Investigation Effect of Drought Stress Ievel of PEG 6000 on Seed Germination Principle and its Relation With Drought Tolerance Index in Promising Lines and Cultivares of Bread Wheat (Triticum. aestivum L.)

In order to investigate the effects of drought stress levels on seed germination and its related traits with drought stress indices, an experiment was conducted in two sparate phases with 40 wheat genotypes under field and laboratory condition for germination stages with 4 level of the polyethylene glycol (PEG) concentrations. The experimental design was factorial based on a randomized complete block design with three replications. The measured traits were radicle length, stem length, radicle length to shoot length ratio, germination rate and germination percentage. The experiment in the filed stage was conducted with 3 replications under both normal and drought stress condition. Result of the laboratory experiment indicated that effects of stress on traits were significant. Also different between genotypes were significant. The highest germination rate and percentage was measured under normal condition with 4.22 days and 79.9% respectively. Moderate level of stress (-3 bar) of drought stress had no significant effect on radical, coleoptile, stem length and dry weight, but reduced the germination rate significantly. In high level of drought stress (-6 bars) all traits were decreased significantly expect radicle length and radicle length to shoot length ratio. In control condition, positive significant correlation was observed between all traits measured in (-6 bars) under laboratory condition, with grain yield and drought tolerance indices. But in slight (-3 bars) and severe stress dry weight and radicle length had positive significant correlation with grain yield. Grain yield of genotypes showed significant differences under field study in both normal and stress condition. Results of correlation between grain yield and drought stress indices showed that stress tolerance index (STI), mean productivity (MP) and geometric mean productivity (GMP) were suitable for the genotypes identification with highest seed yield in both normal and stress conditions according to correlation coefficients between seed and its related traits and grain yield such as correlation coefficients between drought stress indices and grain yield in both normal and stress conditions, revealed that the genotypes number 39 (WS-82-9), 38 (DN-11), 22 (mbul/Alamo/M-73-18) and 25 (Alvd/Aldan/las/3--) were determined as the most tolerant and number 5 (Gasspard) and 40 (Mahdavi) were detected as the most susceptible cultivars for drought stress.