مجله تنشهای محیطی در علوم زراعی
سال هشتم شماره 2 (نیمه دوم 1394)

Occurrence of drought stress at grain filling period is the prominent and inevitable characteristic of arid and semi-arid regions. The objectives of this research were to determine the effect of water deficiency and the role of current photosynthesis on grain filling, photosynthesis and gas exchange. Therefore, an experiment was carried out in a split-plot design based on a randomized complete block design with three replications at the Research Farm of Razi University in Iran during 2010-2011 cropping season. The irrigation treatments including non water stress (full irrigation over the whole season) and water deficiency stress (irrigation cessation after anthesis stage) were considered as main plots, while the factorial combination of eight wheat cultivars including Bahar, Parsi, Pishtaz, Pishgam, Chamran, Zarin, Sivand, Marvdasht and DN-11 line and the source manipulation treatments including control (Non source limitation), defoliation of flag leaf, defoliation of all leaves except the flag leaf, removing awns and shading over ears, were considered as sub-plots. The results showed that, post-anthesis water deficiency significantly decreased grain yield (22.2%) and 1000-seed weight (18.6%) compared to the control treatment and Removal of photosynthetic sources of assimilates reduced grain yield owing to grain weight reduction. The contribution of spike photosynthesis to grain filling (35.4%) was greater than the flag leaf (18.6%) and lower leaves (18.5%) and also, awns had the lowest contribution to grain filling (3.3%). Grain filling period was shortened during water deficiency stress, so that it reduced from 35 days under control conditions to 28 days under stress conditions, whereas it caused an increase in seed filling rate. Moreover, results indicated that photosynthetic source limitations caused an increase in photosynthetic rate and gas exchange. This increase reflects the compensatory role of photosynthetic rate of remained leaves in preventing yield loss.

Rapeseed is one of the most important oilseed crops that has major role in edible oil supply. In order to determine the best cultivar and seed rate for rapeseed and mustard under cold dryland conditions, this factorial experiment was conducted based on RCBD with four replications, two cultivars (Bard-1 and Hyola-401) and five seed rates (2, 3.5, 5, 6.5 and 8 Kg/ha equal to 50, 87, 125, 162 and 200 plants per square meter) during 2004-6 at North Khorasan Dryland Research Station (Shirvan). The traits including emergence and plant establishment percent, days to flowering, plant height, days to maturity, number of pods per plant, number of seeds per pod, thousand- kernel weight and grain yield were recorded. The effect of cultivar on all traits was significant (P < 0.01). Seeding rate had significant effects on days to maturity, days to flowering and emergence and establishment percent (P < 0.01). The cultivar Bard-1 with 814 Kg/ha had higher grain yield than Hyola-401 (736 kg/ha). The greatest seed yield (821 Kg/ha) was obtained where the seeding rate of 6.5 Kg/ha was used. According to the results of this experiment, seeding rate of 6.5 Kg/ha for spring sowing of the hybrid Hyola-401 and oil mustard Bard-1 under cold dryland farming conditions seem suitable. Moreover, sowing 00 and early maturity cultivars are preferable to canola cultivars under dryland farming of cold regions of Iran.

Castor been plant is a forgotten crop which its cultivation has experienced a lot of ups and downs in the world, and given the key role of the castor oil in different industries, an experiment was carried out to study the effect of salicylic acid and spermine on yield and yield components of castor bean under drought stress as split plot based on randomized complete block design with three replications in 2012. The irrigation regime was considered as the main plot, based on the fraction of the class A pan evaporation (0, 0.2 and 1.2% CEA), and spraying of salicylic acid (0, 250 and 500 µM) and spermine (0, 10 µM and 1 mM) were arranged as sub plots. Drought stress significantly decreased the number of capsule per plant, number of seed per plant, grain yield, biological yield, 100- seed weight and harvest index. Salicylic acid and spermine treatments significantly affected the yield and yield components of castor bean under drought conditions. The greatest yield was obtained with 250 µM salicylic acid. Salicylic acid and spermine alleviated the drought stress impact, while the effect of salicylic acid showed a greater significant effect on crop yield than that of spermine treatments.

In order to evaluate the effects of methanol on yield and some quality characteristics of sugar beet (Beta vulgaris L.) under drought and non-drought stress conditions, a study was conducted in maahdasht (Karaj, Iran) in 2012. The first factor was Aqueous solutions of methanol including 0 (control), 7, 14, 21 and 28% (v/v) and the second factor was three levels of irrigation including normal irrigation (irrigation after 40% depletion of available water), mild drought stress (irrigation after 60% depletion of available water) and severe drought stress (irrigation after 70% depletion of available water). These solutions were sprayed over head 3 times in two week intervals on foliage parts of sugar beet during plant growth. The first spraying was done 80 days after crop sowing. In this study, qualitative and quantitative traits like root yield, aboveground yield, white sugar content, root dry matter percent, sugar percent content, Na, K and harmful N amounts, molasses sugar percent, extraction coefficient of white sugar and extractable sugar percent were evaluated. Results indicated that there were significant differences between effects of methanol solutions on root yield, leaf yield, white sugar yield, dry weight of root, molasses, extraction coefficient of sugar, white sugar content, N and Na concentrations. The greatest root yield, aboveground yield, and white sugar yield were gained with 7% (v/v) of methanol with 72.62, 61.76 and 9.91 ton/h, respectively. There were also significant differences between irrigation levels in traits such as root yield, leaf yield, extraction coefficient of sugar, root dry weight percent, sugar content and K and harmful N concentrations and white sugar content.

Water is one of the most important factors for plants growth and development and both weeds and crops compete for it. To investigate the influence of drought stress on competition between grass pea and pigweed, a greenhouse experiment was conducted as randomized complete block design with three replications based on replacement series arrangement at Faculty of Agriculture, University of Birjand in 2012. Treatments were different planting ratio of grass pea– pigweed (100-0, 75-25, 50-50, 25-75, 0-100%) and four water regimes (100, 75, 50 and 25% soil field capacity, FC). Results showed that a reduction of soil water content from 100 to 25% of FC (pot) caused a 95% (P <0.01) in dry matter production of both species in their pure cultivation. The relative yield index, relative invasion index and relative dominance index of these species indicated that, where both plants were competing, pigweed was more competitive than the grass pea at high soil moisture levels (100 to 50% of the soil (pot) field capacity). Although with further soil water reductions to 25% of field capacity, grass pea showed the superiority over wild amaranth, it seems that growing grass pea is not economically justifiable under these circumstances.

In order to determine the relationship between agronomic traits of rice genotypes (6 drought tolerant and one native cultivars) under flooding and drought stress conditions, two separate experiments were conducted as split- plot in randomized block design with tree replications at the research farm of Gonbad Kavous University during spring 2010. The main plots were weed control in three levels (controlling weeds until maximum tillering stage, weed control from maximum tillering till maturity and un-weeded) and sub plots consisted of rice genotypes (Shiroudi, Domsiah, IR70358-84-1-1, IR70358-84-1-2, WAB56-125, IR83752-B-B-12-3 and KORAL). Yield and yield components of cultivars showed significant differences under flooding and drought stress conditions (p<0.05). Moreover, each cultivar had significantly different yield and yield components under the two environments (p<0.05). Considering the correlation coefficients among traits under flooding and drought environments showed that in either of different moisture conditions grain yield had significant and positive correlation with straw yield, harvest index, filled grain number and fertile tiller number. Results of step wise regression showed that under flooding condition, straw yield and harvest index traits and under the drought stress condition, harvest index and straw yield entered the final multiple regression model as important characteristics and effective traits on grain yield (93.4%), respectively. Evaluation of direct and indirect effects of each of the yield components on grain yield via path analysis showed that in each of the different moisture conditions, number of filled grains due to positive and high direct effect and number of fertile tillers due to indirect effect via number of filled grains can be considered as the most important traits for increasing the grain yield.

Rice is one of the most important agricultural products in Iran and all over the world, drought stress is a significant limiting factor in producing this crop. Breeding for drought tolerance could be an effective method to improve yield and its stability in drought regions. In order to determine the drought tolerance, a factorial experiment based on RCBD with three replications was conducted under hydroponic culture conditions at the plant breeding laboratory of Gonbad-e-Kavous University in 2012. Treatments were 22 rice genotypes and drought stress in 2 levels (control and -5Bar). The studied traits included the root dimension, root weight, root number, root length, stem weight, stem length, genotypic code (the relative tolerance of genotypes to drought stress) and biomass. Analysis of variance showed that there were significant differences (p< 0.01) amongst genotypes in all studied traits, which implies the existence of genetic diversity among genotypes. In cluster analysis based on seedlings traits, genotypes which were in a group with the tolerant cultivar Bala were named as the tolerant group and genotypes that were classified in a group with semi-sensitive Azucena were called as the sensitive group. Results of stepwise regression analysis for biomass as dependent variable and other traits as independent variables showed that stem and root weight had the greatest effect (R2=0.61) on the biomass under drought conditions, respectively. The results showed that there was genetic diversity for studied traits amongst the genotypes and they can be used to improve drought tolerance in high-yielding rice varieties.

In order to evaluate crop yield and its components and determination of the most important traits influencing yield, seven genotypes of sunflower were planted under normal irrigation and drought stress conditions in two separate experiments based on randomized complete block design with three replications at Birjand University Research Farm in the cropping season of 2010-2011. Treatments included two levels of stress and normal conditions. Measured traits included yield, seed per head, seed weight, head diameter, plant height, leaf width, leaf length, leaf number, top diameter of the stem, bottom diameter of the stem, petiole length, the distance between ground and head, and the distance between ground and the highest point of the stem. Results of the simple analysis of variance showed that the distance between the ground and head, bottom diameter of the stem, leaf number, plant height, 1000-seed weight and seed yield were significantly different amongst cultivars under both conditions. Compound analysis of variance showed that all traits except the leaf length were significantly different amongst genotypes studied under two conditions and stress effects were significant on yield, 1000-seed weight and head diameter. The correlation between crop yield and seed per head, leaf width, petiole length, top and bottom diameter of the stem, head diameter, 1000- seed weight and the distance between ground and the highest point of the stem was significant under normal condition, while under stress conditions, crop yield merely had significant correlation with seeds per head. Multiple regression results showed that the seeds per head, diameter of head, 1000-seed weight and petiole length were the most influential traits under both conditions. The path analysis showed that the seed per head is the most influential trait in crop yield. Factor analysis identified three and five factors under normal (explained 79.37% of the total variations) and stress conditions (explained 86.88% of the total variations), respectively. Cluster analysis classified genotypes in two and three categories under normal and stress conditions, respectively.

This study was carried out to investigate the genetic variation of sugar beet testcrosses for drought tolerance in the lab (faculty of Tabriz Islamic Azad University) and field conditions (Khorasan Agriculture and Natural Recourses Research Center) in 2010. In the lab study, two factors including 49 genotypes (44 test cross hybrids and 5 control treatments) and 5 drought stress levels (0, -2.5, -5, -7.5 and -10 bar) were analyzed using a factorial experiment based on completely randomized design with three replications. The field study was conducted based on a square lattice design (7 x 7) with three replications. The results showed that genotypes and different stress levels had significant differences for germination percent, radicle, plumule length, and fresh and dry weight of radicle and plumule. Drought tolerant genotypes under lab conditions (genotypes number 1, 10, 22, 23, 32, 41 and 49) were superior to other groups with mean traits of germination percent, and dry weight of plumule and radicle of 43.29%, 4.22 µg and 2.75 µg. In terms of field traits, the drought tolerant group (genotypes number 11, 15, 19, 21 and 43) with white sugar yield of 10.18 t ha-1 was superior to the sensitive group with 5.84 t ha-1 of white sugar yield. The cluster analysis showed the sugar beet genotypes were subdivided into 5 and 4 groups based on traits studied in the lab and field, respectively. These results emphasis on genetic variation for drought tolerance amongst the studied genotypes. Percent of germination and radicle dry weight under stress conditions can be employed as traits that are effective for selection of drought tolerant genotypes under field conditions.

In order to identify the drought tolerant lines of wheat, 67 recombinant inbred lines with their parents (Roshan and Superhead) were studied in two separate experiments based on randomized complete block design with two replications under normal and drought stress conditions during 2011-2012. For identification of drought tolerant lines, seven drought-tolerance/susceptibility indices including stress susceptibility index (SSI), mean productivity (MP), tolerance (TOL), stress tolerance index (STI), geometric mean productivity (GMP), yield index (YI), yield stability index (YSI), the stress tolerance score and factor analysis were used. Analysis of variance showed significant differences among lines for grain yield and drought-tolerance/susceptibility indices under stress and non-stress conditions. The stress tolerance score was successful in separating lines of group A from other groups (B, C, and D). Based on the stress tolerance score and factor analysis, lines 139, 69, 19, 23, 149, 117, 27, 181 and 94 were selected as tolerant lines for further studies.

Oat as one of the cultivated cereals in the most parts of the world has many food and medicinal properties. It has a potential to grow economically in Iran, but like other crops, drought stress could be a limitation in developing and getting desired production. So, in order to study the drought tolerance of 25 oat genotypes, an experiment was conducted in a randomized complete blocks design with three replicates under normal and drought stress conditions in Research Farm of the Campus of Agriculture and Natural Resources, Razi University, Kermanshah, Iran during 2012-2013 cropping season. Based on the potential (Yp) and stress (Ys) yields, 14 quantitative criteria of drought tolerance were calculated. A high positive and significant correlation was observed between Ys and Yp with MP, GMP, STI, YI, HAM, K1STI and K2STI which indicated that these indices were the most suitable indices to screen drought tolerant genotypes. According to all statistical procedures including calculated indices, ranking method, 3D plot, principal components analysis, biplot and cluster analysis, genotypes ‘Ufrgs948886’ and ‘Euro’ were known as superior genotypes under both stress and non-stress conditions.

Salinity is going to become a serious problem in different regions of the world. The saline area is three times larger than lands used for agriculture. Therefore in order to evaluate the effect of salinity on some biochemical and morphological indices of wheat genotypes, a factorial experiment was conducted based on completely randomized design with three replications under hydroponic cultivation conditions. Treatments were two salinity levels (0 dS m-1 (control) and 6 dS m-1) and three wheat genotypes including Tabasi and two mutant lines (T-67-60, T-65-7-1). First, seeds of mutant line, T-67-60 and T-65-7-1 and Tabasi were sterilized to have seedlings free of contaminations. Then, the seeds were placed on wet filter papers in the petri dishes and were placed in an incubator set at 24±1 °C under dark conditions for 3 days. Then seedlings were exposed to salinity and control treatments in Yoshida fluid using hydroponic method. Shoot and root fresh and dry weight, as well as root and shoot length as morphological traits and ascorbic acid, lipoxygenase enzyme (LOX), chlorophyll and TBARM amount as biochemical traits were measured. Results showed that salinity stress had adverse effects on plant growth. LOX, TBARM and chlorophyll level showed significant differences in the studied genotypes under the salinity conditions. Tabasi showed the greatest variations of LOX and TBARM content while the lowest amounts belonged to line T-67-60. Regard to negative correlation between TBARM, LOX and chlorophyll level with salinity tolerance; it seems that T-67-60 mutant line had the highest tolerance compared to the other genotypes.

This study was conducted to evaluate the yield and yield components of promising lines of barley under saline irrigation water (ECw=10 dS/m) at experimental farm of Agriculture and Natural Resources Research Center of Yazd, located in Ardakan during the 2012-2013 growing season. 18 promising lines and two control lines (EMBS-89-18 and Line-4-salt) were studied in a randomized complete block design with three replications. Seedling emergence percent, plant height, number of infertile and fertile tillers, spike length, number of seed per spike, spike yield, seed weight, hectoliter weight, protein, phosphorus and ash content of grain were measured. Salinity has no significant effect on field emergence percentage. There were significant differences in most studied traits among the lines. However, lines were divided into four groups, based on the yield and yield components. A group that consisted 6 lines along with control line EMBS-89-18, produced more yield than other lines. Thus, these lines could be considered for more investigations for cultivation in saline areas. Based on the agronomic characteristics, it can be said that barley genotypes with restricted and faster tillering, higher reproductive components per spike, seed weight and biomass were more tolerant to salinity which could produce acceptable grain yield under these conditions. The stepwise regression analysis showed that 1000-seed weight justified 52% of the variation in grain yield per plant, therefore, it could be concluded that 1000- seed weight was the most important yield component under saline condition.

The salinity of water resources and soil is one of the most important agricultural problems in arid and semi arid regions of Iran. In order to investigate the effects of saline irrigation water on phyllochron and leaf appearance rate of barley cultivars, a factorial experiment based on randomized complete block design with three replications was conducted at the greenhouse of Faculty of Agriculture, University of Mohaghegh Ardabili during 2010. Studied factors were barley cultivars (Makoei, Lisive and Sahand) and salinity of irrigation water in pots in four levels (common water as control as well as irrigating with saline water levels of 20, 40 and 60 Mm using NaCl). Traits such as leaf appearance rate, phyllochron, the number of leaves per plant, leaf area index and leaf dry matter per plant were studied. The results showed that phyllochron (the time interval between the appearance of successive leaves on a shoot) were significantly affected by saline irrigation water, cultivar and interaction of saline irrigation water× cultivar. Increasing salinity increased the phyllochron, while decreased the rate of leaf appearance. There were significant differences amongst cultivars in this regard. Leaf appearance rate of Sahand cultivar was more than other cultivars. Means comparison of treatment compounds of saline irrigation water× cultivar showed that the greatest phyllochron was obtained in treatment compounds of irrigation with salinity 60 Mm × Lisive cultivar and the lowest of it was observed in irrigation with common water × Sahand cultivar. saline irrigation water decreased leaf area index. In all salinity levels, the trend of leaf area index variations was similar until 24 days after sowing. From 24-64 days after sowing, LAI showed a progressive trend, so that it reached to a maximum level at 64 days after sowing and then decreased slowly till 74 days after sowing. This might be related to increased aging of leaves, shedding and competition between plants for light and other resources. The highest leaf area index (1.95) was obtained in treatment compound of irrigation with common water×Sahand cultivar and the least of it (0.89) was observed in irrigation with salinity of 60 Mm×Lisive cultivar. Saline irrigation water reduced the number of leaves per plant and leaf dry weight. It seems that in order to increase the leaf appearance rate, LAI and number of leaves per plant, it can be suggested to employ the Sahand cultivar under irrigation with saline water.

In order to study the effects of exogenous application of salicylic acid (SA) on the growth and some physiological and biochemical responses of sugarcane (Saccharum officinarum L.), a factorial experiment was conducted based on randomized completely design with three replications in a greenhouse at the Institute of Development Research and Training for Sugarcane Crop in Khuzestan, Iran in 2012. Treatments evaluated in this study were three levels of salt stress, including (ECW<1 dS / m, ECW = 3 dS / m, ECW = 6 dS / m), and four concentrations of (SA) including 0, 0.5, 1 and 1.5 mM. Results showed that the effect of salt stress and application of SA were significant (P < 0.05) on various physiological, biochemical and also morphological indices. The foliar application of SA during vegetative phase caused enhancements in plant height, aboveground fresh weight, root fresh weight and a reduction in cell membrane relative permeability. The most effective treatment was spraying with 1 mM SA which resulted in 11.38, 8.88, 18.23,10.61 and 55.80 % increase in plant height‚ shoot fresh weight, root fresh weight, total dry weight, shoot K+/Na+ ratio, respectively, and 15.28 % reduction in plasmalemma permeability in comparison with control treatment. The application of 1.5 mM SA showed less positive impact under salinity stress due to alterations of plant physiological traits compared to other SA concentrations. The results suggested that application of 1 mM SA was effective in reducing the damage of salinity and its foliar application under similar soil and water conditions could be helpful for sugarcane production with salinity up to 3 dS/m.

Applications of chemical substances such as triazoles can alleviate the environmental stresses like cold stress. Therefore, a factorial experimental based on completely randomized design was conducted. Different concentrations of paclobutrazol (0, 10, 20 mg per liter) were applied on seedling roots environment before freezing stress and after that plants were exposed to freezing temperatures (0, -3, -6, -9, -12 and -16°C) under controlled conditions. Before applying freezing temperatures, soluble sugar, proline, total phenol, photosynthetic pigments and DPPH radical scavenging activity were measured. Following exposure to freezing temperatures, cell membrane stability and a temperature lethal to 50% of samples based on electrolyte leakage (LT50el) were determined. Survival and regrowth of plants were determined at three weeks after seedlings recovery under natural conditions. Results showed that the electrolyte leakage remained constant where the temperature was reduced to -9°C, and reducing the temperature to -12° C caused a sharp increase in electrolyte leakage. Moreover, plants survival was not influenced up to -9 ° C, but reducing the temperature to -12°C caused a significant reduction in plant survival. Paclobutrazol application increased chlorophyll a, b, DPPH radical scavenging activity and survival in kochia, whereas decreased proline, soluble carbohydrates, total phenol concentration and electrolyte leakage. Influence of Interaction between temperature and population on total pigments indicated an increase in pigment content in Broojerd population at 20 milligrams per liter of paclobutrazol, and proline and carbohydrates contents were significantly greater in Sabzevar population where no paclobutrazol was applied. Generally, application of 10 and 20 milligrams per liter of paclobutrazol prevented a severe reduction of kochia plants survival under freezing stress.

Cogongrass is one of the most serious weeds in palm groves and sugar cane industry of Khuzestan. Understanding the impact of environmental stresses on the ability of vegetative propagation and rhizome sprouting of this weed can help to control this species. Therefore 5 cm rhizomes with 2-3 mm diameter in two separate tests were conducted based on completely randomized design with 4 replications and 6 drought levels (0, -0.3, -0.6, -0.9, -1.2 and -1.5 MP) using polyethylene glycol 6000 and six salinity levels (0, 3, 6, 9, 12 and 15 dS/m) using sodium chloride at Research Laboratory of the Research Institute for Education Development and Cane Industries of Khuzestan. In this experiment rhizomes were placed in a germinator set at 22/30 ° C and light conditions of 8/16 hours (night / day). The results indicated that increasing drought and salt stresses significantly (p<0.01) decreased the rhizome germination rate and percentage compared to the control treatment. Based on the estimation of 3-Parameter logistic models, the salinity and drought values for 50% reduction in rhizomes germinability were 6.42 dS/m and -0.96 MP, respectively. According to these research findings, cogongrass rhizomes were able to sprout under either salinity or drought stresses, indicating this species is a troublesome noxious weed even under such stresses.

To evaluate the effect of drought stress on some morphological and physiological properties of Echium amoenum Fisch & Mey medicinal plant, an experiment was carried out in completely randomized design with four replications at the research greenhouse of Institute of Medicinal Plants of Iranian Academic Center for Education, Culture and Research (ACECR). In this experiment, the effect of different levels of drought stress including irrigation in field capacity as control treatment and irrigation after discharging 25, 50 and 75 percent of water on plant quantity characteristics (Leaf length and width, Root length, Root and Shoot fresh and dry weight) and quality characteristics (Proline and Total soluble sugar content) in vegetative growth level were investigated under greenhouse conditions. The results showed that drought stress caused a reduction in all morphological characteristics (except for the root length) while the concentrations of proline and leaves total soluble sugar with increasing levels of drought stress were significantly increased compared to control. The results showed that the accumulation of proline and soluble sugars were good indicators of drought tolerance. With increasing levels of drought stress, amount of leaves proline increased more than 5 times compared to control. Also, by increasing the drought stress severity from control (no stress) to 75% depletion of available water treatment, the content of leaves soluble sugars increased 2 times compared to control. Generally, results showed that this plant is tolerant to the drought stress by osmotic adjustment and this mechanism resulted in plant survival under drought stress conditions.

To evaluate the grain yield of fifteen rapeseed genotypes under drought stress using drought resistance indices, an experiment as a randomized complete block design with three replications was performed under irrigated and dryland farming conditions at the research farm of campus of Agriculture and Natural Resources of Razi University of Kermanshah over 2012-2013 cropping season. The sensitivity stress index, tolerance, harmonic mean, geometric mean of the average production, stress tolerance, yield and yield stability were calculated based on grain yield under two conditions. Combine analysis of variance showed that the environment significantly affected grain yield so that the average yield under irrigated environment was more than dryland farming. There was a significant difference between genotypes for grain yield and drought resistance indices under both conditions. Considering correlations of indices showed that MP, GMP and STI had significant correlation with grain yield in both conditions, and based on three-dimensional chart of these indices, genotypes HW113, L146 and L201 were superior genotypes for both conditions. According to the bi-plot of two first principal components, the genotypes HW113, L146 and L201 were the most tolerant to drought stress, and genotypes L72 and OPERA were the most susceptible genotypes to drought stress environment.