Osmotic Adjustment and Growth of Barley Genotypes under Drought Stress

Osmotic adjustment is receiving increasing attention as a probable component of drought resistance in crop plants, including barley ( Hordeum vulgare L.). This work was done to study a possible association between osmotic adjustment and growth under drought stress. Twenty‐six diverse barley genotypes were grown in nutrient solutions in the growth chamber. Drought stress was imposed by adding polyethylene glycol 6000 to the nutrient solution producing a −0.54 MPa solution water potential as compared with controls of pure nutrient solution with a −0.02 MPa of solution potential. Percent growth reduction by drought stress was calculated from growth rates measured under stress and in the controls. Osmotic adjustment was calculated as the difference in osmotic potential at full turgor between stress and controls. Leaf water potentials of genotypes grown under drought stress ranged from −1.37 to −1.51 MPa, but did not differ significantly. For the same leaf water potential, genotypes differed significantly in osmotic adjustment which ranged from −0.17 to 0.46 MPa. Growth reduction by drought stress differed significantly among genotypes with a range of 78.1%. Growth reduction by drought stress was negatively associated with osmotic adjustment across genotypes ( r = −0.80). The association was nonlinear, indicating that growth reduction decreased only as osmotic adjustment increased to about 0.2 MPa or more. These results suggest that induced osmotic adjustment under drought stress may be an important component of drought resistance in barley growth, and it should be evaluated when all genotypes are subjected to the same leaf water status.