Some effects of far‐red irradiation and gibberellic acid on the growth of tomato plants

Abstract

SUMMARYThe effects of supplementary irradiation with a far‐red (FR)‐rich source on tomato plants raised in a growth room with warm‐white fluorescent tubes as the FR‐deficient, primary light source have been studied with and without the application of gibberellic acid (GA).Stem elongation in response to FR was independent of the amount of GA applied. Small but significant increases in fresh weight of leaflet laminae were sometimes obtained with GA. The optimal dose was about one‐eighth of the saturation dose for stem height. By combining the optimal daily GA dose for fresh weight laminae with FR, significant increases were obtained for fresh and dry weights of laminae and for stems plus petioles. The increase in lamina dry weight and leaf area amounted to 55 and 54%, respectively, with 15 days of treatment.It was concluded that GA and FR affect growth in distinct ways. FR may release a growth factor in both leaves and stems and GA probably substitutes for native gibberellins in stems.