جستجوی مقالات مرتبط با کلیدواژه « heat stress » در نشریات گروه « زراعت »

Environmental factors, especially temperature, are very important in the proper occurrence of saffron flower initiation stage during summer. In areas affected by heat stress, any factor that reduces the stress intensity seems to be beneficial in improving saffron reproductive growth. Corm storage under desired environmental condition is a potential strategy, when saffron is grown as an annual crop. In perennial saffron plantation, where the corms spend the flowering stage in the soil, other solutions should be considered for the proper occurrence of the flowering stage. One of these solutions is to use plant residues in the field surface to reduce the soil temperature. The presence of plant residues causes shading on the soil surface, increases the amount of sunlight reflection, reduces evaporation from the soil, regulates the moisture content of the soil, and reduces the temperature at the depth of the corm placement. Another possible solution to adjust the soil temperature during the flower initiation phase of the corm is to carry out summer irrigation, but there is not enough certainty about its usefulness. Therefore, the aim of the current experiment was to investigate the effect of storage conditions of corms, as well as the effect of summer irrigation and the application of plant residue mulch on saffron flowering.

To investigate the effect of corm storage conditions on saffron reproductive growth an experiment was carried out as complete randomized block design with seven treatments and three replicates during 2019 growing season, in Qaen, Iran. Experimental treatments were three types of corm storage inside the soil [corm planting in 5th June (A) with natural soil temperature as control, A + summer irrigation in 5th August and A + mulch application obtained from wheat residues at the rate of 8 ton ha-1)] and three types of corm storage outside the soil [Corm storage at room (ambient temperature) for three months started from 5th June + corm planting in 5th September (B), Corm storage in constant temperature (25 oC and relative humidity of ~40 %) in incubator for three months + B, three months corm storage at variable temperature in incubator (one month in 20, 25 and 20 oC) + B and corm storage in room (up to 5th August) and incubator (up to 5th September) + B.
 

Results showed that summer irrigation increased the number, length and weight of cataphylls compered to control. Corm storage outside the soil (room or incubator) reduced the weight and length of cataphylls. Control and summer irrigation treatments had no significant different in terms of flower number, flowering rate and flower yield, but were superior to other treatments in terms of all the mentioned traits, especially compared with the room storage treatment. The highest values of mean flower weight (0.37 g), flower length (7.6 cm) and stigma length (2.83 cm) were obtained in mulch application treatment. Mulch application failed to improve flower and stigma yields, despite decreasing the soil temperature during the flower initiation stage. The highest values of stigma yield were gained at control, summer irrigation and mulch application (8.07, 7.28 and 6.40 kg ha-1, respectively), which were significantly more than those obtained at room storage (3.24 kg ha-1), storage in incubator with variable temperature (3.68 kg ha-1), storage in room and incubator (3.89 kg ha-1) and storage in incubator with constant temperature (4.28 kg ha-1).
 

Overall, the passage of saffron flower initiation stage inside the soil significantly improved the flowering of the plant compared to the passage of this period outside the soil under room or incubator conditions.

Among the most common problems and stress in the conditions of Khuzestan province, heat stress at the end of the season and the deficiency of nutrients, which occurs in different periods of rapeseed growth, depending on their severity, causes physiological and metabolic disorders and ultimately reduces the yield of rapeseed plants with different intensity depending on the type of plant genotype, they affect

With the aim of evaluating the growth and yield response of rapeseed cultivars (Brassica napus) to boron element levels in late season heat stress conditions caused by late sowings dates, this study was carried out in a split-split plot arrangement in the form of a randomized complete block design with three replications. The expeiment was carried out in the crop year of 2021-2022 in the research farm of Agricultural Sciences and Natural Resources University of Khuzestan. Sowings dates (November 21, December 11, and December 31) in the main plots, four levels of boron (zero, 4, 8, and 12 kg/ha) in the subplots and rapeseed cultivars (RGS, Zafar, and Saffar) in the sub-sub-plots were investigated.

The results of the research showed that sowing date and end of season heat stress in Khuzestan conditions had a significant effect on most of the studied physiological traits, seed yield and biological yield. In addition, the effect of boron on traits such as leaf area index, leaf area ratio, and relative moisture content of leaf water, leakage of electrolytes, grain yield and biological performance was significant. The triple interaction effect of planting date, boron and variety was also significant on traits such as relative moisture content of leaf water, leakage of electrolytes, grain yield, and biological performance. So that with the delay in planting and the consequent increase in temperature and heat stress at the end of the season in the period of growth of the rapeseed plant, it causes a decrease in traits such as leaf area index, relative moisture content of leaf water, leaf area ratio, leaf specific area, seed yield and biological yield. And conversely, due to the heat stress at the end of the season, the leakage of electrolytes and the canopy temperature increased significantly. In general, the highest seed yield was obtained in Safar variety on the sowing date of December 11 and the boron level was 4 kg/ha with an average of 4590 kg/ha. Also, the highest average leaf area index was observed on the first sowing date and Safar variety with an average of 5.43 and the lowest value was observed on the third sowing date and Safar variety with an average of 2.11. It was also observed that the application of boron caused a significant decrease in the leaf area index in all three studied cultivars. This issue can indicate the lower need of boron consumption of the studied cultivars in this experiment.

In general, the heat stress at the end of the season, which occurs in different periods of rapeseed growth, especially the seed filling period, depending on its intensity, causes physiological disorders in the plant and finally affects the grain yield with different intensity and depending on the genotype of the plant. The analyzed rapeseed genotypes also showed tolerance to different levels of boron element in the heat stress conditions of the end of the season and showed different reactions with different amounts of boron consumption per hectare.

Climate change is a very serious threat to crops production in all regions around the world. Heat stress is a consequence of climate change that affects biochemical, physiological and molecular processes of crop plants, causing alterations in crop growth, development, and productivity. Terminal heat stress is the most widespread and type of heat stress in the world that limits crop productivity and ultimately food security. Sunflower is moderately tolerant to heat stress. It can tolerate higher temperatures without suffering from heat stress. However, sunflower is more susceptible to heat stress from early flowering to grain filling. Hence, it may be severely damaged when exposed to terminal heat stress. Biochemical and physiological responses in crop plants are modified under heat stress. It has been shown that tolerance to heat stress in crop plants is associated with an increase in antioxidant enzyme activities. The physiological and biochemical responses to heat stress vary among crop plant species and genotypes which can be used for development of cultivars with high temperature tolerance in crop plants.

This experiment was carried out in 2017-2018 growing season in Ahvaz, Iran, using as split-plot arrangement in randomized complete block design with three replications. Main plots consisted of three sowing date including; 11th November, 11th December and 11th Janauary, and five sunflower cultivars including; Qasem, Fantasia, Shams, Lakomka and Progress were randomized in sublpots. Sowing on 11th November was considered as normal sowing date, and sowing on 11th December and 11th January were delayed and late sowing dates, respectively. In the two latter sowing dates, flowering and grain filling periods were exposed to moderate and severe terminal heat stress.

Terminal heat stress in delayed and late sowing dates caused significant reduction in carotenoid content (27% and 56%, respectively), seed yield (30% and 32%, respectively) and oil yield (18% and 28%, respectively), but increased catalase (63% and 55%, respectively), peroxidase (107% and 56%, respectively) and superoxide dismutase (43% and 67%, respectively) enzyme  activities, carbohydrate concentrations (18% and 30%, respectively) and malondialdehyde concentration (46% and 98%, respectively), when compared to normal sowing date. There was significant differences among sunflower cultivars for most of studied traits. Lakomka cultivar with the highest values of biochemical and physiological indices such as chlorophylle content, antioxidant enzyme activities and carbohydrates concentration and with the lowest malondialdehyde concentration had the highest seed yield (1579 kg.ha-1) and oil yield (608 kg.ha-1) under terminal heat stress.

Exposure to moderate and severe terminal heat stress differently influenced physiological and biochemical traits in sunflower cultivars. The severity of terminal heat stress played an important role in the cultivars responses. Progress cultivar had the lowest reduction in oil and seed yield under terminal heat stress, however, cv. Lakomka showed highest seed and oil yield in all three sowing dates. Therefore, it can be concluded that cv. Lakomka is suitable for being sown in normal, delayed and late sowing dates due to least variability in its seed yield.

In the pursuit of a resilient and progressive agricultural system, the incorporation of diverse fertilizers is deemed essential. This practice not only enhances product quality but also aids in cost reduction. However, over-reliance on a specific type of input can inadvertently lead to unintended repercussions. The unrestricted utilization of chemical fertilizers, for instance, can precipitate adverse outcomes such as imbalanced pH levels, the accumulation of heavy elements, soil structure deterioration, and environmental contamination. Conversely, organic fertilizers, while environmentally friendly, often release nutrients at a slower rate, potentially disrupting optimal plant growth. To attain a balanced and sustainable agricultural approach, the combined application of organic and chemical fertilizers is advocated. Moreover, harnessing the biological potential inherent in soil ecosystems, including beneficial microbial communities encompassing bacteria and fungi, emerges as a promising avenue in cultivating sustainable agriculture. Acknowledging the adverse impact of late-season heat stress on wheat production in Khuzestan and recognizing the significance of reducing chemical fertilizer usage while augmenting organic and biological fertilizers to foster ecological health, this experiment undertakes the exploration of the effects of a synergistic approach. Specifically, it delves into the combined utilization of nitrogen and compost fertilizers, complemented by the incorporation of plant growth-promoting rhizobacteria. This endeavor aims to shed light on how this combined strategy operates within the context of terminal heat stress, assessing its influence on the physiological attributes and yield of the wheat cultivar Chamran 2.

This experiment was carried out as split-split plots based on a randomized complete block design with three replications in the crop year of 2021-2022 in the research farm of Agricultural Sciences and Natural Resources University of Khuzestan. The experimental factors include three planting dates: December 1st, December 20th, and December 10th in the main plots; Six levels of combined use of nitrogen fertilizer with compost fertilizer include control (without nitrogen and organic), 100% nitrogen, 75% nitrogen+ 25% compost, 50% nitrogen+ 50% compost, 25% nitrogen+ 75% compost and 100% compost in sub-plots and two levels of application and non-application of plant growth promoting rhizobacteria in sub-plots. Each sub-plot was 3 meters long and 2 meters wide (with an area of 6 square meters) and included 10 crop lines at a distance of 20 cm from each other. The distance between the main and secondary plots was considered to be half a meter and the distance between the blocks was two meters. After physiological maturity, the plants were harvested and the physiological traits and grain yield were measured.

Variance analysis showed that the interaction effect of planting date, combined use of nitrogen with compost, and plant growth promoting rhizobacteria, on the traits of relative leaf water content, planting to flowering, and grain yield were significant at the 1% probability level. Also, the interaction effect of planting date and the combined use of nitrogen with compost on all traits except the length of the grain filling period and the length of sowing to physiological maturity was significant at the probability level of 1%. The mean comparison showed that the highest relative leaf water content, cell membrane thermostability, and canopy temperature depression were obtained from the treatment of 100% compost, and the highest traits of the length of sowing to flowering and length of sowing to physiological maturity were obtained in the use of 100% nitrogen. Also, the longest grain filling period, grain filling rate, and grain yield were obtained in the combined use of 50% nitrogen+ 50% compost and plant growth-promoting rhizobacteria, and the lowest value was obtained in the control of not using nitrogen and compost. In general, the delay in planting and the occurrence of terminal heat stress caused a decrease in grain yield, but on different planting dates, the combined use of 50% nitrogen+ 50% compost compared to the treatment of 100% nitrogen increased wheat grain yield.

According to the obtained results, in areas with terminal heat stress, the combined use of 50% nitrogen+ 50% compost and plant growth-promoting rhizobacteria can be considered to increase the growth and yield of wheat.

Heat and its effects are considered one of the serious threats and damages to the production of agricultural and horticultural crops in many regions of the world. Therefore, it has led to pervasive changes in terms of morphological, physiological, anatomical, and molecular, which causes a sharp decrease in the economic performance of agricultural products. Nowadays, in order to reduce these inhibitory effects, in addition to classical and conventional breeding methods, modern and molecular methods can be used to identify heat-tolerant genes and use them in breeding programs to improve plant tolerance to environmental stresses.

The selection for heat tolerance among four local cultivars Hovyzeh, Hamar, Red-Anbori, Champa and three promising heat tolerant lines V1, V2 and V3 obtained from the international breeding programs of Khuzestan Agricultural Research and Training Center and Natural Resources were evaluated by osHATS and HSP70 genes qPCR on two experimental cultivation dates: May 20 (unfavorable) and June 20 (favorable) 2022 in Ahvaz.

The results obtained from the analysis of gene expression by qPCR on the date of the first cultivation confirmed the presence of the osHTAS gene in rice varieties and lines so that the local variety Champa, Hovyzeh, and line V2 has a high relative gene expression compared to other varieties and lines studied and they were significantly different from each other. The analysis of the osHTAS gene expression on the second planting date (June) in Ahvaz also shows the presence of the high-temperature tolerance gene in Hovyzeh, Hamar and V2 lines; therefore, the mentioned varieties could be used as parental lines for transfer heat tolerance gene to be used in multi-breeding programs and terms of the relative expression level of the gene, they showed a statistically significant difference with each other. The results of the relative gene expression of the HSP70 gene in the cultivation date of May showed that the local cultivars Champa, Red-Anbori and Hovyzeh had a remarkable superiority over the others. Examining the HSP70 gene expression pattern of rice cultivars and lines on the second planting date also revealed that the local cultivars Red-Anbori, Champa, Hovyzeh, and Hamar showed superiority. The tolerance of local cultivars to heat stress is due to their rapid growth and the creation of a large green cover in the early stages of growth, and their great adaptation to the region's environmental conditions.

Local cultivars can withstand heat stress well with rapid growth and creating much vegetation due to their high adaptability to environmental conditions and the presence of heat stress tolerance genes. They could be used as parental lines in breeding programs.

In order to study the effect of hormone cytokinin on morphological and yield traits of sunflower cultivars under terminal heat stress, a field experiment carried out in a split plot factoril in randomized complete block design with three replications at the research farm of Shahid Chamran University of Ahvaz in 2021. The main plots consisted of three sowing dates; 3 Feb, 18 Feb and 5 Mar, the sub-plot consisted of factorial arrangement of different concentrations of cytokinin (0, 25 and 50 and 75 μm l-1, Kinetin), and sunflower cultivars (Qasem and Oskar). Sowing date with desired temperature considered as control and delayed and late sowing dates considered as mild and severe heat stress so that the flowering and grain filling periods faced with terminal heat stress. Results showed that terminal heat stress in delayed and late sowing dates caused a decrease in plant height, grain number per head, head diameter, 1000-grain weight, biological yield, oil percentage, and oil and grain yield. The optimum hormone concentration needed to exhibit a considerable increase in studied traits of sunflower cultivars under heat stress was 50 μm l-1,particularly, in Late sowing date sunflower plants, foliar application of cytokinin (50 μm l-1) increased grain yield (by 17% and 15%), biological yield (by 5% and 8%), and oil yield (28 and 13%), in Oscar and Qasim cultivars, respectively. Results show that foliar application of cytokinin (50 μm l-1) can be considered as a strategy to enhance the grain yield of sunflower cultivars under under heat stress conditions in tropical regions such as Khuzestan.

Rising temperatures are a severe warning to humans, and heat stress is one of the principal environmental stresses that reduce the yield of crops, including wheat, worldwide. The increase in carbon dioxide in the atmosphere has caused global warming, affecting agriculture in the future. More than 50 countries experience heat stress during the wheat growing season. Therefore, the development of heat-tolerant cultivars is one of the main goals of wheat breeding programs. This study aimed to evaluate the drought tolerance indices and determine the relationships among them and their application in wheat screening programs.

This experiment was performed using alpha-lattice design with two replications in normal and delayed cultivation conditions using 132 wheat genotypes (included 62 Iranian and foreign cultivars and 70 advanced lines). The seeds were obtained from the National Rainfed Agricultural Research Institute and the Seedling and Seed Breeding Institute. Two local control cultivars named Gonbad (Abi cultivar) and Kuhdasht (rainfed cultivar) were selected among the selected genotypes. Based on the yield under non-stress (YP) and stress (YS) conditions, tolerance indices such as stress tolerance index (STI), tolerance index (TOL), Geometric mean production (GMP), mean production index (MP), Harmonic Index (HM), Yield Index (YI), Relative Drought Index (RDI) and yield Stability Index (YSI) were calculated.

The results showed that tolerance indices such as STI, GMP, HM, and MP had a positive and significant correlation with yield under non-stress and stress conditions, and the genotypes with large numerical values for these indices had high yield under stress and non-stress conditions (Fernandez’ A group), which were included genotypes 51, 12, 24, 85, 6, 120, 47, 94 (Bahar), 72, 114, 91, 131, 16, and 127. Tolerance indices were divided into two components that explained 90.79% of the total variance, using principal component analysis. The first component, which explained 60.64% of the total variance, had a correlation of 0.75 and 0.86 with performance under stress and non-stress conditions, respectively. The second component, which explained 30.14% of the total variance, showed a correlation of 0.66 and -0.5% with performance under stress and non-stress conditions, respectively. Based on the two-dimensional plot resulting from principal component analysis, considerable genetic diversity was observed among the studied genotypes.

According to the results, genotypes that perform well under non-stress conditions will not necessarily perform well under stress conditions. Therefore, to select high-yield genotypes under stress conditions, the cultivar selection had to be made in the same stressful environment. In conclusion, it can be said that the identified genotypes using HM, GMP, and MP indices are recommended for cultivation in areas with no stress, but heat stress is likely to occur in some years. In addition, identified genotypes using YSI and RDI indices are recommended for cultivation in areas with severe heat stress at the end of the season. Accordingly, stress-resistant genotypes in F or A group C can be used as germplasm sources with heat-tolerant genes in breeding programs. Also, to locate heat stress tolerance genes, it is possible to use the intersection of genotypes located in group B of Fernandez with genotypes located in group A or C of Fernandez.

In order to evaluate the ability of wheat cultivars to accumulate reserves in the stem and remobilization of these reserves to seeds under heat stress resulting from delayed sowing and to investigate the effect of phosphate-solubilizing bacteria on this ability, this study was carried out as split factorial based on a complete randomized block design with three replications in Haftkol, Khuzestan, Iran, in the growing season of 2016-2017. The main factor consisted of sowing date in two levels (22 November as conventional and 2 January as delayed seeding dates) and a factorial of the two subfactors consisting of five bread wheat cultivars (Chamran2, Mehregan, Sirvan, Shush and Barat) and two levels of application of phosphate solubilizing bacteria, Pseudomonas putida (P13) and Pantoea agglomerans (P5), (inoculation and without inoculation). The results showed that the reduction of stem specific weight (28.5%), stem length (18.7%) and effective grain filling duration (38.3%) were the most important reasons for reducing dry matter remobilization to stem and the efficiency of this remobilization in delayed sowing. At both sowing dates under bacterial seed inoculation conditions, the dry matter remobilization efficiency was 8.5% lower than the non-inoculated conditions. In the conventional sowing date, the relationship between spike weight and dry matter remobilization was positive and significant, but at delayed sowing date, spike weight and grain yield were not significantly related to dry matter remobilization and efficiency. In general, stem specific weight was recognized as the most important factor affecting the accumulation of reserves in the stem and Mehregan cultivar, with the ability to utilize stem reserves, was introduced as a suitable cultivar for delayed cultivation in the region.

Terminal heat stress has been recognized as the most widespread and detrimental type of heat stress in the world. In southern regions of Iran like Khuzestan, delay in planting date causes pollination and grain filling stages to be exposed to high temperatures, resulting in yield reduction. Developing heat tolerant cultivars is one of the ways to deal with heat stress. In this study, to identify resources of heat tolerance in wheat germplasm, a total of 203 bread wheat accessions with three control cultivars were planted in normal and delayed planting dates as an augmented experimental design in Ahwaz and the agronomic traits were evaluated. The results showed that almost all the evaluated traits were reduced in heat stress conditions compared to normal conditions. In both normal and heat stress conditions, some superior accessions were identified in terms of the studied traits compared to the control cultivars. In the biplot based on the principal components under heat stress conditions, 64 accessions along with control cultivars were located in the area of superior characteristics in terms of grain weight of five spikes, number of florets per spike, number of grains per spike, number of spikelets per spike, spike length and plant height. The studied accessions were divided into five groups by cluster analysis. The results showed a high diversity in the studied genetic material and the accessions superior to the control cultivars in terms of the studied traits were identified which can be used in future breeding programs.

The sever heat stress at the end of growing season in potato winter cultivation, always has been one of the major challenges in warm areas of Iran. Heat stress reduces the yield, quality and shelf life of the potato tubers by increasing the amount of respiration and changes at the balance of sugars and starch in the tubers. One of the suitable strategies to reduce the impacts of heat stress on potatoes is the use of calcium, especially calcium nitrate, which has been investigated in this experiment.

This Study conducted as split-split plot experiment based on randomized complete block design with three replications in South Kerman Agricultural Research and Education Center during 2013-2014. The main factor was sowing date: suitable sowing time (31th Dec.) and delay sowing (4th Feb.) and three potato cultivars (Sante, Satina and Milva) were kept in sub-plot. Four calcium treatments (no calcium application, spraying 2500 ppm calcium nitrate in two stages (tuberization and 20 days after tuberization) and spraying 2500 ppm calcium nitrate in three stages (tuberization, 20 and 40 days after tuberization), and soil application of 75 kg/ha calcium nitrate in two stages (tuberizatin and bulking stages) were in sub-sub plots. The measured characteristics included the amount of calcium in the leaf and tuber, the amount of reducing sugars, total sugars and starch in tuber and the rate of rottenness of tubers after 60 days storage.

The results showed that Sante and Satina cultivars had the highest amount of calcium in the tuber, and Milva cultivar had the lowest calcium content. The heat stress at the end of the growing season in delay sowing increased the amount of total and reducing sugars of tubers. The application of calcium especially its soil application, in both delay sowing and suitable sowing time reduced the amount of total and reducing sugars and increased starch and calcium content of the tubers and calcium content of leaves. The application of calcium nitrate in delay sowing reduced the amount of total and reducing sugars as compared to control (non-application of calcium in delay sowing) by 19.4 and 21.9 % respectively, which indicating the impact of calcium application under heat stress conditions on decreasing the tuber sugars and improving quality of tubers. Soil application of calcium in delay sowing reduced the amount of reducing sugars compared to foliar application. Interaction of soil application of calcium nitrate in suitable sowing time (non-stress) and delay sowing (heat stress) had the highest starch and calcium content, respectively. The interaction of sowing date and calcium application on the rate of rottenness of tubers after 60 days storage indicates that the highest levels of rottenness related to the no calcium application in delay sowing, which can be due to impact of higher temperature (heat stress) at the end of the growing season. The application of calcium reduced the rate of rottenness of tubers, so that the reduction in the rate of rottenness of tuber in the soil application of calcium nitrate in delay sowing compared to control (non-application of calcium in delay sowing) was 30.5 percent. There was significant positive correlation between rottenness of tuber and tuber sugars, and significant negative correlation between rottenness with starch and calcium of tuber. The mention results indicate the role of calcium application in improving the shelf life and storage of potato tubers.

The application of calcium in delay sowing (under heat stress) reduced the total and reducing sugars and increased starch and calcium content of the tubers compared to control. Probably due to the effect of calcium on reducing the amount of tuber sugars, as well as its role in strengthening the cell wall of the tuber tissue, the rate of rottenness of tuber decreased. Therefore, the application of calcium nitrate especially its soil application by 75 kg/ha, in order to increasing the shelf life and storage of potato tubers, is recommended in delayed planting in warm southern areas of the Iran.

Heat stress is one of the most important limitations of agricultural production across the world. High temperature significantly influences water status, biosynthetic pathway, morphology, phenology, yield and quality of wheat. In order to study the effects of heat stress on yield and yield components of wheat, 33 spring cultivars were evaluated in two randomized complete block designs with three replications in Ahvaz (hot) and Karaj (moderate climate). Heat stress applied through late sowing, so that the plants encountered to temperatures exceeding 30°c at terminal growth stages. Days to flowering, days to maturity, peduncle length, plant height, spikes per square meter, seed per spike, thousand kernel weight and yield were measured. Analysis of variance and mean comparison indicated that cultivars were significantly different in most of the traits measured. At Ahvaz, Chamran, Kauz and Dez were the most tolerant while Hamoon, Montana and Kavir were the most susceptible cultivars. Kauz, Behrang and Darya were the most tolerant and Babax, Montana and Neyshaboor, the most susceptible ones in Karaj. The number of spikes per square meter and thousand kernel weight were affected the most by heat at Ahvaz. However, at Karaj spikes per square meter and kernels per spike were profoundly impacted by heat stress. Correlation and regression analyses demonstrated that days to maturity and kernels per spike were the most critical, traits for screening under stress in Ahvaz and Karaj conditions, respectively.

In order to investigation the effect of planting date and foliar application Zinc sulfate and Selenium on tolerance to high temperature on two Wheat cultivars one experiment was carried out in a split factorial experiment based on a complete randomized block design with three replications at the experimental farm of Shahid Chamran University of Ahvaz during a growing season 2017-2018. Three factors were investigated in this experiment. initial factor including three planting date (Nov 11, Des 11, Jan 10). The solution type was used as the second factor: 1- foliar application with tap water (control), 2- foliar application with selenium (4 mg/lit), 3- foliar application with zinc sulfate (0.04%) and third factor including two wheat cultivars (Chamran and Star). According to the results in planting date of 20 January, the number of grains per spike decreased in the foliar application treatments by zinc solfate 10%, Selenium 36% and control 33% compared to similar treatments in the planting date of November 20th. In the planting date of January 20, the decrease in grain yield compared to the planting date of November 20th was 49.3% in the control treatment and 49.9% in the selenium treatment While in zinc sulfate treatment, yield reduction was 20.19%. According to the results obtained in folia application, Zn sulfate increased grain yield in two wheat cultivars by increasing the number of grains per spike, 1000- grain weight and grain filling duration.

In this research, the effects of different temperatures treatments including (25 (control), 30, 35, 40 and 50 0C) on pollen germination, pollen tube growth, and pollen morphology were investigated in vitro, and also the effect of late sowing date as heat stress on the number of pollen, also yield and yield components of 10 barley genotype was evaluated in field condition. At 50 0C this decrease was 72 and 60% for germination and length of pollen tube on average. High temperature significantly decreased pollen germination and pollen tube length in all genotypes. Genotypes showed different responses to temperature treatments, indicating different levels of tolerance among genotypes. In vitro, genotypes were divided into three groups according to the TSRI index as tolerant (Jounob, Reyhan 03, Zehak, Nosrat, Khoram), semi-sensitive (Yousef, Izeh, and Mahour) and sensitive (Abidar and Nimrooz) genotypes. Heat stress influenced pollen morphological aberrations, so that high temperature was removed the ornamentation of axin surface. Heat stress led to a decrease in the number of pollen grains per spike (90 %), yield and yield components (40%). These approaches showed that pollen performance may provide useful information to facilitate the investigation of heat-tolerant genotypes in breeding programs suitable for warm climates.

Rice is one of the oldest cultivated crops. Anatomical changes in plants under environmental stress can reduce the vascular bundles area such as Xylem area; as a result, these changes can protect cells from death and dieback. There was a difference in terms of pollen germination at times after anthers’ opening. Variety Minyhui 63 had the highest germination rate (85%) at time 0 or immediately after anthers’ opening; but for variety Rufipogon with lower germination rate (60%), 50% of pollens were alive after 12 min (longer). The lowest germination rate (34%) was observed in hybrid varieties with an average longevity that even after 40 min more than 50% were alive. Simultaneously between opening of florets, anthers causes high self-pollination in rice, but flowering time under stress can postpone the turgidity and growth of pollens. Matsui and Hisashi (2003) reported that positive correlation between the number of pollen on stigma and morphological characteristics.

The current research was done for recognizing the impacts of different planting dates on morphological traits in five cultivars of rice in Khouzetan. An experiment was carried out by 2 factors as split-plot using randomized complete blocks design with three replications in agricultural research station. 3 planting dates (2.15, 3.5, and 3.25) in the main plots and 5 sorts of rice including Hoveize and hamer (heat tolerance), red Anbori and Champa (sensitive), and Daniel (semi-tolerance) were arranged in the sub-plot.

The result of combined analysis showed the reaction of cultivars were completely related to planting dates and significant difference were observed for interaction effects in %1 and %5 probability level. The highest anther length, stigma length and style length were related to planting dates 1, and 3. Meanwhile, the planting dates with longer anther and stigma had more pollen number. But among cultivars the reaction was completely different, and cultivars with longer anther had shorter stigma. Also cultivars with increasing of pollen and anther surface and pollen number and development of pollen nutrition respectively can prevent of pollen abortion and yield reduction. The highest grain yield was related to the suitable planting date (3.5) that had %62.5 and %18/1. Production increase with respect to. 2.15 and 3.25. Because the second planting date had the suitable stigma, style, anther length and so anther width and more pollen number on the stigma that can increase pollen germination and production. Among the sorts, Hoveize was superior than others and it had higher yield with 50.9% and 36.3% respectively than 2 sorts that are sensitive to heat: red Anbory and Champa. The shorter growth duration (10-13 days) with respect to other cultivars and escape of high temperature was adaptation mechanisms of Hoveize. On the other hand cultivars had different reaction in related to temperature condition.

Therefore, we hope to increase production under stress condition whereas breeding objectives concentrate on the lowering vascular bundles and control length of florets components to increase contacts between pollen and florets and finally, fertility.

This study was conducted in order to evaluation of stomata resistance response, transpiration volume for canopy temperature regulation and leaf rolling under drought stress condition for some new hybrids of maize. The experiment was laid out as a factorial design based on randomized complete block with three replications in 2015 and 2016 at Seed and Plant Improvement Institute, Karaj. Three Irrigation levels, include Irrigation after 60, 90 and120 mm cumulative evaporation from evaporation pan class A and four hybrids include KSC 703, KSC704, KSC705 and KSC706 were considered as the factors. The lower stomata resistance and canopy temperature were obtained in KSC 706 and caused not to have any leaf rolling in vegetative stage even under heat condition at noon, on the other hand grain weight was lower in KSC 706 in comparisons to other hybrids under mid and severe drought stress. The maximum and minimum of grain yield were obtained under normal irrigation and severe drought stress condition with average 7.64 and 3.34 ton/he respectively. Difference of grain yield in the hybrids were not significant but the most grain moisture was obtained from KSC 706 with average 17.61%. On the base of this experiment, KSC 706 due to opening the stomata and wasting moisture in environment around root zone via transpiration, may be sensitive to drought stress and it is not recommend for the areas where have limitation in irrigation water, although it can be recommended for tolerate to heat stress under optimum water irrigation condition.

Terminal heat stress is a major abiotic stress especially in tropical and sub-tropical regions that severely reduces crop growth and yield. Safflower (Carthamus tinctorius L.) is an oilseed crop grown mainly for the production of high quality edible oil rich in polyunsaturated acids. This annual crop is native to a climate with a long dry season and a limited rainy season and compares to other annual crops has more resistance to drought stress. In addition, it's resistant to some diseases and susceptible to humidity. Since, to obtain the maximum yield of a crop, it is necessary to escape the development stages of (the/a) plant from unfavorable environmental factors and the full utilization of plant from favorable environmental conditions. Since the length of development stages more affected by temperature and day length, hence sowing date can be selected so that the different stages of plant growth were adapt with optimal temperature and day length. Yau (2006) indicated that later sowing of spring safflower in semi-arid and high elevation Mediterranean environment resulted in lower seed yield and later flowering does not allow an escape from the terminal drought and heat. Yau (2006) indicated that later sowing of spring safflower in semi-arid and high elevation Mediterranean environment resulted in lower seed yield and later flowering does not allow an escape from the terminal drought and heat. The aim of this study was to investigate the yield and yield components of safflower cultivars in response to different sowing data in Ahvaz. In order to study the effect of sowing date on yield and yield components of safflower cultivars, this experiment was carried out as split plot layout based on randomized complete blocks design with three replications in at the research farm of Shahid Chamran University of Ahvaz in 2017-2018. The main factor included three levels of sowing date (11 Dec, 31 Dec and 20 Jan), and a sub factor including four cultivars of safflower (Goldasht, Parnian, Faraman and Sofeh). Data collected on all parameters were analyzed statistically using SAS software and mean comparison was carried out using Duncan test at the 5% of probability level. The studied traits included grain yield, biological yield, harvest index, oil yield, total chlorophyll concentration, catalase and peroxidase enzyme activity and stress susceptibility index. A significant interaction was observed between the levels of sowing date and the cultivars in terms of plant height, weight of plant, biological yield and grain yield. Among the safflower cultivars, the highest weight per plant (143.3 g plant-1), biological yield (23352 kg ha-1), grain yield (4151.1 kg ha-1) and the lowest plant high (128.8 cm), was recorded in Faraman cultivar in sowing date of 11 December. In contrast, grain yield severely decreased in the 20 January sowing date with compared to the 11 December. So that, studied cultivars of Sofeh, Parnian, Faraman and Goldasht cultivar were decreased 53% (1277.3 kg ha-1), 44% (1668.9), 60% (1650.8) and 47% (1887.3), respectively. Under the heat stress, due to delayed planting date and decreased enzymatic activity of catalase, enzyme activity changed and the cultivars exposed to the terminal heat stress, but enzymatic activity of peroxidase increased. Stress susceptibility index (SSI), Parnian and Goldscht cultivars had a high tolerance with mean 0.85 and 0.92, while Faraman and Sofeh cultivars with an index of 1.16 and 1.03 had a high sensitivity to stress. This research appears the delay in optimal planting date leads to synchronize the plant's reproductive stages with a high temperature at the end of the season. As a result, shorter plants, lower biological yield, lower grain and oil yield will be observed, however, the response of the cultivars from each other was different depend on their enzymatic capacity and the ability to maintain chlorophylls. Planting date should be selected such a way that this process does not a coincidence with terminal heat season. So, under hot weather conditions in Khuzestan, selecting the optimum planting date can be an appropriate solution to reduce the negative aspects of the terminal heat stress on the grain yield and component yield of different cultivars of safflower.

Terminal heat stress is one of the most important environmental factors threatening wheat production in Iran and all across the world. In order to study the effectiveness of canopy temperature and Relative water content in screening wheat lines for heat tolerant, ten wheat genotypes were evaluated in three separate randomized complete block design experiments in two years (2015-16 and 2016-17) under non- stress and heat stress conditions at Gonbad and Atrak research stations. Heat stress was applied through three methods including late sowing, plastic greenhouse and field temperature. Canopy temperature, relative water content and grain yield of genotypes were measured. All genotypes showed significant reductions in grain yield under heat stress. Based on grain yield under stress and non-stress conditions, yield loss percentage and Fisher and Maurer susceptibility index, Kauz, Shiroudi and N-92-7 were shown to be tolerant, while Bam and Verinak susceptible to heat stress. Although both canopy temperature and relative water content had a significant correlation with grain yield under heat stress, canopy temperature was significantly different between tolerant and sensitive genotypes, indicating its higher efficiency in screening for heat tolerance.

Terminal heat sterss considered as one of the major challenges of winter production of potato in warm areas of the country including the south of Kerman provience. To determine the suitable strategy for mitigating terminal heat stress injury, a split-split plot experiment based on randomized complete block design with three replications was conducted in South Kerman Agricultural Research and Education Center (Jiroft), Iran, for 2 years (2013 and 2014). The main factor was heat stress: normal (on time planting; Dec. 31) and terminal heat stress (late planting; Feb. 4) and three potato cultivars; Satina, Sante and Milva and four calcium applications; (without calcium nitrate application, foliar application of 2500 mg.l-1 calcium nitrate in two and three stages and soil application of 75 kg.ha-1 calcium nitrate in two stages) were in sub and sub-sub plots, respectively. Results showed that heat stress reduced marketable yield and the weight and number of marketable tubers per plant. Sante and Satina cultivars produced the highest marketable tuber yield in normal condition (47.15 and 44.9 ton.ha-1, respectively), but under heat stress conditions, the difference between marketable tuber yield of those cultivars was not significant. The application of calcium nitrate improved marketable, non-marketable and total tuber yield and its components in potato cultivars and soil application of 75 kg.ha-1 of calcium nitrate was significantly suprior than the other treatments. The interaction effect of terminal heat stress and calcium nitrate applications on marketable and total tuber yield, mean weight and number of marketable and non-marketable tuber was significant. Soil application of calcium nitrate (75 kg.ha-1) increased marketable tuber yield of potato cultivars under normal and terminal heat stress conditions (10.5 and 24.5%, respectively) that revealed the mitigating effect of calcium nitrate on terminal heat stress in potato cultivars. It concluded that soil application of calcium nitrate seems to be an appropriate method to reduce the adverse effects of terminal heat stress in winter potato production.