Effects of Photoinhibition Induced by Water Stress on Growth and Yield of Grain Sorghum

Abstract

The significance of photoinhibition induced by water stress for growth and grain yield of sorghum was investigated by shading water-stressed plants for a 7-day period during panicle development. Thereafter, shading was removed, stressed plants were rewatered, and all plants were kept well-watered until physiological maturity.

Shading water-stressed plants for a 7-day period increased grain number and grain yield of primary heads by 10- and 13-fold, respectively. Even though plants were severely stressed, photoinhibition was only 20%. Moreover, reduction of photoinhibition by shading did not improve carbon supply to the developing panicle. Therefore, the response of grain yield to shading was attributed to a 15% higher average leaf water potential in shaded plants, which arose despite attempts to keep water status similar in shaded and unshaded plants.

The effect of water stress on the primary head was so severe that many plants produced secondary heads. The grain yield from these secondary heads compensated for the low yield of primary heads so that the total dry matter production and total grain yield of water-stressed plants were similar to those of unstressed plants. In view of the ability of this relatively determinate species to compensate for potential yield losses, as well as the mechanisms to avoid water stress, high temperatures and excessive absorption of light, it seems unlikely that photoinhibition induced by water stress will be of agronomic significance in grain sorghum.