Salinity Tolerance Of Crops Research Articles

Leaf mesophyll K+ and Cl− fluxes and reactive oxygen species production predict rice salt tolerance at reproductive stage in greenhouse and field conditions

Extensive research on salinity tolerance in rice has been mostly carried out at the seedling stage in single experimental trials. Here, we aimed to understand the roles of ion transport and oxidative responses of leaf mesophyll in salinity tolerance of rice (Oryza sativa L.) at its reproductive stage using comparative investigations in both greenhouse and field trials. Two experimental trials were conducted to assess the salt tolerance of three rice cultivars at their reproductive stage in greenhouse and field. We employed agronomic, physiological, electrophysiological, molecular and cell imaging techniques to compare physiological response of control and salinity stressed rice plants. Salinity had the most severe effect to Koshihikari, followed by Doongara and Reiziq. We found that K+ retention and low recovery Cl− efflux in mesophyll cells confers salt tolerance in rice. Moderate to strong correlations were found between growth parameters and net K+ flux (r2 = 0.45–0.60), and net Cl− flux (r2 = 0.47–0.72). Also, dynamic ROS production and regulation of the NADPH oxidase gene, OsRBOHD, in mesophyll cells is crucial for salt tolerance of rice at the reproductive stage. OsRBOHD expression was significantly correlated to recovery ion fluxes (r2 = 0.45–0.64). This study brings together, for the first time, potential links between cellular ionic stress and oxidative stress components of salinity tolerance in rice at the reproductive stage in both greenhouse and field conditions. Our study will provide guidance to examine crop salinity tolerance at reproductive stages in controlled environments and natural climatic conditions in the future.

Back to the Wild: On a Quest for Donors Toward Salinity Tolerant Rice.

Salinity stress affects global food producing areas by limiting both crop growth and yield. Attempts to develop salinity-tolerant rice varieties have had limited success due to the complexity of the salinity tolerance trait, high variation in the stress response and a lack of available donors for candidate genes for cultivated rice. As a result, finding suitable donors of genes and traits for salinity tolerance has become a major bottleneck in breeding for salinity tolerant crops. Twenty-two wild Oryza relatives have been recognized as important genetic resources for quantitatively inherited traits such as resistance and/or tolerance to abiotic and biotic stresses. In this review, we discuss the challenges and opportunities of such an approach by critically analyzing evolutionary, ecological, genetic, and physiological aspects of Oryza species. We argue that the strategy of rice breeding for better Na+ exclusion employed for the last few decades has reached a plateau and cannot deliver any further improvement in salinity tolerance in this species. This calls for a paradigm shift in rice breeding and more efforts toward targeting mechanisms of the tissue tolerance and a better utilization of the potential of wild rice where such traits are already present. We summarize the differences in salinity stress adaptation amongst cultivated and wild Oryza relatives and identify several key traits that should be targeted in future breeding programs. This includes: (1) efficient sequestration of Na+ in mesophyll cell vacuoles, with a strong emphasis on control of tonoplast leak channels; (2) more efficient control of xylem ion loading; (3) efficient cytosolic K+ retention in both root and leaf mesophyll cells; and (4) incorporating Na+ sequestration in trichrome. We conclude that while amongst all wild relatives, O. rufipogon is arguably a best source of germplasm at the moment, genes and traits from the wild relatives, O. coarctata, O. latifolia, and O. alta, should be targeted in future genetic programs to develop salt tolerant cultivated rice.

Deploying root microbiome of halophytes to improve salinity tolerance of crops

Salinization of the soils is one of the most prominent problems threatening global food security. Root microbiome engineering using biofertilizers provides a sustainable way to increase agricultural productivity. Halophytes, which are extremely salt-tolerant plants, can tolerate up to 1300 mM NaCl. Members of the halophytic root microbiome now provide a promising solution to meet the increased demand in the agricultural output. Here, we explore the members of this microbiome and explain the plant growth-promoting functions of them. We discuss the manipulation of the root microbiome with synthetic microbial communities including keystone microorganisms of the halophytic root microbiome. Importantly, we provide a simple method in R software to find these putative keystone taxa using network analysis. We believe this strategy will provide a valuable tool for future studies performing the combined investigation of the root bacteria and fungi of halophytes.

Major Achievements of Plant Biotechnology in Crop Improvements

Biotechnology is any technological application that uses biological systems, living organisms, or derivatives thereof, to make or modify products or processes for a specific use. Agricultural biotechnology is the area of biotechnology involving applications to agriculture. Based on an understanding of DNA, scientists have developed solutions to increase agricultural productivity. Integrating recombinant techniques into conventional breeding programs could substantially enhance the efficiency of agricultural research and development. Breeding could be accelerated due to the more targeted transfer of desired genes into the crop. The major transgenic breeding objectives are; improving the agronomic traits and quality traits of different crops. Deliberate alteration of the genome of an organism by introduction of one or a few specific foreign genes is referred to as 'genetic engineering' or 'genetic transformation', and the modified organism is described as a 'transformed' or 'transgenic' organism. Achievements of biotechnology in crops were producing Bt crops, herbicide resistance crops, salinity tolerant crops, drought-tolerant crops and so on. Genetically engineered crop varieties that farmers deploy. Transgenic crops, especially those with resistance to biotic and abiotic stress factors, fit well into small-scale farming systems and can easily be integrated without adjusting traditional cropping practices. The comparatively low setup cost for adopting genetically engineered technologies at the farm level also makes this technology useful for semi-subsistence agriculture. Plant tissue culture also one of the applications of biotechnology used to improve crops and used to increase the speed or efficiency of the breeding process, to improve the accessibility of existing germplasm and to create new variation for crop improvement. Generally, the role of crop biotechnology for food security and poverty reduction should not be overrated. Many problems in low- and middle-income countries are not amenable to technological solutions.

Hyperspectral imaging combined with machine learning as a tool to obtain high-throughput plant salt-stress phenotyping.

The rapid selection of salinity-tolerant crops to increase food production in salinized lands is important for sustainable agriculture. Recently, high-throughput plant phenotyping technologies have been adopted that use plant morphological and physiological measurements in a non-destructive manner to accelerate plant breeding processes. Here, a hyperspectral imaging (HSI) technique was implemented to monitor the plant phenotypes of 13 okra (Abelmoschus esculentus L.) genotypes after 2 and 7days of salt treatment. Physiological and biochemical traits, such as fresh weight, SPAD, elemental contents and photosynthesis-related parameters, which require laborious, time-consuming measurements, were also investigated. Traditional laboratory-based methods indicated the diverse performance levels of different okra genotypes in response to salinity stress. We introduced improved plant and leaf segmentation approaches to RGB images extracted from HSI imaging based on deep learning. The state-of-the-art performance of the deep-learning approach for segmentation resulted in an intersection over union score of 0.94 for plant segmentation and a symmetric best dice score of 85.4 for leaf segmentation. Moreover, deleterious effects of salinity affected the physiological and biochemical processes of okra, which resulted in substantial changes in the spectral information. Four sample predictions were constructed based on the spectral data, with correlation coefficients of 0.835, 0.704, 0.609 and 0.588 for SPAD, sodium concentration, photosynthetic rate and transpiration rate, respectively. The results confirmed the usefulness of high-throughput phenotyping for studying plant salinity stress using a combination of HSI and deep-learning approaches.

Spatial Distribution of Salinity and Sodicity in Arid Climate Following Long Term Brackish Water Drip Irrigated Olive Orchard

The availability of brackish groundwater in the Negev Desert, Israel has motivated the cultivation of various salinity tolerant crops, such as olives trees. The long term suitability of surface drip irrigation (DI) or subsurface drip irrigation (SDI) in arid regions is questionable, due to salinity concerns, in particular, when brackish irrigation water is employed. Nevertheless, DI and SDI have been adopted as the main irrigation methods in olive orchards, located in the Negev Desert. Reports on continued reduction in olive yields and, essentially, olive orchard uprooting are the motivation for this study. Specifically, the main objective is to quantify the spatial distribution of salinity and sodicity in the active root-zone of olive orchards, irrigated with brackish water (electrical conductivity; EC = 4.4 dS m−1) for two decades using DI and subsequently SDI. Sum 246 soil samples, representing 2 m2 area and depths of 60 cm, in line and perpendicular to the drip line, were analyzed for salinity and sodicity quantities. A relatively small leaching-zone was observed below the emitters depth (20 cm), with EC values similar to the irrigation water. However, high to extreme EC values were observed between nearby emitters, above and below the dripline. Specifically, in line with the dripline, EC values ranged from 10 to 40 dS m−1 and perpendicular to it, from 40 to 120 dS m−1. The spatial distribution of sodicity quantities, namely, the sodium adsorption ratio (SAR, (meq L−1)0.5) and exchangeable sodium percentage (ESP) resembled the one obtained for the EC. In line with the dripline, from 15 to 30 (meq L−1)0.5 and up to 27%, in perpendicular to the drip line from 30 to 60 (meq L−l)0.5 and up to 33%. This study demonstrates the importance of long terms sustainable irrigation regime in arid regions in particular under DI or SDI. Reclamation of these soils with gypsum, for example, is essential. Any alternative practices, such as replacing olive trees and the further introduction of even high salinity tolerant plants (e.g., jojoba) in this region will intensify the salt buildup without leaving any option for soil reclamation in the future.

Hydrogeochemical evaluation of groundwater in and around Lakkireddipalli and Ramapuram, Y.S.R District, Andhra Pradesh, India

To evaluate hydrogeochemical evaluation of groundwater for drinking & irrigation practices in and around Lakkireddipalli and Ramapuram, Y.S.R District, Andhra Pradesh, India, thirty groundwater samples were collected during March 2018. Most of the groundwater samples are above the safe limits of W.H.O standards. Groundwater is exceeding the permissible limits of TDS, TH, EC, chloride and sulphates. Geogenic and anthropogenic sources are the main contributing factors for fluoride and nitrate respectively. Rock dominance is the predominant hydrogeochemical factor controlling the water chemistry. Piper's diagram reveals that water is of mixed Ca Mg Cl type. Irrigational water quality indices reveal that majority of groundwater samples falls under the unsuitable category and application of this untreated irrigational water is harmful for the crops and decreases the crop yield. Hence more saline tolerant crops could be suggested to combat soil salinization and application of lime/gypsum may be suggested to bout the soil permeability.

Cross talk between ROS homeostasis and antioxidative machinery contributes to salt tolerance of the xero-halophyte Haloxylon salicornicum

Salinity is a foremost environmental threat that challenges agriculture and food security worldwide. In the present work, physiological, biochemical and anatomical strategies adopted by the xero-halophyte Haloxylon salicornicum in response to salinity was investigated. H. salicornicum plant withstands a prolong treatment of salinity, even under high dose of NaCl (400 mM). Our results showed that both fresh and dry biomass of shoot, plant height, and shoot area increased under low salinity (100–200 mM NaCl), whereas these parameters remained unaffected under high salinity (300–400 mM NaCl). In H. salicornicum, shoot water content (SWC%) was maintained at all levels of salinity. Salt tolerance index of H. salicornicum did not decline with increasing doses of salinity indicating salt tolerance capability of the plant. Although, salinity caused an increase in Na+ content of shoot, but K+ content of shoot remained steady at all levels of salinity. The rate of photosynthesis (PN), stomatal conductance (gs), rate of transpiration (E), water use efficiency (WUE), quantum yield of PSII (ΦPSII), photochemical quenching (qP), and electron transport rate (ETR) remained at par to the control level under low salinity (100–200 mM NaCl) and then reduced significantly under high salinity (300–400 mM NaCl). Salinity had no significant impacts on maximum quantum efficiency of PSII (Fv/Fm) and non-photochemical quenching (NPQ) which implies that PS II remained unaffected by sanity-induced oxidative damage. The levels of H2O2 and NO increased significantly under salinity, whereas the level of O2•− remained unaffected under various levels of salinity. Higher level of H2O2 and NO indicates the signaling role of these molecules. Lipid peroxidation level remained unchanged under low salinity (0–300 mM NaCl), but increased significantly under extreme salinity (400 mM NaCl). Ratio of AsA/DHA (indicator of cellular redox potential) elevated under high salinity (300–400 mM NaCl). The activities of various enzymatic antioxidants like SOD, APX, POX, GR and CAT showed differential responses under salinity. The results propose that coordination between enzymatic and non-enzymatic antioxidative components regulates ROS levels in H. salicornicum and contribute in salt tolerance by maintaining water status, ion homeostasis, redox status of the cells, and efficient protection of PSII form salinity induced oxidative damage. Higher tolerance index, optimal growth and competent antioxidative system make this xero-halophyte a suitable candidate for reclamation of salt degraded agricultural lands and can be a potent genetic resource for the development of salinity tolerant crops.

Inheritance of fruit yield and quality in melon (Cucumis melo L.) grown under field salinity stress

Cultivation of salinity-tolerant crops can help mitigate salinization threats to soil and fresh water resources. This study was conducted to investigate the quantitative genetic basis of yield, yield components, and quality-related traits of salinity-stressed melon (Cucumis melo L.) using 55 melon hybrids and their 11 parents (half diallel). The results of combined ANOVA revealed highly significant effects of salinity and genotype on all the traits studied. Salinity stress influenced the inheritance of all the traits. The lower values of variance components (mainly additive), GCA/SCA ratio, as well as broad- and narrow-sense heritabilities were estimated for saline conditions (ECW = 14 dSm−1) when compared with those obtained under non-saline conditions. Fruit weight was governed by additive effects in non-saline conditions, but largely governed by the dominant nature in saline conditions. Based on the results obtained, especially as reflected by fruit yield, it is possible to develop melon hybrids with higher salinity tolerance than is currently observed in tolerant cultivars. On the other hand, most of the traits contributing to fruit quality are found to be governed by additive effects, allowing for their further improvement through recurrent selection to develop new cultivars of high yield and good quality for cultivation under saline conditions.

Comparative transcriptome analysis of salt-sensitive and salt-tolerant maize reveals potential mechanisms to enhance salt resistance.

Salt stress is a devastating environmental stress that causes plant growth inhibition and yield reduction. The identification of salt-tolerant genes brings hope for the generation of salinity-tolerant crop plants through molecular breeding. In this study, one salt-sensitive and one salt-tolerant maize inbred line were screened from 242 maize inbred lines. Reactive oxygen species (ROS)-related enzyme activities were detected and salt-responsive comparative transcriptome analysis was performed for control and 220 mM NaCl treated maize leaves. Salt-tolerant maize inbred line (L87) showed higher ROS-related enzyme (SOD, POD, APX and CAT) activities and accumulated relatively lower levels of ROS under salt stress. Of the total DEGs, 1856 upregulated DEGs were specific to L87, including stress tolerance-related members of the 70kDa family of heat shock proteins (Hsp70s) and aquaporins. The DEGs involved in the abscisic acid (ABA), ethylene, jasmonic acid (JA) and salicylic acid (SA) signal transduction pathways may determine the difference in salt tolerance between the two varieties, especially one central component SnRK2, that positively regulates ABA signaling and was only upregulated in L87. Analysis of DEGs related to ROS scavenging showed that some peroxidase (POD), glutathione S-transferase (GST), catalase (CAT) and superoxide dismutase (SOD) genes specific to L87 probably enhanced its salt tolerance. The analysis of differentially expressed transcription factors (TFs) suggested that WRKY TFs could contribute to the difference in salt tolerance between the two maize lines. Compared with Salt-sensitive maize inbred line (L29), L87 exhibits specific regulatory mechanisms related to salt tolerance, including plant hormone interactions, ROS scavenging and the regulation of TFs. Our study identifies new candidate genes that may regulate maize tolerance to salt stress and provides useful information for breeding maize with high salt resistance.

Ground-Water Quality in Islamkot and Mithi Talukas of District Tharparkar, Sindh, Pakistan

Surface water supplies are gradually becoming short in arid and semi-arid regions of the world. Thus, assessment of groundwater quality for crop use appears to be very essential for management and utilization of precious natural water resources. This study reports the water quality of 52 hand pumps and one tubewell located in the most remote areas of desert region, viz. Islamkot and Mithi talukas of district Tharparkar. The water samples were collected during April 2016 (just before the start of rainy season). The water samples were analyzed for EC (Electrical Conductivity), pH, CO32-, HCO3-, Cl-, Ca2+, Mg2+ and Na+ concentration. The SAR (Sodium Adsorption Ratio) and RSC (Residual Sodium Carbonates) were estimated using their respective formula. The categorization of water samples based on their soluble salt content clearly revealed that the water bodies of majority (65%) of areas were hazardous, while 25% areas were marginal. Thus, only 11% water samples of the area under study had useable irrigation water. Because of SAR and RSC the majority (89 and 77%, respectively) of water samples were found to be free from the sodicity hazard. The study concluded that salinity, and not sodicity was the major threat to the area under irrigation with these water bodies. It is, therefore, suggested that the salinity tolerant crops and their genotypes may be used in this area to sustain crop production.

Friend or Foe? Chloride Patterning in Halophytes.

In this opinion article, we challenge the traditional view that breeding for reduced Cl- uptake would benefit plant salinity tolerance. A negative correlation between shoot Cl- concentration and plant biomass does not hold for halophytes - naturally salt tolerant species. We argue that, under physiologically relevant conditions, Cl- uptake requires plants to invest metabolic energy, and that the poor selectivity of Cl--transporting proteins may explain the reported negative correlation between Cl- accumulation and crop salinity tolerance. We propose a new paradigm: salinity tolerance could be achieved by improving the selectivity of some of the broadly selective anion-transporting proteins (e.g., for NO3->Cl-), alongside tight control of Cl- uptake, rather than targeting traits mediating its efflux from the root.

Control of xylem Na+ loading and transport to the shoot in rice and barley as a determinant of differential salinity stress tolerance.

Control of xylem Na+ loading has often been named as the essential component of salinity tolerance mechanism. However, it is less clear to what extent the difference in this trait may determine differential salinity tolerance between species. In this study, barley (Hordeum vulgare L. cv. CM72) and rice (Oryza sativa L. cv. Dongjin) plants were grown under two levels of salinity. Na+ and K+ concentrations in the xylem sap, and shoot and root tissues were measured at different time points after stress onset. Salt-exposed rice plants prevented xylem Na+ loading for several days, but failed to control this process in the longer term, ultimately resulting in a massive Na+ shoot loading. Barley plants quickly increased xylem Na+ concentration and its delivery to the shoot (most likely for the purpose of osmotic adjustment) but were able to reduce this process later on, keeping most of accumulated Na+ in the root, thus maintaining non-toxic shoot Na+ level. Rice plants increased shoot K+ concentration, while barley plants maintained higher root K+ concentration. Control of xylem Na+ loading is remarkably different between rice and barley; this difference may differentiate the extent of the salinity tolerance between species. This trait should be investigated in more detail to be used in the breeding programs aimed to improve salinity tolerance in crops.

Transcriptome analysis of grapevine under salinity and identification of key genes responsible for salt tolerance.

The negative effects of soil salinity towards grape yield depend upon salt concentration, cultivar type, developmental stage, and rootstock. Thompson Seedless variety of grape plant is considered moderately sensitive to salinity when grown upon its own root stock. In recent epoch, identification of key genes responsive to salinity offers hope to generate salinity-tolerant crop plants by their overexpression through genetic manipulation. In the present report, salt responsive transcriptome analysis of Thompson Seedless grape variety was done to identify vital genes involved in salinity tolerance which could be used further to generate salt liberal grape plant or other crop plants. Transcriptome libraries for control and 150-mM-NaCl-treated grape leaves were sequenced on Illumina platform where 714 genes were found to be differentially expressed. Gene ontology analysis indicated that under salinity conditions, the genes involved in metabolic process were highly enriched. Keto Encyclopedia of Genes and Genomes analysis revealed that, among the top 22 enriched pathways for the salt stress upregulated genes, the carbohydrate metabolism, signal transduction, energy metabolism, amino acid metabolism, biosynthesis of secondary metabolite, and lipid metabolism pathways possessed the largest number of transcripts. Key salinity-induced genes were selected and validated through qRT-PCR analysis which was comparable to RNA-seq results. Real-time PCR analysis also revealed that after 24days of salinity, the expression of most of the selected key genes was highest. These salinity-induced genes will be characterized further in a model plant and also in Vitis vinifera through transgenic approach to disclose their role towards salt tolerance.

Transgenic Crops Targeting Ion Homeostasis Machinery: Bangladesh Perspective for Adaptation to Climate Change to Ensure Food Security

Salinity stress is one of the major adversarial impacts of climate change that limits crop productivity worldwide, especially in developing countries. To overcome this situation it is necessary to understand the cellular basis of salt stress tolerance mechanisms. Various genes involved in ion exclusion, osmotic tolerance, Reactive Oxygen Species (ROS) scavenging and other regulation mechanisms influence salinity tolerance in crops. Function of these candidate genes/sequences may vary in different plants and within different tissues. For the last two decades, in Bangladesh several approaches have been taken to develop transgenic rice, the staple crop. Work is in progress to monitor stable incorporation of these transgenes. Further evaluation is needed to check their adaptation/resistance in natural environments. Good performance in field conditions will lead to acceptance of these varieties for commercial productions in order to ensure food security.Plant Tissue Cult. & Biotech. 27(2): 241-256, 2017 (December)

Growth, Fiber and Nitrogen Content in Sisal Plants (Furcraea sp) Under NaCl Salinity

Soil contains water and nutrients necessary for the development of cultivated plants and serves as a substrate and support in terrestrial ecosystems. For reasons inherent to the nature of soil, salt content can considerably limit the growth of plants. With the implementation of salinity-tolerant crops, saline soils can be transformed into productive and sustainable areas. In Tunja, Colombia, a trial was developed to quantify the changes in growth, water intake, fiber, nitrogen and chlorophyll content in Furcraea hexapetala plants exposed to NaCl saline conditions. Plantlets obtained from bulbs were grown in an aerated nutrient solution under greenhouse conditions. Measurements of 30, 60 or 90 mmol NaCl was added to the nutrient solution and control plants were left without addition of salt. As a consequence of salinity, leaf area, leaf area ratio, water uptake, absolute growth rate, relative growth rate, fiber content, dry matter, chlorophyll and nitrogen content in leaves were reduced. The accumulation of dry matter in leaves, stem and roots was especially affected when the plants were exposed to 90 mmol of NaCl. Accumulated dry matter increased in the stems, but reduced in the leaves. These results suggest that plants of Furcraea hexapetala can tolerate up to 60 mmol of NaCl (4.9 dS m−1) without substantially affecting the parameters that determine the growth or the fiber content in the leaves.

Soil Chemistry Factors Confounding Crop Salinity Tolerance—A Review

The yield response of various crops to salinity under field conditions is affected by soil processes and environmental conditions. The composition of dissolved ions depend on soil chemical processes such as cation or anion exchange, oxidation-reduction reactions, ion adsorption, chemical speciation, complex formation, mineral weathering, solubility, and precipitation. The nature of cations and anions determine soil pH, which in turn affects crop growth. While the ionic composition of soil solution determine the osmotic and ion specific effects on crops, the exchangeable ions indirectly affect the crop growth by influencing soil strength, water and air movement, waterlogging, and soil crusting. This review mainly focuses on the soil chemistry processes that frustrate crop salinity tolerance which partly explain the poor results under field conditions of salt tolerant genotypes selected in the laboratory.

Smart Engineering of Genetic Resources for Enhanced Salinity Tolerance in Crop Plants

ABSTRACTSalinity is a consistent factor of crop productivity loss in the world and in particular arid and semi-arid areas where the soil salinity and saline water are major problems. Plants employ various mechanisms to cope with salinity stress and activate an array of stress-responsive genes to counteract the salinity-induced osmotic and ionic stresses. Genetic improvement for salinity tolerance is challenging, and thus progress attained over the several decades has been far less than anticipated. The generation of an explosion of knowledge and technology related to genetics and genomics over the last few decades is promising in providing powerful tools for future development of salinity-tolerant cultivars. Despite a major progress in defining the underlying mechanisms of salinity tolerance, there are still major challenges to be overcome in translating and integrating the resultant information at the molecular level into plant-breeding practices. Various approaches have been suggested to improve the efficiency of plant breeding for increasing plant productivity under saline environments. In this context, breeding for salinity tolerance in crops largely depends upon the availability of genetic resources of tolerance, reliable screening techniques, identification of genetic components of tolerance, and successful genetic manipulation of desired genetic backgrounds. The efficiency of selection and breeding in the stressful environments can be improved through marker-assisted selection. To date, this is almost exclusively applied to major genes, but this requires to be extended to quantitative trait loci (QTLs) controlling complex traits such as salinity tolerance to greatly enhance the impact. Moreover, methodologies for high-throughput genotyping, and the development of an array of “functional” markers can be much supportive. The introduction of novel genes or alteration in the expression patterns of the existing genes through the generation of transgenic plants can also be employed to overcome the limits in classical plant breeding. The introgression of wild halophytic attribute genes facilitated by genetic engineering is an alternative approach to bypass interspecific hybridization barriers, which will stimulate breakthrough in the future agriculture. The molecular dissection of salinity-tolerance trait, accompanying the classical quantitative genetics, is a substantial progress in updating tools and methods for the manipulation of plant genomes. Methods of gene discovery such as identification of candidate genes, QTL cloning, linkage and association mapping, and functional genomics such as identification of transcripts and proteins involved in salinity tolerance are necessary to manipulate the molecular mechanisms underlying the complex phenotype of salinity tolerance. Some of the challenges and opportunities have also been addressed in the present review with a particular emphasis on molecular breeding approaches to be employed in combination with other crop improvement strategies to develop salinity-tolerant cultivars.

Salinity-induced reduction in root surface area and changes in major root and shoot traits at the phytomer level in wheat.

The aim of this study was to investigate the effect of salinity stress on root growth at the phytomer level in wheat to provide novel site-specific understanding of salinity damage in roots. Seedlings of 13 wheat varieties were grown hydroponically. Plants were exposed to three concentrations of NaCl, 0 (control), 50 and 100mM, from 47 days after sowing. In a destructive harvest 12 days later we determined the number of live leaves, adventitious roots, seminal roots and newly formed roots at the youngest phytomer; length and diameter of main axes; and length and diameter of root hairs and their number per millimetre of root axis. Elongation rate of main axes and root hair density were then derived. Root surface area at each root-bearing phytomer (Pr) was mechanistically modelled. New root formation was increased by salt exposure, while number of live leaves per plant decreased. The greatest salinity effect on root axis elongation was observed at the youngest roots at Pr1 and Pr2. Both the 50mM and the 100mM levels of salinity reduced root hair length by approximately 25% and root hair density by 40% compared with the control whereas root hairs alone contributed around 93% of the estimated total root surface area of an individual tiller. Decrease in main axis length of new roots, root hair density and root hair length combined to reduce estimated root surface area by 36-66% at the higher NaCl concentration. The varietal response towards the three salinity levels was found to be trait-specific. The data highlight reduction in root surface area as a major but previously largely unrecognized component of salinity damage. Salinity resistance is trait-specific. Selection for retention of root surface area at a specific phytomer position following salt exposure might be useful in development of salinity-tolerant crop varieties.

Economic Impacts of Water Scarcity Under Diverse Water Salinities

Exploitation of alternative water sources is expected to grow in the decades to come in water-stressed countries with fast population growth, especially in regions where a further decline of natural freshwater availability is expected due to climate change. Increasing utilization of non-freshwater usually leads to salinity build-up in fields and water sources as well as accumulation of various pollutants — both having a considerable impact on the suitability of non-freshwater for irrigation due to constraints associated with crop salinity tolerance and food safety regulations. We developed a linked Computable General Equilibrium (CGE) — farm-level model of a water economy with representation for multiple water types characterized by different qualities. We employ the model to assess the impact of water shortage on the Israeli economy, where steadily growing water scarcity leads to an increasing utilization of alternative water sources. We simulate water shortage scenarios based on the Long Term National Master Plan for The Water Economy developed by the Israeli Water Authority (IWA). The linked CGE — farm-level model provides a mechanism for estimating the Constant Elasticity of Substitution (CES) rates between different irrigation water types used in agriculture. This mechanism accounts for the effects of salinity on yields and takes into consideration food safety regulations for irrigating crops with treated wastewater. We demonstrate that, in contrast to previous studies, CES rates between different water types are not identical. The CES rates obtained in our study have relatively low values, which can be attributed to the constraints associated with crop salinity tolerance and food safety regulations. Our results reveal that water shortage can lead to a significant decline of Israel’s GDP, where a considerable part of the decline is attributed to the decrease in agricultural outputs. The magnitude of the impact depends on the underlying assumptions regarding future desalination capacity. To further study the effect of desalination, we run simulations under various desalination levels and examine its impact on the GDP. We also examine the extent to which the impact of water shortage is sensitive to CES rates between different irrigation water types.