ABSCISIC ACID ACCUMULATION AND PHYSIOLOGICAL INDICES IN RESPONSES TO DROUGHT STRESS IN WHEAT GENOTYPES
The aim of this study to determine how tolerant wheat genotypes to drought stress. Three drought tolerant Triticum aestivum L. genotypes; Rizgary, Sham-6 and Abu-Ghraib compared with three drought-susceptible; IPA95, Tammuz-2 and IPA99 under water deficit 20% WHC (Water Holding Capacity). ABA level, drought related parameters; shoot and root dry weights, root and shoot ratio. As well as Leaf relative water content (LRWC %), membrane stability index (MSI %) and proline content determined in the leaves. A considerable increase of ABA noted in drought tolerant as compared to susceptible genotypes under drought stress condition. That is led to reduction in shoot dry weight in Rizgary, Sham-6 and Abu-ghreb; 2.71, 2.70 and 2.62 g/plant respectively. In addition they adapted to proliferate larger root system with 2.63, 2.16 and 1.71 g/plant respectively. Consequently the ratio of root: shoot increased; 0.98, 0.80 and 0.66. Rizgary, Sham-6 and Abu-ghreb retained a significantly higher LRWCs %; 79.81, 77.17 and 78.53 % respectively at 20 % WHC as compared to susceptible genotypes. Membrane Stability Index (MSI %) decreased significantly at lower rate in tolerant genotypes; 65.69, 67.28 and 67.18 % respectively. As well as proline increased as an osmoticum to reduce the harmful effect of drought on plant cell in resistant genotypes; Rizgary, Sham-6 and Abu-ghreb; 0.71, 0.72 and 0.61 mg g-1 D. in sequence as compared to sensitive genotypes. The tolerant genotypes have stronger adaptability mechanisms to cope water scarcity as compared to susceptible genotypes.