EFFECTS OF SALINITY STRESS ON PHYSIOLOGICAL PERFORMANCE OF VARIOUS WHEAT AND BARLEY CULTIVARS

An experiment with factorial arrangement of treatments on a randomized complete block (RCB) design basis with three replications was conducted in a greenhouse during Spring 2010 to investigate changes in sodium ion (Na⁺), potassium ion (K⁺), Na⁺/K⁺ and to determine proline, protein content, and superoxide dismutase (SOD) of four wheat and four barley cultivars. Three salt levels {1, control (no salt), 7, and 13 dS m^?1 [2.5 and 5 g salt [sodium chloride (NaCl) and sodium sulfate (Na₂SO₄) in 1:1 ratio] per kg of soil, respectively]} were used in this investigation. Salt stress treatments were applied 4 weeks after planting (at 2 leaf stage). Leaf samples were taken four weeks after imposition of salt treatment. The results showed that salinity caused an increased in proline and protein content, and SOD in all wheat and barley cultivars. The highest proline and protein content of barley and wheat cultivars at all salinity levels were observed in ‘Nimrooz’ and ‘Bam’ cultivars, respectively. At all salinity levels, wheat and barley cultivars ‘Kavir’ and ‘Nimrooz’, respectively, had the lowest Na⁺ content. Barley cultivar ‘Kavir’ and wheat cultivar ‘Bam’ had higher K⁺ and K⁺:Na⁺ ratios. This might be related to salt tolerance in these two cultivars. Wheat and barley cultivars showed differences with regard to proline, protein, and SOD content, Na⁺, K⁺, and K⁺:Na⁺ ratio, indicating existence of genetic diversity among the cultivars. These findings indicated that higher K⁺, K⁺:Na⁺ ratio, proline, protein, and SOD content could be the key factors, which offer advantage to barley over wheat for superior performance under saline conditions.     

IDENTIFICATION OF GROUNDNUT (ARACHIS HYPOGAEA L.) CULTIVARS TOLERANT OF SOIL SALINITY

Field screening of 83 groundnut cultivars was undertaken for two seasons to assess their tolerance of salinity based on plant mortality and yield attributes. During the dry season, soil salinity of 4 dS m^?1 at sowing and 6–7 dS m^?1 21–98 days after sowing (DAS) caused high mortality without seed formation in any cultivars, however, at salinity 4.5 dS m^?1 during sowing and 3.5–3.0 dS m^?1 15–80 DAS during wet season, 61 cultivars produced seed. The cultivars ‘VRI 3’, ‘UF 70–103’, ‘TKG 19A’, ‘S 206’, ‘Tirupati 4’, ‘M 522’, ‘Punjab 1’, ‘BG 3’, ‘Somnath’ and ‘ICGV 86590’, with high plant stand during both the seasons and over 75 g m^?2 seed yield during wet season, were identified salinity tolerant. However, 15 cultivars with more than 50 g m^?2 seed yield were moderately tolerant and 28 cultivars with less than 25 g m^?2 seed yield were sensitive to salinity.     

Barley growth,yield, antioxidant enzymes,and ion accumulation affected by PGRs under salinity stress conditions

Application of plant growth regulator (PGR) may alleviate some negative effects of environmental stresses such as salinity. A controlled environment experiment was conducted to study barley (Hordeum vulgare L. cv. Reyhane) growth, yield, antioxidant enzymes and ions accumulation affected by PGRs under salinity stress conditions at Shiraz University during 2012. The treatments were PGRs at four levels—water (as control), cycocel (CCC, 19 mM), salicylic acid (SA, 1 mM), and jasmonic acid (JA, 0.5 mM)—and four salinity levels—no stress (0.67 dS m^?1, as control), 5, 10, and 15 dS m^?1, which were arranged in a factorial experiment based on completely randomized design with four replicates. The results showed that salinity stress significantly decreased plant height, peduncle length, leaf area, ear length, grain number, dry weight, grain yield, harvest index, potassium (K⁺) accumulation, and potassium/sodium (K⁺/Na⁺) concentration ratio, which were closely associated with stress severity. However, PGRs compensated some of these negative effects, so that SA foliar application had the most ameliorative effect. Salt stress also increased Na⁺ accumulation as well as the activity of peroxidase, catalase, and superoxide dismutase (SOD). Since ion discrimination and enhanced antioxidant enzymes are associated with salt tolerance, in this experiment PGRs application might have enhanced K⁺ accumulation and antioxidant enzyme activity. The activity of SOD and K⁺/Na⁺ ratio were found to be useful in salt tolerance manipulation in barley plants.     

Evaluation of some rice cultivars’ response to salinity stress using resistance indices

Parts of paddy fields in Mazandaran Province, northern Iran, are confronted with soil and water salinity. To screen proper rice cultivars, an experiment was performed with eight modified rice cultivars under four levels of irrigation water salinity (1, 2, 4 and 6 dS m^?1) with three replications, in Amol, northern Iran. The objective of the present study was the evaluation of eight screening indices for identifying salinity tolerance of these cultivars, so that suitable cultivars can be recommended for the cultivation with saline irrigation water in paddy fields. To evaluate the resistance of these cultivars to salinity stress, different indices were calculated. The results showed that Khazar cultivar was the most salt-sensitive cultivar in all salinity levels. In the irrigation salinity levels of 2 and 4 dS m^?1 Neda cultivar and in the level of 6 dS m^?1 Dasht cultivar were the most salt-resistant cultivars. In the two irrigation salinity levels of 4 and 6 dS m^?1, the mean productivity index was the most effective in the screening of salt-resistant cultivars. Harmonic mean, geometric mean productivity, stress tolerance index and mean productivity indices were found to be the best indices in screening resistant cultivars.     

Performance of Some Wheat Cultivars Under Saline Irrigation Water in Field Conditions

Most of the crop salt tolerance studies are often conducted in a glasshouse and are limited under field conditions. Therefore, the present research study was conducted under field conditions to evaluate the performance of six wheat cultivars at five salinity levels (EC 0, 3, 6, 9, and 12 dS m^?1) in split plot design with three replications. Increasing salinity significantly increased soil pH, electrical conductivity (EC), and sodium adsorption ratio (SAR). Yield parameters of different cultivars were affected more at higher salinity levels than lower in two years. Data over two years revealed that up to EC 9 dS m^?1 cultivars PBW 658 and HD 2967 performed ???better on the absolute yield basis but PBW 621 produced ?higher relative yield. At EC 12 dS m^?1, PBW 658 produced significantly higher grain yield (4.23 t ha^?1) than cultivars HD 2967 (4.11 t ha^?1) and PBW 621 (3.99 t ha^?1); therefore, should be preferred at salinity more than 9 dS m^?1.     

Effect of salinity and arbuscular mycorrhizal fungi on growth and some physiological parameters of Citrus jambheri

Arbuscular mycorrhizal (AM) fungi alleviate the unfavorable effects of salinity stress on plant growth. A pot study was conducted to determine the effects of AM fungi and salt on growth and some physiological parameters of Citrus jambheri rootstock. Four levels of salinity (2, 4, 6, and 8 dS m^?1 as NaCl) and three mycorrhizal treatments (Glomus etunicatum, Glomus intraradices and non-mycorrhizal (NM) control) were used. As salinity increased, all measured characteristics of plants after 4.5-month growth except Na uptake, proline content, and electrolyte leakage decreased. Shoot dry weight and K uptake were significantly higher in G. intraradices-colonized seedlings than NM controls at all salinity levels. Root dry weight and shoot P uptake were significantly higher in G. etunicatum-colonized seedlings than NM controls at all salinity levels. G. intraradices-colonized seedlings had significantly higher proline content than NM controls and G. etunicatum-colonized seedlings at salinity levels of 4, 6 and 8 dS m^?1. The electrolyte leakage percentage was significantly lower in G. intraradices-colonized seedlings than NM controls at all salinity levels. The data demonstrated that mycorrhizal citrus seedlings exhibited greater tolerance to salt stress than NM seedlings and the enhanced proline content seems to be one of the mechanisms involved.     

Effects of Silicon Application on Wheat Growth and Some Physiological Characteristics under Different Levels and Sources of Salinity

We investigated the effects of silicon (Si) and the levels and sources of salinity on the growth and some physiological properties of wheat (Triticum aestivum cv. Chamran) in a sandy loam soil under greenhouse conditions. Treatments comprised four Si levels (8, 50, 100 and 150 mg kg^?1 soil), four salinity levels (0.46, 4, 8 and 12 dS m^?1) and two salinity sources (sodium chloride (NaCl) and four-salt combination). Salts combination included NaCl, sodium sulfate (Na₂SO₄), calcium chloride (CaCl₂) and magnesium sulfate (MgSO₄) at a molar ratio of 4:2:2:1. The experiment was arranged as a completely randomized design in a factorial manner, with three replications. Increasing salinity level resulted in a significant decrease in shoot dry weight, chlorophyll content and catalase (CAT) activity, and it caused a marked increase in proline and glycine betaine (GB) concentrations and superoxide dismutase (SOD) enzyme activity. The stimulating effect on GB accumulation and SOD activity was more intense in NaCl-treated plants. However, the source of salinity had no significant effect on shoot dry weight, chlorophyll and proline concentrations, and CAT activity. Si application enhanced all the above-mentioned parameters, except for proline. The suppressing effect of salinity on shoot dry weight, chlorophyll concentration and CAT activity was alleviated by Si supplementation. The stimulating effects of Si fertilization on shoot dry weight and chlorophyll concentration became more pronounced at higher salinity levels. It could be concluded that a decrease in soil osmotic potential, nutrient imbalance and increasing reactive oxygen species (ROS) in salt-treated plants caused growth suppression, while Si supply decreased the deleterious effects of excess salt on wheat growth. Consequently, it appears that when wheat plants are to be grown in salt-affected soils, it is highly recommended to supply them with adequate available silicon (Si).     

The Induction of Salinity Stress Resistance in Rosemary as Influenced by Salicylic Acid and Jasmonic Acid

This pot study was carried out as a factorial experiment. The foliar application of salicylic acid (SA) and jasmonic acid (JA) both, at three levels and salinity stress at four levels were applied. The results showed that salinity resulted in a significant loss of most morphological traits, protein, total chlorophyll, and catalase activity, whereas leaf proline content, superoxide dismutase activity, peroxidase and chlorophyll b significantly increased. The interaction of the three studied factors influenced protein content and plant weight significantly. Although salinity stress reduced these traits, SA application improved them. Also, SA application entailed the improvements in plant growth, proline, and antioxidant enzymes under salinity stress. Nonetheless, JA application had slight or insignificant impact on the traits. Thus, we can say that rosemary is relatively capable of coping with salinity. But, when the stress is intensified, even the resistance mechanism of the plant fails to counteract the severe stress.     

Effect of salinity and nitrogen on growth,sodium, potassium accumulation,and osmotic adjustment of halophyte Suaeda aegyptiaca (Hasselq.) Zoh

Suaeda aegyptiaca is an important native annual halophyte in salt-affected soils around coastal areas of the Persian Gulf. In order to study the effects of different levels of saturation paste soil salinity (10, 20, 40, 60, and 80 dS m^?1) and nitrogen supply (25, 50, and 75 mg kg^?1 N as urea) on growth and physiological characteristic of S. aegyptiaca, a greenhouse factorial experiment in completely randomized design was conducted with three replications. Salinity treatments were established after early growth of plants and nitrogen was applied in two steps. Results showed that increasing salinity up to 20 dS m^?1 led to increase in dry weight (DW) of plants and this decreased by increasing salinity. Also, DW of plants was significantly increased by application of 75 mg kg^?1 nitrogen. Increasing salinity significantly decreased plant height, chlorophyll index, and total nitrogen content; while proline content and total soluble solids (TSS) were significantly increased. The electrolyte leakage (EL) and sodium concentration were increased under salinity stress. However, further increase in salinity decreased these two parameters. By increasing the nitrogen levels, relative water content (RWC), chlorophyll index, proline, and total nitrogen contents were increased, whereas EL was decreased.     

Integrated effect of potassium humate and α-tocopherol applications on soil characteristics and performance of Phaseolus vulgaris plants grown on a saline soil

Soil salinity is one of the major problems of agriculture that limits plant performance, particularly in arid and semiarid regions. Therefore, the effect of potassium humate (KH) and α-tocopherol (TOC), used singly or in integration, on soil characteristics, and on plant performance, physio-biochemical attributes and antioxidative defense system of Phaseolus vulgaris L. plants grown under salt stress (EC = 6.35–6.42 dS m^?1) was investigated. Half g KH kg^?1 soil was used as soil amendment before sowing and 1.0 mM TOC was used as foliar spray twice; at 25 and 40 days after sowing. Results showed that, KH significantly improved soil physical and chemical properties, which positively reflected on plant growth and productivity, physio-biochemical attributes, mineral nutrients (N, P, K and Ca), osmoprotectants (soluble sugars and proline), non-enzymatic (ascorbic acid, glutathione and TOC) and enzymatic (superoxide dismutase, catalase and guaiacol peroxidase (GPOX)) antioxidants compared to untreated controls. The single TOC foliar application recorded the same positive results of KH. Integrated KH + TOC treatment was most effective compared to the single treatments. The above results recommended benefits of this integrated KH + TOC for the possibility of sustainable agronomic performance of common beans grown on saline soils.     

The role of antioxidative metabolism of tomato leaves in long‐term salt‐stress response

The antioxidative protection system as adaptation strategy to high soil salinity in the leaves of two tomato (Lycopersicon esculentum Mill.) hybrids (Buran F1 and Berberana F1) was investigated. Changes in the activity of superoxide‐dismutase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.11), as well as total and oxidized ascorbate concentrations (AA and DHA) in the plant leaves subjected to three salinity levels (EC 3.80 dS m⁻¹, 6.95 dS m⁻¹, and 9.12 dS m⁻¹) relative to non‐saline control were analyzed during the fruiting phase. The obtained results clearly indicate a relation between SOD activity and AA concentration in the antioxidative protection without any peroxidase‐related H₂O₂ detoxification. Increased SOD activity accompanied by high AA concentration was noticed at all salinity levels, but the response of hybrids was specific for the particular salt concentration. The first salinity level (EC 3.80 dS m⁻¹) induced the highest level of AA in the Buran F1 (70%), while in Berberana F1 hybrid leaves the highest AA concentration (64%) was noticed at the third salinity level (9.12 dS m⁻¹). All salinity levels caused a decline in POD and APX activities in both hybrids. The possibility of a predominant role of ascorbate and SOD in the antioxidative protection of mature tomato leaves under long‐term salt stress is discussed.     

PHYTOTOXIC EFFECTS OF CADMIUM EXPOSURE AND METAL ACCUMULATION IN SUNFLOWER

The phytotoxicity imposed by cadmium (Cd) in sunflower was investigated on biomass, Cd accumulation, superoxide and lipid peroxidation product as well as the activities of superoxide dismutase, catalase and peroxidase. Plants accumulate substantial amount of Cd in different parts, the maximum being in roots, i.e., up to 820 μg g^?1 dry matter. Cadmium induced oxidative stress, indicated by increase in lipid peroxidation and superoxide content with increase in metal supply. Under Cd stress, the activities of superoxide dismutase and catalase declined to a greater extent in roots than in leaves. Even though the peroxidase activity increased in leaves, a decreasing trend was observed in root due to Cd stress. The threshold of toxicity (10% growth reduction) and toxicity (33% growth reduction) values of Cd in sunflower were 14 and 72 μg g^?1 in leaves, 19 and 90 μg g^?1 in stem and 65 and 250 μg g^?1 Cd in roots, respectively.     

GROWTH,YIELD, AND ION RELATIONS OF STRAWBERRY IN RESPONSE TO IRRIGATION WITH CHLORIDE-DOMINATED WATERS

Strawberry is listed as the most salt sensitive fruit crop in comprehensive salt tolerance data bases. Recently, concerns have arisen regarding declining quality of irrigation waters available to coastal strawberry growers in southern and central California. Over time, the waters have become more saline, with increasing sodium (Na⁺) and chloride (Cl^?). Due to the apparent extreme Cl^? sensitivity of strawberry, the rising Cl^? levels in the irrigation waters are of particular importance. In order to establish the specific ion causing yield reduction in strawberry, cultivars ‘Ventana’ and ‘Camarosa’ were grown in twenty-four outdoor sand tanks at the ARS-USDA U. S. Salinity Laboratory in Riverside, CA and irrigated with waters containing a complete nutrient solution plus Cl^? salts of calcium (Ca²⁺), magnesium (Mg²⁺), Na⁺, and potassium (K⁺). Six salinity treatments were imposed with electric conductivities (EC) = 0.835, 1.05, 1.28, 1.48, 1.71, and 2.24 dS m^?1, and were replicated four times. Fresh and dry weights of ‘Camarosa’ shoots and roots were significantly higher than those of ‘Ventana’ at all salinity levels. Marketable yield of ‘Camarosa’ fruit decreased from 770 to 360 g/plant as salinity increased and was lower at all salinity levels than the yield from the less vigorous ‘Ventana’ plants. ‘Ventana’ berry yield decreased from 925 to 705 g/plant as salinity increased from 0.835 to 2.24 dS m^?1. Relative yield of ‘Camarosa’ decreased 43% for each unit increase in salinity once irrigation water salinity exceeded 0.80 dS m^?1. Relative ‘Ventana’ yield was unaffected by irrigation water salinity up to 1.71 dS m^?1, and thereafter, for each additional unit increase in salinity, yield was reduced 61%. Both cultivars appeared to possess an exclusion mechanism whereby Na⁺ was sequestered in the roots, and Na⁺ transport to blade, petiole and fruit tissues was limited. Chloride content of the plant organs increased as salinity increased to 2.24 dS m^?1 and substrate Cl increased from 0.1 to13 mmol_cL^?1. Chloride was highest in the roots, followed by the leaves, petioles and fruit. Based on plant ion relations and relative fruit yield, we determined that, over the range of salinity levels studied, specific ion toxicity exists with respect to Cl^?, rather than to Na⁺ ions, and, further, that the salt tolerance threshold is lower for ‘Camarosa’ than for ‘Ventana’.     

INVESTIGATION OF SALINITY STRESS AND POTASSIUM LEVELS ON MORPHOPHYSIOLOGICAL CHARACTERISTICS OF SAFFRON

A greenhouse research experiment was conducted to investigate the effect of salinity stress and potassium (K) fertilization on biomass accumulation of roots and shoot of saffron plants. Treatments were four levels salinity in the form of sodium chloride (NaCl; 3.4, 6.4, 9.4 and 12.4 dS m^?1) and three levels of potassium (50, 100, and 150 % of Hoagland's nutrition solution base). Results indicated that higher levels of potassium significantly controlled the negative effects of NaCl on length and number of roots as well as fresh weight and number of leaves per plant. Increase in salinity and potassium levels caused a reduction in leaf water content, and enhancement in electrolyte leakage. It seems that in the presence of salinity increasing 50% extra potassium (Based on Hoagland's nutrient solution) in the rhizosphere of saffron can improve damaging effects of NaCl up to 9.4 dS m^?1 of soil solution.     

Differential responses of three chamomile genotypes to salinity stress with respect to physiological,morphological, and phytochemical characteristics

Effect of water salinity was studied in different Matricaria recutita L. genotypes (Isfahan, Ahvaz, and Shiraz) to understand their protective mechanisms and agronomic performance. Based on a split-plot design arranged in a randomized complete-block consisted of four salinity levels as the main plot and three genotypes as the subplots with three replications this field experiment was conducted in 36 plots with 3 m² space in the Isfahan Center for Research of Agricultural Science and Natural Resources during 2014–2015. The findings showed that the three genotypes differed in resistance to salinity and tolerance mechanisms. They have evolved different physiological, morphological, and biochemical adaptations to salt stress. The Ahvaz genotype in the absence of salt, the Isfahan genotype at 6, and the Shiraz genotype at 9 and 12 dS m^?1 sodium chloride (NaCl) were desirable, taking both quantity and quality into consideration. While preserving shoot growth, the Isfahan genotype was more tolerant to 6 dS m^?1 NaCl most likely due to peroxidase activity. The resistance of the Shiraz genotype is associated with root growth stimulation at 9 and Na compartmentation in root at 12 dS m^?1 NaCl. The Isfahan genotype had the highest oil and chamazulene content, which was not affected by salinity. The Shiraz genotype in the control treatment, the Isfahan genotype at 6 and 9 and the Ahavaz genotype at 12 dS m^?1 NaCl synthesized higher flavonoid compounds.     

Protective role of proline against salt stress is partially related to the improvement of water status and peroxidase enzyme activity in cucumber

Abstract

A salt-sensitive cucumber cultivar “Jinchun No. 2” (Cucumis sativus L.) was used to investigate the role of proline in alleviating salt stress in cucumber. Proline was applied twice (day 0 and day 4 after salt treatment) as a foliar spray, with a volume of 25?mL per plant at each time. Plant dry weight, leaf relative water content, proline, malondialdehyde (MDA), Na⁺, K⁺ and Cl^? contents, as well as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) activities in the plants were determined at day 8 after salt treatment. The results showed that 100?mmol?L^–1 NaCl stress significantly decreased plant dry weight, leaf relative water and K⁺ contents, and increased leaf MDA, Na⁺ and Cl^? contents and SOD, POD, CAT and APX activities. However, leaf proline accumulation was not affected by salinity. The exogenous application of proline significantly alleviated the growth inhibition of plants induced by NaCl, and was accompanied by higher leaf relative water content and POD activity, higher proline and Cl^? contents, and lower MDA content and SOD activity. However, there was no significant difference in Na⁺ and K⁺ contents or in CAT and APX activities between proline-treated and untreated plants under salt stress. Taken together, these results suggested that the foliar application of proline was an effective way to improve the salt tolerance of cucumber. The enhanced salt tolerance could be partially attributed to the improved water status and peroxidase enzyme activity in the leaf.     

MODULATION OF PHYSIOLOGICAL AND BIOCHEMICAL METABOLITES IN SALT STRESSED RICE BY FOLIAR APPLICATION OF ZINC

An experiment was conducted to evaluate the effect of zinc (Zn) application on five rice cultivars grown under salt stress conditions. Two salinity levels of 0 and 10 dS m^?1 were created with sodium chloride (NaCl) and foliar spray of Zn (0.05%; Chelated-Zn) was applied. A decrease in growth and yield related parameters were observed under salt stress, which was ameliorated in plants that received Zn foliar spray. Similar effects of salinity and Zn foliar spray were noted on photosynthetic rate, transpiration rate, stomatal conductance, water use efficiency, and water relations of plants. Salt induced increase in sodium (Na) content and decrease in other macro- and micronutrients contents were also reversed by Zn. Other salt tolerance indicating parameters likSe total free amino acids and total soluble sugars increased under Zn spray, clearing its role in improving salt tolerance.     

EFFECT OF SALINIZATION OF SOIL ON GROWTH,WATER STATUS AND NUTRIENT ACCUMULATION IN SEEDLINGS OF ACACIA AURICULIFORMIS (FABACEAE)

Greenhouse experiments were conducted to assess the effects of salinization of soil on emergence, growth, water status, proline content, and mineral accumulation of seedlings of Acacia auriculiformis A. Cunn. ex Benth. (Fabaceae). Sodium chloride (NaCl) was added to the soil and salinity was maintained at 0.3, 3.9, 6.0, 7.9, 10.0, 12.1, and 13.9 dS m^?1. Salinity caused reduction in water potential of tissues, which resulted in internal water deficit to plants. Consequently, seedling growth significantly decreased with increase in soil salinity. Proline content in tissues increased with increase in salinity. Potassium and sodium content significantly increased in tissues as salinity increased. Nitrogen content significantly increased in tissues with salinization of soil. Phosphorus, calcium and magnesium content significantly decreased as salinity increased. Changes in tissues and whole-plant accumulation patterns of other nutrients, as well as possible mechanisms for avoidance of sodium toxicity in this tree species in response to salinity, are discussed.     

Growth and antioxidant responses in mustard (Brassica juncea L.) plants subjected to combined effect of gibberellic acid and salinity

The effects of salt stress on plant growth parameters, lipid peroxidation and some antioxidant enzyme activities [superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), peroxidase (POD, EC 1.11.1.7), glutathione reductase (GR; EC EC 1.6.4.2) and ascorbate peroxidase (APX, EC 1.11.1.11) activity] were studied in the leaves of mustard. Plants were exposed to two different concentrations of NaCl stress (100 and 150 mM) for 45 days and were sprayed with GA₃ (75 ml pot^?1, conc. 75 mg l^?1) once a week. Salt stress resulted in decrease in the growth and biomass yield of mustard but the exogenous application of GA₃ enhanced these parameters significantly. Application of GA₃ counteracted the adverse effects of NaCl salinity on relative water content, electrolyte leakage and chlorophyll (Chl) content. GA₃ was sufficient to attenuate partially the stimulatory effect of NaCl supply on proline and glycinebetaine biosynthesis. GA₃ reduced lipid peroxidation in the leaves, which was increased during salt stress. The activity of all the antioxidant enzymes was increased significantly during salt stress in mustard. The exogenous application of GA₃ decreased the enzyme activity. The results of the present study indicate that usage of GA₃ reduces the harmful effects of salinity and increases resistance to salinity in mustard plant.     

EFFECT OF MIXED-SALT SALINITY ON GROWTH AND ION RELATIONS OF A QUINOA AND A WHEAT VARIETY

ABSTRACT

Salinity is among the most widespread and prevalent problems in irrigated agriculture. Many members of the family Chenopodiaceae are classified as salt tolerant. One member of this family, which is of increasing interest, is quinoa (Chenopodium quinoa Willd.) which is able to grow on poorer soils. Salinity sensitivity studies of quinoa were conducted in the greenhouse on the cultivar, “Andean Hybrid” to determine if quinoa had useful mechanisms for salt tolerant studies. For salt treatment we used a salinity composition that would occur in a typical soil in the San Joaquin Valley of California using drainage waters for irrigation. Salinity treatments (EC_i ) ranging from 3, 7, 11, to 19?dS?m^?1 were achieved by adding MgSO₄, Na₂SO₄, NaCl, and CaCl₂ to the base nutrient solution. These salts were added incrementally over a four-day period to avoid osmotic shock to the seedlings. The base nutrient solution without added salt served as the non-saline control solution (3?dS?m^?1). Solution pH was uncontrolled and ranged from 7.7 to 8.0. For comparative purposes, we also examined Yecora Rojo, a semi-dwarf wheat, Triticum aestivum L. With respect to salinity effects on growth in quinoa, we found no significant reduction in plant height or fresh weight until the electrical conductivity exceeded 11?dS?m^?1. The growth was characteristic of a halophyte with a significant increase in leaf area at 11?dS?m^?1 as compared with 3?dS?m^?1 controls. As to wheat, plant fresh and dry weight, canopy height, and leaf area did not differ between controls (3?dS?m^?1) and plants grown at 7?dS?m^?1. Beyond this threshold, however, plant growth declined. While both quinoa and wheat exhibited increasing Na⁺ accumulation with increasing salinity levels, the percentage increase was greater in wheat. Examination of ion ratios indicated that K⁺:Na⁺ ratio decreased with increasing salinity in both species. The decrease was more dramatic in wheat. A similar observation was also made with respect to the Ca²⁺:Na⁺ ratios. However, a difference between the two species was found with respect to changes in the level of K⁺ in the plant. In quinoa, leaf K⁺ levels measured at 19?dS?m^?1 had decreased by only 7% compared with controls. Stem K⁺ levels were not significantly affected. In wheat, shoot K⁺ levels had decreased by almost 40% at 19?dS?m^?1. Correlated with these findings, we measured no change in the K⁺:Na⁺ selectivity with increasing salinity in quinoa leaves and only a small increase in stems. In wheat however, K⁺:Na⁺ selectivity at 3?dS?m^?1 was much higher than in quinoa and decreased significantly across the four salinity levels tested. A similar situation was also noted with Ca²⁺:Na⁺ selectivity. We concluded that the greater salt tolerance found in quinoa relative to wheat may be due to a variety of mechanisms.