REGULATION OF CHRYSANTHEMUM GROWTH BY SPECTRAL FILTERS

The role of light quality and quantity in regulating growth of vegetative Dendranthema X grandiflorum (Ramat.) Kitamura was evaluated using CuSO4 solutions and water (control) as spectral filters. Copper sulfate filters increased the red (R) : far-red (FR) and the blue (B) : R ratios (R = 600 to 700 nm; FR = 700 to 800 nm; B = 400 to 500 nm) of transmitted light. Photosynthetic photon flux (PPF) under 4%, 8%, and 16% CuSo4 filters was reduced 26%, 36%, and 47%, respectively, from natural irradiance in the greenhouse, which averaged almost-equal-to 950-mu-mol.m-2.s-1. Control treatments were shaded with Saran plastic film to ensure equal PPF as the corresponding CUSO4 chamber. Average daily maxima and minima were 26 +/- 3C and 16 +/- 2C. At the end of the 4-week experimental period, average height and internode length of plants grown under CuSO4 filters were almost-equal-to 40% and 34% shorter than those of plants grown under control filter. Reduction in plant height and internode length was apparent within 1 week after the beginning of treatment. Total leaf area (LA) was reduced by 32% and leaf size (LS) was reduced by 24% under CuSO4 filters. Specific leaf weight (SLW) was higher under CuSO4 filters than for the controls. Irradiance transmitted through CuSO4 filters reduced fresh and dry leaf weights by 30%. Fresh and dry stem weights of plants grown under CuSO4 filters were 60% lower than those of controls. Relative dry matter accumulation into leaves was increased in plants grown under CuSO4 filters while it was reduced in stems. A single application of GA3 before irradiation partially overcame the height reduction under CuSO4 filters, suggesting GA biosynthesis/action may be affected by light quality. Our results imply that alteration of light quality could be used to control chrysanthemum growth as an alternative method to conventional control by chemical growth regulators. Chemical names used: gibberellic acid (GA)