مجله تنشهای محیطی در علوم زراعی
سال سوم شماره 2 (نیمه دوم 1389)

To survey the effect of soil irrigation intervals on grain yield, yield components and harvestindex of bread wheat cultivars, an experiment was conducted based on randomized complete blocks as a split plot design with 4 replicates during 2006-2007 at the experimental farm of Agricultural and Natural Resources Research Center of Yazd. The main plots consisted of four irrigation treatments (8, 10, 12 and 14 days) and the sub-plots consisted of one line and three bread wheat cultivars (Backcross Roshan, Sistan, WS-82-9 and Pishtaz). The results indicated that the irrigation treatments had significant effects on grain yield, yield components and harvest index and there were significant differences between cultivars in terms of grain yield and yield components. Moreover, the interaction effect of irrigation interval x cultivar on grain yield and harvest index was significant (P<0.01). The maximum yield components and harvest index were obtained in 8 and 10 days intervals. 8 days interval showed the highest mean grain yield, while the lowest mean yield components, grain yield and harvest index were observed in 14 days interval. Comparison of the cultivars showed that Sistan and WS- 82-9 had the maximum number of grains per spike and thousand kernel weight, respectively.Pishtaz and Backcross Roshan had the maximum number of spikes per square meter. Also,Sistan and Backcross Roshan had the highest grain yield while the maximum harvest indexbelonged to Sistan, Backcross Roshan and WS-82-9. Based on the study results, 8 daysinterval was recognized as a favourable irrigation period for achieving the greatesteconomical yield in the region, while WS-82-9 showed the greatest drought tolerance andSistan was the most productive cultivar under well-watered conditions.

In order to evaluate the effect of limited irrigation on some morphological characteristics and biological yield of spring safflower cultivars, an experiment was conducted in a spilt plot arrangement based on randomized complete block design with four replications at Research Farm of Faculty of Agriculture, University of Birjand during 2008. Irrigation levels (whole season irrigation, and irrigation till grain filling, flowering, and heading-bud stages) and cultivars (Mahali Isfahan (a local variety), Isfahan28 and IL111) were arranged as main- and subplots, respectively. Results showed that reduction in plant height, the height of first branch from soil surface, number of nodes in main stem and number of primary and secondary branches were observed only in irrigation until heading-bud treatment, but primary and secondary heads diameter and biological yield decreased in all of the irrigation cessation treatments. Safflower cultivar also significantly influenced these traits. The highest plant height, the height of first branch from soil surface, number of nodes in main stem and number of primary and secondary branches and biological yield were obtained at Mahali Isfahan cultivar, indicating its promising production potential in arid and semi-arid regions. In addition, reduction of morphological characteristics and biological yield in all three cultivars were observed in irrigation until heading-bud treatment. It seems that this growth stage is the most susceptible period to water shortage and irrigating at this stage under such a condition can significantly enhance the biological yield.

To evaluate the effect of supplemental irrigation on nutrient uptake, water relations and drought tolerance of safflower, an experiment with four levels of irrigation (no irrigation, irrigation at the heading, flowering and both heading and flowering stages) and three safflower cultivars (Gila, Isfahan local and PI-537636) was conducted as a split plot based on randomized complete block design with three replications at Ardebil Agricultural Research Station during 2008. Irrigation showed significant impact on leaf potassium content, relative water content, leaf water potential and membrane stability. There were significant differences amongst cultivars in terms of sodium, potassium, and calcium content, leaf water potential as well as membrane stability and a significant interaction was also observed between irrigation and cultivar on leaf water potential and membrane stability. The highest water potential (0.57 MPa) and membrane stability (95.3%) was obtained by Gila cultivar when irrigated at heading and flowering stages. PI-537636 genotype showed superiority based on stress susceptibility (SSI) and tolerance (TOL), while Isfahan local variety was superior in terms of the stress tolerance index (STI) and geometric mean productivity (GMP). However, given the fact that the best cultivars are those producing high yields under normal conditions with the minimum yield reduction under drought stress, Isfahan local variety was the preferable cultivar under drought stress conditions.

To evaluate the effect of plant growth regulator (cycocel) on proline, total soluble sugars, protein, oil and fatty acids profile under drought stress, a factorial pot experiment was conducted based on completely randomized design with four replications at Research Laboratory of Yasouj University in the spring of 2009. Treatments were three levels of drought stress including without, mild and severe stress and six concentration levels of cycocel including four foliar sprays 0, 500, 1000 and 1500 ppm during the rapid growth of plant and two seed soaking levels 10-5 and 10-6 mM for 24 hours before planting. Results showed that all levels of cycocel foliar spray increased proline and soluble sugars compared to the control under non-stressed conditions. Stress could significantly increase grain protein, and the 10-6 mM seed soaking treatment increased seed protein (20%) under stress conditions. Increased concentrations of foliar sprayed cycocel reduced oil percentage from 39.2% to 35.7% and stress also decreased this trait. In non-stressed treatment, the level of 10-6 mM cycocel seed soaking showed a positive significant effect on the amount of linolenic acid; while this amount was reduced (15%) by increasing the cycocel spraying concentration. Moreover, drought stress increased the content of saturated fatty acids Oleic, palmatic and stearic. Overall, cycocel could compensate the damages caused by drought stress to some extent.

In recent decades, increased human industrial activities and enormous fertilizer application in agriculture section has promoted heavy metal release into the environment. Pb is one of the most prominent heavy metal contaminant in the ecosystem. In spite of its global importance, there is little knowledge regards mechanisms of lead toxicity in plants. Regarding industrial and medicinal importance of Matricaria chamomilla, the response of this species to lead toxicity was investigated at rosette, shooting and flowering stages. To examine this, plants were transplanted to hydroponic culture at rosette stage and were exposed to different Pb nitrate treatments including 0, 60, 120, 180, 240 μM. Plants were harvested after completing each developmental stages for analysis and studying. The results revealed that the root Pb concentration was greater than that of above ground parts at all studied stages. Examining leaf, stem and root cross sections showed that increased Pb absorption caused similar changes in leaf and stem anatomy at all investigated stages. However, Pb influence on root anatomy was dissimilar at different developmental stages, so that Pb pollution increased the diameter of xylem and vascular tissues at rosette stage but it reduced these traits at shooting stage.

In order to evaluate stem reserves and mobilization efficiency of bread wheat lines underdrought stress at late growing season, an experiment was conducted on 16 advanced bread wheat lines (WS-87 series) using a randomized complete block design with 3 replications during 2009-2010 in Kabootarabad Agricultural Research Station, Isfahan. Drought stress was induced through irrigation cessation after heading. Length and weight of stem components including length and weight of peduncle, length and weight of penultimate internode and weight of remained internodes were measured in 5 steps at 10-day intervals from anthesis to physiological maturity. Mobilized dry matter and mobilization efficiency were calculated for each part of stem and their correlations with grain yield were estimated. Results showed that mobilized dry matter from peduncle varied from 13- 122 mg (lines 9 and 1, respectively), from penultimate internode varied from 75- 122 mg (lines 6 and 1, respectively) and from remained internodes varied from 51- 206 mg (lines 14 and 10, respectively). Total mobilized dry matter from stem varied from 186- 506 mg observed in lines no. 16 and 1, respectively. Mobilization efficiency for peduncle varied from 3. 4- 26. 8% (lines 9 and 3, respectively), for penultimate internode varied from 25. 9- 48. 6% (lines 6 and 8, respectively) and for remained internodes varied from 13. 3- 42. 8% (lines 14 and 10, respectively). Among three parts of stem, penultimate internode had the most important role in mobilized dry matter and mobilization efficiency. Grain yield positively correlated with peduncle length (r= 0. 50٭) and penultimate internode length (r= 0. 53٭).

In order to study the effects of osmotic and salinity stresses on germination and seedlinggrowth indices of Artichoke and Purple coneflower, four separate laboratory experimentswere conducted as completely randomized design with four replications at Crop PhysiologyLaboratory of Ferdowsi University of Mashhad during 2009. Treatments were eight levels of osmotic stress (0, -2, -4, -6, -8, -10, -12 and -14 bar) using PEG 6000 for first and second experiments and six levels of salinity stress using NaCl (0, -1, -3, -5, -7 and -9 bar) for third and fourth experiments. Results showed that Artichoke was more resistant than Purple coneflower to osmotic and salinity stresses. Germination percentages of Artichoke and Purple coneflower were 72 and 5% in -10 bar osmotic stress, respectively; while germination percentages of Artichoke and Purple coneflower were 75 and 8% in -5 bar salinity stress, respectively. Increasing osmotic stress severity increased mean germination time of Artichoke, while the effect of different osmotic stress levels was not significant on mean germination time of Purple coneflower. Radicle / plumule length ratio was increased by increasing osmotic and salinity levels in Artichoke, while this ratio was not varied by osmotic stress and was decreased by salinity stress in Purple Coneflower. Moreover, seedling dry weight was decreased by increasing osmotic and salinity stress in both medicinal plants. Overall, it seems that germination indices and seedling growth in Artichoke were superior to Purple coneflower under stress conditions.

In order to determine the freezing tolerance of sugar beet (Beta vulgaris L.) cultivars under controlled environment, a factorial experiment was conducted based on completelyrandomized design with three replications at College of Agriculture, Ferdowsi University ofMashhad. In this research, eight cultivars including Rasoul, Shirin, IC, 7233 (nationalcultivars), Afshari, Paolina, Rhizofort and Laetitia (foreign cultivars), were exposed to eightfreezing temperatures (0, -2, -4, -6, -8, -10, -12 and -16 °C). Plants were grown under natural environment until 4- to 5- leaf stage and were transferred to thermo-gradient freezer to apply freezing temperatures at early spring. Survival percentage, dry weight, SPAD reading, 50% lethal temperature (LT50) and the temperature for 50% dry matter reduction (RDMT50) of the samples were determined at the end of recovery period (3 weeks after applying freezing temperatures). Results showed that freezing temperature and cultivar significantly influenced the survival percentage, dry weight and SPAD reading (p≤0.01). Decreasing temperature below -8 °C significantly decreased the mean survival percentage of cultivars, while significant reductions of dry weight and SPAD reading comparing with the control (0 °C) were started at temperatures -2°C downward. Moreover, LT50 and RDMT50 of examined cultivars were significantly different (p≤0.01), so that Paolina, Laetitia and Shirin cultivars with LT50 of -11.5 °C and Afshari with LT50 of -9.1 °C had the highest and lowest freezing tolerance, respectively. Afshari showed the highest amount of RDMT50 (= -7.7 °C) amongst beet cultivars. It seems that according to good correlation between RDMT50 and LT50 (r=0.83**), may indicate that using this index might be used for evaluation of freezing tolerance among sugar beet cultivars.