Genetic Variation For Salt Tolerance Research Articles

Similar and divergent responses to salinity stress of jamun (Syzygium cumini L. Skeels) genotypes.

Genetic variation for salt tolerance remains elusive in jamun (Syzygium cumini). Effects of gradually increased salinity (2.0-12.0 dS/m) were examined in 20 monoembryonic and 28 polyembryonic genotypes of jamun. Six genotypes were additionally assessed for understanding salt-induced changes in gas exchange attributes and antioxidant enzymes. Salt-induced reductions in leaf, stem, root and plant dry mass (PDM) were relatively greater in mono- than in poly-embryonic types. Reductions in PDM relative to control implied more adverse impacts of salinity on genotypes CSJ-28, CSJ-31, CSJ-43 and CSJ-47 (mono) and CSJ-1, CSJ-24, CSJ-26 and CSJ-27 (poly). Comparably, some mono- (CSJ-5, CSJ-18) and poly-embryonic (CSJ-7, CSJ-8, CSJ-14, CSJ-19) genotypes exhibited least reductions in PDM following salt treatment. Most polyembryonic genotypes showed lower reductions in root than in shoot mass, indicating that they may be more adept at absorbing water and nutrients when exposed to salt. The majority of genotypes did not exhibit leaf tip burn and marginal scorch despite significant increases in Na+ and Cl-, suggesting that tissue tolerance existed for storing excess Na+ and Cl- in vacuoles. Jamun genotypes were likely more efficient in Cl- exclusion because leaf, stem and root Cl- levels were consistently lower than those of Na+ under salt treatment. Leaf K+ was particularly little affected in genotypes with high leaf Na+. Lack of discernible differences in leaf, stem and root Ca2+ and Mg2+ contents between control and salt treatments was likely due to their preferential uptake. Correlation analysis suggested that Na+ probably had a greater inhibitory effect on biomass in both mono- and poly-embryonic types. Discriminant analysis revealed that while stem and root Cl- probably accounted for shared responses, root Na+, leaf K+ and leaf Cl- explained divergent responses to salt stress of mono- and poly-embryonic types. Genotypes CSJ-18 and CSJ-19 seemed efficient in fending off oxidative damage caused by salt because of their stronger antioxidant defences. Polyembryonic genotypes CSJ-7, CSJ-8, CSJ-14 and CSJ-19, which showed least reductions in biomass even after prolonged exposure to salinity stress, may be used as salt-tolerant rootstocks. The biochemical and molecular underpinnings of tissue tolerance to excess Na+ and Cl- as well as preferential uptake of K+, Ca2+, and Mg2+ need to be elucidated.

Salinity and sodicity stresses differentially influence growth and physiology in sapota (Achras zapota L.)

Salt stress adversely affects the growth and physiological relations in most tree fruit species. Little is known about genetic variation for salt tolerance, and the physiological mechanisms underlying salt tolerance in sapota (Achras zapota), an underutilized fruit crop valued for its nutritive and medicinal properties. Here, we examined the effects of saline (ECiw 4, 8, 12, and 16 dS/m) and sodic (RSC 2.5 and 5.0meq/l) water treatments on plant growth, physiology, and ion homeostasis in the different genotypes of Sapota. Although saline and sodic treatments appreciably reduced the plant growth (i.e., by 20–50%) compared to salt-free plants, genotypes ‘CSRS-13’ and ‘CSRS-15’ performed better than others. Salt-induced reductions in leaf area were indicative of the ability of sapota to better acclimatize to prolonged salinity stress by regulating the biomass production. Saline and sodic irrigation treatments increased the leaf Na+ and decreased the leaf K+; albeit with clear-cut genotypic differences. We observed better ion homeostasis in genotype ‘CSRS-17’ under salinity stress, and better physiological adaptations in genotypes ‘CSRS-11’ and ‘CSRS-17’ under sodicity stress. Principal Component Analysis revealed strikingly different responses of sapota genotypes to ‘low’ and ‘high’ salinity/sodicity treatments. Strong cultivar-specific responses to salinity and sodicity stresses evinced the existence of genetic variation for salt tolerance in sapota. Overall, our findings demonstrated the feasibility of sapota cultivation in areas with moderate sodicity (RSC ∼2.5 meq/l), and moderate-to-high salinity (∼8.0 dS/m).

The characterization of wheat genotypes for salinity tolerance using morpho-physiological indices under hydroponic conditions

Salinity affects plant growth, development, yield, and is a big challenge for wheat growth across the globe. Possible feasible solution is creation of salt-tolerant material, genetic variation is a criterion to developing genetically superior individuals. To assess the genetic variation for salt tolerance, nationally and internationally-derived 81 wheat genotypes were selected and evaluated in 0- and 150-mM salt in nutritional culture at seedling stage. Results indicate that salinity levels reveal significant (p ≤ 0.01) differences for fresh root weight (RW), shoot length (SL), fresh shoot weight (SW), total plant length (TL), total fresh weight (TW), root/shoot weight ratio (RSWR), root/shoot length ratio (RSLR), and relative growth rate for weight (RGR-Wt). While, there was no difference for root length (RL). Hierarchical Clustering and Pairwise correlation analysis showed TW, RGR-Wt, SL, SW, and RW were positively correlated among themselves, whereas RL had poor correlations with all the traits except TL and RSLR. Hence, selection of SL can improve the performance of other parameters. Based on PCA analysis, SW and RGR-Wt were the major discriminative components for wheat genotypes. Present study explained that shoot related parameters could be used as a selection criterion to categorize salt-tolerant genotypes. Outperforming genotypes 1104 and 1106 in saline conditions could be used as parents in creation of salt-tolerant wheat genotypes, and parameters such as SL, SW, TW, and RGR-Wt for early screening will be important for creating salt-tolerant and high yielding wheat genotypes.

The use of osmoregulators and antioxidants to mitigate the adverse impacts of salinity stress in diploid and tetraploid potato genotypes (Solanum spp.)

BackgroundMany arid and semi-arid areas endure from extensive salinization of agricultural land. Nevertheless, it must either develop salinity-tolerant varieties or use agronomic treatments to alleviate the symptoms of stress. Although the cultivated potato, Solanum tuberosum L., is relatively salt sensitive, salinity tolerance was demonstrated in several Solanum relatives. Knowledge of genetic variation for salinity tolerance across diverse species is required for breeding of salinity-tolerant cultivars. Higher osmotic pressures associated with salinity impede plant development and cause plant death; yet, the exogenous application of cellularly recognized molecules to withstand such stress might be a key method.ResultsIn vitro studies were performed to determine how much genetic variability for salinity tolerance exists in S. tuberosum (tbr), a tetraploid species and S. chacoense (chc), a diploid species in which 13 genotypes were evaluated under 100, 200 or 300 mmol L−1 NaCl and the average tested parameters were compared with the control (no stress). A further experiment was conducted to investigate the effect of exogenous application of osmoregulators and antioxidants, namely, glycine betaine (GB), proline (P) and salicylic acid (SA) at 400, 200 and 100 mg L−1, respectively, which applied solely to counteract the harmful effect of stress on potato plants. The results showed that when plants exposed to salinity, root characteristics, plantlet water content % (PWC), chlorophyll and K+ content, and callus formation all substantially reduced; however, Cl− and Na+ levels, as well as catalase and peroxidase activity, were elevated. In general, chc showed more tolerance compared to tbr with genetic diversity within and among species. Under stress, chc clones, ‘A-6’, ‘C-8’ and ‘D-2’ and tbr cultivars, ‘Diamond’ and ‘Russet Burbank’ were more tolerant and yielded the greatest salinity tolerance index. Under stress but with applied GB, SA and P, the adverse consequences of stress were relieved. GB was found to be a good treatment for enhancing all the examined traits.ConclusionThe results indicated that there is a significant genetic variation in salt tolerance between (tbr) cultivars and (chc) clones. GB followed by SA and P could completely or partly reverse the adverse impact of salinity stress on potato plants.Graphical

Identification of genetic variation for salt tolerance in Brassica napus using genome-wide association mapping.

Soil salinity negatively impacts rapeseed (Brassica napus) crop production. In particular, high soil salinity is known to hinder seedling growth and establishment. Identifying natural genetic variation for high salt tolerance in Brassica napus seedlings is an effective way to breed for improved productivity under salt stress. To identify genetic variants involved in differential response to salt stress, we evaluated a diverse association panel of 228 Brasica napus accessions for four seedling traits under salt stress to establish stress susceptibility index (SSI) and stress tolerance index (STI) values, and performed genome-wide association studies (GWAS) using 201,817 high-quality single nucleotide polymorphic (SNP) markers. Our GWAS identified 142 significant SNP markers strongly associated with salt tolerance distributed across all rapeseed chromosomes, with 78 SNPs in the C genome and 64 SNPs in the A genome, and our analyses subsequently pinpointed both favorable alleles and elite cultivars. We identified 117 possible candidate genes associated with these SNPs: 95/117 were orthologous with Arabidopsis thaliana genes encoding transcription factors, aquaporins, and binding proteins. The expression level of ten candidate genes was validated by quantitative real-time PCR (qRT-PCR), and these genes were found to be differentially expressed between salt-tolerant and salt-susceptible lines under salt stress conditions. Our results provide new genetic resources and information for improving salt tolerance in rapeseed genotypes at the seed germination and seedling stages via genomic or marker-assisted selection, and for future functional characterization of putative gene candidates.

Development and Application of Image-Based High-Throughput Phenotyping Methodology for Salt Tolerance in Lentils

Soil salinity is a major abiotic stress in Australian lentil-producing areas. It is therefore imperative to identify genetic variation for salt tolerance in order to develop lentil varieties suitable for saline soils. Conventional screening methods include the manual assessment of stress symptoms, which can be very laborious, time-consuming, and error-prone. Recent advances in image-based high-throughput phenotyping (HTP) technologies have provided unparalleled opportunities to screen plants for a range of stresses, such as salt toxicity. The current study describes the development and application of an HTP method for salt toxicity screening in lentils. In a pilot study, six lentil genotypes were evaluated to determine the optimal salt level and the growth stage for distinguishing lentil genotypes using red–green–blue (RGB) images on a LemnaTec Scanalyzer 3D phenomics platform. The optimized protocol was then applied to screen 276 accessions that were also assessed earlier in a conventional phenotypic screen. Detailed phenotypic trait assessments, including plant growth and green/non-green color pixels, were made and correlated to the conventional screen (r = 0.55; p < 0.0001). These findings demonstrated the improved efficacy of an image-based phenotyping approach that is high-throughput, efficient, and better suited to modern breeding programs.

Salt-tolerance diversity in diploid and polyploid cotton (Gossypium) species.

The development of salt-tolerant genotypes is pivotal for the effective utilization of salinized land and to increase global crop productivity. Several cotton species comprise the most important source of textile fibers globally, and these are increasingly grown on marginal or increasingly saline agroecosystems. The allopolyploid cotton species also provide a model system for polyploid research, of relevance here because polyploidy was suggested to be associated with increased adaptation to stress. To evaluate the genetic variation of salt tolerance among cotton species, 17 diverse accessions of allopolyploid (AD-genome) and diploid (A- and D-genome) Gossypium were evaluated for a total of 29 morphological and physiological traits associated with salt tolerance. For most morphological and physiological traits, cotton accessions showed highly variable responses to 2weeks of exposure to moderate (50mm NaCl) and high (100mm NaCl) hydroponic salinity treatments. Our results showed that the most salt-tolerant species were the allopolyploid Gossypium mustelinum from north-east Brazil, the D-genome diploid Gossypium klotzschianum from the Galapagos Islands, followed by the A-genome diploids of Africa and Asia. Generally, A-genome accessions outperformed D-genome cottons under salinity conditions. Allopolyploid accessions from either diploid genomic group did not show significant differences in salt tolerance, but they were more similar to one of the two progenitor lineages. Our findings demonstrate that allopolyploidy in itself need not be associated with increased salinity stress tolerance and provide information for using the secondary Gossypium gene pool to breed for improved salt tolerance.

Adaptation of sugarcane plants to saline soil

Sugarcane is an important crop in tropical regions of the world, often being exposed to environments with high salinity, but little is known of genetic variation in salt tolerance. The aim of this work was to compare the performance of two genetically diverse cultivars of sugarcane under different concentrations of salinity (0, 40, 80 and 160 mM NaCl) over a period of 30 days. SP 81–3250 was more salt-tolerant and maintained its rate of biomass production, photosynthesis and leaf area up to 160 mM NaCl, whereas IAC 87–3396 was sensitive to 80 mM NaCl. SP 81–3250 maintained very low concentrations of Na+ in both leaves and roots with increasing time and salinity, whereas in IAC 87–3396 the Na+ concentrations were 2–5 times higher. SP 81–3250 ha d a greater accumulation of proline, and lower lipid peroxidation, whereas glycine betaine and sucrose concentrations were similar in the two cultivars. This suggests that the tolerance of SP 81–3250 to high salinity was due to its ability to exclude Na+ while taking up water from the soil, and that measurements of Na+ concentration in leaves could be used to select salt-tolerant genotypes for saline areas.

Salinity Responses of Selected Introgressed Cotton Lines Grown in Two Soils from Organic and Conventional Cotton Production

Cotton yield is adversely affected by various stresses including salinity. Genetic variation in salt tolerance is often evaluated in potting soil media irrigated with saline solutions but not a field soil. This study evaluated the efficacy of screening four introgressed Upland genotypes from a backcross Gossypium hirsutum L. × G. barbadense L. inbred line population grown in two soils, i.e., an organic farm loam soil or a conventional farm clay soil. The genotypes were treated with NaCl for three wk at concentrations of 0 or 200 mM starting at the second true leaf stage. Chlorophyll content and fluorescence, plant height, leaf length, main stem node number and internode length, shoot biomass, and number of fruiting sites at three, six and nine week intervals (WT) were measured. Significant genotypic variation at three and six WT was observed, suggesting that salt tolerance screening in early cotton establishment is optimal. The salt treatment had negative effects on all growth traits except chlorophyll content and fluorescence. The organic farm loam soil amended with dairy manure had higher pre-treatment salinity content than the conventional farm clay, resulting in greater initial growth suppression at zero WT. However, the manure-amended soil showed less reduction in vegetative and reproductive growth after more prolonged salt treatment, suggesting that more scrutiny may be needed in soils treated with carbon-based fertilizers. The lack of genotype by soil or treatment interactions suggests that soil type had little bearing in screening cotton genotypes for salt tolerance and that control (non-saline) treatments may not be needed for cotton salt tolerance screening. Finally, this pot study demonstrates that three to six weeks of salt treatments after the second true leaf stage is an adequate duration of time to screen for cotton salt tolerance.

Qualitative and quantitative variation in the mechanisms of salinity tolerance determined by multivariate assessment of diverse rice (Oryza sativa L.) genotypes

Climate change-induced events are causing salinization of many rice-growing areas, requiring the identification of new sources of genetic variation for salt tolerance in plant genetic resources since commonly grown cultivars are sensitive to salt. To identify the level of salt tolerance across a wide range of genotypes, we used a multivariate screening method using multiple growth and physiological traits simultaneously. For this purpose, four indica, two japonica and two wild rice genotypes were grown hydroponically under 40 and 80 mM NaCl stresses; fourteen different growth, qualitative and physiological traits, e.g. plant height, biomass, root and shoot elongation rates, and tissue ion accumulation, were recorded. In general, indica varieties performed better than both japonica and wild species. Our approach identified the existence of qualitatively different mechanisms of salt tolerance across the genotypes. For example, Pokkali, a salt-tolerant indica variety, displayed both ‘Na exclusion’ and ‘ion balance’ mechanisms, whereas PSBRc50 and IR58 showed only ‘Na exclusion’, and the Japonica genotypes Banikat and Nipponbare showed only ‘ion balance’. The results demonstrated that the tolerance is dependent on the level of stress and that this varies between genotypes; Nipponbare is moderately tolerant to 40 mM NaCl but not to 80 mM. We also suggest that the use of multivariate analyses can simplify the complex salinity tolerance picture and can effectively reveal the salinity tolerant genotype from a wide range of germplasm. The results reported here identify different physiological mechanism of tolerance across the genotypes and provide a sound basis for future studies examining their underlying molecular mechanisms.

Genetic variation in wheat germplasm for salinity tolerance atseedling stage: improved statistical inference

Salinity is the major threat to global wheat production, particularly in arid and semiarid areas. Breeding salt-tolerant cultivars is one feasible solution, while the presence of genetic variation is a prerequisite for genetic improvement. To detect genetic variation for salt tolerance in wheat, a total of 150 wheat genotypes were tested for seedling-stage tolerance response at 300 mM NaCl in hydroponic culture. Significant differences (P ≤ 0.001) were identified in wheat for seedling traits, and 20 salt-tolerant and 5 susceptible genotypes were selected on the basis of root and shoot weights. These 25 genotypes were tested for salt-tolerance response at the early developmental stage in hydroponic culture at 0, 70, 140, 210, 280, and 350 mM NaCl salinity levels. GGEbiplot analysis was used for measuring salt tolerance for relative growth rates of root length, shoot length, and plant weight. Genotypes DH-3, 9436, DH-14, Chenab-2000, DH-13, WN-174, WN-150, STW-135, 066284, and DH-2 were the most salt-tolerant and 4072, WN-64, WN-60, WN-165, and WN-140 were the most susceptible. Biplot analysis appeared advantageous over salt-tolerance indices due to its graphical nature and ability to demonstrate genotype A— environment interactions.

Genetic Variation in Salt Tolerance during Seed Germination in a Backcross Inbred Line Population and Advanced Breeding Lines Derived from Upland Cotton × Pima Cotton

ABSTRACTSeed germination is a crucial phase of the plant life cycle that affects its establishment and productivity. However, information on salt tolerance at this phase is limited. Pima cotton (Gossypium barbadense L.) may be more salt tolerant during germination than Upland cotton (Gossypium hirsutum L.) based on its evolutionary and breeding history. The objective of this study was to evaluate germination salt tolerance of introgressed lines derived from hybrids between the two species under standard controlled conditions. A backcross inbred line (BIL) population of 146 lines from a cross between Upland cotton ‘Sure‐Grow’ (SG) 747 and ‘Pima S‐7’ (Test 1) and 120 advanced breeding lines from ‘Acala 1517‐99’ × Pima Phy 76 (Test 2) were evaluated for germination under 200 mM NaCl and nonsalt (control) conditions. Based on reduction in seed germination under NaCl conditions, G. barbadense parents were significantly more tolerant than the Upland parents. There were significant effects of genotype, treatment, and genotype × treatment interaction in both tests. The heritability for seed germination was moderate, ranging from 0.39 to 0.43 with at least two genes estimated. The genetic result is corroborated by the identification of many salt tolerant BILs and advanced breeding lines. This study has provided one of the first lines of evidence that the introduction of salt tolerance at seed germination from Pima into Upland cotton may be attainable.

Genetic variation in salt tolerance at the seedling stage in an interspecific backcross inbred line population of cultivated tetraploid cotton

Soil salinity reduces cotton growth, yield, and fiber quality and has become a serious problem in the arid southwestern region of the Unites States. Development and planting of salt-tolerant cultivars could ameliorate the deleterious effects. The objective of this study was to assess the genetic variation of salt tolerance and identify salt tolerant genotypes in a backcross inbred line (BIL) population of 142 lines from a cross of Upland (Gossypium hirsutum) × Pima cotton (G. barbadense) at the seedling growth stage. As compared with the non-saline (control) conditions, seedlings under the salinity stress (200 mM NaCl) showed a significant reduction in all the plant growth characteristics measured, as expected. Even though the two parents did not differ in salt response as measured by percent reduction, significant genotype variations in the BIL population were detected for all traits except for leaf number. Based on percent reduction of the traits measured, several BILs were more salt tolerant than both parents. The results indicate that transgressive segregation occurred during the process of backcrossing and selfing even though both parents were not salt tolerant during seedling growth. Coefficients of correlation between all the traits were significantly positive, indicating an association between the traits measured. The estimates of broad-sense heritability were 0.69, 0.46, 0.47, 0.43, and 0.49 for plant height, fresh weight of shoot and root, and dry weight of shoot and root, respectively, indicating that salt tolerance during cotton seedling growth is moderately heritable and environmental variation plays an equally important role. The overall results demonstrate that backcrossing followed by repeated self-pollination is a successful strategy to enhance salt tolerance at the seedling stage by transferring genetic factors from Pima to Upland cotton.

Salt Stress Induced Variation in DNA Methylation Pattern and Its Influence on Gene Expression in Contrasting Rice Genotypes

BackgroundSalinity is a major environmental factor limiting productivity of crop plants including rice in which wide range of natural variability exists. Although recent evidences implicate epigenetic mechanisms for modulating the gene expression in plants under environmental stresses, epigenetic changes and their functional consequences under salinity stress in rice are underexplored. DNA methylation is one of the epigenetic mechanisms regulating gene expression in plant’s responses to environmental stresses. Better understanding of epigenetic regulation of plant growth and response to environmental stresses may create novel heritable variation for crop improvement.Methodology/Principal FindingsMethylation sensitive amplification polymorphism (MSAP) technique was used to assess the effect of salt stress on extent and patterns of DNA methylation in four genotypes of rice differing in the degree of salinity tolerance. Overall, the amount of DNA methylation was more in shoot compared to root and the contribution of fully methylated loci was always more than hemi-methylated loci. Sequencing of ten randomly selected MSAP fragments indicated gene-body specific DNA methylation of retrotransposons, stress responsive genes, and chromatin modification genes, distributed on different rice chromosomes. Bisulphite sequencing and quantitative RT-PCR analysis of selected MSAP loci showed that cytosine methylation changes under salinity as well as gene expression varied with genotypes and tissue types irrespective of the level of salinity tolerance of rice genotypes.Conclusions/SignificanceThe gene body methylation may have an important role in regulating gene expression in organ and genotype specific manner under salinity stress. Association between salt tolerance and methylation changes observed in some cases suggested that many methylation changes are not “directed”. The natural genetic variation for salt tolerance observed in rice germplasm may be independent of the extent and pattern of DNA methylation which may have been induced by abiotic stress followed by accumulation through the natural selection process.

Regeneration Capacity of Cell Suspension Culture in Malaysian Rice Genotypes under Salinity Stress

Rice, a salt-sensitive species has a substantial genetic variation for salt tolerance within the cultivated gene pool. This study describes the establishment of cell suspension culture system and analysis of proline content of the selected rice genotypes under in vitro salt stress. The cell suspension cultures, initiated from the friable seed-derived callus, were established in MS medium supplemented with different concentrations of 2,4-D (0-25 μM) and subjected to different concentrations of NaCl (0-250 mM). The average Settled Cell Volume (SCV) of different clumps sizes was recorded. The results showed that MR219-4 exhibited the highest cell growth rate and regeneration capacity. The 750 μm sieved clumps have higher cell mass than the 500 and 250 μm sieved cell size. The shoot-regeneration capacity was maximum in 1/2 MS medium supplemented with 10 μM BAP. However, low regeneration capacity was obtained in NaCl treatments. MR219 (control) and MR219-9 appeared to be more NaCl tolerant than MR219-4. In addition, all genotypes significantly synthesized proline under NaCl conditions as demonstrated by the proline accumulation and MR219-4 revealed the lowest content among genotypes studied. These genotypes can be good model systems for studying the physiological mechanisms associated with in vitro selection for salt stress. This finding also suggests that proline may play a crucial role in protecting rice cells under salinity stress.

RAS1, a quantitative trait locus for salt tolerance and ABA sensitivity in Arabidopsis.

Soil salinity limits agricultural production and is a major obstacle for feeding the growing world population. We used natural genetic variation in salt tolerance among different Arabidopsis accessions to map a major quantitative trait locus (QTL) for salt tolerance and abscisic acid (ABA) sensitivity during seed germination and early seedling growth. A recombinant inbred population derived from Landsberg erecta (Ler; salt and ABA sensitive) x Shakdara (Sha; salt and ABA resistant) was used for QTL mapping. High-resolution mapping and cloning of this QTL, Response to ABA and Salt 1 (RAS1), revealed that it is an ABA- and salt stress-inducible gene and encodes a previously undescribed plant-specific protein. A premature stop codon results in a truncated RAS1 protein in Sha. Reducing the expression of RAS1 by transfer-DNA insertion in Col or RNA interference in Ler leads to decreased salt and ABA sensitivity, whereas overexpression of the Ler allele but not the Sha allele causes increased salt and ABA sensitivity. Our results suggest that RAS1 functions as a negative regulator of salt tolerance during seed germination and early seedling growth by enhancing ABA sensitivity and that its loss of function contributes to the increased salt tolerance of Sha.

Variation in salinity tolerance, early shoot mass and shoot ion concentrations within Lotus tenuis: towards a perennial pasture legume for saline land

Perennial legumes are needed for productive pastures in saline areas. We evaluated 40 lines of Lotus tenuis for tolerance to salinity at both germination and vegetative growth stages. Salt tolerance during the early vegetative stage was assessed in a sand-tank experiment with NaCl concentrations of 0–450 mm NaCl for 5 weeks. Most L. tenuis lines were more salt tolerant and had at least 50% lower shoot Na+ plus Cl– (% dry mass (DM)) compared with some other common pasture legumes, Medicago sativa, M. polymorpha and Trifolium subterraneum. Within L. tenuis significant variation in salt tolerance was found, with C50 values (concentrations of NaCl that decreased shoot dry matter to 50% of control) ranging from ~100 to 320 mm. Shoot concentrations of Cl–, Na+ and K+ did not always correlate with salt tolerance; some tolerant lines had low shoot Na+ and Cl– (and thus better nutritive value), while others tolerated high shoot Na+ and Cl–. We also found variation within L. tenuis for salt tolerance of seeds, with lines ranging from 0 to 70% germination after recovery from a prior exposure to 800 mm NaCl for 15 days. There was no relationship between salinity tolerance of scarified seeds and subsequent growth of seedlings; therefore, testing of seeds alone would not be an appropriate screening method for salt tolerance in L. tenuis. This study of 40 L. tenuis lines has shown significant genetic variation for salt tolerance within this species, and we have identified key lines with potential to be productive in saltland pasture systems.

Relative Salt Tolerance Of South Khorasan Millets

Abstract Millets are important agricultural crops for arid regions due to short life span and their resistance to salinity and drought conditions. In Iran, three main species of millets including proso millet (Panicum miliaceum), foxtail millet (Setaria italica) and pearl millet (Pennisetum glaucum) are cultivated in Shouthern Khorasan province, eastern Iran. In order to assess inter-specific genetic variation for salt tolerance at vegetative and reproductive stage, an experiment was conducted in split plot based on completely randomized block design. Nine genotypes of these millets collected from four different regions of the Shouthern Khorasan province (Ghaen, Sarayan, Nehbandan, and Birjand) were subjected to three levels of salinity stress (1.5, 5.5, and 9.5 dS/m). Although the yield and other yield related parameters of millets decreased by salinity stress, this reduction was more prominent only at high level of salinity (9.5 dS/m). Remarkable differences among same species from different areas were observed. Growth and yield capacity of three millet species from Birjand were also different. Of three millets, pearl millet from Birjand followed by foxtail millet, showed maximum yield potential under both salt stress and normal conditions. Of genotypes of foxtail millets, genotype from Sarayan exhibited maximum growth and yield potential under saline conditions. In contrast in proso-millets, genotype from Ghaen showed higher salt tolerance. Thus, salt tolerance varies in three millets from different regions, which could be further explored in future research.

A Rapid and Effective Method for Screening Salt Tolerance in Soybean

Salinity has been recognized as a constraint for soybean [Glycine max (L.) Merr.] production in many regions worldwide. Fortunately, genetic variation in salt tolerance is available in the soybean germplasm bank. However, current screening methodologies for salt‐tolerant genotypes are time‐consuming and often ineffective because of their limitations in detecting and measuring plant response to salinity. The objective of this study was to develop a rapid visual method for screening soybean genotypes in response to salt stress based on foliar symptoms. Soybean seedlings were grown in hydroponics with 0, 40, 80, 120, or 160 mM NaCl. Visual foliar symptoms of excessive NaCl were evident at 26 d after planting (14 d in 120 and 160 mM NaCl treatment). The NaCl level of 120 mM was most effective for salt‐tolerance screening based on visual foliar symptoms on a group of differential genotypes. Chloride includers (‘Williams’, ‘Clark’, ‘HBK R4924’, and ‘Dare’) exhibited interveinal chlorosis, while Cl excluders (‘S‐100’, ‘Lee 68’, and ‘HBK R5525’) showed no chlorosis at the 120 mM NaCl level. At this critical selection level (120 mM NaCl), average leaf Na and Cl− contents were 2.64 and 1.96 times higher, respectively, for Cl includers than for Cl excluders. Plant damage was more evident at 120 and 160 mM NaCl, as demonstrated by the decreased shoot and root biomass and near maximum accumulation of Na and Cl− in the tissue. There was a significant and negative correlation (r = −0.69, p = 0.0006) between relative root dry weight and Cl− concentration in the leaf. This methodology is simple, rapid, and effective for selection of Cl tolerant genotypes with a minimum investment of cost and time.

Comparative Transcriptional Profiling of Two Contrasting Rice Genotypes under Salinity Stress during the Vegetative Growth Stage

Rice (Oryza sativa), a salt-sensitive species, has considerable genetic variation for salt tolerance within the cultivated gene pool. Two indica rice genotypes, FL478, a recombinant inbred line derived from a population developed for salinity tolerance studies, and IR29, the sensitive parent of the population, were selected for this study. We used the Affymetrix rice genome array containing 55,515 probe sets to explore the transcriptome of the salt-tolerant and salt-sensitive genotypes under control and salinity-stressed conditions during vegetative growth. Response of the sensitive genotype IR29 is characterized by induction of a relatively large number of probe sets compared to tolerant FL478. Salinity stress induced a number of genes involved in the flavonoid biosynthesis pathway in IR29 but not in FL478. Cell wall-related genes were responsive in both genotypes, suggesting cell wall restructuring is a general adaptive mechanism during salinity stress, although the two genotypes also had some differences. Additionally, the expression of genes mapping to the Saltol region of chromosome 1 were examined in both genotypes. Single-feature polymorphism analysis of expression data revealed that IR29 was the source of the Saltol region in FL478, contrary to expectation. This study provides a genome-wide transcriptional analysis of two well-characterized, genetically related rice genotypes differing in salinity tolerance during a gradually imposed salinity stress under greenhouse conditions.