Differences between two grain sorghum genotypes in adaptation to drought stress. III. Physiological responses

Abstract

A sorghum hybrid (E-57) giving a higher yield under rain-fed systems of production was studied to examine the physiological basis of this effect. A comparison was made with another hybrid (TX-671) with similar maturity. E-57 was able to maintain stomatal opening to a lower leaf water potential than TX-671 because of its greater capacity to osmoregulate. In E-57 osmotic potential declined due to active solute accumulation, thus maintaining turgor as leaf water potential declined to - 2.0 MPa. In contrast, TX- 671 could only maintain this adjustment to - 1.4 MPa. The differences in osmoregulation were associated with maintenance of leaf area, water extraction and possibly root growth by E-57. This indicated that osmoregulation enabled photosynthesis to continue and that a significant amount of the resultant assimilate may have been diverted to root growth.