Morphological Changes in the Shoot Apex Predicts Anthesis Time in Chrysanthemum morifolium

We investigated the relationship between shoot apex morphology and anthesis time in five cultivars of Chrysanthemum morifolium flowering in summer. Fluctuating weather conditions in nature make stable production of agricultural crops difficult. The timing of floral induction and flower formation are determined by environmental factors such as day length and temperature. Although genetic analyses using model plants have provided a lot of knowledge regarding the molecular mechanism of flowering, it is difficult to apply to agricultural plants growing in the field because of the inconstant weather and lack of molecular analysis tools of many farmers. A simple morphological marker that enables farmers to predict anthesis time is useful for stable production of field-grown crops. We examined the shoot apex morphology of five Chrysanthemum morifolium cultivars weekly. Measurement of the shoot apex diameter by image analysis software showed that the shoot apex enlargement can be separated two phases, early slow-growth and later rapid-growth phases. We defined the developmental stages of the shoot apex in C. morifolium and found that the diameter of the shoot apex and developmental stages had a proportional relation. Each cultivar had a different inclination in an approximation straight line in the later rapid-growth phase. Comparison of the shoot apex morphology and weather records revealed different responses to the ambient temperature among the cultivars. The data suggest that weekly observation of the shoot apex makes it possible to characterize the cultivar and can be used to predict anthesis time. This is useful as a simple morphological marker for stable production of C. morifolium grown outdoors.