Among different environmental stresses, Drought is of great importance that induces a highly negative effect on crop production. In order to evaluate Drought tolerance in dryland wheat genotypes, 36 genotypes were studied in a randomized complete block design with three replications under rainfed (Drought stress) and supplemental irrigation conditions during 2016– 2017 growing season in Research Farm of Moghan College of Agriculture and Natural Resources. Results showed that there are significant differences among genotypes for grain yield in both rainfed and supplemental irrigation conditions. Combined analysis of variance over two experiments showed that Drought stress significantly increased grain yield. Under supplemental irrigation conditions, the genotypes 22, 34 and 21 had the highest grain yield by an average of 3. 143, 3. 089 and 2. 921 t/ha and under rainfed condition, genotypes 20, 22 and 27 produced the highest grain yield with an average of 2. 647, 2. 610 and 2. 558 t/ha, respectively. In order to identify Drought tolerance genotypes, Drought resistant indices such as tolerance index (TOL), stress susceptibility index (SSI), mean productivity (MP), geometric mean productivity (GMP), stress tolerance index (STI) and yield stability index (YSI) were used. GMP, MP and STI indices were highly correlated with grain yield under both stress and non-stress conditions. Therefore, they were introduced as suitable indices to identify superior genotypes for both environmental conditions. Based on principal component analysis and three dimensional graph, genotypes 22, 34, 33 and 15 were identified as Drought tolerant genotypes and 7, 17, 14 and 1 were identified as Drought sensitive genotypes. Cluster analysis with Ward's method based on grain yield under supplemental irrigation (Yp) and rainfed (Ys) conditions and Drought tolerance indices divided the 36 genotypes into four major groups. Therefore, this result was consistent by results from principal component analysis.

Drought stress is considered as one of the most important abiotic stresses which damages tobacco production in many countries including Iran. Thus, an investigation of Drought tolerant genotypes is one of the most important goals in tobacco breeding projects in Iran. Towards this end, in the present investigation, 15 hybrids of tobacco including 10 Iranian and 5 international hybrids were evaluated in a RCBD with three replications in two different environments (water stress and normal irrigation) in the Tirtash and Rasht Tobacco Research Station in 2007, where some tolerant indices were studied. Based on the dry leaf yield potential (Yp) and yield stability (YS), some such quantitative criteria of Drought resistance as: Mean Productivity (MP), Tolerance Index (TOL), Geometric Mean Productivity (GMP), Harmonic Mean (Harm), Stress Susceptibility Index (SSI) were figured out. High significant differences were observed among genotypes for all the indices as well as for potential vs. stress yields, indicating the existence of genetic variation and possibility of selection for Drought resistance.Correlation analysis among indices, along with potential and stress dry leaf yield indicated that MP, GMP and STI comprised the most suitable criteria for screening tobacco genotypes. Multivariate analysis biplot indicated that k394xNC89, NC55 and NC89xCoker347 in Tirtash and CC27 and Coker 254xVE1 in Rasht yielded the highest, and were tolerant to Drought stress. Distribution of the genotypes in the biplot space indicated the presence of genetic diversity among the genotypes for Drought stress.

Breeding and release of high yielding and Drought tolerant varieties along with advance agronomic practices are effective ways to manage Drought and water deficit in agriculture. This experiment was conducted in order to identify tolerant genotypes to Drought and evaluation of main characters and Drought resistance indices on 20 bread wheat genotypes (18 promising  lines and 2 checks, Sardari and Azar-2) during three cropping seasons (2002-2005) in two locations, Kermanshah province, Sararood station (moderate cold area) and Maragheh, Maragheh station (cold area). The genotypes were evaluated in a RCBD design fashion with four replications. Simple and combined analyses of variance for three years were carried out. The results showed significant differences among genotypes in different irrigation application. The highest grain yield, yield stability, and Drought tolerance were belonged to the genotypes nos.1 (14 Gene Bank Material), 2 (914 Gene Bank Material), 4 (F9.10/May"s"//Sabalan), 19 (Sardari), 20 (Azar-2), 3 (Turkey 13//F9.10/Maya"s") and 14 (Fengkang15/Sefid), under different irrigation scheme. Evaluation of stress tolerance indices i.e. stress tolerance index (STI), geometric mean productivity (GMP) and Mean productivity (MP) also showed the superiority of the above mentioned genotypes. Evaluation of different stress tolerance indices indicated that STI is a general index which can be used as selection criteria in breeding programs.

In order to evaluation of genetic diversity of spring barley genotypes, screening Drought resistance indices andidentification of Drought resistance varieties, 16 variaties of spring barley were evaluated in a randomised complete block design with three replications under two conditions including normal irrigated and Drought stress on flowering stage in West Azerbaijan Agricultural and Natural Research Centre. Based on the potential (Yp) and stress (Ys) yield, quantitative Drought resistance criteria such as: mean productivity (MP), tolerance index (TOL), geometric mean productivity (GMP), harmonic mean (HM), stress susceptibility index (SSI) and stress tolerance index (STI) were calculated. Generally in both conditions, variety Kavir/Badia with average yield of 2152 kgha-1 and variety Union 300-4 with average yield of 498.6 kgha-1 had the maximum and minimum values of yield. In both normal and Drought stress conditions, the highest value of MP, GMP and HM were possessed to genotype "Kavir/Badia". Correlation analysis between Drought resistance indices with potential and stress yields revealed that indices including MP, GMP, HM and STI are most suitable criteria for screening barley’s genotypes. Varieties "Kavir/Badia" and "Rihane-O5" were chosen as best Drought resistant regarding to these four criteria and high values of Yp and Ys. Multivariate biplot display that the varieties "Kavir/Badia" and "Rihane-O5", "Gorgan/CM67/Pro/Svo" and "Hebe" were located next to the vectors of Drought resistance indices MP, GMP, HM and STI. Also, distribution of the varieties in the biplot space manifested the presence of genetic diversity among the varieties for Drought stress. Cluster analysis indicated that the farthest genetic distance were exist between two Drought resistant varieties including "Kavir/Badia" and "Rihane-O5" and two susceptible varieties including "Local- chek" and "West Azerbaijan landrace".

In order to evaluate Drought resistance in barely genotype and for screening Drought tolerance indices, 26 genotypes of barley were tested in a randomized complete block design with three replications under normal and water stress conditions in the faculty of Agriculture, University of Tehran. Based on the yield potential (Yp) and yield stability (Ys), some quantitative criteria of Drought resistance such as: mean productivity (MP), tolerance index(TOL), geometric mean productivity (GMP),harmonic mean(HM), stress susceptibility index (SSI) and stress tolerance index (STI) were figured out. High significant differences were observed among genotypes for all indices and for potential and stress yields, indicating the existence of genetic variation and possibility of selection for Drought resistance as well as possibility of hybridization for the genetic and breeding studies. The highest potential and stress yield, MP, GMP, and STI belonged to Genotypes Radical, Badia and Sina. Correlation analysis among indices, potential and stress yield indicated that the most suitable criteria for screening barley genotypes were MP, GMP, and STI. Regarding these criteria and high Yp and Ys, the most Drought tolerance genotypes were identified as Kavir, Badia, Radical, Terean 78 and Sina. Multivariate biplot indicated that genotypes Badia, Kavir, Radical, Terean 78 and Sina were located close to the vectors of such Drought tolerance indices, as: MP, GMP and STI. Distribution of the genotypes in the biplot space indicated the presence of genetic diversity among the genotypes for Drought stress. Cluster analysis placed genotypes in three groups as based on information of either of the two conditions, with tolerant genotypes being placed in different clusters.

Introduction: Drought stress affects 40-60% of agricultural lands all over the world (Bray, 2002). With a precipitation of 240 mm/year, Iran is located in arid and semi-arid region of the Earth. Due to the shortage of rainfall in Iran, a considerable part of crop breeding programs is devoted to research concerning Drought tolerance. These efforts have resulted in the introduction of stable and Drought tolerant varieties. Although barley is more tolerant to Drought stress compared to other cereals, it is susceptible to moisture shortage during tillering and grain formation stages, which will result in yield losses. Yield provides the most direct index for evaluating response of crops to environmental stresses. Although grain yield is affected by environmental factors, it is an index to evaluate response of cereals to environmental stress...

In a study to select sensitive and tolerant soybean lines to Drought stress and superior genotypes, 80 soybean lines were obtained from crosses of Karbin × Fora cultivars along with L. 17 cultivar as control in the Lurestan-Saraab Research Farm during crop rotation 2016-2017. The cultivars were evaluated in the form of a lattice design 9×9 with two replications. The results of the analysis of variance showed significant differences between the control and experimental lines and also between the blocks for different traits. According to the results of stepwise regression and principal component analysis (PCA), traits were grouped into four components, accounting for about 62% of the total variation. The evaluation of grain yield potential and accurate PCA evaluation of the traits led to the selection of superior lines in the experiment. Results showed that plant height, number of pods per plant, number of seeds per pod, and 100-seed weight can be used as the criteria for selection of soybean crops to improve seed yield in Drought stress condition.

In order to identify Drought tolerant varieties using Drought tolerance indices, 24 genotypes of wheat were planted in a randomized complete block design with three replications under rainfed and irrigated conditions at the Research field of Agriculture faculty, Islamic Azad University of Sanandaj. Drought tolerance indices including mean productivity (MP), tolerance index (TOL), geometric mean productivity (GMP), stress susceptibility index (SSI) and stress tolerance index (STI) were calculated on the basis of grain yield per plant under irrigated (Yp) and rainfed (Ys) conditions. Highly significant differences were observed among genotypes for all indices, potential and stress grain yield that indicated the present of genetic variation. It's possible selection among genotypes for Drought tolerance, hybridization for the genetic studies and breeding programs. Correlation analysis between grain yield per plant in the rainfed and irrigated conditions with Drought tolerance indices showed the MP, GMP and STI indices are suitable for screening wheat genotypes. Regarding these criteria and high grain yield in both of two conditions Quds, Azar2, Kavir, Chamran and Mahdavi were diagnosed Drought tolerant genotypes. Gabriel Biplot Multivariate chart showed Quds, Azar2, Kavir, Chamran and Mahdavi genotypes were located near to the vectors of Drought tolerance indices, MP, GMP and STI. Finally, Azar2, Quds and Kavir genotypes were introduced as the most tolerant genotypes because they produced the highest performance in rainfed condition. The distribution of genotypes in Gabriel Biplot space showed the genetic variation among genotypes to Drought stress.

Drought tolerance is a quantitative trait and immeasurable directly. Hence, for assessing Drought tolerance related characters should be measured. Drought related characters such as root architecture and water use efficiency are quantitative traits and their phenotypic assessment, especially under filed conditions, is difficult. Consequently marker assisted selection is a superior tool for overcoming this problem. At this research genetic control of Drought related characters was assessed using QTL analysis method. A set of 220 double haploid lines, derived from Kukri (Drought sensitive) and RAC875 (Drought tolerant), were used. Overall, 35 QTL on 11 chromosomes were identified. Ten QTL had R2>10. 63% of identified QTLs were located on B genome that shows the substance of this genome in Drought tolerance. Root system and water use efficiency are two imperative Drought tolerant mechanisms. But their phenotypic assessment under Drought condition is either difficult or impossible. Hence these two worthwhile mechanisms are ignored at breeding programs. At this research 3 QTLs on chromosomes 1B, 5A and 5B were identified for root number that explained 39.7 percent of phenotypic variations. Also 3 QTLs on chromosomes 1B, 4B and 6D were responsible for genetic control of water use efficiency and explained 30 percent of phenotypic variation. Root number and water use efficiency have genotypic correlation, the genotypes with more root had more water use efficiency. Leaf width is the most important related character for early vigor. Five QTLs on chromosomes 2B, 2D, 3D, 5A and 6A were identified for leaf width that explained 41.6 percent of phenotypic variations. Selecting genotypes, using Marker assisted selection (MAS), for favorable alleles that has been identified in this study such as Gwm0304b and Barc0256 may allow to improve Drought tolerant mechanisms, consequently yield at Drought prone environments.