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The aims of this study were to assess the effects of drought stress on peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT) activities as well as free proline content and growth parameters of Pistacia khinjuk seedlings under drought stress. Therefore, the one-year seedlings of Pistacia khinjuk subjected to water stress (25%, 50%, 75%, and 100% field capacity) for 8 months in greenhouse condition. Results showed that drought stress decreased height, collar diameter, shoot dry weight and root dry weight of P. khinjuk seedlings. But it had different effects onantioxidant enzyme activities in root and shoot of P. khinjuk seedlings. Drought stress increased CAT activity in shoot and root of seedlings and its activity was higher in 25% field capacity (FC) than other treatments. Also, the POD enzyme activity increased in root and shoot of seedlings subjected to drought stress. The SOD activity was at the lowest level in 100% FC than other treatments. The results also showed that free proline accumulation was lower in well watered seedlings and increased under drought stress.

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Limited water for irrigation and the coincidence of early growth of sugar beet (Beta vulgaris L.) with the late growth of winter cereals in the Northeast (NE) of Iran, force farmers, to allocate their limited irrigation water to the cereal crops and thus their sugar beet crop is subjected to an early water stress. Finding cultivars which are able to withstand early water stress without a significant yield reduction is critical to the farmers’ economy. This study was conducted over a two-year period (1998 and 1999) to evaluate the response of nine sugar beet genotypes to drought stress and to determine the crop traits associated with drought resistance. The results showed that stomatal conductance, leaf-air temperature difference and proline accumulation were associated with levels of water stress in sugar beet genotypes. Among these indices, leaf-air temperature difference was a more precise parameter to measure. A negative correlation between Δ T (leaf -air temperature) and stomatal conductance was found. The correlation coefficients for 1998 and 1999 were -0.87 and -0.58, respectively. There was a positive correlation between Δ T and proline accumulation in sugar beet genotypes. The correlation coefficients for the 1998 and 1999 experiments were 0.61 and 0.49, respectively. The shoot: root ratio (S:R) measured at the end of the stress period showed that genotypes with a lower S:R often had a greater stomatal conductance. In general, genotypes with a lower S:R at the end of the stress period usually had a greater root dry weight. The correlation coefficients of S:R with root dry weight at the end of the stress period were -0.96 and -0.65 for 1998 and 1999, respectively.

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The responses of yield and yield components of 24 advanced bread wheat genotypes to pre- and post-anthesis drought stress conditions were studied at Ardabil Agricultural Re-search Station during the 1997-2000 cropping seasons. Results showed that genotypes produced significantly lower spikes No./m2, seeds No./spike and grain yield under pre- than in post-anthesis drought stress conditions. However, an average of 1,000 kernel weight of genotypes under pre-anthesis was higher than under non-stress and post-anthesis drought stress conditions. Selection based on TOL and SSI identified the drought tolerant genotypes with low grain yield. However, selection based on MP, GMP and STI identified drought tolerant genotypes with a high yield. Genotypes No. 13, 14 and 21 were determined as desirable genotypes based on their high grain yield under non-stress, pre-anthesis and post-anthesis drought stress conditions. The interaction effect of genotype x year was significant for membrane stability and membrane damage, however, the interac-tion effect of genotypes stages of measurement (booting and heading) were not signifi-cant. On the basis of these results, genotypes No. 13, 14 and 21 with low membrane dam-age were also identified as drought tolerant genotypes. It can be concluded that the labo-ratory test can be an useful tool in a breeding program for improving drought tolerance in wheat.

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Abstract:
Aim: With global warming and limited water resources in the world, especially in arid lands of Iran, managing the production of forest seedlings in the country's nurseries is facing a special challenge. In this regard, the study of drought tolerant plants to select them in the mass seedling production programs can be useful.
Material and methods: Potted seedlings of Persian oak (Quercus brantii Lindl.), pistachio (Pistacia atlantica Desf.), Judas-tree (Cercis siliquastrum L.) and black poplar (Populus nigra L.) exposed to a normal irrigation scheme (100% field capacity) and drought-stressed (30% field capacity) conditions were examined over a period of 120 days in a greenhouse of Bam Khorramabad Nursery to judge their tolerance for drought stress.
Findings: Drought-tressed seedlings from all species had a lower content of chlorophyll a, chlorophyll b, total chlorophyll and carotenoids compared to the control plots, but the content of proline and malondialdehyde (MDA) did, however, increase. Under stress conditions, MDA content in black poplar, Judas-tree, Persian oak and pistachio was 174, 121, 105 and 102% higher than the control seedlings, respectively, and this increase in black poplar over other species ranged from 93.5 to 176.5%.
Conclusion: This study confirms that among four tree species, black poplar has lowest tolerance to drought stress. Thus, Persian oak, pistachio and Judas-tree, should be prioritized in the mass seedling production programs of nurseries in arid areas suffering from limited water resources, due to their higher tolerance to water scarcity.

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Aims: Drought limits plant growth and productivity throughout the world. Narrow-leaved plantain (Plantago lanceolata L.) is widely used to treat some human diseases and reduce antibiotic nutrition. This study aimed to examine the response of four local ecotypes of P. lanceolata to different drought stress levels in a field experiment.
Materials & Methods: A split-plot design was conducted using a randomized complete block design (RCBD) with three replications at the farm of Research Institute of Forests and Rangelands, Karaj, Iran, 2018. The main factor was drought stress at three levels (D1= normal irrigation, D2= drought stress after the flowering stage with supplemental irrigation at the filling stage, and D3= stop irrigation after flowering. The second factor contained four ecotypes: G1-Arak, G2-Khoramabad, G3-Meshkinshahr1, and G4-Meshkinshar2. Data were collected and statistically analyzed for grain yield and yield components.
Findings: Results showed a significant effect of drought stress and ecotype on all traits except root lengths (p<0.05). The ecotype × drought stress interaction effects were significant for spike number per plant, leaf number per plant, leaf width, and plant height (p<0.05). The mean values of grain yield in D1, D2, and D3 were 729.41, 660.81, and 595.95 kg.h^-1, respectively.
Conclusion: The highest grain yield of 670.92 kg.h^-1 was obtained from G1-Arak. This ecotype produced higher grain yields under mild and severe stress than the other ecotypes and was recommended for breeding improved varieties.
 

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The effect of different fertilizing systems and drought stress during grain development on grain minerals of barley (Hordeum vulgare L.) was studied in field experiments on a clay-loamy soil during 2007 and 2008 growing seasons. The treatments consisted of three irrigation regimes (main plots) of: Non-stressed (NS, normal irrigation continued until the end of plant physiological maturity), Moderate Stress (MS, irrigation ceased from the beginning of flowering to the beginning of grain filling stage and Severe Stress (SS, irrigation ceased from the beginning of flowering stage up to the end of physiological maturity) along with six fertilizing regimes consisting of no fertilizer application (control) (NF), phosphorous and nitrogen Biofertilizers (BF), 100% Chemical fertilizer (NPK) (CF), Vermicompost (VC) 5 t ha-1, 50% Chemical fertilizer (NPK)+50% Vermicompost (2.5 t ha-1) (CV), and 50% Chemical fertilizer (NPK)+ Biofertilizer (CB), assigned to the sub plots. Drought stress significantly increased grain minerals of N, Zn and Mn by 12, 27, and 7% as compared with control (NS), respectively. Average grain nitrogen concentration in chemical fertilizer (CF) treatment was significantly more than those in the other treatments followed by integrated fertilizing systems (CB and CV). Phosphorous concentration in grains produced in BF fertilizer medium was significantly higher than those in other treatments. Grain Fe and Zn concentrations increased through vermicompost application. However, Mn concentration was higher in grains fertilized with chemical fertilizer. It can be concluded that in barley production under water deficit conditions, grain mineral quality could be improved through integrated fertilizer application.

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Investigating the role of drought stress conditions on physiological characteristics of plant may provide means to understand basic drought resistance. Differences in leaf emergence rate, leaf relative water content (RWC), membrane stability index (MSI), leaf mass area (LMA), net photosynthesis (Anet), stomatal conductance (gs), transpiration rate (E), intercellular CO2 concentration (Ci), water use efficiency (Anet/gs) and recovery of gas exchange were investigated in two-year-old grapes of three Vitis vinifera L. cultivars ("Khoshnave", "Bidane-Sefid" and "Askari"), subjected to progressive drought stress (soil water potential: -0.2, -0.6, -1, and -1.5 MPa). The results showed temporary reduction in RWC, MSI, leaf emergence rate, LMA, Anet, gs and E. Ci decreased with increasing drought stress. "Khoshnave" grape showed a higher photosynthesis rate than "Bidane-Sefid" and "Askari". Higher LMA of "Khoshnave" may be attributed to the potential for carbon absorbance and higher Anet as compared to the other two cultivars. Complete recovery of Anet for all cultivars occurred one day after rewatering at -0.6 MPa and four days after rewatering at -1 MPa treatments. Complete recovery of gs was not observed in either one or four days after rewatering except for "Askari". The results showed that Anet of "Khoshnave" recovered quickly as compared to those in the other two cultivars. Water use efficiency was maximum in all cultivars under -1 MPa treatment. Similar patterns of Anet/gs were observed for the three cultivars. "Khoshnave" had higher Anet/gs as compared to "Askari" and "Bidane-Sefid" under severe drought stress conditions. "Khoshnave" cultivar, with a higher Anet, higher leaf emergence rate, higher LMA, rapid recovery of Anet, higher Anet/gs was found to be promising for cultivation in rain-fed areas across the west of Iran in comparison with the other cultivars.

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It is suggested that cultivars of wheat (Triticum aestivum L.) with regulated growth and development would be able to produce higher yields under water-limited conditions, which is crucial in future food production. Water use efficiency (WUE) is worthy of exploration in this regard. In this study, the effects of nitrogen fertilizer levels (0, 40 and 80 kg Nha-1) and a plant growth retardant (Chlormequat Chloride = CCC) on WUE of four dryland wheat cultivars (Agosta, Nicknejad, Azar-2 and Fin-15) were examined in a field experiment during 2006-07 and 2007-08 growing seasons at College of Agriculture, Shiraz University, Iran. The results showed that there existed significant differences between cultivars for grain yield, biomass and WUE. In the first season, the highest grain yield and biomass production (192.4 and 431.2 gm-2, respectively) were obtained from Nicknejad cultivar, CCC application and using 80 kg Nha-1, and in the second season, from Azar-2 cultivar (121.5 and 333.5 gm-2, respectively). CCC and nitrogen had significant effects on photosynthesis rate and WUE in both seasons. Interaction of CCC and 80 kg Nha-1 on WUE were significant in both seasons (1.24 and 2.72 gm-2mm-1, respectively). It is suggested that interactive application of CCC and nitrogen fertilizer could have beneficial effects on wheat grain yield under similar agro-climatic conditions.

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In order to assess drought tolerance of mycorrhizal petunia plants (Petunia hybrida cv. Mix), a greenhouse experiment was carried out with two different mycorrhizae species (Glomus mosseae and Glomus intraradices) applied singly or in combination at two phosphorous (P) levels (0 and 100 mg kg-1 dry soil) and three irrigation regimes (100% field capacity (FC) as control, 75% FC producing moderate water stress and 50% FC producing severe water stress). Both mycorrhizal endophytes established well on roots of the petunia plants with higher colonization values at lower P concentration and lower colonization rate at increasing water stress. Mycorrhizal colonization generally enhanced plant vegetative and reproductive growth, both under full and reduced field capacities and with and without P fertilization. The content of soluble sugar in AMF-inoculated leaves was higher than that in non-AMF-inoculated plant leaves in response to drought treatments but proline level did not show any significant increase in mycorrhizal treatments at the same conditions. This study confirms that mycorrhizal colonization can mitigate the adverse effects of water stress on treated plants restoring most of the key growth parameters to levels similar or close to those in unstressed plants.

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This study was conducted to determine the effects of arbuscular mycorrhizal fungi (Glomus mosseae and Glomus intraradices) symbiosis on mineral uptake of two pistachio cultivars (Pistacia vera cv. Qazvini and Pistacia vera cv. Badami-Riz-Zarand) grown in the greenhouse under different drought stress levels. Drought stress (DS) reduced the mycorrhizal colonization in both cultivars as well as nutrient uptake. The mycorrhizal plants had higher P, K, Zn and Mn concentrations than non-mycorrhizal plants regardless of soil moisture conditions while Cu and Fe concentrations were unchanged. Distribution of elements was affected by AMF treatments where all except P were accumulated more in leaves than in roots. Contrastingly, under drought conditions, the absorbed elements tended to remain in root tissue. In the case of P and Mn uptake, Qazvini was superior in comparison with Badami. In conclusion, it is suggested that AMF inoculation improves drought tolerance of pistachio cultivars at least in part through the enhanced uptake of slowly diffusing mineral ions such as PO4^2- and Zn²⁺. Moreover, arbuscular mycorrhizal (AM) colonization provides better osmotic adjustment which can be correlated with K⁺ accumulation in top portions of inoculated plants. Results of this study also emphasized that ‘Qazvini’ cultivar may be more tolerant to drought than ‘Badami’.

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Common Vetch ( Vicia sativa L.) an annual forage, belonging to the Fabaceae family is one of the highly cultivated forage legumes in Iran. Drought stress is a serious adverse factor that limits plant growth and productivity, inducing a range of physiological as well as biochemical responses in plants. It may also lead to generation of oxygen activated species which in turn result in cell destruction. In this study, physiological and biochemical responses of six common vetch genotypes to two levels of drought stress (30 and 10% left of FC) were investigated at their early growth stages. Results indicate that drought stress significantly affects the Relative Water Content (RWC), Electro Leakage (EL), photosynthetic pigments, and total carotenoids. The obtained results indicated drought induced changes in the activities of such antioxidant enzymes as Catalase, Glutathione Peroxidase and Ascorbate Peroxidase. There was also found a reverse relationship between Catalase and Ascorbate Peroxidase activities in the studied genotypes. Obtained results clearly show that there are highly genotype-dependent responses to drought stress at biochemical level in common vetch genotypes, with each genotype responding to stress in a genotype-specific manner. These results may be helpful in breeding programs related to drought stress resistance.

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In this research, some of the echo-physiological characteristics of pistachio trees were studied to understand crop response to drought stress and determine the best irrigation interval. This experiment was carried out in an orchard with a sandy loam textured soil and a commercial cultivar of pistachio named Ouhadi grafted on Pistacia vera L. rootstock for three years. The irrigation system selected was surface flooding with intervals of 30, 50, 80, and 110 days. These intervals were chosen so as to resemble common irrigation intervals of pistachio orchards in the region. This enabled a comparison between the best and worst conditions of trees in respect to drought stress. Total irrigation water received was a constant depth of water to all treatments. Quantitative and qualitative yield such as weight of fresh and dry nuts, percent of blank and split nuts, and number of nuts per ounce, vegetative and echo-physiological characteristics were considered and measured. In terms of yield quantity and quality, the results showed vegetative and echo-physiological attributes to be significantly different between the treatments of 30, 80 and 110 days irrigation intervals. This means that with an increase in irrigation intervals and considering soil water holding capacity, soils were not able to provide enough moisture for the plant to carry out its normal metabolic activities. However, in the prolonged irrigation intervals, there were not much differences between treatments i.e. the pistachio tree could adapt itself to the naturally occurring environmental stress conditions. 

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Canopy temperature (CT) is used as a selection tool to improve crop adaptation to drought. The aim of this work was to investigate association of some photosynthetic characters with CT during grain filling in three cereal species. For this objective, a two-year study (2009-2011) was carried out in Kurdistan Province in western Iran. Four genotypes of triticale, three cultivars of bread wheat, and a new variety of barley were compared under well watered (WW, Ψ_{soil water}= -3 bar) and deficit water (DW, Ψ_{soil water}= -12 bar) conditions in a randomized complete block design (RCBD) with a split-plot arrangement. Compared with well-watered plants, water stressed plants displayed 1.44°C higher canopy temperature irrespective of plant species. Under water stress condition, the high yielding genotypes had lower canopy temperature than low yielding ones by 1.23°C. Results showed that under water deficit condition triticale relative to commercial cultivar of wheat and barley had a higher adaptability to drought as indicated by its higher yield (59.5 g m^-2 more than average) and lower CT (0.28°C lower than average). The main physiological traits correlated with canopy temperature under DW treatment were stomatal conductance (g_s) (r= -0.73*), photosynthetic rate (P_n) (r= -0.76*), the maximal quantum yield of primary photochemistry (F_v/F_m) (r= - 0.71*), chlorophyll content at grain filling (r= -0.72*) and leaf temperature (LT) (r= 0.82**). Thus, canopy temperature seems to play an important role in the physiological basis of grain yield in different cereal species, and can be used as a selection tool in breeding programs under water deficit condition in Iran. 

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Drought sensitivity is considered as a major concern for chickpea (C. arietinum) seed production. Determination of drought adaptation mechanisms is an essential constituent of this crop breeding programs. With this purpose, the present research was conducted to distinguish the molecular basis of chickpea drought tolerance using cDNA-AFLP approach. The expression profile was compared between drought tolerant (ICCV2 and FLIP9855C) and susceptible lines (ILC3279) of chickpea under three drought treatments including well-watered, intermediate, and severe stress; where soil water content was kept at 85–90%, 55–60%, and 25–30% of Field capacity, respectively. Totally, 295 transcript-derived fragments (TDFs) were visualized. Among the differentially expressed TDFs, 72 TDFs were sequenced. Sequenced cDNAs were categorized in different functional groups involved in macromolecules metabolism, cellular transport, signal transduction, transcriptional regulation, cell division and energy production. Based on the results, ribosomal protein S8, mitochondrial chaperone, proteases, hydrolases, UDP -glucuronic acid decarboylase, 2-hydroxyisoflavanone dehydratase, NADPH dehydrogenase, chloride channels, calmodulin, ABC transporter, histone deacetylase and factors involved in chloroplast division were among genes that were affected by drought stress. Similarity search in data base showed that cell wall elasticity, isoflavonoids, maintenance of structure and function of proteins through increase in expression of mitochondrial chaperones, programed cell death, and remobilization of storage material from leaves to seeds were among mechanisms that distinguished differences between drought tolerant and drought susceptible lines.

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Drought is still accounted as a serious agronomic problem and also one of the most important factors contributing to crop yield loss. The effect of sodium silicate (Na₂SiO₃, abbreviated as Si) was investigated on the four major antioxidant enzyme activities and five other relevant components in two different grapevine cultivars (Vitis vinifera L., cvs Mish Pestan and Sahebi, as tolerant and sensitive cultivars) under drought stress. The experiment was performed in a completely randomized design including three treatments i.e. the control, drought with no Si, and Si-drought (0.004M sodium silicate kg^-1 soil), with three replications in a greenhouse. The results indicated that Si partially offset the negative impacts of drought stress by increasing the tolerance of grapevine by rising antioxidant enzyme activities and soluble protein content. Si treatment significantly affected the enzyme activities in both cultivars. Water stress induced a decrease in total Chlorophyll (Chl) and total protein contents, which was much larger in no-Si stress than in Si treatment. The results indicated that sodium silicate might decrease drought stress damages by raising the antioxidant enzymes activity.

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To develop synthetic varieties, not only the estimation of General Combining Ability (GCA) for forage production is required but also the stability of GCA for parental genotypes is necessary. Little is known about genetic analysis and selection for high production, combining ability, and stability in grasses. In this study, half-sib families derived from the polycross of 25 smooth bromegrass genotypes were evaluated under 10 environments (combination of five years and two moisture environments, including non-stressed and drought stress conditions). Considerable variation for genetic and Genotype×Environment (G×E) interaction was found among half-sib families. Low broad sense heritability (27%) was found for forage yield indicating that selection based on an index may be more useful for improvement of this trait in recurrent selection programs. On the other hand, since the interactions of genetic by environment are significant, selection of superior genotypes for development of synthetic varieties should be done based on multi-environments trails.

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Cumin (Cuminum cyminum L.) is the second most popular spice in the world and one of the important medicinal plants in Iran. Cumin seed yield is highly affected by water stress, which is one of the most important abiotic stresses affecting seed yield. So far, drought tolerance studies in cumin have been done on limited cumin ecotypes. In the present investigation, forty-nine diverse cumin ecotypes were tested under normal and water stress conditions during 2013 and 2014. The experiment was conducted under two different irrigation regimes of normal irrigation and mid/late season water stress i.e., during flowering. Each of experiments was conducted in a simple lattice design with two replications. The combined analysis of variance showed significant differences among all sources of variation. Twelve drought tolerance indices were calculated based on seed yield under drought and irrigated conditions. Yield under stress and non-stress conditions was significantly and positively correlated with Geometric Mean Productivity Geometric Mean Productivity (GMP), Stress Tolerance Index (STI), Harmonic Mean (HM), Drought Resistance Index (DI), modified Stress Tolerance Index in normal irrigation (K1STI), modified Stress Tolerance Index in stress irrigation (K2STI), Stress Non-stress Production Index (SNPI) and Stress Tolerance Score (STS). PCA and cluster analysis were followed to reveal the relationship among different indices. To visualize the GE interaction effects on cumin seed yield, the data were subjected to GGE-Biplot analysis. Finding superior ecotypes in each environment was done using GGE-Biplot. Regarding mean yield and drought tolerance indices, ecotypes from Maneh (Northern Khorasan), Shahmirzad (Semnan), and Rafsanjan (Kerman) were identified as the most favorable candidates for further research in cumin breeding programs. GC/MS analyses of elite ecotype Kerman (Rafsanjan) was also done for both conditions, the main components of essential oil were found to be γ-terpinene, β-pinene, m-cymene, and cuminic aldehyde.

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Fifteen endemic ecotypes of the fenugreek were evaluated under well-watered and water deficit stressed conditions in the lysimetric system. Results of analysis of variance revealed that there was significant genotypic diversity for all of the traits, except root branch number. Also, ecotype × water treatment interaction was significant for all traits, except days to ripening, canopy temperature, and grain weight. Based on structural equation modeling, predictors in the causal diagram could explain 59%, 29%, 65%, and 51% of the total variation of dependent traits consisting root length, stem diameter, shoot dry weight, and percent assimilate partitioned to grain, respectively. These dependent traits had high broad sense heritability and explained 100% variation of grain weight. Transpiration efficiency had a positive effect on grain weight through stem diameter, root length, shoot dry weight, and percent assimilate partitioned to grain. Results of membership function value of drought tolerance index and heat map clustering revealed that Jahrom ecotype was a highly drought susceptible ecotype, and Yazd and India were drought susceptible ecotypes. Also, Tiranchi and Shiraz were identified as drought tolerant ecotypes. Overall, under water stress conditions, the drought tolerant ecotypes had deeper roots than the other ones. Therefore, these ecotypes might be considered as donor parents in fenugreek breeding programs.