مجله تنشهای محیطی در علوم زراعی
سال پنجم شماره 1 (نیمه اول 1391)

Application of plant growth regulators (PGRs) could be one of the methods to compensate for the harmful effects of drought stress, as the most important factor limiting wheat yield. To examine the effect of two PGRs; cycocel (CCC) and salicylic acid (SA) on grain yield and its components of a bread (Roshan) and a durum (Yavarous) wheat under different water regimes [normal (as control), moderate and severe drought], field and greenhouse experiments were carried out at the Research Field and Greenhouse of College of Agriculture, Shiraz University during 2009-2010 growing season. Field and greenhouse experiments were organized as a split factorial based on randomized complete block design and completely randomized design, respectively. Results showed that drought stress caused remarkable reductions in ear length, grain number per spikelet, grain and spikelet number per ear, grain yield, biological yield and harvest index. The highest and lowest effects of drought stress were observed in biological yield and 1000- grain weight, respectively. PGRs increased ear length, grain number per spikelet, grain and spikelet number per ear, 1000- grain weight as well as the grain yield. SA and CCC application was associated with enhancement and reduction in biological yield, respectively. Harvest index was increased in CCC treated plants. Responses of Roshan cultivar yield and its components to drought stress and both PGRs application were more than Yavarous. Also it appeared that Roshan cv. had more grain yield, and Yavarous had higher resistance to drought stress. Although drought stress caused reductions in most yield components of wheat, PGRs application could alleviate a part of these harmful effects. Therefore application of these PGRs, especially CCC, is recommended under drought stress conditions.

In a 2-year field experiment (2009-10 and 2010-11) 30 wheat cultivars were compared under with and without late season drought stress conditions. The experiments were conducted as a split plot based on randomized complete block design with four replicates at Research Farm of College of Agriculture, Shiraz University. Drought stress treatments (without stress, as control, and irrigation cutting off at anthesis stage) and wheat cultivars were assigned into main plots and sub plots, respectively. In this study mean productivity (MP), stress susceptibility index (SSI), stress tolerance index (STI), geometric mean productivity (GMP), tolerance (TOL), and yield stability index (YSI) were calculated based on grain yield under both with and without drought stress conditions. The results showed where irrigation cut off at anthesis, Kavir cultivar with 390.48 g/m2 had the greatest grain yield; while, under normal irrigation treatment the greatest grain yield was achieved from Shiroudi cultivar (873.83 g/m2). Comparison of means under normal irrigation conditions showed that Ghods cultivar (57.7 grains per spike) and Yavarous cultivar (20.72 grains per spike) had the highest and lowest grains per spike, respectively. Under drought stress conditions, the highest and lowest grains per spike were obtained by Zarin (39.4 grains per spike) and Souraplata (9.9 grains per spike), respectively. In the present study, 1000- grain weight was significantly different between irrigation treatments. Sistan cultivar had the greatest (45 g) 1000- grain weight under normal conditions, and Omid cultivar produced the greatest (35 g) 1000- grain weight under terminal drought stress conditions. Comparison of the mean of wheat cultivars showed that highest grain yield was achieved under stress and non-stress conditions in Kavir and Derakhshan cultivars, respectively. The lowest grain yield under both conditions was obtained from Veernak cultivar. The results of this investigation indicated that GMP, STI and MP, which had the highest significant correlation with the grain yield under both conditions, were assigned as the most appropriate indices for evaluating the drought tolerance of cultivars.

Effects of water stress on plants are complex and depend on the developmental stage and their growth stages. Limitation of the amount of moisture in the soil will be adversely affected plants yield through reductions in photosynthesis, leaf area production, nutrient absorption and assimilates transportation to grains. To evaluate effects of water stress applied at various growth stages combined with different nitrogen fertilizer amounts on grain yield, yield components, essential oil and thymoquinone content of Black Cumin (Nigella Sativa L.) a split plot experiment based on RCBD was conducted with three replications in 2011 at Agricultural Research Station, Zahak, located at 20 km south of Zabol. Water stress was considered as the main plot and stress treatments were created by withholding irrigation at different plant growth stages including: W1 (control), W2 (withholding irrigation at stem elongation stage until flowering), W3 (withholding irrigation at flowering stage until the beginning of grain filling) and W4 (withholding irrigation at flowering stage until the termination of grain filling) and four levels of nitrogen fertilizer including N1 (control), N2 (30 kg N.ha-1), N3 (60 kg N.ha-1) and N4 (90 kg N.ha-1) were assigned as sub plots. Results showed that water stress imposed at each growth stage led to a reduction in grain yield of Nigella Sativa. The maximum reduction rate (about 40.9%) was observed at W4 treatment. Water stress significantly reduced the biological yield, number of branches per plant, number of follicles per plant, number of seeds per follicle, number of seeds per plant and 1000- seed weight, whereas significantly increased the essential oil and thymoquinone contents. The maximum impact on all these traits was observed at W4 treatment. Among the nitrogen levels, N3 had the greatest impact on yield, yield components, essential oil percentage and thymoquinone in Nigella Sativa. In this experiment, interaction effect between water stress and nitrogen had only significant impact on essential oil and seed thymoquinone content, while it had no significant effect on all other studied traits. The maximum amount of essential oil and thymoquinone was obtained at W4N3 treatment.

Salicylic acid (SA), as a plant growth regulator, has an important role in alleviating the oxidative damages caused by drought stress in plant cells. In order to study the effect of different levels of SA on soluble protein content, the activity of enzymatic and non-enzymatic antioxidants including peroxidase, superoxide dismutase, ascorbate peroxidase enzymes, ascorbic acid and hydrogen peroxide and malondialdehyde levels and some physiological characteristics of two chickpea cultivars, [Kaka (MCC414) and Jam (MCC361)] under drought stress conditions, a factorial experiment was arranged based on completely randomized design with three levels of SA (0, 0.5 and 1 mM) and two moisture regimes, including drought stress (25% of field capacity) and control (100% field capacity) with three replications. Salicylic acid solutions at 0.5 and 1 mM concentrations were sprayed on leaves at intervals of 15, 25 and 35 days after sowing. Control plants were sprayed with distilled water. Results showed that at 25% field capacity, just peroxidase activity was enhanced in both cultivars. Drought stress reduced membrane stability index and PSΙΙ photochemical efficiency. Only in MCC414 cultivar, SA increased hydrogen peroxide and malondialdehyde contents under drought stress. SA significantly increased the activity of antioxidant enzymes including peroxidase and superoxide dismutase in MCC414 cultivar and ascorbate peroxidase enzyme activity in both MCC414 and MCC361. SA had not significant effect on the ascorbic acid content (P<0.05). Results suggested that SA at 0.5 and 1 mM concentrations could considerably improve membrane stability index and enhance PSΙΙ photochemical efficiency through reducing chlorophyll fluorescence under 25% field capacity.

Salinity stress is a major limiting factor for biomass production, especially in arid and semi-arid regions of Iran. Furthermore, the existence of vast areas of saline lands, and various halophytic species tend to utilize saline soil and water resources. To evaluate some physiological traits of fodder halophytes, an experiment was conducted at Salinity Research Station of Chah-Afzal, Yazd in 2009-2010. Nine forage halophytic species were propagated in the greenhouse, and then transferred to the field. The statistical design was complete randomized block with three replicates. During the growth season, plants were irrigated with saline water (8.39 dSm-1). At the end of the experiment, some physiological characteristics including water content, ash percent, canopy broadness and some mineral elements (Na+, K+, Cl-) were measured. Results showed significant physiological differences among halophytes, which could be related to different fodder potential of the halophytes. Among the halophytes, K. indica, S. aculeata and A. halimus could be considered as the most promising species in forage production based on the higher forage yield, low ash content and low amounts of Na and Cl ions. Considering the fact that high salt content in halophytes caused some limitations for forage palatability, S. aculeata could be selected as a suitable fodder species based on low ash content and low Na+/K+ ratio.

In order to investigate the effect of different concentrations of sodium bicarbonate on performance of four major varieties of cabbage, a greenhouse a factorial experiment was conducted based on a completely randomized design with three replications and two factors, including variety in four levels (cauliflower, cabbage, Brussels sprouts and kohl rabi) and sodium bicarbonate in three levels (0, 10 and 20 mM). Germinated seeds at four-leaf stage were transferred to four-liter pots containing aerated nutrient solution. After growing for 30 days, seedlings were treated with sodium bicarbonate for two months. Results showed that leaf and root dry weight significantly decreased by increasing the sodium bicarbonate concentration. Chlorophyll a, chlorophyll b, Fv/Fm and PI decreased in all varieties as a response to enhancement of sodium bicarbonate concentrations. The lowest reduction in chlorophyll a and chlorophyll b was observed in cabbage and cauliflower. Osmosis regulation processes were activated in cabbage plants in response to increase in sodium bicarbonate concentrations, as increases in proline and soluble carbohydrate were observed in kohl rabi plants. Increase of sodium bicarbonate concentrations led to reductions in P, K, Mg, Fe, Zn and Mn as well as increase in Na and Ca in all plants. Sodium bicarbonate stress, at 20 mM, led to a significant reduction in Fe concentration in leaf and root, so that Fe concentration of leaf decreased 150 percent at this level compared to the control. In association with variety results, the greatest Fe concentrations were observed in kohl rabi and cabbage plants.

To evaluate the freezing tolerance of seven wild oat genotypes (DR4, NR11, SOR1, STR1, ZR5, SM, SKh), a factorial experiment was performed based on completely randomized design with three replications at Ferdowsi University of Mashhad, Faculty of Agriculture in 2009. Amongst these wild oat genotypes, two of them (SM, SKh) were reported as herbicide susceptible, while herbicide resistance had been reported for the rest of them. Wild oat genotypes were exposed to seven freezing temperatures (-3, -6, -9, -12, -15,-18 and -21°C). Potted plants were grown in natural conditions and maintained for acclimation until 3-4 leaf stage and then, the plants were subjected to freezing temperature (FT) regimes using a thermo-gradient freezer. Plant electrolyte leakage, lethal temperature for 50% of samples based on electrolyte leakage (LT50el) and temperature for 50% dry weight reduction (RDMT50) were determined. Results showed that the effect of frost temperature, and genotype on the rate of electrolyte leakage and LT50el of genotypes was significant (P <0.01). Reducing the temperature less than - 9 °C increased electrolyte leakage in all genotypes. Among wild oat genotypes, SM and Skh showed the greatest and lowest cold tolerance according to LT50el and RDMT50, respectively. While this experiment confirmed differences in freezing tolerance amongst wild oat genotypes based on their geographical origins, results showed that herbicide resistance in wild oat may lead to change some other plant characteristics such as cold tolerance. So that based on these results, wild oat herbicide resistant genotypes (DR4 NR11, SOR1, STR1, and ZR5) had greater LT50el values comparing with Khoozestaan sensitive genotype (Skh).

In order to study the effect of drought stress on morphological traits, yield and yield components of sweet corn, a split plot factorial experiment based on RCBD was conducted with four replications at the experimental field of the agricultural and natural resources research center of Khorasan-Razavi (Tourogh station of Mashhad) in 2010,. Responses of three sweet corn hybrids (including two sweet and one super sweet hybrid) to three different water levels in two planting methods, were studied. Water levels [I1: 100%-(full irrigation or control), I2: 80% (moderate stress), and I3: 60% (severe stress) of field capacity] were assigned as main plots, while in sub plots, cultivar (Ksc403, Merit and Absizhen) and planting method (planting on the ridges or on the ditches) were combined as a factorial arrangement. Crop yield and 17 effective characteristics of sweet corn plants were studied in this study. Analysis of variance showed that there were significant differences between different hybrids in terms of evaluated traits. Drought stress also significantly affected all measured characteristics. Correlation analysis showed that in normal irrigation and drought stress conditions, ear length, leaves number above main ear and seed row per ear showed the greatest positive correlation with kernel yield. Stepwise regression analysis and principal component analysis showed that, 1000- seed weight, anthesis-silking duration (ASI) and kernel number in ear were the most limiting traits in sweet corn production.