Long-term Exposure of Mother Plants to Low Temperatures Delays Flowering of Japanese Autumn-flowering Chrysanthemum morifolium Ramat. ‘Jinba’ and ‘Seiko no Aki’

Abstract

To clarify the reason for delayed flowering of Chrysanthemum morifolium ‘Jinba’ cuttings propagated from mother plants during winter and spring production, the effects of growing temperatures of mother plants, and those of rooted cuttings grown in long days or short days, on vegetative growth and flowering in three autumn-flowering Chrysanthemum cultivars were investigated. Rooted cuttings of ‘Jinba’, propagated from mother plants exposed to two temperature regimes, were planted on December 26 and grown in two temperature regimes with long days. Plants with each treatment were then grown with short days using two temperature regimes. Flowering of rooted cuttings propagated from mother plants exposed to ambient low temperatures and grown at 25/10°C (7:00–19:00/19:00–7:00) with long days, and subsequently grown at 25/20°C or 25/10°C with short days, was delayed 11.4 and 14.4 days, respectively, compared with cuttings propagated from mother plants grown at a minimum temperature of 15°C. In a further experiment, the mother plants of three autumn-flowering cultivars were grown at four temperature regimes of 7°C, 10°C, 13°C, or 16°C for 50 days. Flower budding of ‘Jinba’ and ‘Seiko no Aki’ was delayed and the increase in leaf number (ILN) with short days was greater when mother plants were grown at 7°C or 10°C compared with plants grown at 16°C. In contrast, flower budding of ‘Shuho no Chikara’ cuttings propagated from mother plants grown at 7°C or 10°C was accelerated and the ILN decreased compared with those grown at 16°C. Clearly, delayed flowering of ‘Jinba’ and ‘Seiko no Aki’ was due to long-term exposure of mother plants to temperatures below 10°C. For suitable flowering of these cultivars, mother plants should be grown at a temperature exceeding about 15°C or the plants must be grown at a high temperature with long days for several weeks.