Flower formation in<i>Chrysanthemum morifolium</i>: the influence of light level

Abstract

SummaryGroups of chrysanthemum plants were transferred from a constant light level of 63 J cm-2 day-1 to higher levels at the start of short days, and at weekly intervals thereafter. The plants remained in their new light regime for one or two weeks before they were returned to the lower level. The results showed that flower initiation began earliest if transfer was made to a light level of 125 J cm-2 day-1 for two weeks at the start of short days. This benefit was retained throughout the subsequent period of growth at the lower light level and resulted in earlier flowering.The average level of visible radiation received in glasshouses in winter, even on the South Coast of England, is only 67 J cm-2 day-1 in the worst two months. The data suggest that if artificial light is used during this period to supplement the natural light and to raise the level of light energy received to at least 125 J cm-2 day-1 for the first two weeks of short days, earlier and more uniform flowering should . be obtained.Further experiments showed that transfer to a constant level as low as 31 J cm-2 day-1, following an initial two-week period at 125 J cm-2 day-1, did not stop the further development of flowers which were initiated by this treatment, and open flowers were obtained after 11 to 12 weeks of short days. The quality of such flowers, however, was poor, owing to the low level of energy received, namely 47 J cmr2 day-1 averaged over the whole growing period.