Studies on the retardation of chrysanthemum flowering by the spray of the growth substance. V

Abstract

1) This study was carried out to examine the effect of shading with marsh-reed screens, which was applied at different stages of flower development, on retardation of flowering, using three chrysanthemum varieties, Okayamaheiwa, Matsunohomare and Shintoa, and to observe the combined effect of reduced light intensity and spray of the plant regulators (NAA and gibberellin) on growth and flowering of Okayamaheiwa.2) Growth and flowering were retarded in Okayamaheiwa variety when the reduced light intensity of 25-30% was given prior to flower bud differentiation. However, no effect on growth was observed when the reduced light was given after flower bud differentiation, and the later the treatment was begun the smaller the effect on the development of flower buds. And, there was no effect of the treatment begun five days after budding on retardation of flowering. Different results were obtained in the varieties, Matsunohomare and Shintoa. The flower bud development was retarded in them even if the treatments were started after the initiation of flower buds.3) Growth and flowering were retarded heavily in the variety Okayamaheiwa under the very reduced light intensity of 6-7%, while no effect was observed when the treatment was started 15 days after budding.4) Application of NAA (50ppm), gibberellin (50 ppm) or combined solution of NAA (50ppm) and gibberellin (50ppm) was made under different light intensities. NAA or the combined solution showed greater effect on flowering retardation under the reduced light intensity of 25-30%, while gibberellin alone gave no influence in spite of the reduced light intensity.5) Growth was promoted, but budding received no influence under the reduced light intensity of 33-38%, even when the treatment was started prior to the flower bud initiation. Under this light intensity, the foliar spray of NAA or the combined solution of NAA and gibberellin resulted in a remarkable inhibitory influence on flower bud development. Application of gibberellin showed a slight promotion of budding under the natural light intensity, while it showed no effect under the reduced light intensity.6) No marked effect was obtained by the spray of the plant regulators on the rate of growth.7) The number of ray flowers was decreased under the reduced light intensity.