Assessment of tolerance to salt stress in Kenyan tomato germplasm

Tomato is an important vegetable crop in Kenya and the development of salt tolerant cultivars would enhance its productivity in the vast marginal areas of the country. This study was aimed at determining the magnitude of genotypic variability for salt tolerance in the Kenyan tomato germplasm. Pot experiments with 22 landraces and 9 market cultivars were laid out as a two and four replicate split-plot design in glasshouse in Experiments 1 and 2, respectively. Salt treatments in Experiment 1 were 0 and 5 g NaCl kg^-1 resulting into 0.5 and 9.1 dS m^-1 of the soil saturation extracts, respectively. In Experiment 2 the treatments were 0, 4, and 8 g NaCl kg^-1 soil corresponding to 0.5, 7.4, and 14.2 dS m^-1, respectively. Data were recorded on agronomic and biochemical parameters. The germplasm showed large variation for salt tolerance. Fruit and seed production at soil salinity of 14.2 dS m^-1 demonstrated that these tomatoes are fairly tolerant of NaCl. Osmotic adjustment was achieved by higher fruit electrical conductivity, brix and total titratable acidity. Low and high contents of K⁺, Ca²⁺ and Mg²⁺ within tomato tissues and soil, respectively, under salt treatment, confirmed competition and antagonism involving Na⁺ and these cations. Low Na⁺ and Cl^- contents in the fruit at 7.4 dS m^-1 revealed their exclusion and ensured production of physiologically normal seeds and nutritionally healthy fruits. Two landraces ‘Chwerotonglo’ and ‘Nyanyandogo’ were identified as salt tolerant. Comparatively, the market cultivars showed superior fruit yields despite their susceptibility to salinity. Accordingly, tolerance of landraces in combination with superior yields of the market cultivars is suitable for tomato improvement for salt tolerance. This revised version was published online in July 2006 with corrections to the Cover Date.     

In vitro selection of wheat callus tolerant to high levels of salt and plant regeneration

Summary Embryogenic calli isolated from immature embryos of four wheat cultivars were subjected to three in vitro selection methods for salt tolerance. The effect of NaCl on the selected and unselected cell lines has been investigated. The results indicated that the relative growth rate of callus decreased as the concentration of NaCl increased in both callus lines. The selected callus line gave a higher growth weight in the presence of NaCl in the medium and was highly significant as compared with unselected callus line across medium protocols in all wheat cultivars. The dry weight of both kinds of callus lines of all wheat cultivars increased markedly with increasing NaCl concentration in most cases. The Na⁺ and Cl^- contents of both callus lines were increased with increasing salinity levels while K⁺ content was decreased. The selected callus line of each cultivar at the same salinity level produced significant amounts of Na⁺, K⁺ and Cl^- higher than the unselected callus line in most salinity levels. However, the unselected callus lines of the cultivars Giza-157 and Sakha-90 at the same salinity level produced significant amounts of K⁺ higher than the selected callus line in most salinity levels. The proline content of both kinds of callus lines for all wheat cultivars was increased with increasing salinity level. However, the selected callus line gave a significantly higher proline content than the unselected callus line in all wheat cultivars at the same Salinity level. Results from the in vitro selection for NaCl tolerance showed that the stepwise method of increasing NaCl in the medium was more effective for plant regeneration than other methods.     

Growth‐Related Changes in Subcellular Ion Patterns in Maize Leaves (Zea mays L.) under Salt Stress

Na⁺ accumulation in the leaf apoplast has been suggested to lead to dehydration, later wilting and finally, the death of the affected leaves. Our aim has been to evaluate whether the reduction in the plant growth of sensitive maize in response to salinity is correlated with higher amounts of Na⁺ and Cl^? concentrations in the leaf apoplast. Subcellular ion patterns in intact leaves were investigated by using deionised water infiltration. We found an increase in soluble Na⁺ and Cl^? concentrations of about 16‐ and 4‐fold, respectively, compared with the control. These concentrations characterized the apoplasts of expanding leaves that had entirely developed under salinity. Interestingly, the K⁺ concentration was significantly reduced by 64 % compared with its control in the symplast under salinity. Our finding of a significantly decreased Ca²⁺ concentration in shoots suggested a possible association of Ca²⁺ concentration with the reduction in leaf expansion under salinity. As the absolute increase in the apoplastic Na⁺ concentration during salt treatment was much lower compared with the increase in the symplastic Na⁺ concentration, salt treatment in maize appears not to result in osmotic stress imposed by a high apoplastic Na⁺ concentration as has been suggested for other plant species (Oertli hypothesis).     

Effects of Soil Salinity and Plant Density on Yield and Leaf Senescence of Field‐Grown Cotton

The response of cotton to constant salinity has been well documented under controlled conditions, but its response to changing salinity under field conditions is poorly understood. Using a split‐plot design, we conducted a 2‐year field experiment to determine the effects of soil salinity and plant density on plant biomass, boll load, harvest index and leaf senescence in relation to cotton yield in three fields with similar fertility but varying salinity. The main plots were assigned to weak (electrical conductivity of soil saturated paste extract, ECe = 5.5 dS m^?1), moderate (ECe = 10.1 dS m^?1) and strong (ECe = 15.0 dS m^?1) soil salinity levels, while plant density (3.0, 4.5 and 7.5 plants m^?2) was assigned to the subplots. Soil salinity had a negative effect on seedcotton yield, but the negative effect was compensated for by increased plant density under strong‐salinity conditions. Seedcotton yield under weak salinity changed little with varying plant density, but the medium plant density yielded better than the low or high plant density under moderate salinity. Plants accumulated 49 and 112 % more Na⁺ in leaves under moderate and strong salinity than under weak salinity. Strong salinity also led to higher boll load and early leaf senescence. Plant density had no effect on Na⁺ accumulation in leaves, but greatly reduced boll load and delayed leaf senescence. Plant biomass, maximum leaf area index and harvest index were greatly affected by salinity, plant density and their interaction. Accelerated leaf senescence under strong salinity was attributed to the high boll load and increased accumulation of toxic ions like Na⁺ in leaves, while delayed leaf senescence with increased plant density was attributed to the reduced boll load. Optimal yield can only be obtained with proper coordination of total biomass and harvest index by modification of plant density based on salinity levels.     

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.     

Pear (Pyrus communis) and quince (Cydonia oblonga) roots exhibit different ability to prevent sodium and chloride uptake when irrigated with saline water

Soil salinity is a major constraint to the cultivation of horticultural crops. In the present study, potted trees of the pear variety Abbé Fetel, either with their own roots or grafted on different rootstocks, received irrigation water at two levels of salinity to: (i) evaluate the effect of the rootstock genotype on the vegetative growth; (ii) assess their differential ability to take up and partition sodium (Na⁺) and chloride (Cl⁻); (iii) verify the effect of salinity on the uptake of major cations (potassium, calcium and magnesium). Irrigation water at 5.0 dS m⁻¹ only slightly reduced vegetative growth regardless the genotype used as rootstock, suggesting a relative degree tolerance of pear (Pyrus communis) to soil salinity, at least in the short term. Quince (Cydonia oblonga) and pear rootstock genotypes had a contrasting effect on the uptake of chloride and sodium and differed regarding their ability to exclude these ions from the foliage. Quinces significantly increased their uptake of sodium and chloride when irrigated with saline water, while pear roots adopted an ion exclusion strategy to avoid accumulation of Na⁺ and Cl⁻. Trees grafted on quinces accumulated a significant amount of Cl⁻ in the leaves, but were able to store most absorbed Na⁺ in their roots, a mechanism that prevented xylem loading and transport to the leaves. No effect of salinity on the uptake of potassium (K⁺), calcium (Ca²⁺) and magnesium (Mg²⁺) was recorded; however, leaf potassium concentration was markedly lower when roots belonged to quince than to pear. The ability of pear genotypes to take up K⁺ occurred in control trees and was unaffected by saline treatment and might be related to the strategy adopted by pears to exclude Na⁺ due to a high selectivity K⁺/Na⁺.     

Estimation of salt tolerance in Andrographis paniculata accessions using multiple regression model

The complexity and polygenic nature of the salt tolerance trait in plants needs to develop a multiple indicator in the screening process. The mentioned issue led us to carry out an experiment to identify tolerant genotypes through multiple parameters in Andrographis paniculata. For this purpose, the 40-days seedlings were grown in different salinity levels (control, 4, 8, 12 and 16?dS?m^?1) on Hoagland??s medium. The results indicated that salinity had a significant effect on the morphological, physiological and biochemical traits. All measured morphological traits, and chlorophyll, K⁺ and Ca²⁺ content were significantly decreased with increasing salinity levels, while proline and Na⁺ content increased. The present exploration revealed that, salt tolerance index (STI), using the multiple regression model, demonstrated a more stable trend than the single variable assay (total dry weight). Furthermore, STI based on multiple regression analysis gives an accurate definition of salt-tolerant individuals. Under salt stress, tolerant accessions had high STI and produced higher proline, K⁺ and Ca²⁺, and lower Na⁺ content than sensitive accessions. Cluster analysis based on related traits to STI, indicated high similarity in each group. These outcomes can be utilized to evaluate the salt tolerance threshold in the species and may have a great advantage over conventional methods. Probably, our upshots can be applied in the next breeding programs to develop salt-tolerant varieties.     

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.     

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.     

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).     

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.     

Salt‐Induced Regulation of Some Key Antioxidant Enzymes and Physio‐Biochemical Phenomena in Five Diverse Cultivars of Turnip (Brassica rapa L.)

A greenhouse experiment was carried out to examine the differential morpho‐physiological responses of five cultivars of turnip (Brassica rapa L.) to salt stress. Five diverse cultivars of turnip (shaljum desi surakh, shaljum purple top, shaljum golden bal, neela shaljum, and peela shaljum) were subjected for 6 weeks to varying levels of NaCl, i.e. 0, 80 and 160 mm in Hoagland’s nutrient solution in sand culture. Imposition of varying levels of salt substantially decreased shoot and root fresh and dry weights, chlorophyll contents, leaf osmotic potential, relative water contents, different gas exchange attributes, total phenolics, malondialdehyde, activities of superoxide dismutase, peroxidase catalase, and leaf and root K⁺ levels while enhanced the proline contents, membrane permeability, level of H₂O₂, leaf and root Na⁺ and Cl^? and leaf Ca²⁺ in all turnip cultivars under study. Of all cultivars, peela shaljum and neela shaljum were consistently higher in their growth than the other turnip cultivars at all salt concentrations of the growth medium. Photosynthetic capacity (A) and stomatal conductance (g_s) were higher in high biomass‐producing cultivars, i.e. peela shaljum and neela shaljum, which provide to be potential selection criteria of salt tolerance in turnip. However, the regulation of antioxidant system was cultivar‐specific under saline conditions.     

Effects of Salinity and Soil–Drying on Radiation Use Efficiency,Water Productivity and Yield of Quinoa (Chenopodium quinoa Willd.)

Drought and salinity reduce crop productivity especially in arid and semi‐arid regions, and finding a crop which produces yield under these adverse conditions is therefore very important. Quinoa (Chenopodium quinoa Willd.) is such a crop. Hence, a study was conducted in field lysimeters to investigate the effect of salinity and soil–drying on radiation use efficiency, yield and water productivity of quinoa. Quinoa was exposed to five salinity levels (0, 10, 20, 30 and 40 dS m^?1) of irrigation water from flower initiation onwards. During the seed‐filling phase the five salinity levels were divided between two levels of irrigation, either full irrigation (FI; 95 % of field capacity) or non‐irrigated progressive drought (PD). The intercepted photosynthetically active radiation was hardly affected by salinity (8 % decrease at 40 dS m^?1) and did not differ significantly between FI and PD. Radiation use efficiency of dry matter was similar between salinity levels and between FI and PD. In line with this, no negative effect of severe salinity and soil–drying on total dry matter could be detected. Salinity levels between 20 and 40 dS m^?1 significantly reduced the seed yield by ca. 33 % compared with 0 dS m^?1 treatment owing to a 15–30 % reduction in seed number per m², whereas the seed yield of PD was 8 % less than FI. Consequently, nitrogen harvested in seed was decreased by salinity although the total N‐uptake was increased. Both salinity and drought increased the water productivity of dry matter. Increasing salinity from 20 to 40 dS m^?1 did not further decrease the seed number per m² and seed yield, which shows that quinoa (cv. Titicaca) acclimated to saline conditions when exposed to salinity levels between 20 and 40 dS m^?1.     

Genetic basis of physiological traits related to salt tolerance in tomato, Lycopersicon esculentum Mill.

Genetic relationships between salt tolerance and expression of various physiological traits during vegetative growth in tomato, Lycopersicon esculentum Mill., were investigated. Parental, F₁, F₂ and backcross progeny of a cross between a salt tolerant (PI174263) and a salt sensitive tomato cultivar (‘UCT5’) were evaluated in saline solutions with electrical conductivity of 0.5 (non-stress) and 20 dS/m (salt stress). Absolute growth, relative growth, tissue ion content, leaf solute potential and the rate of ethylene evolution were measured. Growth of both parents was reduced under salt stress; however, the reduction was significantly less in PI174263 than ‘UCT5’, suggesting greater salt tolerance of the former. Under salt stress, leaves of PI174263 accumulated significantly less Na⁺ and Cl^? and more Ca²⁺ than leaves of ‘UCT5’. Across parental and progeny generations, growth under salt stress was positively correlated with leaf Ca²⁺ content and negatively correlated with leaf Na⁺ content. In contrast, no correlation was observed between growth and either leaf solute potential or the rate of ethylene evolution under salt stress. Generation means analysis indicated that under salt stress both absolute and relative growth and the Na⁺ and Ca²⁺ accumulations in the leaf were genetically controlled with additivity being the major genetic component. The results indicated that the inherent genetic capabilities of PI174263 to maintain high tissue Ca²⁺ levels and to exclude Na⁺ from the shoot were essential features underlying its adaptation to salt stress and that these features were highly heritable. Thus, tissue ion concentration may be a useful selection criterion when breeding for improved salt tolerance of tomato using progeny derived from PI174263.     

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.     

Genetic analysis of sodium,potassium and chloride ion content inLycopersicon

Summary Plants of the salt-sensitiveL. esculentum, the halophytic wild speciesL. pennellii, their F₁ hybrids and the interspecific F₂ generation were grown in Hoagland's liquid culture containing 100 mM NaCl and 6 mM K⁺. Analysis of the Na⁺, Cl^- and K⁺ ions contents of the leaves showed, as observed also in previous studies, that the cultivated parent accumlated more K⁺ and less Na⁺ than the wild parent. A total of 117 F₂ plants were assayed for 15 electrophoretically detectable isozyme markers which map to nine of the twelve tomato chromosomes. Four loci, all with a similar quantitative effect on Na⁺ and Cl^- uptake, were identified by virtue of their linkage to isozyme markers. Two other loci were found to affect K⁺ uptake. This study demonstrates the potential value of using genetic markers in order to gain a better understanding of the genetic basis of quantitative traits associated with the response of plants to salinity stress.     

A Comparison of Screening Criteria for Salt Tolerance in Wheat under Field and Controlled Environmental Conditions

Although many screening criteria have been suggested to distinguish between genotypes for their salt tolerance under controlled environmental conditions, there is a need to test these criteria in the field. Saline soils are often complex and, therefore, unlikely to show a simple relationship to controlled conditions. To address this deficit, different agronomic and physiological screening criteria for salt tolerance in wheat at different stages were examined under both field and controlled conditions. Four wheat genotypes differing in their salt‐tolerance levels were grown in salt‐affected soil at two different locations and also under greenhouse conditions. Dry weight and leaf area of the upper and lower two leaves of the main stem and total dry weight at Zadoks scale 47 were measured in plants grown under field conditions. The concentrations of Cl^?, Na⁺, K⁺ and Ca²⁺ in the upper and lower two leaves of the main stem at Zadoks scale 47 and different yield components were measured in plants grown under both conditions. Our results indicate that measurements derived from the upper two leaves of the main stem were generally more effective as screening criteria than those from the lower two leaves. Correlation coefficients between grain yield and either dry weight or leaf area of the upper two leaves of the main stem indicated that dry weight is inferior to leaf area as a screening criterion under field conditions. Number of sterile spikelets per plant performed well under both conditions, whereas the number of spikelets per plant and 1000‐grain weight failed to distinguish the differences of salt‐tolerance levels among genotypes accurately. Weight and number of grains per plant and number of fertile spikes per plant were poor criteria under controlled conditions, but effective under field conditions. The maintenance of low Cl^? and Na⁺ concentrations in the upper two leaves offered the best guide to salt tolerance under both conditions. Potassium concentration was a poor criterion compared with the selectivity of K⁺ over Na⁺, which was useful under both field and controlled conditions. Calcium concentration and Ca²⁺ over Na⁺ selectivity in the upper and/or lower two leaves of the main stem were also effective in ranking genotypes according to their salt tolerance under both field and controlled conditions. Therefore, we conclude that simple measurements of the upper two leaves of the main stem including a straightforward measurement of leaf area, visually estimating the number of sterile spikelets, and a quick, practical determination of Na⁺ and Ca²⁺ concentration constitute effective criteria to screen wheat genotypes for salt tolerance under both field and controlled conditions.     

Screening of diverse tall fescue population for salinity tolerance based on SSR marker-physiological trait association

Soil salinity is a notorious abiotic stress which constrains plant growth and limits crop productivity. Recent advances in phytogenetics especially the discovery of marker-trait association have facilitated the efficient selection of stress-tolerant crops. The objective of this study was to evaluate tall fescue (Festuca arundinacea Schreb.) accessions growing under salt stress in order to identify salt-tolerant and salt-sensitive genotypes using physiological and molecular markers. The population consisted of 114 diverse tall fescue accessions which were assessed using 99 simple sequence repeat (SSR) markers and five functional physiological traits i.e., turf quality, leaf water content, chlorophyll content, relative growth rate, and evapotranspiration rate. Salinity stress induced great variations among the functional physiological traits and there were significant correlations among them. The population structure analysis revealed two distinct populations, while association mapping between the SSRs and phenotypic traits identified significant associations. In addition, the accessions that maintained relatively higher physiological traits had a significantly lower accumulation of Na⁺ and Cl^? in the roots compared to those whose functional traits declined. We identified six most salt-tolerant accessions due to their high values of physiological parameters and significantly low accumulation of Na⁺ and Cl^? in the roots. Similarly, we identified six accessions we considered to be most salt-sensitive as observed by high Na⁺ and Cl^? accumulation plus a decline in the physiological activities. Our findings are helpful to tall fescue breeders with a goal of producing tall fescue cultivars with enhanced salt tolerance.     

Salt Stress Delayed Flowering and Reduced Reproductive Success of Chickpea (Cicer arietinum L.), A Response Associated with Na+ Accumulation in Leaves

Salinity is known to reduce chickpea yields in several regions of the world. Although ion toxicity associated with salinity leads to yield reductions in a number of other crops, its role in reducing yields in chickpea growing in saline soils is unclear. The purpose of this study was to (i) identify the phenological and yield parameters associated with salt stress tolerance and sensitivity in chickpea and (ii) identify any pattern of tissue ion accumulation that could relate to salt tolerance of chickpea exposed to saline soil in an outdoor pot experiment. Fourteen genotypes of chickpea (Cicer arietinum L.) were used to study yield parameters, of which eight were selected for ion analysis after being grown in soil treated with 0 and 80 mm NaCl. Salinity delayed flowering and the delay was greater in sensitive than tolerant genotypes under salt stress. Filled pod and seed numbers, but not seed size, were associated with seed yield in saline conditions, suggesting that salinity impaired reproductive success more in sensitive than tolerant lines. Of the various tissues measured for concentrations of Cl^?, Na⁺ and K⁺, higher seed yields in saline conditions were positively correlated with higher K⁺ concentration in seeds at the mid‐filling stage (R² = 0.55), a higher K⁺/Na⁺ ratio in the laminae of fully expanded young leaves (R² = 0.50), a lower Na⁺ concentration in old green leaves (R² = 0.50) and a higher Cl^? concentration in mature seeds. The delay in flowering was associated with higher concentrations of Na⁺ in the laminae of fully expanded young leaves (R² = 0.61) and old green leaves (R² = 0.51). We conclude that although none of the ions appeared to have any toxic effect, Na⁺ accumulation in leaves was associated with delayed flowering that in turn could have played a role in the lower reproductive success in the sensitive lines.