Effects of Daylength and Temperature on Capitulum Initiation and Development of Garland Chrysanthemum (Chrysanthemum coronarium L.).

Abstract

Effects of daylength and temperature on capitulum initiation and development of garland chrysanthemum (Chrysanthemum coronarium L.) were investigated. Four cultivars different in earliness to flower were used. When the cotyledon expanded, the seedlings were transferred to phytotron for 75 days at 15, 20, 25 and 30°C under short day (10 h) or long day (16 h), respectively. Capitulums of “Hakata kairyo chuba” were initiated at 15 and 20°C under long day, 30 days after the treatment. The floral stages at 15 and 20°C were late floret-forming and early floret-forming stages, respectively. Fortyfive days after the treatment, floral stages at 15 and 20°C under long day further developed to early corolla-forming stages. Sixty days after the treatment, capitulums at all temperatures under long day were initiated and those floral stages in plots 15, 20, 25 and 30°C were late corolla-forming stage, late corolla-forming stage, early corolla-forming stage and late involucre-forming stage, respectively. Capitulums of “Otafuku” 60 days after treatment, and of “Kabuhari” and “Oba” 75 days after treatment were initiated at 15°C under long day, but they were not initiated under short day. In the case of “Hakata kairyo chuba” whose capitulums were initiated in any temperature, the lower the growing temperature, the fewer the number of nodes from cotyledon to capitulum. From these results, it was deduced that capitulum initiation of garland chrysanthemum was induced by long day, and the lower the growing temperature, the more it was promoted.