The effect of light stress originating from artificial partial shading and from selfshading caused by dense planting on the grain yield of five maize communities differing genotypically in earliness was studied. The sensitivity of plants in different growth stages to light stress was also investigated. Finally, the possibility of relieving the light stress by manipulating leaf inclination was tested in dense populations.
Increasing the density of a 5 plantsim 2 community by two and a half times seemed as detrimental for grain yield per plant as decreasing the community's illumination by half by shading. The relative performance of hybrids was changed both by artificial shading and by self-shading. No relationship was found between earliness and response to light stress nor between the response to artificial shading and the response to self-shading resulting from dense planting.
Both pot and field trials showed higher sensitivity of plants to light stress during the period 10--20 days after silking than during earlier periods.
Leaf erectness caused a small grain yield increase in the 10 plantsim 2 density when soil conditions were optimum. Under soil moisture stress it had no effect in the I0 plantsIm 2 density while it depressed yield at higher densities.