THE EFFECT OF VARIOUS WAVEBANDS OF SUPPLEMENTARY RADIATION ON THE PHOTOPERIODIC RESPONSE OF CERTAIN PLANTS

Abstract

3 long-day plants, Callistephus chinensis, var. Heart of France, Scabiosa atropurpurea, var. Azure Fairy, and Spinacia oleracea, var. Nobel, and 4 short-day plants. Soya max, var. Mukden, Xanthium pennsylvanicum, Salvia splendens, var. Fairly Tall, and Tithonia speciosa were grown in subirrigation nutrient soln. culture. They were given natural short winter days and days lengthened to 24 hrs. by blue radiation (4047 and 4358 A), yellow-green (5770 and 5791 A), and red (6400-9000 A) of approx. 100 ergs/cm.2/sec, and blue of 400 ergs/cm.2/sec. All the long-day plants set macroscopic flower buds under red and yellow-green radiation; spinach and Scabiosa failed to set buds under blue or the short-day condition. All the short-day plants flowered under the short-day condition and blue radiation, but failed to set buds under either red or yellow-green. The red radiation caused an increase in dry matter in all the plants studied. In some cases, the yellow-green and blue radiations also brought about an increase in total dry wt. Except with Scabiosa, the red and yellow-green caused a decrease in the % of dry matter. The higher blue radiation also caused a decreased % dry matter with spinach, Xanthium, and soybean. Height was increased under the red and yellow-green with all the plants, the increase being much greater with the long-day than with the short-day plants. Top-root ratio increased under the longer wavebands in all cases with the exception of Xanthium where the ratio decreased. With aster, spinach, and soybean, the ratio was increased also by the blue but not to the extent occurring under the red. Leaf area for aster and soybean was increased progressively from the short day through the blue, high intensity blue, yellow-green, and red. Evidently it is the longer wavelengths of the visible spectrum that are primarily effective in producing the flowering and vegetative effects secured under long-day treatments with both the long- and short-day plants used. The initial photo-chemical step appears to be similar for all the plants tested.