Identification of high long-day leaf number cultivars and prevention of premature budding by cold pre-treatment for fine control of flowering in summer-to-autumn-flowering chrysanthemum (Chrysanthemum morifolium Ramat.)

Abstract

SummaryWhen maintained continuously under long-day (non-inductive) photoperiodic conditions, chrysanthemum (Chrysanthemum morifolium Ramat.), a short-day plant, eventually initiates flower buds. This floral initiation is termed ‘premature budding’ in commercial chrysanthemum production. Premature budding, which reduces cut-flower quality, is often observed in summer-to-autumn-flowering cultivars. The timing of flower initiation under non-inductive photoperiods depends on the number of leaves that a plant has formed below the terminal flower bud. This leaf number indicates whether a cultivar will form flower buds prematurely during a non-inductive photoperiod. Two summer-flowering, ten summer-to-autumn-flowering, and six autumn-flowering chrysanthemum cultivars were grown under controlled conditions to measure the number of leaves produced under a non-inductive photoperiod with a night-break. The average number of leaves per plant ranged from 13.8 for ‘Tasogare’, to 69.1 for ‘Furamu’. These data can be used to identify cultivars that will exhibit minimal flower-bud formation under night-break conditions. The numbers of leaves were greater in plants subjected to a 12-week cold treatment prior to planting, suggesting that premature budding could be inhibited by a prolonged cold pre-treatment. We also examined whether the cold treatment of stock plants was an effective means to prevent premature budding. The incidence of premature budding was reduced in rooted cuttings obtained from cold-treated stock plants of the summer-to-autumn-flowering cultivars ‘Nagano Queen’, ‘Ariesu’, ‘Sei-un’, ‘Oruka’, and ‘Floral Yuka’. Without a cold treatment, cuttings from these cultivars showed premature budding. This result suggests that a prolonged cold pre-treatment of stock plants could prevent both premature budding and reduced cut-flower quality in summer-to-autumn-flowering chrysanthemum cultivars.