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A two-year field experiment was conducted to study the effect of three zinc levels 0, 20 kg ZnSO4 ha−1 and 20 kg ZnSO4 ha−1 + foliar spray of 0.5% ZnSO4 solution on plant height, leaf area, shoot biomass, photosynthetic rate and chlorophyll content in different wheat genotypes. Increasing zinc levels was found to be beneficial in improving growth and physiological aspects of genotypes. Soil application + foliar spray proved to be the best application in improving all the parameters. Zinc application brought about a maximum increment limit of 41.8% in plant height, 101.8% in leaf area, 86% in shoot biomass and 51.1% in photosynthetic rate irrespective of stages and year of study. A variation was found to occur among genotypes in showing responses towards zinc application and PBW 550 was found to be more responsive.

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The impact of foliar spray fertilizers (Aton Az) on the resistance of spring barley (Hordeum vulgare L.) against to individual and combined UV-B radiation and drought effects were investigated. Barley seeds were sown in pots prepared with neutral pH peat substrate. When the 2nd true leaf unfolded, i.e. 7 days after germination, the first spray with microelement and free amino acid fertilizers was carried out; two days after this application, the different irradiation (1 and 3 kJm–2 d–1) UV-B doses and drought effects were started. Exposure lasted for 6 days. The main characteristics of all investigated indicators were assessed at the end of exposure. The largest positive effects of fertilizers on the photosynthetic rate and water use efficiency of barley were found solely under the impact of drought. Foliar spray fertilizers decreased oxidative stress injury in the leaves by decreasing the malondialdehyde content under solely effects of drought and UV-B radiation, while under the combined effect of the mentioned stress factors, the changes were statistically insignificant. A stronger positive impact of foliar fertilization was detected on the content of photosynthetic pigments (a and b) at solely UV-B radiation effect than at combined effect of investigated factors, when significant changes were detected only in individual cases.

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The effect of different concentrations of salinity (NaCl up to 250 mM) was studied on the germination, dry matter production and some relevant metabolic parameters of two lines (Sakha 69 and Sakha 164) and one variety (Stork) of wheat (Triticum aestivum L.). During the germination and seedling stages the experimental lines tolerated lower and moderate doses of salinity, while the variety was significantly retarded at the lower and moderate levels and completely inhibited at higher doses of salinity. The water content remained more or less unchanged in the two lines under saline conditions, whereas in Stork increasing salinity resulted in a significant decrease in water content. A stimulation of the net photosynthetic rate in both lines, Sakha 69 and Sakha 164, was observed at moderate salinity, but the highest levels proved to be inhibitory. In the Stork variety all salinization levels inhibited photosynthetic activity. The respiration rate in the two tested lines was influenced from salinity levels of 150 mM upwards and increased progressively with the salinity level. In Stork plants increasing salinity levels increased the respiration rate. The soluble sugar and soluble protein contents of the lines increased with increasing salinity. The opposite pattern was revealed in the case of Stork. The amino acid content, including proline, increased significantly with an increase in salinity in all tested plants. the potassium/sodium ratio decreased significantly with a rise in salinization.

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). Stomatal conductance ( g s ) and net photosynthetic rate ( P N ) were measured on sunny days between 10:00 and 11:00 hr on the youngest fully expanded leaves using a portable photosynthesis system (Handheld Photosynthesis System, CI-340, CID Bio

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Gimenez, C., Mitchell, V. J., Lawlor, D. W. (1992). Regulation of photosynthetic rate of two sunflower hybrids under water stress. Plant Physiology 98 516–524 Lawlor D. W. Regulation of

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Increasing NaCl levels retarded the net photosynthetic rate, biosynthesis of photosynthetic pigments and membrane integrity of maize and sunflower seedlings; a serious effect was exhibited when NaCl was applied at high concentration. On the other hand, the K + efflux increased at increasing NaCl levels. In addition, the various salt levels induced considerable variations in the concentrations of sodium, potassium, calcium and magnesium. The vitamins applied were generally effective in partially or completely countering the inhibitory effects of salt stress on net photosynthetic rate, pigments biosynthesis and membrane integrity, exerting a stimulatory action on these parameters, especially in plants subjected to moderate and low salinity levels. The leakage of K + was reduced by the application of both ascorbic acid (AsA) and thiamine (B 1 ). Soaking the seeds of salt-stressed plants in AsA or B 1 had a favourable effect on the accumulation of certain ions and antagonized or ameliorated the inhibitory effect of salt stress.

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The present study combined evaluations of agronomic parameters such as roots morphometry (using the WinRhizo program) and leaf gas exchange, in order to detect features in the root system which allow the maintenance of photosynthetic rates and productivity in four maize genotypes contrasting for tolerance to water deficit (WD), two tolerant (DKB 390 and BRS1055) and two sensitive (BRS 1010 and 2B710). The genotypes showed similar tolerance to dehydration of leaf tissue, but the tolerant genotypes DKB 390 and BRS1055 presented higher photosynthetic rate and yield compared to the sensitive BRS 1010 and 2B710. Nevertheless, divergent strategies of adaptation to drought among tolerant genotypes were observed. The genotype DKB 390 presented physiological mechanisms in shoots responsible for minimizing water loss, which decreases the dependence of root adjustments to increase the absorption of water. In turn, the BRS 1055 genotype showed a drought avoidance strategy by producing fine roots associated with a higher leaf area.

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Field crops are subjected to numerous inconsiderate climatic hazards that negatively affect physiological processes, growth and yield. Drought is one of the major abiotic factors that limits the agricultural productivity especially in the arid and semi-arid areas of the globe. Silicon (Si) is a naturally occurring beneficial nutrient which modulates plant growth and development events and has been known to improve the crop tolerance to abiotic stresses. With the objective to investigate the role of silicon nutrition on maize hybrids under limited moisture supply, a two year field study was conducted during 2010–11 at Post Graduate Research Station (PARS), University of Agriculture Faisalabad, Pakistan. We evaluated growth of two maize hybrids P-33H25 and FH-810 under well watered (100% field capacity) and water deficit situation (60% field capacity) as affected by Si application. Silicon was added in soil @ 100 mg/kg using Calcium Silicate as source. Water deficit condition significantly reduced agro-morphological and physiological attributes of maize plants. Silicon application significantly increased the plant height, leaf area index, yield and related attributes along with improvement in photosynthetic rate, leaf water status and osmotic adjustment under limited moisture supply. It was concluded that silicon application to droughtstressed maize enhanced its growth and yield owing to improved photosynthetic rate, higher osmotic adjustment, increased water status and lowered transpiration.

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Cotula coronopifolia is a wild annual Asteraceae that grows in periodically-flooded prone environments and seems highly tolerant to periodic flooding. Seedlings of about 15 cm were collected directly from the edge of Soliman sabkha (N-E Tunisia, semi-arid stage) and grown under greenhouse conditions. Two treatments were considered: drainage and flooding. After 56 days of treatment, flooded plants showed a pronounced growth increase. This performance was essentially associated with significant increment in biomass production of both shoots and roots (about 220% of the control). The appropriate response to flooding was also characterized by the ability of the species to maintain its water status under such conditions. Neither water content nor water potential showed a significant variation as compared to those of non-flooded plants. However, transpiration rate decreased slightly but significantly in flooded plants (from 0.86 to 0.64 mmol H2O m−2 s−1). Na+ and K+ concentrations were practically maintained under waterlogging conditions, except a significant increase of Na+ content in roots of flooded plants (157% of the control). These responses were concomitant with maintenance of photosynthetic rate. However, the contents of chlorophylls a and b increased to 167% and 295%, respectively. It seems that the enhancement in these photosynthetic pigments together with a significant improvement in water use efficiency (from 4.66 to 6.07 mmol CO2 mol−1 H2O) allowed to the species to compensate the decrease in photosynthetic rate. At the anatomical level, this species responded to flooding by a significant development of its root aerenchyma (+63%) and an increase in the lignification of its stem xylem tissues (+37%). Based on the presented data, the plant fitness under flooding conditions was a result of dynamic readjustment of several morphological, physiological, and anatomical adaptive traits. Flood requirement together with salt tolerance are responsible for the predominance of C. coronopifolia in a large area in its natural biotope where most plants cannot tolerate interactive effects of flooding and salinity.

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