The Effects of Light Intensity at Different Stages in Flower Initiation and Development of Chrysanthemum morifolium

Abstract

Rooted chrysanthemum cuttings were raised in growth cabinets at a ‘standard’, constant light level of 125 J cm −2 day −1 and were induced to flower by giving daily cycles of 8 h light followed by 16 h of uninterrupted darkness. Samples were transferred at weekly intervals to either a higher light level of 375 J cm −2 day −1 or a lower light level of 31 J cm −2 day −1 where they remained for 2 weeks before they were returned. It was shown that receptacle formation normally began in the second week of inductive short-days (short-days 8–14) and floret initiation in the third week (short-days 15–21) when plants were grown throughout in the standard environment Receptacle formation was delayed and significantly more leaves were formed below the flower if short-days 8–14 were spent in low light. Transfer to high light for this period had no apparent effect Transfer to low light at the onset of floret formation retarded their further development and reduced the total number of florets formed Transfer to high light at this stage slightly increased the number of florets formed but did not appear to affect their development. The data for stage of flower development after 11 weeks of growth reflected these effects of light level on the early development of the apex The total and flower dry weights of plants transferred to low light for 2 weeks were generally smaller than those of plants which had remained throughout in the standard condition High light only produced lasting increases in weight when the transfers were made during the later stages of growth. Most of the additional dry matter formed at this time was accounted for in increased flower weight The correlation between flower development and flower weight ratio previously found under constant environments also applied to transferred plants except when the light level was changed for the last 2 weeks of growth; relatively high values of flower weight ratio were then obtained by transfer to high light and relatively low values by transfer to low light.