BIOCHEMICAL AND PHYSIOLOGICAL-RESPONSES OF 9 SPRING WHEAT (TRITICUM-AESTIVUM) CULTIVARS TO DROUGHT STRESS AT REPRODUCTIVE STAGE IN THE TROPICS

Wheat crops are most likely to experience drought after anthesis under most growing conditions in the humid tropics. Nine spring wheat cultivars (seven from Nepal and two from the Philippines) grown in pots were exposed to 0, 4, 8, 12, and 16 days of water stress starting at 50% head emergence under glass house conditions. The experiment was conducted under dry tropical environment at Los Banos, Philippines. Concurrent measurement of leaf water potential (LWP), upper (R(u)) and lower (R(l)) leaf surface stomatal resistance on the flag leaf, soil water potential (SWP), nitrate reductase activity (NRA) and free proline determination were made at the end of the 4, 8, 12, and 16 days of withholding irrigation. NL 370, NL 496, NL 292 and Siddhartha exhibited a drought avoidance mechanism by maintaining relatively higher LWP under water stress. Stomatal resistance (R(s)) increased more in the lower than in the upper leaf surface under drought stress. Lerma 52, Triveni, and Trigo 1 had sharp rise in their R(s) even at mild stress in contrast to other cultivars which had a gradual increase in R(s) as drought progressed. Early maturing cultivars, namely: NL 496, NL 370, Siddhartha and NL 292 had higher NRA than late maturing cultivars under stressed conditions. NRA decreased with increase in drought conditions. Leaf proline increased as the drought progressed. Leaf proline had significant correlation with LWP (r = -0.80**), SWP (r = -0.48**) and R(s) (r = 0.56**). NL 496, NL 370, NL 292 and Trigo 2 had higher SWP under different drought durations. Considering the responses under different drought durations, early maturing cultivars, namely: Siddhartha, NL 292, NL 370 and NL 496 are classified as drought resistant and mid as well as late maturing cultivars namely Trigo 1, UP 262, Lerma 52 and Triveni as drought susceptible cultivars.