Growth Properties and Ion Distribution in Different Tissues of Bread Wheat Genotypes (Triticum aestivum L.) Differing in Salt Tolerance

Four bread wheat genotypes differing in salt tolerance were selected to evaluate ion distribution and growth responses with increasing salinity. Salinity was applied when the leaf 4 was fully expanded. Sodium (Na⁺), potassium (K⁺) concentrations and K⁺/Na⁺ ratio in different tissues including root, leaf‐3 blade, flag leaf sheath and flag leaf blade at three salinity levels (0, 100 and 200 mm NaCl), and also the effects of salinity on growth rate, shoot biomass and grain yield were evaluated. Salt‐tolerant genotypes (Karchia‐65 and Roshan) showed higher growth rate, grain yield and shoot biomass than salt‐sensitive ones (Qods and Shiraz). Growth rate was reduced severely in the first period (1–10 days) after salt commencements. It seems after 20 days, the major effect of salinity on shoot biomass and grain yield was due to the osmotic effect of salt, not due to Na⁺‐specific effects within the plant. Grain yield loss in salt‐tolerant genotypes was due to the decline in grain size, but the grain yield loss in salt‐sensitive ones was due to decline in grain number. Salt‐tolerant genotypes sequestered higher amounts of Na⁺ concentration in root and flag leaf sheath and maintained lower Na⁺ concentration with higher K⁺/Na⁺ ratios in flag leaf blade. This ion partitioning may be contributing to the improved salt tolerance of genotypes.     

Using Growth and Ionic Contents of Wheat Seedlings as Rapid Screening Tool for Salt Tolerance

High germination percentage with vigorous early growth is preferred for harvesting good wheat stand under saline soils. Therefore, an attempt for rapid screening of wheat genotypes for salt tolerance was made in this study. Eleven wheat genotypes including salt tolerant check Kiran-95were subjected to salinity (120 and 160 mMNaCl) along with non-saline control. Results showed a gradual decrease in seed germination and restricted seedling growth in tested wheat genotypes in response to increasing NaCl concentration in nutrient solution. Among the genotypes, NIA-AS-14-6 and NIA-AS-14-7 exhibited more sensitivity towards the salt stress at the germination stage but NIA-AS-14-6 performed quite satisfactorily later on at the seedling stage. Wheat genotypes NIA-AS-14-2, NIA-AS-14-4, NIA-AS-14-5, NIA-AS-14-10, and Kiran-95 showed better performance in term of root-shoot length, plant biomasses (fresh and dry), K⁺:Na⁺ ratio with least Na⁺ content, and high accumulation of K⁺ at higher levels of NaCl stress. On the basis of overall results, the categorization of genotypes was carried out as sensitive, moderately tolerant, and tolerant. Wheat genotypes NIA-AS-14-2, NIA-AS-14-4, NIA-AS-14-5, NIA-AS-14-10, and Kiran-95 grouped as tolerant, moderately salt tolerant group comprised of NIA-AS-14-1, NIA-AS-14-3, NIA-AS-14-6, and NIA-AS-14-8, whereas, NIA-AS-14-7 and NIA-AS-14-9 were found sensitive to salt stress. Principal component analysis revealed that components I and II contributed 70 and 16.5%, respectively. All growth parameters are associated with each other except RDW. In addition to growth traits, low Na⁺ and improved K⁺ content with better K⁺:Na⁺ ratio may be used for screening of salt tolerance in wheat as potential physiological criteria.     

Screening sorghum genotypes for salinity tolerant biomass production

Genetic improvement of salt tolerance is of high importance due to the extent and the constant increase in salt affected areas. Sorghum [Sorghum bicolor (L.) Moench] has been considered relatively more salt tolerant than maize and has the potential as a grain and fodder crop for salt affected areas. One hundred sorghum genotypes were screened for salinity tolerance in pots containing Alfisol and initially irrigated with a 250-mM NaCl solution in a randomized block design with three replications. Subsequently 46 selected genotypes were assessed in a second trial to confirm their responses to salinity. Substantial variation in shoot biomass ratio was identified among the genotypes. The performance of genotypes was consistent across experiments. Seven salinity tolerant and ten salinity sensitive genotypes are reported. Relative shoot lengths of seedlings were genetically correlated to the shoot biomass ratios at all stages of sampling though the relationships were not close enough to use the trait as a selection criterion. In general, the whole-plant tolerance to salinity resulted in reduced shoot Na⁺ concentration. The K⁺/Na⁺ and Ca²⁺/Na⁺ ratios were also positively related to tolerance but with a lesser r ². Therefore, it is concluded that genotypic diversity exists for salt tolerance biomass production and that Na⁺ exclusion from the shoot may be a major mechanism involved in that tolerance.     

Maize genotypes with deep root systems tolerate salt stress better than those with shallow root systems during early growth

Maize (Zea mays L.) is susceptible to salinity but shows genotypic variation for salt tolerance. How maize genotypes with contrasting root morphological traits respond to salt stress remains unclear. This study assessed genotypic variation in salinity tolerance of 20 maize genotypes with contrasting root systems exposed to NaCl for 10 days (0, 50 mM or 100 mM NaCl, added in four increments every other day from 14 days after transplanting, DAT) in a semi-hydroponic phenotyping system in a temperature-controlled greenhouse. Considerable variation was observed for each of the 12 measured shoot and root traits among the 20 genotypes under NaCl treatments. Salt stress significantly decreased biomass production by up to 54% in shoots and 37% in roots compared with the non-saline control. The 20 genotypes were classified as salt-tolerant (8 genotypes), moderately tolerant (5) and salt-sensitive (7) genotypes based on the mean shoot dry weight ratio (the ratio of shoot dry weight at 100 mM NaCl and non-saline control) ± one standard error. The more salt-tolerant genotypes (such as Jindan52) had less reductions in growth, and lower shoot Na⁺ contents and higher shoot K⁺/Na⁺ ratios under salt stress. The declared salt tolerance was positively correlated with shoot height, shoot dry weight and primary root depth, and negatively correlated with shoot Na⁺ content at 100 mM NaCl. Primary root depth is critical for identifying salt responsiveness in maize plants and could be suggested as a selection criterion for screening salt tolerance of maize during early growth. The selected salt-tolerant genotypes have potentials for cultivation in saline soils and for developing high-yielding salt-tolerant maize hybrids in future breeding programmes.     

Identification of pearl millet [Pennisetum glaucum (L.) R. Br.] lines tolerant to soil salinity

Crop tolerance to salinity is of high importance due to the extent and the constant increase in salt-affected areas in arid and semi-arid regions. Pearl millet (Pennistum glaucum), generally considered as fairly tolerant to salinity, could be an alternative crop option for salt affected areas. To explore the genotypic variability of vegetative-stage salinity tolerance, 100 pearl millet lines from ICRISAT breeding programs were first screened in a pot culture containing Alfisol with 250 mM NaCl solution as basal application. Subsequently, 31 lines including many parents of commercial hybrids, selected from the first trial were re-tested for confirmation of the initial salinity responses. Substantial variation for salinity tolerance was found on the basis of shoot biomass ratio (shoot biomass under salinity/ non-saline control) and 22 lines with a wide range of tolerance varying from highly tolerant to sensitive entries were identified. The performance of the genotypes was largely consistent across experiments. In a separate seed germination and seedling growth study, the seed germination was found to be adversely affected (more than 70% decrease) in more than half of the genotypes with 250 mM concentration of NaCl. The root growth ratio (root growth under salinity/control) as well as shoot growth ratio was measured at 6 DAS and this did not reflect the whole plant performance at 39 DAS. In general, the whole plant salinity tolerance was associated with reduced shoot N content, increased K⁺ and Na⁺ contents. The K⁺/Na⁺ and Ca⁺⁺/Na⁺ ratios were also positively related to the tolerance but not as closely as the Na⁺ content. Therefore, it is concluded that a large scope exists for improving salt tolerance in pearl millet and that shoot Na⁺ concentration could be considered as a potential non-destructive selection criterion for vegetative-stage screening. The usefulness of this criterion for salinity response with respect to grain and stover yield remains to be investigated.     

Evaluating Predictive Values of Various Physiological Indices for Salinity Stress Tolerance in Wheat

Soil salinity is a worldwide issue that affects agricultural production. The understanding of mechanisms by which plants tolerate salt stress is crucial for breeding varieties for salt tolerance. In this work, a large number of wheat (Triticum aestivum and Triticum turgidum) cultivars were screened using a broad range of physiological indices. A regression analysis was then used to evaluate the relative contribution of each of these traits towards the overall salinity tolerance. In general, most of the bread wheats showed better Na⁺ exclusion that was associated with higher relative yield. Leaf K⁺/Na⁺ ratio and leaf and xylem K⁺ contents were the major factors determining salinity stress tolerance in wheat. Other important traits included high xylem K⁺ content, high stomatal conductance and low osmolality. Bread wheat and durum wheat showed different tolerance mechanisms, with leaf K⁺/Na⁺ content in durum wheat making no significant contributions to salt tolerance, while the important traits were leaf and xylem K⁺ contents. These results indicate that Na⁺ sequestration ability is much stronger in durum compared with bread wheat, most likely as a compensation for its lesser efficiency to exclude Na⁺ from transport to the shoot. We also concluded that plant survival scores under high salt stress can be used in bread wheat as a preliminary selection for Na⁺ exclusion gene(s).     

Mapping QTLs for salt tolerance with additive,epistatic and QTL × treatment interaction effects at seedling stage in wheat

Quantitative trait loci (QTLs) for salt tolerance with additive, epistatic and QTL × treatment interaction effects at seedling stage in wheat were identified. A set of 131 recombinant inbred lines derived from cross Chuan 35050 × Shannong 483 were evaluated under salt stress and normal conditions. Wide variation was found for all studied traits. A total of 18 additive and 16 epistatic QTLs were detected, among which five and 11 were with significant QTL × treatment effects. Ten QTL clusters were identified, and each may represent a single gene or closely linked genes. The locus controlling shoot K⁺/Na⁺ concentration ratio and shoot Na⁺ concentration on chromosome 5A may be identical to Nax2. The interval Xgwm6‐Xgwm538 on chromosome 4B for total dry weight was also identified in a previous study, both near the marker Xgwm6. The marker Xgwm6 may be useful for marker‐assisted selection. Six pairs of homoeologous QTLs were detected, showing synteny among the A, B and D genomes. These results facilitate understanding the mechanisms and the genetic basis of salt tolerance in wheat.     

Genetic analysis of salt tolerance at seedling and reproductive stages in rice (Oryza sativa)

Salinity is a major abiotic stress that limits rice production across rice areas as high‐yielding modern rice varieties are generally sensitive to salt stress. The study was conducted to deduce heritability and combining ability estimates of rice for various morphological and physiological traits using a 7 × 7 full‐diallel‐cross analysis at seedling and reproductive stages. The salinity stress treatment was 12 dS m^?1 at the seedling stage and 8 dS m^?1 at the reproductive stage. Diallel analysis revealed high for salinity tolerance scores and shoot height, moderate for shoot dry weight and root dry weight and low for Na⁺ and K⁺ concentrations and K⁺/Na⁺ ratio. The low‐to‐moderate narrow‐sense heritability for number of panicles, number of fertile spikelets, grain weight, spikelet fertility and K⁺/Na⁺ ratio suggests a large breeding population and delayed selection for tolerance until later generations. Significant maternal effects indicate that selection of the female parent is very important for desired trait development. The results of this study confirmed that salinity tolerance at the seedling and reproductive stages is regulated by a different set of genes that could be pyramided using different donors to enhance the level of tolerance.     

Genetic Variation for Salinity Tolerance in Pakistani Rice (Oryza sativa L.) Germplasm

Soil salinity is one of the major production constraints. Development and planting of salt‐tolerant varieties can reduce yield losses due to salinity. We screened 185 rice genotypes at germination stage in petri dishes under control, 50, 100 and 150 mm salt stress, and at seedling stage in Yoshida's hydroponic nutrient solution under control, 50 and 100 mm salt stress. At germination stage, 15 genotypes including Nona Bokra, Sonahri Kangni, 7421, 7423 and 7467, whereas at seedling stage, 28 genotypes including Nona Bokra, Jajai‐77, KSK‐133, KSK‐282, Fakhr‐e‐Malakand, Pakhal, IR‐6, Khushboo‐95, Shahkar and Shua‐92 were found salt tolerant. Basmati‐370, Mushkan, Homo‐46 and accessions 7436, 7437 and 7720 were sensitive to salinity at both germination and seedling stage. We further screened a subset of 33 salt‐tolerant and salt‐sensitive genotypes with SSR markers. Four SSR markers (RM19, RM171, RM172 and RM189) showed significant association with two or more of the studied traits under 50, 100 and 150 mm salt stress. These markers may be further tested for their potential in marker‐assisted selection. The salt‐tolerant genotypes identified in this study may prove useful in the development of salt‐tolerant rice varieties in adapted genetic background.     

Response of Wheat Varieties from Semi-arid Regions of Jordan to Salt Stress

This study was carried out to determine the effects of salinity levels (control, 6, 12 and 18 dS m^?1) on germination, seedling growth, some agronomic traits and proline accumulation in leaves of nine wheat varieties adapted to semi‐arid areas of Jordan. The tested wheat materials included eight durum wheat varieties (Haurani 27, Acsad 65, Om Rabbeeh, Sham 1, Safra Ma’an, Katma, Al‐Samra and F8) and one bread wheat variety (Diel Harthon). Final germination percentage, shoot and seminal root length, and all growth and yield parameters were significantly (P < 0.05) decreased by increasing salinity level. Proline content was significantly (P < 0.05) increased by increasing salinity. There were significant variety × salt interactions (P < 0.05) on final germination percentage, seminal root length, grain yield and yield‐related traits indicating that the varieties responded to salt differently. Sham 1 did not show any decrease in germination ability at the different salinity levels. Haurani 27, Acsad 65, Al‐Samra and Diel Harthon showed a nonsignificant reduction in germination potential at low and intermediate salt levels. Safra Ma’an and Al‐Samra showed the lowest reduction in seminal root length at low salt level and consequently exhibited the lowest stress susceptibility index ‘S’ values. Grain yield‐based stress susceptibility index ‘S’ indicated that Haurani 27, Acsad 65, Katma, Al‐Samra, F8 and Diel Jardoon were more salt tolerant than Om Rabbeeh, Sham 1 and Safra Ma’an. In conclusion, a similar salt tolerance was observed at different growth stages in Haurani 27, Acsad 65 and Al‐Samra. Consequently, these three varieties could be considered as salt tolerant and accordingly they are suitable for durum wheat improvement. Furthermore, Sham 1 had the highest ability to germinate at high salinity level indicating that it has a genetic potential for salt tolerance, at least at this stage of its life cycle.     

Differences in Ion Accumulation and Salt Tolerance among Glycine Accessions

Salinity reduces crop yield by limiting water uptake and causing ion‐specific stress. Soybean [Glycine max (L.) Merr.] is sensitive to soil salinity. However, there is variability among soybean genotypes and wild relatives for salt tolerance, suggesting that genetic improvement may be possible. The objective of this study was to identify differences in salt tolerance based on ion accumulation in leaves, stems and roots among accessions of four Glycine species. Four NaCl treatments, 0, 50, 75 and 100 mm , were imposed on G. max, G. soja, G. tomentella and G. argyrea accessions with different levels of salinity tolerance. Tolerant genotypes had less leaf scorch and a greater capacity to prevent Na⁺ and Cl^? transport from soil solution to stems and leaves than sensitive genotypes. Magnitude of leaf injury per unit increase in leaf Na⁺ or Cl^? concentrations was lower in tolerant than in susceptible accessions. Also, plant injury was associated more with Na⁺ rather than with Cl^? concentration in leaves. Salt‐tolerant accessions had greater leaf chlorophyll‐meter readings than sensitive genotypes at all NaCl concentrations. Glycine argyrea and G. tomentella accessions possessed higher salt tolerance than G. soja and G. max genotypes.     

Salt Tolerance is Associated with Differences in Ion Accumulation,Biomass Allocation and Photosynthesis in Cowpea Cultivars

Cowpea is widely cultivated in arid and semi‐arid regions of the world where salinity is a major environmental stress that limits crop productivity. The effects of moderate salinity on growth and photosynthesis were examined during the vegetative phase of two cowpea cultivars previously classified as salt‐tolerant (Pitiúba) and salt‐sensitive (TVu). Two salt treatments (0 and 75 mm NaCl) were applied to 10‐day‐old plants grown in nutrient solution for 24 days. Salt stress caused decreases (59 % in Pitiúba and 72 % in TVu) in biomass accumulation at the end of the experiment. Photosynthetic rates per unit leaf mass, but not per unit leaf area, were remarkably impaired, particularly in TVu. This response was unlikely to have resulted from stomatal or photochemical constraints. Differences in salt tolerance between cultivars were unrelated to (i) variant patterns of Cl^? and K⁺ tissue concentration, (ii) contrasting leaf water relations, or (iii) changes in relative growth rate and net assimilation rate. The relative advantage of Pitiúba over TVu under salt stress was primarily associated with (i) restricted Na⁺ accumulation in leaves paralleling an absolute increase in Na⁺ concentration in roots at early stages of salt treatment and (ii) improved leaf area (resulting from a larger leaf area ratio coupled with a larger leaf mass fraction and larger specific leaf area) and photosynthetic rates per unit leaf mass. Overall, these responses would allow greater whole‐plant carbon gain, thus contributing to a better agronomic performance of salt‐tolerant cowpea cultivars in salinity‐prone regions.     

Na+ Retention in the Root is a Key Adaptive Mechanism to Low and High Salinity in the Glycophyte,Talinum paniculatum (Jacq.) Gaertn. (Portulacaceae)

Talinum paniculatum is an important leafy vegetable and medicinal plant, used in many parts of South America, Africa and Asia. Its adaptation to abiotic stress has received little attention and therefore worthy of interest, especially as environmental conditions are rendering arable lands increasingly unfavourable for agriculture. Therefore, this study was undertaken to examine the influence of salt stress on the vegetative growth of the plant by subjecting seedlings to 0, 25, 50, 100, 200 and 300 mm NaCl stress for 10 days. The dry weight, ion concentrations, relative water content, oxidative damage, proline, osmotic potential and some antioxidants were determined. The plants were found to retain Na⁺ mainly in the root, with less affected leaf K⁺ concentration, and consequently very low shoot Na⁺/K⁺ ratios (<0.2) under all the stress treatments. The proline content significantly increased under the 100–300 mm treatments (18‐ to 244‐fold), with a corresponding significant reduction in osmotic potential and hence high osmotic adjustment. The antioxidant enzyme activities and non‐enzyme antioxidants showed significant increase only under the highest salinity. Taken together, these results suggest that shoot Na⁺ exclusion is characteristic of this plant and is mainly responsible for its adaptation to low salinity.     

Yield potential and salt tolerance of quinoa on salt‐degraded soils of Pakistan

Quinoa is recently introduced to Pakistan as a salt‐tolerant crop of high nutritional value. Open field trials were conducted to evaluate its performance on normal and salinity/sodicity‐degraded lands at two locations of different salinity/sodicity levels, S₁ (UAF Farm, Normal Soil), S₂ (Paroka Farm UAF, saline sodic), S₃ (SSRI Farm, normal) and S₄ (SSRI Farm, saline sodic) during 2013–2014. Two genotypes (Q‐2 and Q‐7) were grown in lines and were allowed to grow till maturity under RCBD split‐plot arrangement. Maximum seed yield (3,062 kg/ha) was achieved by Q‐7 at normal field (S₁) soil which was statistically similar with yield of same genotype obtained from salt‐affected field S₂ (2,870 kg/ha). Furthermore, low yield was seen from both genotypes from both S₃ and S₄ as compared to S₁ and S₂. Q‐7 was best under all four conditions. Minimum yield was recorded from Q‐2 (1,587 kg/ha) at S₄. Q‐7 had higher SOD, proline, phenolic and K⁺ contents, and lower Na⁺ content in leaves as compared to Q‐2. High levels of antioxidants and K⁺/Na⁺ of Q‐7 helped to withstand salt stress and might be the cause of higher yields under both normal and salt‐affected soils. Seed quality (mineral and protein) did not decrease considerably under salt‐affected soils even improved seed K⁺, Mg²⁺ and Mn²⁺.     

Root Nitrogen Remobilization and Ion Status of Two Alfalfa (Medicago sativa L.) Cultivars in Response to Salinity Stress

In a pot experiment the responses of two alfalfa cultivars differing in salt tolerance were evaluated in terms of root nitrogen remobilization rates (RNRR) and their relationship with the ionic status of the plants. A split‐plot design with factorial treatments in three replications was used. Three levels of salinity stress with electrical conductivities (EC_s) of 1.2, 7 and 12 ds m^?1 were established in irrigation water by using tap water with and without NaCl. The average data taken from plant materials at three defoliations were used for statistical analysis. Each time, plant materials were harvested at the 10 % flowering stage and then 10 days later. From the results observed, it was found that alfalfa shoot growth is highly dependent on RNRR under salinity stress. However, the total N reserves within the roots do not appear to be a limiting factor. The high positive correlation coefficient between shoot K⁺/Na⁺ and RNRR (r = 0.77; P = 0.01) indicates that lower demands for N because of diminished metabolic activities within the shoot sink may have reduced the rates of root N utilization. Unlike in some other species, the shoot K⁺ concentration and contents of alfalfa plants were significantly reduced by increasing salt stress. However, a relatively suitable K⁺/Na⁺ ratio of 7.1 is maintained in the shoots at the second level of salinity, as lowering the rates of salt induced an increase in Na⁺ uptake (Na exclusion). The salt tolerance recognized in the Bami cultivar may be attributed to the 339 % increase in its selectivity rates of K⁺ over Na⁺ in ion transport from the soil to the shoots, as the shoot Na⁺ content did not increase with increasing salt levels.     

Understanding physiological and morphological traits contributing to drought tolerance in barley

Drought stress is a major limiting factor for crop production in the arid and semi‐arid regions. Here, we screened eighty barley (Hordeum vulgare L.) genotypes collected from different geographical locations contrasting in drought stress tolerance and quantified a range of physiological and agronomical indices in glasshouse trails. The experiment was conducted in large soil tanks subjected to drought treatment of eighty barley genotypes at three‐leaf stage and gradually brought to severe drought by withholding irrigation for 30 days under glasshouse conditions. Also, root length of the same genotypes was measured from stress‐affected plants growing hydroponically. Drought tolerance was scored 30 days after the drought stress commenced based on the degree of the leaf wilting, fresh and dry biomass and relative water content. These characteristics were related to stomatal conductance, stomatal density, residual transpiration and leaf sap Na, K, Cl contents measured in control (irrigated) plants. Responses to drought stress differed significantly among the genotypes. The overall drought tolerance was significantly correlated with relative water content, stomatal conductance and leaf Na⁺ and K⁺ contents. No significant correlations between drought tolerance and root length of 6‐day‐old seedling, stomatal density, residual transpiration and leaf sap Cl^? content were found. Taking together, these results suggest that drought‐tolerant genotypes have lower stomatal conductance, and lower water content, Na⁺, K⁺ and Cl^? contents in their tissue under control conditions than the drought‐sensitive ones. These traits make them more resilient to the forthcoming drought stress.     

Biochar Mitigates Salinity Stress in Potato

A pot experiment was conducted in a climate‐controlled greenhouse to investigate the growth, physiology and yield of potato in response to salinity stress under biochar amendment. It was hypothesized that addition of biochar may improve plant growth and yield by mitigating the negative effect of salinity through its high sorption ability. From tuber bulking to harvesting, the plants were exposed to three saline irrigations, that is 0, 25 and 50 mm NaCl solutions, respectively, and two levels of biochar (0 % and 5 % W/W) treatments. An adsorption study was also conducted to study the Na⁺ adsorption capability of biochar. Results indicated that biochar was capable to ameliorate salinity stress by adsorbing Na⁺. Increasing salinity level resulted in significant reductions of shoot biomass, root length and volume, tuber yield, photosynthetic rate (A_n), stomatal conductance (g_s), midday leaf water potential, but increased abscisic acid (ABA) concentration in both leaf and xylem sap. At each salinity level, incorporation of biochar increased shoot biomass, root length and volume, tuber yield, A_n, g_s, midday leaf water potential, and decreased ABA concentration in the leaf and xylem sap as compared with the respective non‐biochar control. Decreased Na⁺, Na⁺/K⁺ ratio and increased K⁺ content in xylem with biochar amendment also indicated its ameliorative effects on potato plants in response to salinity stress. The results suggested that incorporation of biochar might be a promising approach for enhancing crop productivity in salt‐affected soils.     

Effect of Salinity Stress on Growth and Nutrient Composition of Three Soybean (Glycine max L. Merrill) Cultivars

Soil salinity is a major limitation to legume production in many areas of the world. The salinity sensitivity of soybean was studied to determine the effect of salinity on seed germination, shoot and root dry weights, and leaf mineral contents. Three soybean cultivars, Lee, Coquitt, and Clark 63, were planted in soils of different salinity levels. The electrical conductivity (EC) of the soils used in this experiment was 0.5 dS m^?1. The soil salinity treatments were 0.5, 2.5 4.5, 6.5 and 8.5 dS m^?1. Saline drainage water from a drainage canal with an EC of 15 dS m^?1 was used to treat the soil samples in order to obtain the desired salinity levels. Germination percentages were recorded 10 days after planting. Shoot and root dry weights of 45‐day‐old plants were measured. Nutrient concentrations for Na⁺, K⁺, Ca²⁺, Mg²⁺ and Cl^? were determined. Germination percentages were significantly reduced with increasing salinity levels. The cultivar Lee was less affected by salinity stress than Coquitt and Clark 63. At 8.5 dS m^?1 a significant reduction in plant height was found in all three cultivars. However, Lee plants were taller than plants of the other two cultivars. Salinity stress induced a significant increase in leaf sodium (Na⁺) and chloride (Cl^?) in all cultivars. However, the cultivar Lee maintained lower Na⁺ and Cl⁺ concentrations, a higher potassium (K⁺) concentration and a higher K⁺/Na⁺ ratio at higher salinity levels than Coquitt and Clark 63. Saline stress reduced the accumulation of K⁺, calcium (Ca²⁺) and magnesium (Mg²⁺) in the leaves of the cultivars studied. This study suggests that Lee is the most tolerant cultivar, and that there is a relationship between the salt tolerance of the cultivar and macronutrient accumulation in the leaves.     

Changes in Hormonal Balance: A Possible Mechanism of Pre‐Sowing Chilling‐Induced Salt Tolerance in Spring Wheat

There is a lack of knowledge about factors contributing to the chilling‐induced alleviatory effects on growth of plants under salt stress. Thus, the primary objective of the study was to determine whether chilling‐induced changes in endogenous hormones, ionic partitioning within shoots and roots and/or gaseous exchange characteristics is involved in salt tolerance of two genetically diverses of wheat crops. For this purpose, the seeds of two spring wheat (Triticum aestivum) cultivars, MH‐97 (salt intolerant) and Inqlab‐91 (salt tolerant) were chilled at 3°C for 2 weeks. The chilled, hydroprimed and non‐primed (control) seeds of the two wheat cultivars were sown in both Petri dishes in a growth room and in the field after treatment with 15 dS m^?1 NaCl salinity. Chilling was very effective in increasing germination rate and subsequent growth when compared with hydropriming and control under salt stress. Results from field experiments clearly indicated the efficacy of chilling over hydropriming in improving shoot dry biomass and grain yield in either cultivar, particularly under salt stress. This increase in growth and yield was related to increased net photosynthetic rate, greater potential to uptake and accumulate the beneficial mineral elements (K⁺ and Ca²⁺) in the roots and reduced uptake and accumulation of toxic mineral element (Na⁺) in the shoots of both wheat cultivars when grown under salt stress. Salt‐stressed plants of both wheat cultivars raised from chilled seed had greater concentrations of indoleacetic acid, abscisic acid, salicylic acid and spermine when compared with hydropriming and control. Therefore, induction of salt tolerance by pre‐sowing chilling treatment in wheat could be attributed to its beneficial effects on ionic homeostasis and hormonal balance. The results presented are also helpful to understand the chilling‐induced cross adaptation of plants in natural environments. Moreover, efficacy of pre‐sowing chilling treatment over hydropriming suggested its commercial utilization as a low risk priming treatment for better wheat crop production under stressful environments.     

Variation in Salinity Tolerance in Sunflower (Helianthus annum L.)

Forty-five accessions of sunflower collected from different countries were screened for salinity tolerance after 2 weeks growth in sand culture salinized with 150 meq l^?1 of NaCl₂+ CaCl₂ (1:1 ratio equivalent wt. basis) in half strength Hoagland's nutrient solution. The results for plant biomass of 45 accessions show that there was considerable variation in salinity tolerance. In a further greenhouse experiment, the salinity tolerance of three tolerant (HO-1, Predovik, Euroflor) and two sensitive (SMH-24, 9UO-985) lines (selected on the basis of their performance in the seedling experiment) was assessed at the adult stage to evaluate the consistency of salinity tolerance at different growth stages. All three salt tolerant accessions produced significantly greater plant biomass, seed yield and seed oil content than the salt sensitive accessions. The tolerant accessions accumulated less Cl^? and more K⁺ in the leaves under saline conditions compared with the salt sensitive accessions. The salt tolerant accessions also maintained relatively high leaf K:Na ratio and K⁺ versus Na⁺ selectivity. Although statistically nonsignificant, all three tolerant accessions had greater soluble carbohydrates, soluble proteins, total free amino acids and proline in the leaves than the sensitive accessions. A field trial conducted in a salt-affected field confirmed the greenhouse results of the selected accessions. This study shows that salinity tolerance of sunflower does not vary with stage of plant cycle, so selection for increased salt tolerance can be carried out at the initial growth stage. Secondly, it is found that there is great variation of salt tolerance in sunflower. Low uptake of Cl^?, high uptake of K⁺, and maintenance of high K:Na ratios and K⁺ versus Na⁺ selectivity in the leaves and possibly the accumulation of organic osmotica such as soluble carbohydrates, soluble proteins, proline and free amino acids seem to be the important components of salt tolerance in sunflower.