Effects of Irradiation Time and Light Intensity for Night-break Using Compact Self-ballasted Fluorescent Lamps of Red Light on the Flowering and Spray Formation of Spray-type Chrysanthemums

The effects of the irradiation time and light intensity for night-break using compact self-ballasted fluorescent lamps of red light on the flowering and spray formation of spray-type chrysanthemums were investigated with two types of cultivar, the autumn-flowering cultivar ‘Lineka Dark’ and the summer-to-autumn-flowering cultivar ‘Koiaromu’. Compact self-ballasted fluorescent lamps of red light (21 W), which have rich red light with a peak wavelength of 660 nm developed as a trial model, and incandescent lamps (75 W) as a control were used for light sources. The minimum photosynthetic photon flux density (PPFD) for the inhibition of flower bud initiation, resulting in normal spray flower formation, by irradiation with the compact self-ballasted fluorescent lamps of red light was smaller than that by irradiation with incandescent lamps under the same night-break time. In the autumn-flowering cultivar, the minimum PPFD for the inhibition of flower bud initiation was identified under 1-h night-break treatment with compact self-ballasted fluorescent lamps of red light, whereas no value was indicated with incandescent lamps. In the autumn-flowering and summer-to-autumn-flowering cultivars, as the product of the minimum PPFD and irradiation time was almost constant by irradiation with compact self-ballasted fluorescent lamps of red light, it is considered that the minimum PPFD is inversely related to the irradiation time on minimum fluence. These results indicate that the product of the minimum PPFD and irradiation time can be explained by the Bunsen-Roscoe law of reciprocity.