Selection For Salt Tolerance Research Articles

Genome-wide association analysis and genomic prediction of salt tolerance trait in soybean germplasm.

Soybean is an important protein and oil crop, and improving yield has traditionally been a major breeding goal. However, salt stress is an important abiotic factor that can severely impair soybean yield by disrupting metabolic processes, inhibiting photosynthesis, and hindering plant growth, ultimately leading to a decrease in productivity. This study utilized phenotypic and genotypic data from 563 soybean germplasms sourced from over 20 countries. Employing four distinct models-we performed a genome-wide association study (GWAS) using four models, including MLM, MLMM, FarmCPU, and BLINK in GAPIT 3, we conducted a Genome-Wide Association Study (GWAS) to identify single nucleotide polymorphism (SNP) associated with salt tolerance in soybean. Subsequently, these identified SNP were further analyzed for candidate gene discovery. Using 34,181 SNPs for genomic prediction (GP) to assess prediction accuracy. Our study identified 10 SNPs significantly associated with salt tolerance, located on chromosomes 1, 2, 3, 7, and 16. And we identified 11 genes within a 5 kb window upstream and downstream of the QTLs on chromosomes 1, 3, and 16. Utilizing the GWAS-derived SNP marker sets for genomic prediction (GP) yielded r-values greater than 0.35, indicating a higher level of accuracy. This suggests that genomic selection for salt tolerance is feasible. The 10 identified SNP markers and candidate genes in this study provide a valuable reference for screening and developing salt-tolerant soybean germplasm resources.

Deciphering the Genetic Mechanisms of Salt Tolerance in Sorghum bicolor L.: Key Genes and SNP Associations from Comparative Transcriptomic Analyses.

Sorghum bicolor L. is a vital cereal crop for global food security. Its adaptability to diverse climates make it economically, socially, and environmentally valuable. However, soil salinization caused by climate extremes poses a threat to sorghum. This study aimed to identify candidate salt-tolerant genes and single nucleotide polymorphisms (SNPs) by performing a comparative transcriptome analysis on a mutant sorghum line and its wild type. The mutant line was generated through gamma ray exposure and selection for salt tolerance. Phenotypic measurements were taken, followed by mRNA sequencing and variant calling. In this study, potential genes and non-synonymous SNPs associated with salt tolerance were inferred, including LOC8071970, LOC8067721, LOC110430887, LOC8070256, and LOC8056880. These genes demonstrated notable differences in nsSNPs in comparison to the wild type, suggesting their potential roles in salt tolerance. Additionally, LOC8060874 (cyanohydrin beta-glucosyltransferase) was suggested as a key gene involved in salt tolerance due to its possible role in dhurrin biosynthesis under salt stress. In upcoming research, additional reverse genetics studies will be necessary in order to verify the function of those candidate genes in relation to salt stress. In conclusion, this study underscores the significance of investigating salt tolerance mechanisms and the potential key genes associated with salt tolerance in sorghum. Our findings may provide insights for future breeding strategies aimed at enhancing salinity tolerance and crop productivity.

Effect of NaCl on Morphophysiological and Biochemical Responses in Gossypium hirsutum L.

Soil salinity is increasing due to several factors such as climate change and areas with uneven rainfall. This increase in level of salinity compelled the cotton breeders to develop a new germplasm that exhibit the suitable for salty soil. This study aimed to determine the salt tolerance of 50 accessions of Gossypium hirsutum in hydroponic conditions having three levels of NaCl, i.e., 0 mM, 150 mM, and 200 mM. The experiment was carried out in a completely randomized design with a factorial arrangement. Morphological, physiological, and biochemical attributes were estimated in these genotypes. The Na+/K+ ratio was determined by dry digestion method. Salt-susceptible and -tolerant genotypes were identified by biplot and cluster analysis. The genotypes showed significant differences for morphophysiological and biochemical parameters. In control, Cyto-515 showed enhanced growth with shoot length (30.20 cm), root length (20.63 cm), fresh shoot weight (2.34 g), and fresh root weight (0.93 g), while under 150 mM and 200 mM salinity levels, MNH-992 had the maximum root length (15.67 cm) and shoot length (24.67 cm). At a 150 mM salinity level, maximum levels of antioxidants were found in Kehkshan and CIM-595, while at a 200 mM salinity level, AA-703, CIM-595, and Kehkshan showed maximum values of antioxidants. The highest Na+/K+ ratio was observed in VH-363 and FH-114, while Kehkshan had lowest Na+/K+ ratio. The biplot analysis revealed that Kehkshan, CIM-595, VH-330, Cyto-178, MNH-992, and Cyto-515 were widely dispersed and distant from the origin, and exhibiting variability for morphophysiological and biochemical traits under the salt stress. In terms of performance across the treatments, accessions MNH-992, Kehkshan, Cyto-515, and CIM-595 performed significantly better. Peroxidase activity, proline contents, H2O2 determination, and Na+/K+ ratio were shown to be useful for the salt tolerance selection criteria. The potential of such salt tolerant accessions (MNH-992, Kehkshan, Cyto-515, and CIM-595) could be assessed after planting in salt affected areas and could be used in breeding programs for the development of diverse salt tolerant new genotypes of upland cotton.

Transcriptome and GWAS Analyses Reveal Candidate Gene for Root Traits of Alfalfa during Germination under Salt Stress

Alfalfa growth and production in China are negatively impacted by high salt concentrations in soils, especially in regions with limited water supplies. Few reliable genetic markers are currently available for salt tolerance selection. As a result, molecular breeding strategies targeting alfalfa are hindered. Therefore, with the continuous increase in soil salinity in agricultural lands, it is indispensable that a salt-tolerant variety of alfalfa is produced. We collected 220 alfalfa varieties around the world for resequencing and performed genome-wide association studies (GWASs). Alfalfa seeds were germinated in saline water with different concentrations of NaCl, and the phenotypic differences in several key root traits were recorded. In the phenotypic analysis, the breeding status and geographical origin strongly affected the salt tolerance of alfalfa. Forty-nine markers were significantly associated with salt tolerance, and 103 candidate genes were identified based on linkage disequilibrium. A total of 2712 differentially expressed genes were upregulated and 3570 were downregulated based on transcriptomic analyses. Some candidate genes that affected root development in the seed germination stage were identified through the combination of GWASs and transcriptome analyses. These genes could be used for molecular breeding strategies to increase alfalfa's salt tolerance and for further research on salt tolerance in general.

Heritability estimation of high salt tolerance in razor clam (Sinonovacula constricta)

As an important marine mollusk, the growth and development of razor clams (Sinonovacula constricta) are affected by salinity. Genetic selection for salt tolerance is an imperative and effective approach to the improvement of growth and production. To examine whether the tolerance to high salt can be included in razor clam breeding programs, we conducted a genetic analysis of high salt tolerance using three phenotypes and four statistical models. The correlation between tolerance and growth traits was evaluated simultaneously. In this study, we used 9-day experimental stress data of 1005 individuals from 17 full-sib families (the offspring of 17 sires and 17 dams). The survival rate of the families ranged from 0% to 100%, suggesting that the viability of razor clams was different under diverse high salt stress. A positive Pearson and Spearman correlation existed between high salt tolerance and growth traits. A very high genetic correlation (0.886–0.999) was also observed between them, indicating indirect breeding was feasible. Heritabilities of tolerance to high salt were from low to high, with values of 0.55–0.64, 0.11, and 0.047–0.487 for trait TS (test survival), trait DD (day of death), and trait TDS (test-day survival), respectively. The Pearson correlation coefficients of families estimated breeding values between different models ranged from 0.921 to 0.998 which indicated a near-identical ranking of families. This study demonstrated that the salt tolerance of razor clams could be improved genetically through selective breeding. Overall, cross-sectional threshold and linear repeatability models were the most appropriate in estimating heritability for salt tolerance with trait TS and trait TDS in this species. Our study provides important information to guide the effective selection for salt tolerance in S. constricta.

Chlorophyll fluorescence, ion uptake, and osmoregulation are potential indicators for detecting ecotypic variation in salt tolerance of Panicum antidotale Retz*

Efficient selection for salt tolerance using the choice of physiological traits is of great importance. In the present study, seven ecotypes of Panicum antidotale (four from the Cholistan Desert and three from the non-Cholistani area) were evaluated after three weeks of salt stress. Results showed that shoot fresh biomass decreased by 74 and 83% respectively in Cholistani, and non-Cholistani ecotypes under salt-stressed conditions compared to control. Ecotypes from the Cholistan were more salt-tolerant (average dry biomass, 4.02 g) than non-Cholistani ones (average dry biomass, 3.14 g). Averaged across the Cholistani and non-Cholistani ecotypes, Cholistani ecotypes accumulated lower Na+ (72%) and/or higher K+ (179%) concentrations in their leaves than non-Cholistani ecotypes. However, parallels between the degree of salt sensitivity and relative water content, leaf water potential, leaf osmotic potential, and leaf turgor potential could not be generalized. In Cholistani ecotypes under salt stress, the total soluble protein on average was higher (11.51%) compared to non-Cholistani ecotypes (8.5%). Chlorophyll a decreased (0–20%) in all populations due to salt stress and it was positively associated with solar energy absorption and electron transport but could not be used to discriminate the populations. Chlorophyll fluorescence data indicated that salt stress damaged PSII functionality and electron transport further than QA −. The effective quantum yield of PSII, performance index, antenna size, energy flux for electron transport, rate of PSII reaction center closure positively correlated with salt tolerance of P. antidotale.

In vitro screening: The best method for salt tolerance selection among pistachio rootstocks

Soil and water salinity are among the main limiting environmental aspects in crop production. This study has been done in order to find the most salt tolerant genotype among five candidate Pistacia vera L. genotype (Akbari, Ahmad-Aghaee, Italyayi, Badami, and Ghazvini) through the selection under in vitro condition. At the first step of salt tolerance selection, 40 shoots of each P. vera genotype were screened on Murashige-Skoog’s (MS) medium containing 120 mM NaCl in order to find the highest salt tolerant genotypes. At the second step of screening, the responses of seven selected P. vera single shoots (from the previous screening) and UCB-1 to three concentrations of NaCl (0, 60 and 120 mM) were investigated under in vitro condition. Increasing salinity level significantly reduced stem elongation, leaf number, fresh weight, starch, chlorophyll index and K + content of pistachio genotypes. In contrast, the content of soluble sugars, proline, malondialdehyde (MDA), Na + and Cl - significantly increased with increasing salinity level. Based on the PCA analysis, Akbari 2 with the lowest reduction in percentage of stem elongation (26%), fresh weight (37%) and starch content (24%) showed the highest performance under severe salt stress (120 mM). Moreover, the highest leaf number, proline, chlorophyll index and K + content, as well as the lowest percentage of MDA, Na + and Cl - , belonged to Akbari 2 under highest salinity level. The selected genotype can be mass propagated from one tolerant single plant of Akbari 2 via in vitro propagation.

Networks of Physiological Adjustments and Defenses, and Their Synergy With Sodium (Na+) Homeostasis Explain the Hidden Variation for Salinity Tolerance Across the Cultivated Gossypium hirsutum Germplasm.

The abilities to mobilize and/or sequester excess ions within and outside the plant cell are important components of salt-tolerance mechanisms. Mobilization and sequestration of Na+ involves three transport systems facilitated by the plasma membrane H+/Na+ antiporter (SOS1), vacuolar H+/Na+ antiporter (NHX1), and Na+/K+ transporter in vascular tissues (HKT1). Many of these mechanisms are conserved across the plant kingdom. While Gossypium hirsutum (upland cotton) is significantly more salt-tolerant relative to other crops, the critical factors contributing to the phenotypic variation hidden across the germplasm have not been fully unraveled. In this study, the spatio-temporal patterns of Na+ accumulation along with other physiological and biochemical interactions were investigated at different severities of salinity across a meaningful genetic diversity panel across cultivated upland Gossypium. The aim was to define the importance of holistic or integrated effects relative to the direct effects of Na+ homeostasis mechanisms mediated by GhHKT1, GhSOS1, and GhNHX1. Multi-dimensional physio-morphometric attributes were investigated in a systems-level context using univariate and multivariate statistics, randomForest, and path analysis. Results showed that mobilized or sequestered Na+ contributes significantly to the baseline tolerance mechanisms. However, the observed variance in overall tolerance potential across a meaningful diversity panel were more significantly attributed to antioxidant capacity, maintenance of stomatal conductance, chlorophyll content, and divalent cation (Mg2+) contents other than Ca2+ through a complex interaction with Na+ homeostasis. The multi-tier macro-physiological, biochemical and molecular data generated in this study, and the networks of interactions uncovered strongly suggest that a complex physiological and biochemical synergy beyond the first-line-of defense (Na+ sequestration and mobilization) accounts for the total phenotypic variance across the primary germplasm of Gossypium hirsutum. These findings are consistent with the recently proposed Omnigenic Theory for quantitative traits and should contribute to a modern look at phenotypic selection for salt tolerance in cotton breeding.

Response to salt stress imposed on cultivars of three turfgrass species: Poa pratensis, Lolium perenne, and Puccinellia distans

AbstractCool‐season turfgrasses can be subjected to salt stress through a variety of sources, and selection for salt tolerance is an increasingly high priority. Two of the main turfgrass species in temperate regions are perennial ryegrass (Lolium perenne L.) (PRG) and Kentucky bluegrass (Poa pratensis L.) (KBG), and greenhouse evaluations have occurred to rank and characterize salt tolerance in each species. However, salt tolerance in a field setting in a semiarid climate has not been tested, and the genetic mechanisms by which each species specifically responds to salt stress is still unclear. In this study, we evaluated salt tolerance of 10 PRG and 12 KBG entries in a field setting and compare their salt tolerances to two alkaligrass cultivars. Using electrolyte leakage (EL) and turf green cover, tolerant and susceptible cultivars and accessions were identified from both species. Transcriptome‐level gene expression analysis was applied on a subset of the entries, and 62 differentially expressed transcripts were shared among the three species with a preponderance of transcripts involving carbohydrate metabolism, oxidation‐reduction processes, and ion transport within the cell. Upon further gene enrichment analysis of KBG, more transcripts in those three categories were found. The differentially expressed transcripts (DETs) represent mechanisms by which PRG and KBG respond to salt stress, as well as targets for selection for salt tolerance.

Physiological and Biochemical Responses to Salt Stress of Alfalfa Populations Selected for Salinity Tolerance and Grown in Symbiosis with Salt-Tolerant Rhizobium

Alfalfa and its rhizobial symbiont are sensitive to salinity. We compared the physiological responses of alfalfa populations inoculated with a salt-tolerant rhizobium strain, exposed to five NaCl concentrations (0, 20, 40, 80, or 160 mM NaCl). Two initial cultivars, Halo (H-TS0) and Bridgeview (B-TS0), and two populations obtained after three cycles of recurrent selection for salt tolerance (H-TS3 and B-TS3) were compared. Biomass, relative water content, carbohydrates, and amino acids concentrations in leaves and nodules were measured. The higher yield of TS3-populations than initial cultivars under salt stress showed the effectiveness of our selection method to improve salinity tolerance. Higher relative root water content in TS3 populations suggests that root osmotic adjustment is one of the mechanisms of salt tolerance. Higher concentrations of sucrose, pinitol, and amino acid in leaves and nodules under salt stress contributed to the osmotic adjustment in alfalfa. Cultivars differed in their response to recurrent selection: under a 160 mM NaCl-stress, aromatic amino acids and branched-chain amino acids (BCAAs) increased in nodules of B-ST3 as compared with B-TS0, while these accumulations were not observed in H-TS3. BCAAs are known to control bacteroid development and their accumulation under severe stress could have contributed to the high nodulation of B-TS3.

Physiological and biochemical response of Phoenix dactylifera L. Hayani cv. embryogenic callus and somatic embryos to salt stress under in vitro conditions

Salinity stress as a major abiotic stress has influenced more than 6% of the world land which isincreasing daily due to climate changes. The effect of salinity on callus regeneration and organogenesis of datepalm was tested under in vitro conditions. This study was conducted to investigate the effect of salt stress oncallus proliferation, somatic embryo formation of ‘Hayani’ date palm in vitro. The embryogenic callus wassubjected to MS medium with BA at 0.05 mg/l and NAA at 0.1 mg/l supplied with different sodium chloride(NaCl) concentrations (0, 500, 1000, 1500 and 2000 ppm) for 2 subcultures. Salinity affects severalphysiological and biochemical processes. The investigated parameters include embryogenic callus growth,differentiation to form somatic embryos, fresh weight of both callus and embryos, biochemical analysis such astotal carbohydrates, proline, protein content and minerals in embryogenic callus and somatic embryos. Lowlevels of abiotic stress factors can induce favorable responses in the growth and differentiation. However, highlevels are detrimental resulting in reduced growth and some cell death. The callus fresh weight and the numberof embryos were enhanced by adding 500 and 1000 ppm NaCl to the proliferation medium; higher saltconcentrations affected the callus regeneration negatively, where at 2000 ppm NaCl the less somatic embryoswere formed. High concentrations of NaCl (1500 and 2000 ppm) decreased total soluble carbohydrates in bothembryogenic callus and somatic embryos, proline content increased gradually as the external concentration ofNaCl increased and the protein content decreased in both embryogenic callus and somatic embryos with theincrease of NaCl concentration in culture media to 2000 ppm. Salinity inhibits water uptake and increases theconcentration of toxic ions such as Na+and reduced the K+ content. Tissue culture with the use of this techniquewould allow selection for salt tolerance in the date palm. In fact, somatic embryos subjected to 500 and 1000ppm NaCl concentrations were successfully regenerated into plantlets.

Identification of new loci for salt tolerance in soybean by high-resolution genome-wide association mapping

BackgroundSalinity is an abiotic stress that negatively affects soybean [Glycine max (L.) Merr.] seed yield. Although a major gene for salt tolerance was identified and consistently mapped to chromosome (Chr.) 3 by linkage mapping studies, it does not fully explain genetic variability for tolerance in soybean germplasm. In this study, a genome-wide association study (GWAS) was performed to map genomic regions for salt tolerance in a diverse panel of 305 soybean accessions using a single nucleotide polymorphism (SNP) dataset derived from the SoySNP50K iSelect BeadChip. A second GWAS was also conducted in a subset of 234 accessions using another 3.7 M SNP dataset derived from a whole-genome resequencing (WGRS) study. In addition, three gene-based markers (GBM) of the known gene, Glyma03g32900, on Chr. 3 were also integrated into the two datasets. Salt tolerance among soybean lines was evaluated by leaf scorch score (LSS), chlorophyll content ratio (CCR), leaf sodium content (LSC), and leaf chloride content (LCC).ResultsFor both association studies, a major locus for salt tolerance on Chr. 3 was confirmed by a number of significant SNPs, of which three gene-based SNP markers, Salt-20, Salt14056 and Salt11655, had the highest association with all four traits studied. Also, additional genomic regions on Chrs. 1, 8, and 18 were found to be associated with various traits measured in the second GWAS using the WGRS-derived SNP dataset.ConclusionsA region identified on Chr. 8 was identified to be associated with all four traits and predicted as a new minor locus for salt tolerance in soybean. The candidate genes harbored in this minor locus may help reveal the molecular mechanism involved in salt tolerance and to improve tolerance in soybean cultivars. The significant SNPs will be useful for marker-assisted selection for salt tolerance in soybean breeding programs.

Biochemical, physiological and phenological genetic analysis in common bean (Phaseolus vulgaris L.) under salt stress

Salinity is one of the most important abiotic stresses affecting agricultural productivity. The present study investigated combining abilities, heterosis and heritability estimates of common bean under salinity conditions for biochemical, physiological and phenological traits using a half-diallel cross. The salinity stress treatments were applied during all the vegetative cycle. Genetic analysis revealed highly significant genotypic variations between the four parents and their six hybrids, indicating a genetic variability and possibility of genetic improvement using such genetic material of common bean for salinity tolerance. Both general (GCA) and specific (SCA) combining abilities were highly significant for all the studied traits under all conditions, revealing the important role of both additive and dominant gene effects in the inheritance of these traits. The ratio GCA/SCA indicated preponderance of the additive effects for all the studied characters. The parental genotypes Améliore Roza and Coco nain proved to be the best combiners for salinity tolerance; on the other hand the crosses namely Amina × Améliore Roza; MGT × Améliore Roza and Coco nain × Amina recorded significant heterosis percentage relative to mid-parent (MP) and better parent (BP) for almost all the traits, the same crosses recorded significantly positive SCA effects. Diallel analysis revealed high heritability in broad-sense for salinity tolerance, while moderate to high narrow-sense heritability suggests a large breeding population and possible selection for salt tolerance. The results of this study confirmed that salinity tolerance is expressed by a different set of genes that could be pyramided using different genotypes to enhance salinity tolerance.

Genetic Selection for Salt Tolerance in Some Egyptian Wheat Genotypes (Triticum aestivum L.) via Tissue Culture

Five wheat genotypes and their hybrids under four salinity (sea water) levels were considered for tissue culture and randomly amplified polymorphic DNA (RAPD). The genotypes and the hybrids differed in their ability to callus induction, callus fresh weight and regeneration. Among the genotypes, Sakha 93 (P1) followed by Line WB19 (P5) was the most tolerant genotypes for salinity and gave the highest growth rate (46.6%) and (46.3%), respectively while Giza 168 (P3) was the most sensitive one to salinity with lowest growth rate (26.6%). All hybrids scored higher averages in callus growth rate than their parents. P1 × P5 followed by P1 × P2 and P1 × P4 produced the highest growth rate 75.6, 59.1 and 52.6% over hybrids while P3 × P4 had the lowest rate 28.5%, respectively. The hybrid P1 × P5 gave the highest percentage of plant regeneration over all genotypes and their hybrids followed P2 × P5, P1 × P2 and P4 × P5. The highest number of RAPD specific markers scored for hybrid P1 × P5 was (6 markers), while Line WB19 (P5), P1 × P2 and P2 × P5 were (4 markers). These markers can be verified as the RAPD markers associated with salt tolerance.Plant Tissue Cult. & Biotech. 26(1): 25-36, 2016 (June)

Development of in vitro propagation system for Atriplex halimus L.

Explants excised from adult shrubs were surface sterilized and cultured on Murashige and Skoog (MS) basal medium in the presence of plant growth regulators (PGRs) at different concentrations. A high multiplication rate of 7.2-fold was achieved every four weeks on MS medium supplemented with 4.44 μM BA, 0.49 μM IBA and 0.58 μM GA3. Rooting was achieved with 73% efficiency within 2-4 weeks on agar-gelled MS basal medium free of PGRs. Rooted plantlets were gradually acclimatized to field conditions over 5-6 weeks with 65% efficiency. For in vitro selection for salt tolerance, MS medium was supplemented with increasing concentrations of NaCl ranging between 25 and 1000 mM. This study has demonstrated that in vitro shoots could tolerate up to 600 mM NaCl with optimal growth at 200 mM, while higher concentrations of NaCl affected growth negatively. Growth and shoot number decreased with increasing NaCl concentration with all plantlets died at 1000 mM NaCl.

Genetic Analysis of F<sub>4</sub> Rice Lines for Salt Tolerance at the Reproductive Stage

A total of 29 lines of F4 population of rice along with their parents Binadhan-5 (high yielding and salt susceptible) and Harkuch (salt tolerant landrace) were evaluated for salt tolerance at the reproductive stage with EC 6 dS/m following IRRI standard protocol. High heritability coupled with high genetic advance was observed in plant height in salinized and non-salinized conditions. High heritability along with high genetic advance was also found in number of filled grains/plant in saline condition. These characters were under additive gene control and selection for salt tolerance might be effective. Number of filled grains/plant showed significant positive correlation with grain yield/plant. Path analysis revealed that number of filled grains/plant had positive and maximum direct effect on grain yield/plant. Therefore, number of filled grains/plant should be given the importance in selection of rice lines under saline condition.DOI: http://dx.doi.org/10.3329/pa.v21i1-2.16746 Progress. Agric. 21(1 & 2): 31 - 38, 2010

Influence of intracellular Na+, K+ and Cl- on the salt tolerance in suspension cell cultures of Medicago media

In the process of selection for salt tolerance, it is important to understand the physiological basis of ion management executed by the cells through the exclusion, accumulation or maintenance of ratios of specific ions. Intracellular accumulation of Na + , K + and Cl- ions in the cells in vitro was studied as a factor in salt tolerance in suspension cultures of Medicago media cv. Rambler. Cells selected for NaCl tolerance (R151-S) and the non-selected R151 (normal) cells were grown in MS medium containing 0, 100, 250, 400 and 550 mM NaCl, Na + , Cl - or K + for 5 weeks and examined for relative growth rate per week (RGR/week) and intracellular concentration of Na + , Cl - and K + ions. R151-S cells were found to be significantly more tolerant to the elevated Na + and Cl- levels than R151. When the effects of Na + and Cl - ions were compared, R151-S appeared to be more tolerant of higher concentrations of Cl - as compared to the equimolar concentrations of Na + . As the concentration of NaCl in the medium increased, the intracellular concentrations of Na + increased, though not at a proportional rate. Also, when the external Cl- concentration increased, there was no significant change in the intracellular accumulation of Na + . On the contrary, intracellular Na + decreased when the external K + was increased. In the cells adapted to high concentration of NaCl, the concentration of intracellular K + was lower than the non-adapted cells. The adequate intracellular K + concentration for optimum growth in M. media suspension cultures was found to be 3000 µM/g dry weight. Excess or deficiency of intracellular K + caused severe reduction in the growth rates in all cell lines. Key words : Salt tolerance, Medicago media, suspension cell culture, intracellular ions, organic relative growth rate.

Towards in vitro selection studies for salinity tolerance in Canino apricot cultivar. Effect of gamma irradiation on in vitro mutation and selection for salt-tolerance

In vitro mutation method was used to obtain salt-tolerant clone in apricot. Small propagules of Canino apricot cultivar were irradiated with gamma ray at doses of 0, 10, 25, 35, 50, 75 and 100 Gy. After 30 days from treatment, both the radio sensitivity and post-irradiation recovery were assessed as the number of proliferated shoots per explants, fresh weight of cultures, shoot length and productivity of irradiated explants. A sudden and sharp decrease in the survival percentage occurred with the dose 75 Gy, while the highest dose (100 Gy) was lethal for all propagules. A marked decline in the number of regenerated shoots per explant and fresh weight of produced cultures was associated with an increase of irradiation doses. Doses in the range of 10-75 Gy, which preserved high survival percentage of irradiated explants, seemed to be more suitable for in vitro mutation in Canino apricot cultivar. Irradiated shoots were exposed to different concentrations of NaCl which were added to the multiplication medium at the rates of 25, 50, 75, 100, 125 mM and after 30 days, vigorous shoots were selected from salinity treatments. In conclusion, apricot tissues exposed to different doses of gamma irradiation in the range of 10-75 Gy, followed by culturing the plantlets produced in a medium containing additional salts (ranging from 25 to 125 mM) can be considered a good method to identify the most tolerant mutants to salts in apricot cultivars.

An in vitro radiation induced mutagenesis-selection system for salinity tolerance in sugarcane

In vitro radiation induced mutagenesis-selection was employed for salt tolerance in popular Indian sugarcane cv. Co 86032. Radiosensitivity characterized in terms of growth rate and cell viability indicated 20 Gy as LD50 for embryogenic sugarcane callus cultures. Response of embryogenic calli exposed to different NaCl concentrations (85.6, 128.3, 171.1, 213.9 or 256.7 mM) indicated significant progressive decrease in cell viability and increase in membrane damage rate with increasing salt concentration. Based on these results, 20 Gy irradiated calli were stressed with 85.6 or 171.1 mM NaCl for selection for salt tolerance. Both irradiated or non-irradiated calli exhibited reduced growth rate compared to their respective controls, however, the extent of growth rate reduction was more in un-irradiated stressed calli. Further, in order to study the effect of auxin on salt selection, the calli were cultured on NaCl selection medium supplemented with or without auxin (2, 4-D). The growth rate was higher when NaCl media was supplemented with the auxin than that of without auxin. The calli exposed to 171.1 mM NaCl accumulated more proline than the control and 85.6 mM NaCl stressed irradiated or nonirradiated calli. Proline accumulation in the calli exposed to 85.6 mM NaCl without 2, 4-D was significantly higher than that of the calli stressed at the same salt concentration with 2, 4-D. The irradiated calli stressed with 85.6 mM NaCl medium with or without 2, 4-D accumulated more proline than the nonirradiated calli exposed to the respective salt treatments. Thus, the results suggest in vitro mutagenesis-selection as a powerful tool for enhanced tolerance to abiotic stresses, which may improve the competitiveness of the popular sugarcane cultivars and their commercial cultivation in saline areas.

Mapping of QTLs Controlling Na+, K+ and CI− Ion Concentrations in Salt Tolerant Indica Rice Variety CSR27

Soil salinity and sodicity are major constraints to rice production in about twenty per cent of the irrigated crop land. Inbuilt genetic tolerance to salinity is the most economical and environmentally sustainable way to solve this problem. A mapping population of 200 F2 plants and their corresponding F3 families, derived from a cross between a salt tolerant indica rice variety CSR27 and a salt sensitive variety MI48 were used to map OTLs for salt tolerance. Seventeen different parameters, including seedling salt injury score, Na+, K+, CI− concentrations and Na+/K+ ratio in leaf and stem tissues at vegetative and reproductive stages were mapped. A framework linkage map was constructed using 79 SSR and EST markers distributed over the twelve rice chromosomes at an average interval of 20.7cM and total map distance of 1634.5 cM. Twenty five major OTLs, each explaining more than ten per cent of the trait phenotypic variance, were mapped on chromosomes 1, 2, 3 and 8. These included one OTL for seedling salt injury score, nine for Na+ concentration, three for K+ concentration and four for Cl− concentration in leaf and stem tissues at vegetative and reproductive stages. The Na+/K+ ratio, an important ion balancing parameter for the salt tolerance, was controlled by eight OTLs explaining phenotypic variance in the range of 42.88–52.63%. Four OTL intervals were robust with major effect and having OTLs for multiple salt tolerance parameters that might be governed by common or tightly linked genes. One major OTL for multiple salt tolerance parameters on chromosome 8 and three major OTLs for CI− ion concentration are novel for this study. The OTLs identified here will serve as a base for fine mapping, gene tagging and marker assisted selection for salt tolerance in rice.