Plant Maturity and Vernalization Affect Flowering in Dianthus japonicus Thunb.

Abstract

Dianthus japonicus Thunb. (D. japonicus) is a biennial with promising floricultural traits, but its commercial appeal is limited by the long time between propagation and flowering. We assessed the effect of juvenile phase, vernalization, and photoperiod on flowering of D. japonicus. Plants were grown in a plug until they had acquired nine, 14, or 16 leaf pairs, and then exposed to a vernalization period of 0, 3, 6, or 12 weeks at 5°C. At the end of the vernalization period, plants were transferred to either long-day treatment or short-day treatment for 10 weeks. In D. japonicus, the numbers of new nodes and leaves were correlated with the vernalization period. Plant height was correlated with the number of leaf pairs. As the vernalization period lengthened, the plants produced more nodes and leaves regardless of their growth stage. The maximum plant height increase was over 24.7 cm in the plants that had 16 leaf pairs at 10 weeks after the start of the photoperiod treatment, regardless of the photoperiod. Plants with 14 or 16 leaf pairs and a vernalization period of 12 weeks flowered regardless of photoperiod treatment. None of the plants that had been vernalized for less than 12 weeks flowered or produced flower buds. We noted a significant difference in the flowering response among plants based on the number of leaf pairs and vernalization period. We conclude that D. japonicus plants must form 14 to 16 leaf pairs before they can respond to vernalization and require at least 12 weeks of vernalization before flowering. This species has a qualitative response to vernalization and is day-neutral.