Effects of Shading the First Leaf on Growth of Barley Plants

Plants of barley were grown under controlled conditions and the first or second leaves covered with tubular shades thus reducing the light intensity at the leaf surface to low levels. Expansion of the shaded leaves was not prevented, but appearance of the next leaf but one and all subsequent leaves on the mainstem was delayed by up to 3 days. Primordia of the first four leaves were present in the dry grain. Shade treatment delayed slightly the initiation of the eighth and subsequent leaves and transition to the double ridge stage at the mainstem apex. Shading the first leaf caused a temporary reduction in the rate of dry-matter increase of plants, but after 14 days the rate was similar to that of control plants. Smaller effects were found when the second leaf was shaded. Dry-matter production followed two logarithmic phases in the period prior to awn emergence, and rates for the whole plant and for plant parts were similar for control and shaded plants. Thus, apart from the initial perturbation, shading had no effect on growth in terms of rate of dry-weight gain. Shade treatment did not affect weight per grain or numbers of grain per ear, but over-all yield of grain was significantly reduced since shading delayed the appearance of tillers and also reduced the number of tillers bearing grain. The effect of shade was especially marked on tillers originating on primary tillers. Similar qualitative effects on tiller development were found in an experiment on wheat.