Additive effects of Na+ and Cl- ions on barley growth under salinity stress

Soil salinity affects large areas of the world's cultivated land, causing significant reductions in crop yield. Despite the fact that most plants accumulate both sodium (Na(+)) and chloride (Cl(-)) ions in high concentrations in their shoot tissues when grown in saline soils, most research on salt tolerance in annual plants has focused on the toxic effects of Na(+) accumulation. It has previously been suggested that Cl(-) toxicity may also be an important cause of growth reduction in barley plants. Here, the extent to which specific ion toxicities of Na(+) and Cl(-) reduce the growth of barley grown in saline soils is shown under varying salinity treatments using four barley genotypes differing in their salt tolerance in solution and soil-based systems. High Na(+), Cl(-), and NaCl separately reduced the growth of barley, however, the reductions in growth and photosynthesis were greatest under NaCl stress and were mainly additive of the effects of Na(+) and Cl(-) stress. The results demonstrated that Na(+) and Cl(-) exclusion among barley genotypes are independent mechanisms and different genotypes expressed different combinations of the two mechanisms. High concentrations of Na(+) reduced K(+) and Ca(2+) uptake and reduced photosynthesis mainly by reducing stomatal conductance. By comparison, high Cl(-) concentration reduced photosynthetic capacity due to non-stomatal effects: there was chlorophyll degradation, and a reduction in the actual quantum yield of PSII electron transport which was associated with both photochemical quenching and the efficiency of excitation energy capture. The results also showed that there are fundamental differences in salinity responses between soil and solution culture, and that the importance of the different mechanisms of salt damage varies according to the system under which the plants were grown.     

Compatible solute accumulation and stress-mitigating effects in barley genotypes contrasting in their salt tolerance

The accumulation of compatible solutes is often regarded as a basic strategy for the protection and survival of plants under abiotic stress conditions, including both salinity and oxidative stress. In this work, a possible causal link between the ability of contrasting barley genotypes to accumulate/synthesize compatible solutes and their salinity stress tolerance was investigated. The impact of H(2)O(2) (one of the components of salt stress) on K(+) flux (a measure of stress 'severity') and the mitigating effects of glycine betaine and proline on NaCl-induced K(+) efflux were found to be significantly higher in salt-sensitive barley genotypes. At the same time, a 2-fold higher accumulation of leaf and root proline and leaf glycine betaine was found in salt-sensitive cultivars. The total amino acid content was also less affected by salinity in salt-tolerant cultivars. In these, potassium was found to be the main contributor to cytoplasmic osmolality, while in salt-sensitive genotypes, glycine betaine and proline contributed substantially to cell osmolality, compensating for reduced cytosolic K(+). Significant negative correlations (r= -0.89 and -0.94) were observed between Na(+)-induced K(+) efflux (an indicator of salt tolerance) and leaf glycine betaine and proline. These results indicate that hyperaccumulation of known major compatible solutes in barley does not appear to play a major role in salt-tolerance, but rather, may be a symptom of salt-susceptibility.     

Salicylic Acid-Mediated Regulation of Morpho-Physiological and Yield Attributes of Wheat and Barley Plants in Deferring Salinity Stress

Salinity has been observed to be a global problem that impede the physiological characteristics of plants. Salicylic acid (SA) as a phytohormone play multifaceted role in plants in terms of development as well as stress management. The current study was conducted to evaluate the effect of salinity and salicylic acid on the performance of wheat and barley plants under field experimentation followed by on-farm study to validate the results. This research was firstly conducted in a 4-year research barley field (2012–2013 and 2013–2014) and wheat (2014–2015 and 2015–2016) and subsequently in an on-farm research in four places (2017–2018). Results depicted that salinity decreased plant yield components and altered ion concentrations (Na⁺/K⁺) causing reduced grain and biological yield. However, SA foliar application induced yield components, especially grain number of plants in both years in non-saline and saline conditions. Exogenously SA application not only led to higher grain yield of barley and wheat but also significantly improved their salt tolerance. Our findings revealed that optimum SA concentrations for achieving highest barley yield were 0.85 and 0.78 mM under saline and non-saline conditions, respectively, while on-farm scale studies observed that foliar application of SA increased grain and biological yield of wheat in Ardakan, Ashkzar (saline soil and water) and Mehrabad (non-saline field) regions. There was no significant effect in Tijerd, a completely non-saline field. The grain yields were higher in SA-treated Ardakan, Ashkzar, and Mehrabad plants in field by 19, 16, and 15%, respectively. Based on present detailed studies, it was concluded that SA improved salinity tolerance and increased crop yield. So, optimum concentration (1.0–1.5 mM) with proper time application (double ridges), SA increased wheat and barley yields up to 20%. Therefore, SA priming could be used as a potent strategy to cope up salinity stress from plants.

     

Novel screening protocol for precise phenotyping of salt-tolerance at reproductive stage in rice

The present study reports an unequivocal and improved protocol for efficient screening of salt tolerance at flowering stage in rice, which can aid phenotyping of population for subsequent identification of QTLs associated with salinity stress, particularly at reproductive stage. To validate the new method, the selection criteria, level and time of imposition of stress; plant growth medium were standardized using three rice genotypes. The setup was established with a piezometer placed in a perforated pot for continuous monitoring of soil EC and pH throughout the period of study. Further, fertilizer enriched soil was partially substituted by gravels for stabilization and maintaining the uniformity of soil EC in pots without hindering its buffering capacity. The protocol including modified medium (Soil:Stone, 4:1) at 8 dS m^?1 salinity level was validated using seven different genotypes possessing differential salt sensitivity. Based on the important selection traits such as high stability index for plant yield, harvest index and number of grains/panicle and also high K⁺ concentration and low Na⁺– K⁺ ratio in flag leaf at grain filling stage were validated and employed in the evaluation of a mapping population in the modified screening medium. The method was found significantly efficient for easy maintenance of desired level of soil salinity and identification of genotypes tolerant to salinity at reproductive stage.     

The potential of leaf chlorophyll content to screen bread-wheat genotypes in saline condition

Physiological traits, which are positively associated with yield under salt-stress conditions, can be useful selection criteria in screening for salt tolerance. We examined whether chlorophyll (Chl) content can be used as screening criterion in wheat. Our study involved 5 wheat genotypes under both saline and nonsaline field conditions as well as in a sand-culture experiment. Salt stress reduced significantly biomass, grain yield, total Chl and both Chl a and b in all genotypes. In the sand-culture experiment, Chl accumulation was higher in PF70354/BOW, Ghods, and H499.71A/JUP genotypes at nonsaline control, moderate, and high salt concentrations, respectively. In the field experiment, genotype H499.71A/JUP belonged to those with the highest Chl density. The SPAD (Soil Plant Analysis Development) meter readings were linearly related to Chl content both in the sand-culture and in the field experiment. However, salt stress affected the calibration of SPAD meter. Therefore, separate Chl-SPAD equations were suggested for saline and nonsaline conditions. The correlation coefficients between the grain yield and SPAD were positive and significant both in the sand culture and in the field experiment. These findings suggested that SPAD readings could be used as a tool for rapid assessment of relative Chl content in wheat genotypes. It could be used for the indirect selection of high-yielding genotypes of wheat under saline condition in sand-culture and field experiments.     

Salinity-yield response functions of barley genotypes assessed with a triple line source sprinkler system

Evaluation of the salt tolerance of crop cultivars under field conditions is greatly complicated by the typical temporal and spatial variability of soil salinity. We obtained the grain yield – salinity response functions of 124 barley genotypes by growing them in ten salinity treatments imposed by a Triple Line Source Sprinkler (TLS) system during five consecutive years. Additional objectives were to ascertain the consistency and reproducibility over years of these functions, to quantify the deleterious effects of saline sprinkling irrigations, and to assess correlations between salinity tolerance and leaf sap salt concentration. The consistency and reproducibility of the response functions within and between years were adequate (only 8% of the response functions were discarded for statistical reasons). The Y _m (grain yield without salinity) and the EC₅₀ (the EC _e that reduces yield by 50%) estimates were not correlated (P > 0.05) suggesting that the most productive genotypes were not necessarily less salinity tolerant. Y _m was positively and significantly (P < 0.01) correlated with Y₆ and Y₁₂ (fitted grain yields at EC _e values of 6 dS m^-1, and 12 dS m^-1, respectively), indicating that it is a useful statistic in the selection of barley genotypes most productive under medium and high salinities. Foliar salt uptake due to saline sprinkling irrigations decreased the EC₅₀ by around 50% as compared with the salinity tolerance obtained with surface irrigation systems. No consistent relationships were found between either Y _m or EC₅₀ and the leaf sap osmotic potential, Cl, Ca, Na and K concentrations. They could not therefore be used in screening for salinity tolerance of barley. On the basis of the evidence from the present study, Y _m is the best statistic for predicting the most productive barley genotypes in salt-affected soils. This revised version was published online in June 2006 with corrections to the Cover Date.     

Foliar and root absorption of Na+ and Cl− in maize and barley: Implications for salt tolerance screening and the use of saline sprinkler irrigation

Above-canopy sprinkler irrigation with saline water favours the absorption of salts by wetted leaves and this can cause a yield reduction additional to that which occurs in salt-affected soils. Outdoor pot experiments with both sprinkler and drip irrigation systems were conducted to determine foliar ion accumulation and performance of maize and barley plants exposed to four treatments: nonsaline control (C), salt applied only to the soil (S), salt applied only to the foliage (F) and salt applied to both the soil and to the foliage (F+S). The EC of the saline solution employed for maize in 1993 was 4.2 dS m^–1 (30 mM NaCl and 2.8 mM CaCl₂) and for barley in 1994, 9.6 dS m^–1 (47 mM NaCl and 23.5 mM CaCl₂). The soil surface of all pots was covered so that in the F treatment the soil was not salinized by the saline sprinkling and drip irrigation supplied nutrients in either fresh (treatments C and F) or saline water (treatments S and F+S).Saline sprinkling increased leaf sap Na⁺ concentrations much more than did soil salinity, especially in maize, even though the saline sprinkling was given only two or three times per week for 30 min, whereas the roots of plants grown in saline soil were continuously exposed to salinity. By contrast, leaf sap Cl^– concentrations were increased similarly by saline sprinkling and soil salinity in maize, and more by saline sprinkling than saline soil in barley. It is concluded that barley leaves, and to a greater extent maize leaves, lack the ability to selectively exclude Na⁺ when sprinkler irrigated with saline water. Moreover, maize leaves selectively absorbed Na⁺ over Cl^– whereas barley leaves showed no selectivity. When foliar and root absorption processes were operating together (F+S treatment) maize and barley leaves accumulated 11–14% less Na⁺ and Cl^– than the sum of individual absorption processes (treatment F plus treatment S) indicating a slight interaction between the absorption processes. Vegetative biomass at maturity and cumulative plant water use were significantly reduced by saline sprinkling. In maize, reductions in biomass and plant water use relative to the control were of similar magnitude for plants exposed only to saline sprinkling, or only to soil salinity; whereas in barley, saline sprinkling was more detrimental than was soil salinity. We suggest that crops that are salt tolerant because they possess root systems which efficiently restrict Na⁺ and Cl^– transport to the shoot, may not exhibit the same tolerance in sprinkler systems which wet the foliage with saline water. ei]T J Flowers     

Response of barley and wheat to phosphorus in the presence of chloride and sulphate salinity

Summary The study was conducted in a greenhouse and under field conditions. In the greenoouse, barley was grown to maturity in pots on a sandy soil which contained 80 and 120 meq/l of chloride and sulphate dominant salts in its saturation extract, to which 0, 10, 25 and 50 ppm P were added. In the field study, wheat was grown on loamy sand soils having 0, 25, 50 and 75 kg/ha added P levels and irrigated with either Cl- or SO₄-dominant saline waters (EC=15–19 mmhos/cm). The results of the greenhouse study indicated that at maturity barley straw and grain yield was significantly increased by 50 ppm of added P both on the non-saline control and the Cl-treatments. However, 25 ppm P was optimal on the SO₄-treatments. The Cl content of plants was significantly decreased and S was increased with the increase in the P content of soil. A synergistic relation between the S and P content of barley shoots was observed. In the field study wheat grain yield responded significantly to P applications upto 50 kg/ha level on the Cl-site and there was no response to applied P on the SO₄-site, although the former contained more Olsen's P than the latter. The results suggested that P requirement of wheat and barley was greater on Cl- than on SO₄-salinity.     

Grafting raises the salt tolerance of tomato through limiting the transport of sodium and chloride to the shoot

With the aim of determining whether grafting could improve salinity tolerance of tomato (Lycopersicon esculentum Mill.), and what characteristics of the rootstock were required to increase the salt tolerance of the shoot, a commercial tomato hybrid (cv. Jaguar) was grafted onto the roots of several tomato genotypes with different potentials to exclude saline ions. The rootstock effect was assessed by growing plants at different NaCl concentrations (0, 25, 50, and 75 mM NaCl) under greenhouse conditions, and by determining the fruit yield and the leaf physiological changes induced by the rootstock after 60 d and 90 d of salt treatment. The grafting process itself did not affect the fruit yield, as non-grafted plants of cv. Jaguar and those grafted onto their own root showed the same yield over time under non-saline conditions. However, grafting raised fruit yield in Jaguar on most rootstocks, although the positive effect induced by the rootstock was lower at 25 mM NaCl than at 50 and 75 mM NaCl. At these higher levels, the plants grafted onto Radja, Pera and the hybrid VolgogradskijxPera increased their yields by approximately 80%, with respect to the Jaguar plants. The tolerance induced by the rootstock in the shoot was related to ionic rather than osmotic stress caused by salinity, as the differential fruit yield responses among graft combinations were mainly related to the different abilities of rootstocks to regulate the transport of saline ions. This was corroborated by the high negative correlation found between fruit yield and the leaf Na(+) or Cl(-) concentrations in salt-treated plants after 90 d of salt treatment. In conclusion, grafting provides an alternative way to enhance salt tolerance, determined as fruit yield, in the tomato, and evidence is reported that the rootstock is able to reduce ionic stress.     

Time‐course analysis of salicylic acid effects on ROS regulation and antioxidant defense in roots of hulled and hulless barley under combined stress of drought,heat and salinity

Greater crop losses can result from simultaneous exposure to a combination of drought, heat and salinity in the field. Salicylic acid (SA), a phenolic phytohormone, can affect a range of physiological and biochemical processes in plants and significantly impacts their resistance to these abiotic stresses. Despite numerous reports involving the positive effects of SA by applying each abiotic stress separately, the mechanism of SA‐mediated adaptation to combined stresses remains elusive. This study, via a time‐course analysis, investigated the role of SA on the roots of hulled and hulless (naked) barley (Hordeum vulgare L. ‘Tarm’ and ‘Özen’, respectively), which differed in salt tolerance, under the combined stress of drought, heat and salt. The combined stress caused marked reductions in root length and increases in proline content in both genotypes; however, Tarm exhibited better adaptation to the triple stress. Under the first 24 h of stress, superoxide dismutase (SOD; EC.1.15.1.1) and peroxidase (POX; EC.1.11.1.7) activity in the Tarm roots increased remarkably, while decreasing in the Özen roots. Furthermore, the Tarm roots showed higher catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APX; EC 1.11.1.11) and glutathione reductase (GR; EC 1.6.4.2) activity than the Özen during the combined stresses. The sensitivity of hulless barley roots may be related to decreasing SOD, POX, CAT and GR activity under stress. Over 72 h of stress, the SA pretreatment improved the APX and GR activity in Tarm and that of POX and CAT in Özen, demonstrating that exogenously applied SA regulates antioxidant defense enzymes in order to detoxify reactive oxygen species. The results of this study suggest that SA treatment may improve the triple‐stress combination tolerance in hulled and hulless barley cultivars by increasing the level of antioxidant enzyme activity and promoting the accumulation of proline. Thus, SA alleviated the damaging effects of the triple stress by improving the antioxidant system, although these effects differed depending on characteristic of the hull of the grain.     

Sustainable wheat (Triticum aestivum L.) production in saline fields: a review

Abstract

A large part of global agricultural fields, including the wheat (Triticum aestivum L.) ones, are subjected to various stresses including salinity. Given the increasing world population, finding methods and strategies that can alleviate salinity stress on crop yield production is of outmost importance. The presented review has consulted more than 400 articles related to the clean and sustainable production of wheat in saline fields affected by biological, environmental, economical, and social parameters including the important issue of climate change (global warming). The negative effects of salt stress on plant growth and the techniques, which have been so far detected to alleviate salinity stress on wheat growth have been analyzed and presented. The naturally tolerant species of wheat can use a range of mechanisms to alleviate salinity stress including sodium exclusion, potassium retention, and osmoregulation. However, the following can be considered as the most important techniques to enhance wheat tolerance under stress: (1) the biotechnological (crop breeding), biological (soil microbes), and biochemical (seed priming) methods, (2) the use of naturally tolerant genotypes, and (3) their combined use. The proper handling of irrigation water is also an important subject, which must be considered when planting wheat in saline fields. In conclusion, the sustainable and cleaner production of wheat under salt stress is determined by a combination of different parameters including the biotechnological techniques, which if handled properly, can enhance wheat production in saline fields.     

Response of rice varieties to soil salinity and air humidity: A possible involvement of root-borne ABA

In a phytotron experiment four rice varieties (Pokkali, IR 28, IR 50, IR 31785-58-1-2-3-3) grown in individual pots were subjected to low (40/55% day/night) and high (75/90%) air humidity (RH), while soil salinity was gradually increased by injecting 0, 30, 60 or 120 mM NaCl solutions every two days. Bulk root and stem base water potential (SWP), abscisic acid (ABA) content of the xylem sap and stomatal resistance (rs) of the youngest fully expanded leaf were determined two days after each salt application. The SWP decreased and xylem ABA and rs increased throughout the 8 days of treatment. The effects were amplified by low RH. A chain of physiological events was hypothesized in which high soil electric conductivity (EC) reduces SWP, followed by release of root-borne ABA to the xylem and eventually resulting in stomatal closure. To explain varietal differences in stomatal reaction, supposed cause and effect variables were compared by linear regression. This revealed strong differences in physiological reactions to the RH and salt treatments among the test varieties. Under salt stress roots of IR 31785-58-1-2-3-3 produced much ABA under low RH, but no additional effect of low RH on rs could be found. By contrast, Pokkali produced little ABA, but rs was strongly affected by RH. RH did not affect the relationships EC vs. SWP and SWP vs. ABA in Pokkali, IR 28, and IR 50, but the relationship ABA vs. rs was strongly affected by RH. In IR 31785-58-1-2-3-3 RH strongly affected the relationship SWP vs. ABA, but had no effect on ABA vs. rs and EC vs. rs. The results are discussed regarding possible differences in varietal stomatal sensitivity to ABA and their implications for varietal salt tolerance.     

Expression of the Arabidopsis vacuolar H+‐pyrophosphatase gene (AVP1) improves the shoot biomass of transgenic barley and increases grain yield in a saline field

Cereal varieties with improved salinity tolerance are needed to achieve profitable grain yields in saline soils. The expression of AVP1, an Arabidopsis gene encoding a vacuolar proton pumping pyrophosphatase (H⁺‐PPase), has been shown to improve the salinity tolerance of transgenic plants in greenhouse conditions. However, the potential for this gene to improve the grain yield of cereal crops in a saline field has yet to be evaluated. Recent advances in high‐throughput nondestructive phenotyping technologies also offer an opportunity to quantitatively evaluate the growth of transgenic plants under abiotic stress through time. In this study, the growth of transgenic barley expressing AVP1 was evaluated under saline conditions in a pot experiment using nondestructive plant imaging and in a saline field trial. Greenhouse‐grown transgenic barley expressing AVP1 produced a larger shoot biomass compared to null segregants, as determined by an increase in projected shoot area, when grown in soil with 150 mm NaCl. This increase in shoot biomass of transgenic AVP1 barley occurred from an early growth stage and also in nonsaline conditions. In a saline field, the transgenic barley expressing AVP1 also showed an increase in shoot biomass and, importantly, produced a greater grain yield per plant compared to wild‐type plants. Interestingly, the expression of AVP1 did not alter barley leaf sodium concentrations in either greenhouse‐ or field‐grown plants. This study validates our greenhouse‐based experiments and indicates that transgenic barley expressing AVP1 is a promising option for increasing cereal crop productivity in saline fields.     

Quantitative trait loci for salinity tolerance in barley (Hordeum vulgare L.)

Salinity stress is a major limitation in barley production. Substantial genetic variation in tolerance occurs among genotypes of barley, so the development of salt-tolerant cultivars is a potentially effective approach for minimizing yield losses. The lack of economically viable methods for screening salinity tolerance in the field remains an obstacle to breeders, and molecular marker-assisted selection is a promising alternative. In this study, salinity tolerance of 172 doubled-haploid lines generated from YYXT (salinity-tolerant) and Franklin (salinity-sensitive) was assessed in glasshouse trials during the vegetative phase. A high-density genetic linkage map was constructed from 76 pairs of simple sequence repeats and 782 Diversity Arrays Technology markers which spanned a total of 1,147 cM. Five significant quantitative trait loci (QTL) for salinity tolerance were identified on chromosomes 1H, 2H, 5H, 6H and 7H, accounting for more than 50% of the phenotypic variation. The tolerant variety, YYXT, contributed the tolerance to four of these QTL and Franklin contributed the tolerance to one QTL on chromosome 1H. Some of these QTL mapped to genomic regions previously associated with salt tolerance in barley and other cereals. Markers associated with the major QTL identified in this study have potential application for marker-assisted selection in breeding for enhanced salt tolerance in barley.     

Glycinebetaine in saline conditions: an assessment of the current state of knowledge

Salt stress is one of the environmental threats that have devastating impacts on plant distribution, growth and production. Different plants are believed to have salt tolerance mechanisms that occur at the cellular level. One facet of the cellular mechanisms of adaptation to salinity stress is to accumulate either inorganic and/or organic solutes. Glycinebetaine (GB), as well as other organic solutes, has been referred to as compatible solutes, for the reason that they are innocent with essential biochemical reactions even at high concentrations. GB has been assumed to be involved in osmotic adjustment and/or osmoprotection of cellular functional macromolecules and, hence, can improve tolerance to saline conditions. However, the exact mechanism and direct evidences for such correlative data are still lacking despite many attempts to improve growth under saline conditions by exogenous application as well as genetic engineering of metabolic pathways involved in metabolism of GB. Despite the enormous amount of information accumulated in this regard, the exact function of GB in the adaptation to saline environments is not fully clear to this point, and even GB functions have been argued. Because of that, inconsistencies exist in the published data regarding GB accumulation and functions under salt stress. In this review, we provide an update on evidence supporting each of these arguments to reassess how GB affects plant growth and physiological traits under salt imposition, and whether its effects correlate with salt tolerance.     

Relationship between salt tolerance and photosynthetic machinery performance in citrus

In citrus, salt stress has been related to the build up of chloride ions in plant tissues that affect photosynthesis, growth and yield. We investigated the effects of salt stress on the stability of the photosynthetic machinery with respect to the relative salt tolerance of different citrus genotypes including: Swingle Citrumelo, Carrizo citrange, C35 citrange, Cleopatra mandarin and Forner-Alcaide #5. Under identical salt-stress conditions, Forner-Alcaide #5 and Cleopatra mandarin accumulated less chloride ions in leaves than the other genotypes and showed a better plant performance. Chlorophyll fluorescence parameters indicated severe impairments of photosynthetic activity in salt-sensitive Citrumelo and citranges but Cleopatra and Forner-Alcaide #5 were less affected. In addition, differences in photosynthetic responses between these two moderately tolerant genotypes suggested different strategies to cope with salinity. The high tolerance to salinity shown by Forner-Alcaide #5 can be associated to the ability of keeping an active photosynthetic system at elevated saline conditions whereas the tolerance of Cleopatra was linked to rapid reductions of net photosynthetic rate, stomatal conductance, performance of PSII and photosynthetic efficiency.     

Indole acetic acid (IAA) induced changes in growth, relative water contents and gas exchange attributes of barley (Hordeum vulgare L.) grown under water stress conditions

Effect of different concentrations of indole acetic acid (IAA) under varying soil water deficit conditions on two barley cultivars viz. B-99094 and Jau-87 was investigated in soil filled earthen pots. There were six treatments including control each with four replicates. Three concentrations of IAA (0, 15 and 30 mg l⁻¹) were applied as foliar spray 30 days after germination. After hormone application, half of the pots were subjected to one cycle of water stress (withholding of water till incipient wilting), followed by regular watering. Plant height, photosynthetic rate, transpiration rate, stomatal conductance, water use efficiency relative water content, dry biomass, and grain yield/plant were significantly reduced by water stress. However, IAA treatments alleviated the adverse effect of water stress and successful in enhancing the plant growth and yield of barley cultivars. Barley cultivar Jau-87 performed better than B-99094. IAA application␣was effective in enhancing growth and photosynthetic efficiency of barley both under normal and water stress conditions.     

Salinity Adaptation and the Contribution of Parental Environmental Effects in Medicago truncatula

High soil salinity negatively influences plant growth and yield. Some taxa have evolved mechanisms for avoiding or tolerating elevated soil salinity, which can be modulated by the environment experienced by parents or offspring. We tested the contribution of the parental and offspring environments on salinity adaptation and their potential underlying mechanisms. In a two-generation greenhouse experiment, we factorially manipulated salinity concentrations for genotypes of Medicago truncatula that were originally collected from natural populations that differed in soil salinity. To compare population level adaptation to soil salinity and to test the potential mechanisms involved we measured two aspects of plant performance, reproduction and vegetative biomass, and phenological and physiological traits associated with salinity avoidance and tolerance. Saline-origin populations had greater biomass and reproduction under saline conditions than non-saline populations, consistent with local adaptation to saline soils. Additionally, parental environmental exposure to salt increased this difference in performance. In terms of environmental effects on mechanisms of salinity adaptation, parental exposure to salt spurred phenological differences that facilitated salt avoidance, while offspring exposure to salt resulted in traits associated with greater salt tolerance. Non-saline origin populations expressed traits associated with greater growth in the absence of salt while, for saline adapted populations, the ability to maintain greater performance in saline environments was also associated with lower growth potential in the absence of salt. Plastic responses induced by parental and offspring environments in phenology, leaf traits, and gas exchange contribute to salinity adaptation in M. truncatula. The ability of plants to tolerate environmental stress, such as high soil salinity, is likely modulated by a combination of parental effects and within-generation phenotypic plasticity, which are likely to vary in populations from contrasting environments.     

Identification of quantitative trait loci for ion homeostasis and salt tolerance in barley (Hordeum vulgare L.)

Ion homeostasis is considered to be one of the most important mechanisms underlying salt stress tolerance. We used the Steptoe × Morex barley doubled haploid population to screen for genetic variation in response to salinity stress at an early development stage in a hydroponics system, focusing on ion homeostasis. Salinity induced a strong adverse effect on growth of the parents and their derived population, with Steptoe as the more tolerant parent. Steptoe maintained higher concentrations of K⁺, Na⁺ and Cl^? in the roots and a similar shoot/root ion ratio (<1) under stress conditions compared to control conditions. In contrast, Morex had higher concentrations of these ions in the shoots under stress and a doubled shoot/root ion ratio relative to control conditions, indicating that salt exclusion might contribute to the higher tolerance of Steptoe. Correlation and path analysis demonstrated that shoot Cl^? contents most strongly affected salt tolerance and suggest that both Na⁺ and Cl^? contents are important for salinity stress tolerance in barley. We identified 11 chromosomal regions involved in the control of the variation observed for salt tolerance and various salt stress response traits, including Na⁺, Cl^? and K⁺ contents in shoots. Two specific regions on chromosomes 2H and 3H were found controlling ion contents and salt tolerance, pointing to genes involved in ion homeostasis that contribute to salt tolerance.