الفهرس 
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Abstract
Most of the present study was carried out at laboratories of the Genetics Dept., Faculty of Agriculture, Minia University, Egypt. Experiments of the gene expression were carried out at the Biochemistry and Physiology Dept., School of Pharmacy & Food Science, Barcelona University, Spain. It aimed at discriminate between drought tolerant and susceptible wheat genotypes originated from a broad scope of diverse ancestors and attempting to identify expressions of some genes involved in drought tolerance in some of chosen wheat genotypes.
For this purpose several wheat genotypes were subjected to estimate drought tolerance potentialities throughout a series of PEG6000 (Polyethylene glycol) treatments in sequential pot experiments. Out of them, fifty-nine genotypes were chosen in a preliminary experiment in which seedlings were germinated on five concentrations [0.0% 5%, 10%, 15% and 20% (w/v)] of PEG6000 to determine their drought tolerance potentialities. Three physical traits [i.e. shoot fresh weight (SFW), root fresh weight (RFW) and root/shoot fresh weight(R/SFW)] of the 25 days old wheat seedling were calculated and statistically analyzed. Grouping of these genotypes into different categories was done according to their drought tolerant potentialities depending on the measurements of the SFW, RFW and R/SFW traits. Subsequently, genotypes following each category could be selected as reliable representatives for their corresponding group only if they comply with the proposed criteria. The results indicated that AL t12, DEB, NOOR, SNO and AUS genotypes were the most relevant genotypes to drought tolerant group (DTG), while ALt6, Alt1, CL A45, C426, SAH 1, GM9 and AG 3 genotypes were selected to represent drought moderate-susceptible group (DMG). Finally, drought susceptible group (DSG) seemed to be represented by AR, OKR, AB, MSR 2, DK 52 and ALt10 genotypes.
Further PEG6000 experiment was carried out on seedling plants of 18 chosen genotypes. They were germinated and treated with 0.0% 5%, 10%, 15% and 20% of PEG6000 for 15 days. Afterwards, analysis of SFW, RFW, R/S FW, chlorophyll content, proline content and molecular makers (RAPD and ISSR) were conducted. Moreover, expression of three drought-related genes in only 9 genotypes was also achieved to confirm the selected genotypes reliability and eligibility for being categorized in their corresponding groups.
Data of the SFW analysis revealed that genotypes representatives of DTG did not show any significant variations between 15% PEG treatment with those of the control plants, while both DMG and DSG representative genotypes exhibited significant variations between 15% PEG treatment. Moreover, DSG representative genotypes were the most severely affected under drought condition. The RFW and R/S FW analysis indicated that the impact of PEG treatment on this trait is less than the genotype impact. The results also showed no significant variation in almost all studied genotypes when PEG treatment is compared to the control plants. Data showed that RFW and R/S FW should not be taken as a significant parameter regarding drought-tolerance characteristics exposed by 15-days old wheat seedling.