Effect of Vernalization and Photoperiod On Flowering of Summer-Flowering Chrysanthemum

Chrysanthemum × morifolium ‘Qiyuetaohua’ is a ground-cover cultivar characterized by flowering in early summer in Beijing, China. To identify the photoperiod respond type and effectively utilize the early flowering trait, vernalization and photoperiod requirement for flower bud initiation and development were investigated, as measured by the days to the appearance of the bud and the terminal flower. All rooted cuttings were obtained from stock plants maintained in a vegetative state with long day (LD=14 to 16h photoperiod plus night interruption lighting, 2200 to 0200HR, using 400W incandescent lamps) and 24°C/20°C (day/night) temperatures. After rooting in sand for ten days with the same conditions as the stock plants, the treated rooted cuttings were vernalized for four weeks at temperature 3-7°C under LD condition and then transferred to three photoperiod treatments: short days (SD=black cloth pulled 0800/1600HR, providing 16h darkness), LD, natural day lengths during March to July at Beijing, China under greenhouse conditions with same temperature as stock plants. All summer-flowering ‘Qiyuetaohua’ treated by low temperature initiated flower buds and developed to anthesis at three photoperiod treatments. The mean days to flower bud initiation and development for vernalized plants at LD were 90 and 110 days, respectively, which showed 5 and 8 days earlier than that at SD. The mean days to flower bud initiation and development for vernalized plants at ND were 94 and 116 days respectively. However, the controlled plants (no vernalization) never developed any flower at any photoperiod treatments and remain vegetative for treated time. The results indicated that Chrysanthemum × morifolium ‘Qiyuetaohua’ is a day-neutral plant after vernaliztion and the early flowering phenotype under natural conditions could be attributed to low temperature at seedling stage.

Dr. Qixiang Zhang is the corresponding author.