microcuttings, derived from in vitro multiplication can be influenced by growing conditions during acclimatization. The aim of the study was to accelerate growth and improve quality of plantlets of two cultivars of daylilies ‘Fire Agate’ and ‘Polish Truffle’. Two concentrations of CO2 (350 and 1000 µmol mol-1), two irradiance levels (50 and 150 µmol m-2 s-1 PPFD) and two growing media (peat with perlite and pear with coir, 3:1 v/v) were tested during 8 weeks of acclimatization. Enrichment with CO2 of and higher irradiance level significantly improved growth of both daylily cultivars. Plantlets of ‘Polish Truffle’ grown at higher irradiance level had more leaves with higher length, irrespectively of CO2 enrichment. Longer leaves had plants grown in medium consisted of peat and perlite. In case of ‘Fire Agate’ the number of leaves was not affected by any experimental factor but leaves of plants grown at higher irradiation level were 12% longer. Fresh and dry weight of aerial part and root system of daylilies were significantly higher when plants were grown with CO2 enrichment and higher irradiation level than plant grown at control conditions. Better root system with longer roots of both cultivars had plantlets grown in medium consisting of peat and perlite than in peat and cocopeat (coir).