Genetic Variation In Salinity Tolerance Research Articles

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

Evaluating salinity tolerance in progeny of domestic and wild barley crosses at germination stage

AbstractSalinity is one of the most important challenges facing future global barley (Hordeum vulgare L.) productivity, as it causes major reduction in germination, growth, grain yield, and quality. Screening germplasm for salinity tolerance at germination is vital to breeding programs because germination is the first stage of plant growth and occurs near the soil surface where salt can accumulate in high concentrations. This experiment was conducted to assess salinity tolerance of 249 genotypes (64 diploid (2×) H. vulgare crosses; 174 tetraploid (4×) H. vulgare crosses; and 11 parents) at the seed germination stage. Salinity treatments applied at imbibition included concentrations of 0, 100, 200, and 300 mM salinity and were maintained for 10 d. Analysis of variance of all families indicated significant (P ≤ .001) genotype × salinity interaction for final germination percentage (FG%), corrected germination percentage (CG%), and germination index (GI) at all treatment levels, indicating high genetic variation for salinity tolerance among screened genotypes. The mean of all measured parameters (FG%, CG%, and GI) decreased as salinity concentration increased. These responses can be used to identify genotypes with salinity tolerance at germination. At 300 mM salinity, progenies in 2× Families 1 and 2 were 14.3 and 12.5% saline tolerant, respectively. A total of 29 progenies from 4× families were tolerant to 300 mM treatment at germination. These progenies would have an economic value for improving barley tolerance for salinity.

A large-scale screening of quinoa accessions reveals an important role of epidermal bladder cells and stomatal patterning in salinity tolerance

The presence of epidermal bladder cells (EBCs) in halophytes allows considerable amount of Na+ being accumulated in these external structures, away from the metabolically active mesophile cells. Also, stomatal patterning may represent a primary mechanism by which plants can optimise its water-use efficiency under saline condition. This investigation was aimed to explore the varietal differences in a salinity tolerance of quinoa (Chenopodium quinoa) by evaluating a broad range of accessions and linking the overall salinity tolerance with changes in stomatal characteristics and EBC parameters. One hundred and fourteen accessions were grown under temperature-controlled glasshouse under non-saline and 400 mM NaCl conditions, and different physiological and anatomical characteristics were measured. Accessions were classified into three classes (sensitive, intermediate and tolerant) based on a relative dry weight defined as salinity tolerance index (STI). Results showed a large variability in STI indicating a strong genetic variation in salinity tolerance in quinoa. Bladders density was increased in a majority of accessions under saline condition while the bladder’s diameter remained unchanged; this resulted in a large variability in a bladder’s volume as a dependant variable. Stomata density remained unchanged between saline and non-saline conditions while the stomata length declined between 3% to 43% amongst accessions. Leaf Na+ concentration varied from 669 μmol/gDW to 3155 μmol/gDW under saline condition and, with an exception of a few accessions, leaf K+ concentration increased under saline conditions. Correlation analysis indicated a significant positive association between EBC diameter and STI on one hand and EBC volume and STI on the other hand, in a salt-tolerant group. These observations are consistent with the role of EBCs in sequestration of toxic Na+ in the external structures, away from the cytosol. A negative association was found between EBC density and diameter in salt-sensitive plants. A negative association between STI and stomata length was also found in a salt-tolerant group, suggesting that these plants were able to efficiently regulate stomatal patterning to balance water loss and CO2 assimilation under saline conditions. Both salt-sensitive and salt-tolerant groups had the same Na+ concentration in the shoot under saline conditions; however, a negative association between leaf Na+ concentration and STI in salt-sensitive plants indicated a more efficient Na+ sequestration process into the EBCs in salt-tolerant plants.

Salinity tolerance in Australian wild Oryza species varies widely and matches that observed in O. sativa

BackgroundSoil salinity is widespread in rice-producing areas globally, restricting both vegetative growth and grain yield. Attempts to improve the salt tolerance of Asian rice, Oryza sativa—the most salt sensitive of the major cereal crops—have met with limited success, due to the complexity of the trait and finite variation in salt responses among O. sativa lines. Naturally occurring variation among the more than 20 wild species of the Oryza genus has great potential to provide breeders with novel genes to improve resistance to salt. Here, through two distinct screening experiments, we investigated variation in salinity tolerance among accessions of two wild rice species endemic to Australia, O. meridionalis and O. australiensis, with O. sativa cultivars Pokkali and IR29 providing salt-tolerant and sensitive controls, respectively.ResultsRice plants were grown on soil supplemented with field-relevant concentrations of NaCl (0, 40, 80, and 100 mM) for 30 d, a period sufficient to reveal differences in growth and physiological traits. Two complementary screening approaches were used: destructive phenotyping and high-throughput image-based phenotyping. All genotypes displayed clear responses to salt treatment. In the first experiment, both salt-tolerant Pokkali and an O. australiensis accession (Oa-VR) showed the least reduction in biomass accumulation, SES score and chlorophyll content in response to salinity. Average shoot Na+/K+ values of these plants were the lowest among the genotypes tested. In the second experiment, plant responses to different levels of salt stress were quantified over time based on projected shoot area calculated from visible red-green-blue (RGB) and fluorescence images. Pokkali grew significantly faster than the other genotypes. Pokkali and Oa-VR plants displayed the same absolute growth rate under 80 and 100 mM, while Oa-D grew significantly slower with the same treatments. Oa-VR showed substantially less inhibition of growth in response to salinity when compared with Oa-D. Senescence was seen in Oa-D after 30 d treatment with 40 mM NaCl, while the putatively salt-tolerant Oa-VR had only minor leaf damage, even at higher salt treatments, with less than a 40% increase in relative senescence at 100 mM NaCl compared to 120% for Oa-VR.ConclusionThe combination of our two screening experiments uncovered striking levels of salt tolerance diversity among the Australian wild rice accessions tested and enabled analysis of their growth responses to a range of salt levels. Our results validate image-based phenotyping as a valuable tool for quantitative measurement of plant responses to abiotic stresses. They also highlight the potential of exotic germplasm to provide new genetic variation for salinity tolerance in rice.

Salinity tolerance among a large range of bermudagrasses (Cynodon spp.) relative to other halophytic and non-halophytic perennial C4 grasses

The increasing demand on potable water has resulted in a greater reliance on poorer quality water, including saline sources, for maintaining forage and turfgrasses in agricultural and urban landscapes. Consequently, it will be crucial to identify grasses that can tolerate saline irrigation water. This study aimed to determine salinity tolerance among a large range of bermudagrasses relative to other perennial C4 grasses and test the relationship between salt tolerance and drought resistance. We report the salinity tolerance of 70 genotypes of mostly Australian bermudagrass ecotypes that were compared to halophytic cultivars of seashore paspalum (Paspalum vaginatum Swartz) and a non-halophytic cultivar of Queensland blue couch (Digitaria didactyla Willd) using a flood and drain sand culture system with salt treatments 1–40dSm−1. For the first time for C4 grasses, salt tolerance was determined by comparing total biomass of the grasses with and without salt treatment. Large genetic variation in salinity tolerance was identified and six bermudagrasses collected from saline habitats had salinity tolerance equal to that of seashore paspalum under the salinity treatments used in this study. There was no correlation between salt tolerance and drought resistance phenotypes determined from our previous research. Canopy temperature differential during salt stress was negatively correlated (r=−0.71 to −0.91, P<0.001) to salt tolerance and has potential to be used for screening bermudagrasses for salt tolerance using flood and drain sand culture. Salinity levels above 20dSm−1 for 8 weeks appeared to be effective for detecting large variation for salt tolerance in bermudagrass.

A pedigree-based experiment reveals variation in salinity andthermal tolerance in the salmon louse, Lepeophtheirus salmonis.

The salmon louse is a highly abundant ectoparasitic copepod of salmonids in the North Pacific and Atlantic. Widespread and rapid development of resistance to chemical agents used to delouse salmonids on marine farms is now threatening the continued development of the aquaculture industry and have served as a potent catalyst for the development of alternative pest management strategies. These include freshwater and warm‐water treatments to which the louse is sensitive. However, given the well‐documented evolutionary capacity of this species, the risk of developing tolerance towards these environmental treatments cannot be dismissed. Two common‐garden experiments were performed using full‐sibling families of lice identified by DNA parentage testing to investigate whether one of the fundamental premises for evolution, in this context genetic variation in the capacity of coping with fresh or warm water, exists within this species. Significant differences in survival were observed among families in both experiments, although for the salinity experiment, it was not possible to unequivocally disentangle background mortality from treatment‐induced mortality. Thus, our data demonstrate genetic variation in tolerance of warm water and are suggestive of genetic variation in salinity tolerance. We conclude that extensive use of these environmental‐based treatments to delouse salmonids on commercial farms may drive lice towards increased tolerance.

Exploring genetic variation for salinity tolerance in chickpea using image-based phenotyping

Soil salinity results in reduced productivity in chickpea. However, breeding for salinity tolerance is challenging because of limited knowledge of the key traits affecting performance under elevated salt and the difficulty of high-throughput phenotyping for large, diverse germplasm collections. This study utilised image-based phenotyping to study genetic variation in chickpea for salinity tolerance in 245 diverse accessions. On average salinity reduced plant growth rate (obtained from tracking leaf expansion through time) by 20%, plant height by 15% and shoot biomass by 28%. Additionally, salinity induced pod abortion and inhibited pod filling, which consequently reduced seed number and seed yield by 16% and 32%, respectively. Importantly, moderate to strong correlation was observed for different traits measured between glasshouse and two field sites indicating that the glasshouse assays are relevant to field performance. Using image-based phenotyping, we measured plant growth rate under salinity and subsequently elucidated the role of shoot ion independent stress (resulting from hydraulic resistance and osmotic stress) in chickpea. Broad genetic variation for salinity tolerance was observed in the diversity panel with seed number being the major determinant for salinity tolerance measured as yield. This study proposes seed number as a selection trait in breeding salt tolerant chickpea cultivars.

Genetic variation in Southern USA rice genotypes for seedling salinity tolerance.

The success of a rice breeding program in developing salt tolerant varieties depends on genetic variation and the salt stress response of adapted and donor rice germplasm. In this study, we used a combination of morphological and physiological traits in multivariate analyses to elucidate the phenotypic and genetic variation in salinity tolerance of 30 Southern USA rice genotypes, along with 19 donor genotypes with varying degree of tolerance. Significant genotypic variation and correlations were found among the salt injury score (SIS), ion leakage, chlorophyll reduction, shoot length reduction, shoot K+ concentration, and shoot Na+/K+ ratio. Using these parameters, the combined methods of cluster analysis and discriminant analysis validated the salinity response of known genotypes and classified most of the USA varieties into sensitive groups, except for three and seven varieties placed in the tolerant and moderately tolerant groups, respectively. Discriminant function and MANOVA delineated the differences in tolerance and suggested no differences between sensitive and highly sensitive (HS) groups. DNA profiling using simple sequence repeat markers showed narrow genetic diversity among USA genotypes. However, the overall genetic clustering was mostly due to subspecies and grain type differentiation and not by varietal grouping based on salinity tolerance. Among the donor genotypes, Nona Bokra, Pokkali, and its derived breeding lines remained the donors of choice for improving salinity tolerance during the seedling stage. However, due to undesirable agronomic attributes and photosensitivity of these donors, alternative genotypes such as TCCP266, Geumgangbyeo, and R609 are recommended as useful and novel sources of salinity tolerance for USA rice breeding programs.

Testing for beneficial reversal of dominance during salinity shifts in the invasive copepod Eurytemora affinis, and implications for the maintenance of genetic variation.

Maintenance of genetic variation at loci under selection has profound implications for adaptation under environmental change. In temporally and spatially varying habitats, non-neutral polymorphism could be maintained by heterozygote advantage across environments (marginal overdominance), which could be greatly increased by beneficial reversal of dominance across conditions. We tested for reversal of dominance and marginal overdominance in salinity tolerance in the saltwater-to-freshwater invading copepod Eurytemora affinis. We compared survival of F1 offspring generated by crossing saline and freshwater inbred lines (between-salinity F1 crosses) relative to within-salinity F1 crosses, across three salinities. We found evidence for both beneficial reversal of dominance and marginal overdominance in salinity tolerance. In support of reversal of dominance, survival of between-salinity F1 crosses was not different from that of freshwater F1 crosses under freshwater conditions and saltwater F1 crosses under saltwater conditions. In support of marginal overdominance, between-salinity F1 crosses exhibited significantly higher survival across salinities relative to both freshwater and saltwater F1 crosses. Our study provides a rare empirical example of complete beneficial reversal of dominance associated with environmental change. This mechanism might be crucial for maintaining genetic variation in salinity tolerance in E. affinis populations, allowing rapid adaptation to salinity changes during habitat invasions.

Screening for salinity stress tolerance in rice and finger millet genotypes using shoot Na+/K+ ratio and leaf carbohydrate contents as key physiological traits

A study was conducted to find out the genetic variation for salinity tolerance in rice and finger millet genotypes. Twenty finger millet and sixteen rice genotypes were screened for their tolerance/susceptibility against salinity under hydroponics in greenhouse conditions. Screening resulted in the identification of contrasting genotypes in both the crops. Among the rice genotypes, IR 29 was found to be susceptible and FL 478 was found to be tolerant to salinity stress. Among the finger millet genotypes, CO 12 was susceptible and Trichy 1 was tolerant to salinity stress. Two genotypes showing contrasting behavior to salt stress were analyzed for their shoot Na+ to K+ ratio and leaf carbohydrate contents to understand the physiological basis of salinity tolerance. In rice and finger millet, the shoot Na+/K+ ratio was found to be significantly lower, and the carbohydrate contents were much higher in the tolerant FL 478 and Trichy 1 relative to IR29 and CO 12 upon salinity treatment. Lower shoot Na+/K+ ratio coupled with higher carbohydrate contents could serve as indices to screen genotypes tolerant to salinity stresses.

Salinity tolerance and ion accumulation in chickpea (Cicer arietinum L.) subjected to salt stress

Chickpea (Cicer arietinum L.) is considered a salt sensitive species, but some genetic variation for salinity tolerance exists. The present study was initiated to determine the degree of salt tolerance among chickpea genotypes, and the relationship between salt tolerance and ion accumulation in leaves and reproductive tissues. Three experiments were conducted in a glasshouse in Perth, Western Australia, in which up to 55 genotypes of chickpea were subjected to 0, 40 or 60 mM NaCl added to the soil to determine the variation in salt tolerance, and the association between salt tolerance and reproductive success. Pod and seed numbers, seed yield and yield components, pollen viability, in vitro pollen germination and in vivo pollen tube growth, were used to evaluate reproductive success. Leaves, flowers and seeds were sampled in the reproductive phase to measure the concentrations of sodium, potassium and chloride ions in these organs. When grown in soil with 40 mM NaCl, a 27-fold range in seed yield was observed among the 55 chickpea genotypes. The increased salt tolerance, as measured by yield under salinity or relative yield under saline conditions, was positively associated with higher pod and seed numbers, and higher shoot biomass, but not with time to 50 % flowering nor with the number of filled pods in the non-saline treatment. Pod abortion was higher in the salt sensitive genotypes, but pollen viability, in vitro pollen germination and in vivo pollen tube growth were not affected by salinity in either the salt tolerant or salt sensitive genotypes. The concentrations of sodium and potassium ions, but not chloride, in the seed were significantly higher in the sensitive (106 μmol g−1 DM of sodium and 364 μmol g−1 DM of potassium) than in the tolerant (74 and 303 μmol g−1 DM, respectively) genotypes. Sodium and potassium, but particularly chloride, ions accumulated in leaves and in pod wall, whereas accumulation in the seed was much lower. Considerable genotypic variation for salt tolerance exists in chickpea germplasm. Selection for genotypes with high pod and/or seed numbers that accumulate low concentrations of salt in the seed will be beneficial.

Mapping salinity tolerance during Arabidopsis thaliana germination and seedling growth.

To characterize and dissect genetic variation for salinity tolerance, we assessed variation in salinity tolerance during germination and seedling growth for a worldwide sample of Arabidopsis thaliana accessions. By combining QTL mapping, association mapping and expression data, we identified genomic regions involved in salinity response. Among the worldwide sample, we found germination ability within a moderately saline environment (150 mM NaCl) varied considerable, from >90% among the most tolerant lines to complete inability to germinate among the most susceptible. Our results also demonstrated wide variation in salinity tolerance within A. thaliana RIL populations and identified multiple genomic regions that contribute to this variation. These regions contain known candidate genes, but at least four of the regions contain loci not yet associated with salinity tolerance response phenotypes. Our observations suggest A. thaliana natural variation may be an underutilized resource for investigating salinity stress response.

Genetic variability of salinity tolerance in spring wheat (Triticum aestivum L.)

Salinity is one of the most damaging agro-environmental problems limiting plant growth and development in most parts of the world. The problem of salinity existed long before human beings and the start of agricultural practice and today it has become a very serious problem for crop production, particularly in arid and semi-arid regions, which constitute about one third of the world's land surface. The magnitude of genetic variation for salinity tolerance in spring wheat and broad-sense heritabilities has been estimated at different salinity levels. The 68 genotypes responded with different behaviors to increasing salinity levels in the growing medium. Responses of different genotypes to increased salinity levels in reduced growth were found, with those originating from Australia exhibiting a significant increase in salinity tolerance compared with others, originating from Pakistan. Plant vigor and salinity tolerance were found to have no significant correlation as measured by relative growth rates in saline environments. The relative growth rate of various accessions grouped on the basis of different geographic origin and different genes of various stresses also were not different significantly from each other, which suggests that different genes may be controlling the characteristic, from a single major dominant or from recessive genes. Estimated broad-sense heritability indicated that phenotypic variance exceeded that of genotypic by nearly two orders of magnitude. This study was to determine genetic and phenotypic relationships between plant performance in the presence of NaCl at three developmental stages in wheat. These results suggest that improvement in salinity tolerance in spring wheat is possible through selection and breeding.

Genetic Variation for Salinity Tolerance in Spring Wheat

In order to determine the magnitude of genetic variation for salinity tolerance in spring wheat, broad sense heritabilities of different yield components and seed yield were estimated for two F2 populations. One population was derived from a cross of salt tolerant cv LU26S (from Pakistan) and salt tolerant cv Kharchia (from India). The second F2 population was derived from a cross of cv LU26S and cv Candeal (from CIMMYT). Both F2 populations and their corresponding parents were grown in pots containing soil salinized with 2.81 (control), 8, 16, and 24 dS/m prepared by dissolving NaCl + CaCl2 (1:l by wt.) in full strength Hoagland nutrient solution. Broad sense heritability estimates, calculated at different salinity levels, of number of tillers per plant ranged from 0.49 to 0.60; of 1000 seed weight, from 0.57 to 0.80; of number of grains per spike, from 0.64 to 0.78; and of seed yield, from 0.60 to 0.91. These results suggest that improvement in salinity tolerance in the spring wheat is possible through selection and breeding.

Screening methods for salinity tolerance: a case study with tetraploid wheat

Fast and effective glasshouse screening techniques that could identify genetic variation in salinity tolerance were tested. The objective was to produce screening techniques for selecting salt-tolerant progeny in breeding programs in which genes for salinity tolerance have been introduced by either conventional breeding or genetic engineering. A set of previously unexplored tetraploid wheat genotypes, from five subspecies of Triticum turgidum, were used in a case study for developing and validating glasshouse screening techniques for selecting for physiologically based traits that confer salinity tolerance. Salinity tolerance was defined as genotypic differences in biomass production in saline versus non-saline conditions over prolonged periods, of 3–4 weeks. Short-term experiments (1 week) measuring either biomass or leaf elongation rates revealed large decreases in growth rate due to the osmotic effect of the salt, but little genotypic differences, although there were genotypic differences in long-term experiments. Specific traits were assessed. Na+ exclusion correlated well with salinity tolerance in the durum subspecies, and K+/Na+ discrimination correlated to a lesser degree. Both traits were environmentally robust, being independent of root temperature and factors that might influence transpiration rates such as light level. In the other four T. turgidum subspecies there was no correlation between salinity tolerance and Na+ accumulation or K+/Na+ discrimination, so other traits were examined. The trait of tolerance of high internal Na+ was assessed indirectly, by measuring chlorophyll retention. Five landraces were selected as maintaining green healthy leaves despite high levels of Na+ accumulation. Factors affecting field performance of genotypes selected by trait-based techniques are discussed.

Comparative Salinity Responses among Pigeonpea Genotypes and Their Wild Relatives

Soil salinity can be a major constraint to pigeonpea (Cajanus cajan (L.) Millsp.) in the regions where it is predominantly grown. This study was conducted to assess the extent of genetic variation for salinity tolerance in the germplasm of pigeonpea and its wild relatives. Solution culture experiments in a greenhouse and controlled environment chamber were conducted to screen a range of cultivated pigeonpea genotypes for ability to germinate and grow up to 60 d under saline conditions. Several wild relatives of pigeonpea were screened for salinity response in a sand culture system in a greenhouse. Among cultivated pigeonpea genotypes, ICPL 227 was one of the most tolerant and HY 3C one of the most sensitive genotypes tested. None of the pigeonpea genotypes tested were able to survive beyond 30 d at 8 dS m−1 or higher salinity levels. The extent of variation in salinity response among cultivated pigeonpea genotypes appeared too limited to warrant genetic enhancement of salinity tolerance. Among the wild relatives of pigeonpea, various species of Atylosia, Rynchosia, and Dunbaria showed a wide range of variation in their salinity tolerance (critical levels from 4 to 12 dS m−1): A. albicans (W. &amp; A.) Benth., and A. platycarpa could grow in a sand culture system at 12 dS m−1 and Rynchosia albiflora could not tolerate salinity levels above 4 dS m−1. These results suggest that using wild relatives for genetic improvement may increase salinity tolerance of pigeonpea.

Variation in growth and survival between two anadromous strains of Canadian Arctic charr ( Salvelinus alpinus) during long-term saltwater rearing

Two strains of Arctic charr ( Salvelinus alpinus) were reared in ambient saltwater for a 9-month period. Atlantic salmon ( Salmo salar) were reared under similar conditions for comparison of saltwater performance with that of Arctic charr in terms of aquaculture potential. There were significant differences in growth and survival between the two strains of charr. The development of a bimodal distribution in weight was evident in one strain of charr. Final mean weight of upper modal Arctic charr exceeded final mean weight of Atlantic salmon. A “critical size” for long-term saltwater survival of these two strains of Arctic charr is suggested by the weight distribution among mortalities. Genetic variation in salinity tolerance in Arctic charr is demonstrated.