Abstract
In a study of photoperiod response, twenty-two Japanese cultivars were compared with five cultivars normally grown in English all-year-round (AYR) schedules. Cultivars which naturally flower in Japan in September or earlier (early-flowering) reacted as quantitative short-day plants. Both flower bud initiation and development occurred more rapidly in short days (SD) as compared with long days (LD). Only the cultivar, Mezame, approached day-neutrality. Autumn and winter-flowering (late- flowering) cultivars responded as quantitative short-day plants, as did the English AYR cultivars. The early-flowering cultivars differed from the late-floweringtypes in that lateral flower buds and often the terminal flower buds developed to anthesis in LD.
The number of leaves produced in LD before terminal bud initiation by the early- flowering Japanese cultivars increased as natural flowering season became later. It seems likely, therefore, that long-day leaf number plays a part in determining natural flowering season in these cultivars. Similarly bud development time in SD may play a part in determining natural flowering season in the late-flowering cultivars.
At least two of the Japanese cultivars possessed characteristics which might usefully be incorporated into English AYR cultivars.
