مجله تنشهای محیطی در علوم زراعی
سال پنجم شماره 2 (نیمه دوم 1391)

Drought stress is one of the most important environmental abiotic stresses that reduces crop yield especially in arid and semi-arid regions of the world. One of the useful strategies in regard to plant breeding for drought resistance is maintaining and exploiting the diversity that exists amongst different varieties. In order to identify the sources of resistance and drought tolerance indices، 39 varieties of spring wheat were cultivated in a split plot design with 3 replications in the Research Field of Faculty of Agricultur، Mohaghegh Ardabili University، Iran. Stress levels، which were arranged as the main plots، included control (full irrigation)، 2/3 of irrigation requirement and 1/3 of irrigation requirement. Varieties were considered as sub plots. Under 2/3 irrigation، Sepahan، karaj3، Bahar and Yavaroos were the best varieties in terms of the Stress Tolerance Index (STI)، Geometric Mean Productivity (GMP) and Harmonic Mean Productivity (HARM) indices; whereas under 1/3 irrigation، Hirmand، Bahar، Yavaroos and Marvdasht were the best ones based on the mentioned indices. Under non- stressed (control) conditions، the greatest grain yield correlation coefficient was obtained with STI، GMP and HARM، respectively، while under 2/3 irrigation، the greatest grain yield correlation coefficient was obtained with HARM، GMP and STI indices، respectively. Moreover، based on the biplot graph resulted from principle component analysis، in 2/3 irrigation، Moghan1، Golestan، Kavir، Maroon، Karkheh، Chanaab، Germezak، Tajan، Bahar and Sepahan; and in 1/3 irrigation، Golestan، Germezak، Niknejad، Maroon، Darab، Falat، Arta، Marvdasht، Bahar and Hirmand were the most tolerant genotypes.

In order to compare the reaction of 13 millet accessions from gen bank collection to late season drought stress and with the aim of completion of gen bank information، specific assessments and determination of the best indices for drought tolerance، two separate experiments based on randomized complete block design with three replications were conducted at the Agricultural Research Center of Southern Khorasan during 2005 and 2006. The first experiment was conducted under normal irrigation and the second experiment was taken place under drought stress conditions (irrigation up to the 10% of panicle emergence). Experiment treatments included 13 millet accessions. Results showed that accessions number 15-143 (Southern Khorasan) and 15-24 (Yazd) had the highest two years average for grain and dry forage yields and number 15-132 (Hamadan) had the lowest grain yield among all accessions. Evaluation of accessions in terms of drought tolerance was made using MP، TOL، SSI، GMP، STI and HARM indices. HARM، GMP and STI were recognized as the best indices for severance of drought tolerant accessions according to the high correlation of these indices with grain and dry forage yields under stressed and non-stressed conditions. Based on using three dimensional graphics and accessions positioning on it، numbers 15-143 (Southern Khorasan)، 15-131 (Southern Khorasan) and 15-24 (Yazd) were identified as the most yielding and tolerant accessions to drought stress.

Introduction of physiological indices in relation to safflower drought tolerance has important role in selection of tolerant varieties. To study the effect of drought stress on some physiological characteristics of spring safflower، a field experiment was carried out in 2010 as a split-plot based on randomized complete block design with three replications at Research Farm Faculty of Agriculture of Yasouj University. Main factor included of irrigation after 70، 140 and 210 mm evaporation from class A evaporation basin and sub-factor included of four spring safflower varieties (Esfahan 14، Local variety of Esfahan، Goldasht and Sina 411). Results showed that interaction of varieties and drought stress and simple effect of experimental treatments was not statistically significant for chlorophyll fluorescence. Interaction of varieties and stress was statistically significant for relative water content، leaf proline content، leaf soluble sugar content. Maximum leaf relative water content in irrigation after 70 (83. 83 percent)، 140 (82. 62 percent) and 210 (83. 22 percent) mm evaporation was belonged to Goldasht. Maximum proline content (167. 87 µmol g-1 leaf fresh weight) in irrigation after 140 mm evaporation was belonged to Esfahan 14. Maximum leaf soluble sugar content in irrigation after 70 (632. 81 mg g-1 leaf fresh weight)، 140 (677. 56 mg g-1 leaf fresh weight) and 210 (678. 71 mg g-1 leaf fresh weight) mm evaporation was belonged to Sina 411. We can say low level of water result in increase in proline amount in Esfahan 14 and increase in soluble sugar content in Sina 411.

In order to study the effect of drought stress at different reproductive growth stages and N rates on yield and water use efficiency (WUE) of fennel، a research was conducted as a split-plot experiment based on a RCBD with three replications، at Research Field of Islamic Azad University of Birjand in 2010. The main plot was irrigation at three levels (irrigation cease at flowering and seed-filling stages as well as optimum irrigation) and the sub-plot was N fertilizer at four rates (0، 60، 120 and 180 kg N. ha-1). Results showed that applying drought stress at flowering and seed-filling stages compared to optimum irrigation decreased umbel number per plant by 48. 2 and 28. 8%، seed number per umbel by 39. 4 and 22. 4%، seed yield by 69. 7 and 52. 6% and WUE for seed production by 65. 6 and 65. 9%، respectively. Moreover، increasing the nitrogen rate from 0 to 120 kg N. ha-1 increased the umbel number per plant، seed yield، biological yield and WUE for seed and biomass production by 22. 1، 24. 3، 21. 8، 34. 5 and 20. 4%، respectively. The interaction effect of irrigation x nitrogen was only significant in umbel number per plant and seed yield of fennel. In general، according to results of the current study، application of optimum irrigation with 60 kg N. ha-1 can be recommended for fennel cultivation in the region due to preventing environmental problems as well as providing desirable yield and WUE of fennel.

Drought stress is one of the most important factors that limit plant production in the semi-arid areas. Thus، in order to investigate the effects of Azotobacter bacteria، mycorrhiza fungus and zinc sulfate on the growth and yield of fenugreek، a field experiment was conducted at the Agricultural Research Farm of Shahrekord University during the growing season of 2011-2012. Two levels of irrigation (including complete irrigation as no stress and deficit irrigation at early flowering for 12 days as drought stress) were combined as main plots factor and seven fertilizer treatments consisted of control (NPK)، zinc sulfate، Azetobacter، mycorrhizae، zinc sulfate + Azetobacter، zinc sulfate + mycorrhizae، zinc sulfate + mycorrhizae + Azetobacter as subplot factor in a split-plot experiment design with three replications. The results showed that under complete irrigation conditions، the highest leaf area index was recorded in zinc sulfate and mycorrhizae treated plant. Also، the greatest of pods/plant، seeds/pod، and 1000 seed weights were associated in zinc sulfate + Azetobacter، zinc sulfate، and zinc sulfate + mycorrhizae treatments، respectively. The highest grain yield (2245 kg/ha) was observed in zinc sulfate + mycorrhizae treatment (P≤0. 05) under complete irrigation conditions. But، there were no significant differences among fertilizer treatments under drought stress conditions. In conclusion، under complete irrigation it is important the combined application of chemical fertilizer and under drought stress conditions، as well as mycorrhizae for improving in grain yield of fenugreek and sustaining optimum crop production.

Salinity stress can severely affect rice plants at seedling stage. In order to study the laser irradiations effect on characteristics associated with the salt tolerance of rice at seedling stage، a nutrient solution experiment was conducted as a factorial arrangement based on completely randomized design with three factors including four salinity levels (0، 30، 60، and 90 mM sodium chloride)، two laser levels (Irradiated and non-irradiated seeds as the control) and two cultivar levels (susceptible- IR29 and tolerant- FL478) with three replications in the greenhouse of Tehran University. Results indicated that using laser treatment in both cultivars significantly increased plant height، shoot dry weight، leaf relative water content، root length، root volume، root dry weight، while significantly decreased SPAD value and cell membrane electrolyte leakage percentage. Moreover، in laser- irradiated treatments shoot dry weight enhancement and SPAD values reduction، were higher in cultivar IR29 comparing to cultivar FL478 at all salinity levels. While FL478 showed greater relative water content، this could be possibly due to the greater stability of the membrane in holding water. According to the results of these experiments، it appears that laser rays induce bio-stimulations in plants which can be effective in salinity tolerance.

Increased need for salinity tolerant plants continues due to increased use of saline water for irrigation in arid and semiarid regions. Kochia، a halophyte، which may be provided a good source of forage for livestock by using saline water. In order to investigate the salinity effect on some physiological characteristics of kochia، an experiment was conducted with supply of K+ and Ca+2 in green house and hydroponic condition. Two salinity levels including 20 dS m-1 and 40 dS m-1 and control (non saline water) and KCl (10mM)، CaCl2 (10mM) and KCl with CaCl2 (5 mM) using split plot design، based on RCBD allocated in main and sub plot with six replications respectively. The results showed that increasing salinity significantly decreased spad value، F''v، F''v/F''m، photosynthetic pigments، total phenol، relative water content، membrane stability index، DPPH - radical scavenging activities and total dry matter production. Calcium applied enhanced rates of photosynthesis، chlorophyll a، chlorophyll b، MSI، DPPH - radical scavenging activities and potassium applied enhanced RWC in salinity stress. Application of calcium with potassium reduces the effect of salinity on F''o، F''m، F''v، F''v/F''m، total phenol and total dry matter production. Correlation coefficients showed significant correlation between dry matter production and all traits except photosynthesis، chlorophyll a to b ratio and DPPH - radical scavenging activities. Generally based on this it is appear that results application of K+ with Ca+2 alleviated effect of salinity and improved dry matter production of kochia.

To investigate the effect of water stress on morphological and agronomical characteristics of sunflower (oilseed hybrid Allestar)، an experiment based on randomized complete block design was conducted with three replications at the Experimental Station of Islamic Azad University، Tabriz branch. Water stress was applied as irrigation after five evaporation levels (50، 100، 150، 200 and 250 mm) from evaporation pan class A. Results showed that، increasing water stress significantly decreased head diameter، number of seeds per head، 100- seed weight، oil percent، harvest index، leaf area index and seed yield. Mean seed yield decreased from 4460، kg ha-1 in control (50 mm) to 3460، 3200، 2210، and 1810 kg ha-1 for 100، 150، 200، 250 mm evaporation، respectively. It was also revealed that leaf area index was the most sensitive morphological trait to water deficit and was declined significantly by increased drought stresses. Any delayed irrigation resulted in reduced crop yields through shortened reproduction period، reduced number of seeds produced and inability of assimilate transportation for seed filling.