Seasonal variability in dormancy and flowering competence in Chrysanthemum: Chilling impacts on shoot extension growth and flowering capacity

Abstract

Chrysanthemum (Chrysanthemum morifolium Ramat.), an herbaceous perennial short-day plant, shows seasonality in its regulation of shoot extension growth and flowering capacity. To enhance our understanding of the physiological mechanisms of the seasonality in chrysanthemum, we investigated the changes in growth and flowering capacity, and the variation among cultivars. We also evaluated seasonal changes and the response to chilling in shoot extension and flowering capacity in chrysanthemum under controlled environmental conditions (20°C/15°C (light/dark) with a 12-h light period). Both shoot extension and flowering capacity under the subsequent growing conditions were regulated by the temperature of prior growing conditions. After the temperature increased over the summer, chrysanthemums showed a reduced ability for extension growth, and became more difficult to induce flowering. Chilling stimulated the extension growth of shoots when the meristems were entering a dormant state. Chilling had the opposite effect on two regulatory pathways involved in flowering capacity. A pathway related to the meristem dormant state was suppressed by exposure to chilling and induced flowering, and chilling activated an inhibitory regulator in parallel.