Increasing the planting densities has been used as an effective approach for increasing crop yield per unit land area.However,plants compete with neighboring vegetation for light when planting at high densities.The shade of nearby vegetation reduces the ratio of red to far-red light,triggering a series of responses known collectively as shade avoidance syndrome (SAS): including accelerated elongation of stems,elevated leaf angles to the horizontal,reduced branching and early flowering.Although the SAS is thought to provide an adaptive advantage by increasing a plants ability to compete for limited resources in natural settings,it is often accompanied by reduced investments in other organs such as roots and leaf blades,and other potentially deleterious effects on a plants fitness,disease resistance,and yield.