Tall Sorghum Plants Use Water More Efficiently Than Short Ones

Abstract

Increased plant height in sorghum has been associated with higher grain yield, but the underlying physiological causes of this relationship are not clear. One possible mechanism conferring this yield advantage of taller plants may be transpiration efficiency (TE), which is defined as the amount of biomass produced per unit of water transpired. To test this hypothesis, we grew plants of different height in mini lysimeters. Individual plants were grown in each lysimeter and weekly water use was determined until anthesis by weighing. After anthesis the plants were harvested and their biomass determined. The experiment included three pairs of isogenic lines, which differed at one of the possible four height loci. In addition, one of the pairs was used in hybrid combination. To account for potential interactions between height and tiller number, we also included a pair in which we removed tillers. There was a consistent trend for greater TE in the taller plants when all pairs were contrasted. This was only significant for one pair. De-tillering reduced TE in both the tall and short lines. In hybrid combination, both tall and short plants had relatively high TE. The tall hybrid plants had slightly greater TE (ns) than their short counterparts. The trend for higher TE in tall plants indicates that there may be opportunities to exploit taller sorghum in water-limited environments.