Application of physiological and biochemical indices as a screening technique for drought tolerance in wheat genotypes

With a view to understanding the traits which can be used as a quick criteria for drought tolerance, field and laboratory experiments were used to evaluate nine wheat ( Triticum aestivum L.) genotypes; seven local varieties with two introduced genotypes from International Center for Agricultural Research in the Dry Areas (ICARDA). The field experiment was grown under two water regimes ( stress and non stress treatments). The stress treatment induced by withholding irrigation after emergence and giving two supplementary irrigations, one after 60 days post-sowing and the other after 90 days post-sowing and non stress ( well-watered). Combined analysis of variance over two seasons showed highly significant differences among wheat genotypes in all the studied traits and water stress decreased them significantly. The superior genotypes 1,2 and 6 which gave higher relative water content (RWC) accumulated more free proline ( Pro) and had lower drought susceptibility index ( S) values, whereas genotypes 3, 4 and 9 had the lowest RWC, Pro accumulation and had the highest S values. Indicating that accumulated Pro acts as a compatible solute regulating and reducing water loss from the cell during episodes of water deficit. High RWC and Pro over-accumulation were recognized as beneficial drought tolerance indicators and may be used as selection criteria in wheat breeding program. Effects of drought stress in laboratory experiment were induced by polyethylene glycol ( PEG) ( 0, 15 and 25%, with three replicates) and applied on germination of wheat genotypes seeds. The PEG induced a drop in the shoot, root biomass and coleoptiles length which was the greatest in genotypes 3, 4 and 9, while the decrease in genotypes 1, 2 and 6 was little under the various levels from PEG. The variability of leaf-proteins was analyzed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). It is concluded that leaf protein profiles could be useful marker in the studies of genetic variation and classification of adapted cultivars under control and stress conditions.