Development Of Salt-tolerant Cultivars Research Articles

A Review on Understanding the Effects and Mechanisms of Salinity Tolerance in Rice (Oryza sativa L.)

Salinity, along with drought, is one of the key abiotic stressors that has posed a danger to the advancement and evolution of cereal crops like rice and wheat. Water shortage and a lack of irrigation water availability are the main causes of salty soil formation. Rice is salt sensitive and glycophyte, wheat is moderately salt tolerant. Wild tolerant cultivars like Oryza coarctata and Oryza alta are more tolerant than traditional cultivars such as Pokkali and Nona Bokra in rice. Salt stress affects crop plants’ processes like ionic imbalance, osmotic and oxidative stress. Na+ should be low in the shoots of the plant which is restricted by various transporters in the cell membrane of the roots in soil. High K+ & Na+/K+ homeostasis should be maintained. Many RILs and NILs have been developed which acts as a donor for salinity tolerant genes. FL478 is a recombinant inbred line in which candidate genes are situated in the Saltol region of chromosome 1 region which is obtained by a cross between Pokkali x IR29. Increase in world’s population, rice output must be increased by at least 25% by 2030 and 50% by 2050.Salinity stress is a polygenic character which involves several genes works in harmony. For evolution of salinity tolerant cultivars, we need to access the physiological, biochemical genetic responses of the crop plant which helps in transfer of candidate genes from donor parents to elite high yielding salt sensitive cultivars. Especially in rice salt tolerant mechanisms like, Ion equilibrium regulation, Adjustment of osmotic potential, Reduction of ROS, Nutrient disequilibrium, and Regulation of PGRs. Conventional, MABC, MAS and direct gene transfer by transgenic methods. This review paper's main objective is to understand the mechanisms of the crop plants to salinity effects and development of salt tolerant cultivars by modern approaches which fulfill the food scarcity of staple food crops with increasing population.

Genetic networks underlying salinity tolerance in wheat uncovered with genome-wide analyses and selective sweeps.

A genetic framework underpinning salinity tolerance at reproductive stage was revealed by genome-wide SNP markers and major adaptability genes in synthetic-derived wheats, and trait-associated loci were used to predict phenotypes. Using wild relatives of crops to identify genes related to improved productivity and resilience to climate extremes is a prioritized area of crop genetic improvement. High salinity is a widespread crop production constraint, and development of salt-tolerant cultivars is a sustainable solution. We evaluated a panel of 294 wheat accessions comprising synthetic-derived wheat lines (SYN-DERs) and modern bread wheat advanced lines under control and high salinity conditions at two locations. The GWAS analysis revealed a quantitative genetic framework of more than 200 loci with minor effect underlying salinity tolerance at reproductive stage. The significant trait-associated SNPs were used to predict phenotypes using a GBLUP model, and the prediction accuracy (r2) ranged between 0.57 and 0.74. The r2 values for flag leaf weight, days to flowering, biomass, and number of spikes per plant were all above 0.70, validating the phenotypic effects of the loci discovered in this study. Furthermore, the germplasm sets were compared to identify selection sweeps associated with salt tolerance loci in SYN-DERs. Six loci associated with salinity tolerance were found to be differentially selected in the SYN-DERs (12.4Mb on chromosome (chr)1B, 7.1Mb on chr2A, 11.2Mb on chr2D, 200Mb on chr3D, 600Mb on chr6B, and 700.9Mb on chr7B). A total of 228 reported markers and genes, including 17 well-characterized genes, were uncovered using GWAS and EigenGWAS. A linkage disequilibrium (LD) block on chr5A, including the Vrn-A1 gene at 575Mb and its homeologs on chr5D, were strongly associated with multiple yield-related traits and flowering time under salinity stress conditions. The diversity panel was screened with more than 68 kompetitive allele-specific PCR (KASP) markers of functional genes in wheat, and the pleiotropic effects of superior alleles of Rht-1, TaGASR-A1, and TaCwi-A1 were revealed under salinity stress. To effectively utilize the extensive genetic information obtained from the GWAS analysis, a genetic interaction network was constructed to reveal correlations among the investigated traits. The genetic network data combined with GWAS, selective sweeps, and the functional gene survey provided a quantitative genetic framework for identifying differentially retained loci associated with salinity tolerance in wheat.

Identifying the genetic control of salinity tolerance in the bread wheat landrace Mocho de Espiga Branca.

Salinity tolerance in bread wheat is frequently reported to be associated with low leaf sodium (Na+) concentrations. However, the Portuguese landrace, Mocho de Espiga Branca, accumulates significantly higher leaf Na+ but has comparable salinity tolerance to commercial bread wheat cultivars. To determine the genetic loci associated with the salinity tolerance of this landrace, an F2 mapping population was developed by crossing Mocho de Espiga Branca with the Australian cultivar Gladius. The population was phenotyped for 19 salinity tolerance subtraits using both non-destructive and destructive techniques. Genotyping was performed using genotyping-by-sequencing (GBS). Genomic regions associated with salinity tolerance were detected on chromosomes 1A, 1D, 4B and 5A for the subtraits of relative and absolute growth rate (RGR, AGR respectively), and on chromosome 2A, 2B, 4D and 5D for Na+, potassium (K+) and chloride (Cl-) accumulation. Candidate genes that encode proteins associated with salinity tolerance were identified within the loci including Na+/H+ antiporters, K+ channels, H+-ATPase, calcineurin B-like proteins (CBLs), CBL-interacting protein kinases (CIPKs), calcium dependent protein kinases (CDPKs) and calcium-transporting ATPase. This study provides a new insight into the genetic control of salinity tolerance in a Na+ accumulating bread wheat to assist with the future development of salt tolerant cultivars.

Physiological response of wheat seeds grown under NaCl and HgCl2 stress

<p class="abstract"><strong>Background:</strong> Plants are continuously exposed to various abiotic and biotic stresses like cold, high temperature, drought, salinity and exposure to heavy metals. However, it is also argued that the effect of these stresses on the germination of seeds represents the most critical aspect of plant survival. The aim of the study was to observe the differences in germination potential of seeds in the presence of salt and heavy metal stress.</p><p class="abstract"><strong>Methods:</strong> The seeds were germinated under the effect of NaCl (0, 25, 50, 75, 100mM) and HgCl<sub>2</sub> (0.001, 0.01, 0.1 and 1 ppm), Timson’s index was calculated as a growth identifier, average shoot length and RWC was calculated for surviving seedlings. </p><p class="abstract"><strong>Results:</strong> Germination rate was observed to decrease with increasing concentrations of the NaCl and HgCl<sub>2</sub>. The maximum germination (100%) was recorded in NaCl (25 Mm,) treatment and the minimum percentage of germination was observed as 84% in HgCl<sub>2</sub> (1 mg/ml). The maximum shoot length was observed in HgCl<sub>2</sub> (0.001 mg/ml) with average shot length of 16.50 cm and 13.92 cm of NaCl (25 mM) respectively. It was also observed that the seedlings having high RWC were more resistant against salinity stress.</p><p><strong>Conclusions:</strong> The use of both genetic modification as well as traditional breeding approaches are to be needed so as to unravel the mechanisms to salinity tolerance and at the same time to involve in the development of salt-tolerant cultivars that are better to adapt with any increase in soil salinity constraints. </p>

A Short Review on the Development of Salt Tolerant Cultivars in Rice

Rice is staple food for half of the world. With a population of almost 9.6 billion by the year 2050, there is a dire need of developing techniques to improve the crop plants, not only in terms of better yield but also to withstand harsh environmental conditions and stresses like drought, temperature, flood and salinity. Salinity is second to drought stress and hence it is very important to develop crops tolerant to salinity stress. This review discusses the mechanisms of salt tolerance and the recent developments in understanding the complex tolerance phenomena. One way to address the salinity issue is to develop tolerant rice varieties using conventional and modern breeding techniques for which screening the rice germplasm for the varieties with desired traits is critical. Conventional methods to develop tolerant rice varieties are discussed along with modern biotechnology techniques are also discussed. Quantitative Trait Loci (QTL) and Marker Assisted Selection (MAS) are promising techniques. In addition to these modern techniques, some recent developments in the fields of transgenic plants, haploid breeding and Somaclonal variations have also been discussed. The limited knowledge about molecular and genetic mechanisms to tolerate abiotic stresses, however is a barrier to efficiently develop tolerant cultivars. A combination of conventional and modern biotechnology techniques could possibly open up the new ways.

Response of Rice under Salinity Stress: A Review Update

Salinity has been a key abiotic constraint devastating crop production worldwide. Attempts in understanding salt tolerance mechanisms has revealed several key enzymes and altered biochemical pathways inferring resistance to crop plants against salt stress. The past decades have witnessed extensive research in development of salt tolerant cultivars via conventional means, improvised by modern era molecular tools and techniques. Rice (Oryza sativa L) is the staple food crop across several countries worldwide. Being a glycophyte by nature, its growth is severely imparted in presence of excess salt. Rice is susceptible to salinity specifically at the early vegetative and later reproductive stages and the response of the crop to excessive salt toxicity at biochemical and molecular level as well as physiological level is well studied and documented. An understanding of the specific response of rice to ion accumulation at the toxic level can aid in identifying the key factors responsible for retarded growth and limited production of rice with the future scope of mitigating the same. The present review summarizes the differential responses of rice, in particular, to salt toxicity enumerating the detailed morphological, physiological, biochemical and molecular changes occurring in the plant. An attempt to explain salinity tolerance and its future scope and implications in screening for salt tolerance has also been elucidated in the present study.

Overcoming Salinity Barriers to Crop Production Using Traditional Methods

Salinity is a major problem in arid and semi-arid regions, where irrigation is essential for crop production. Major sources of salinity in these regions are salt-rich irrigation water and improper irrigation management. The effects of salinity on crops include inhibition of growth and production, and ultimately, death. There are two main approaches to alleviating the adverse effects of salinity on agricultural crops: (i) development of salt-tolerant cultivars by screening, conventional breeding or genetic engineering, and (ii) the traditional approach dealing with treatments and management of the soil, plants, irrigation water, and plant environment. The success of the first approach is limited under commercial growing conditions, because salt-tolerance traits in plants are complex. The present paper reviews, analyzes, and discusses the following traditional approaches: (i) improving the plant environment, (ii) exploiting interactions between plant roots and bacteria and fungi, and (iii) treating the plant directly. With respect to improving the plant environment, we review the possibilities of decreasing salt content and concentration and improving the nutrient composition and concentration in the root zone, and controlling the plant's aerial environment. The interactions between salt-tolerant bacteria or mycorrhizal fungi and root systems, and their effects on salt-tolerance, are demonstrated and discussed. Discussed treatments aimed at alleviating salinity hazard by treating the plant directly include priming of seeds and young seedlings, using proper seed size, grafting onto tolerant rootstocks, applying non-enzymatic antioxidants, plant growth regulators or compatible solutes, and foliar application of nutrients. It can be concluded from the present review that the traditional approaches provide promising means for alleviating the adverse effects of salinity on agricultural crops.

Heritability and gene effects for salinity tolerance in cucumber (Cucumis sativus L.) estimated by generation mean analysis

Cucumber production is greatly reduced by high salinity. Our recent identification of cucumber genotypes with relative tolerance to salinity provides the potential for development of salt tolerant cultivars if the mode of inheritance for this trait is known. In this study, two cucumber parental lines, 11411S (P1, salt tolerant), 11439S (P2, salt sensitive) were crossed to study gene actions responsible for inheritance of salinity tolerance (TOL), relative leaf number (RLN14), area of second largest fully expanded leaf (LA) and vine length (VL) under saline growing conditions. The six populations denoted as P1, P2, F1, B1 (F1×P1), B2 (F1×P2) and F2 (F1×F1) were subjected to 80mM NaCl stress in greenhouse pot experiments and data subjected to generation mean analysis. Epistatic gene effects on all the traits were not detected by A, B, C scaling test while joint scaling test showed the presence of non-allelic interactions for all the traits. TOL and RLN14 were predominantly under additive gene effect while inheritance LA was largely influenced by dominance and additive gene effects. Dominant gene effect significantly controlled the inheritance of VL. The narrow sense heritability for TOL, RLN14, VL and LA was 0.57, 0.26, 0.74 and 0.66, respectively. VL and LA registered significant positive heterobeltiosis. The presence of dominance gene effect and low heritability of photosynthesis enhancing trait, RLN14 makes it impractical to improve salinity through simple selection or pedigree breeding. Simultaneous selection for RLN14 and TOL in segregating population at advanced filial generations in this cross may be useful in developing cucumber varieties with increased salinity tolerance. Alternatively, intermating of superior segregants may be explored to concentrate the favorable genes for salt tolerance.

Construction of Two Suppression Subtractive Hybridization Libraries and Identification of Salt-Induced Genes in Soybean

Soybean is planted worldwide and its productivity is significantly hampered by salinity. Development of salt tolerant cultivars is necessary for promoting soybean production. Despite wealth of information generated on salt tolerance mechanism, its basics still remain elusive. A continued effort is needed to understand the salt tolerance mechanism in soybean using suitable molecular tools. To better understand the molecular basis of the responses of soybean to salt stress and to get an enrichment of critical salt stress responsive genes in soybean, suppression subtractive hybridization libraries (SSH) are constructed for the root tissue of two cultivated soybean genotypes, one was tolerant and the other was sensitive to salt stress. To compare the responses of plants in salt treatment and non-treatment, SSH1 was constructed for the salt-tolerant cultivar Wenfeng 7 and SSH2 was constructed for the salt-sensitive cultivar Union. From the two SSH cDNA libraries, a total of 379 high quality ESTs were obtained. These ESTs were then annotated by performing sequence similarity searches against the NCBI nr (National Center for Biotechnology Information protein non-redundant) database using the BLASTX program. Sixty-three genes from SSH1 and 49 genes from SSH2 could be assigned putative function. On the other hand, 25 ESTs of SSH1 which may be not the salt tolerance-related genes were removed by comparing and analyzing the ESTs from the two SSH libraries, which increased the proportion of the genes related to salt tolerance in SSH1. These results suggested that the novel way could realize low background of SSH and high level enrichment of target cDNAs to some extent.

Gene Expression Profiling of Plants under Salt Stress

Soil salinity is among the leading environmental stresses affecting global agriculture, causing billions of dollars in crop damages every year. Regardless of the cause, ion toxicity, water deficit, or nutritional imbalance, high salinity in the root zone severely impedes normal plant growth and development, resulting in reduced crop productivity or crop failure. Development of salt-tolerant cultivars is an attractive and economical approach to solving this problem. Although several salt-tolerant plant genotypes have been developed through transgenic approaches, often they have failed or exhibited limited success under field saline conditions. This is due to several reasons, including the fact that plant growth and development under saline conditions in the field is often influenced by cumulative effects of multiple environmental stresses and genetic factors, which may not have been considered during the development of salt-tolerant transgenic plants. Adoption of inappropriate screening techniques or selection criteria may also lead to selection of genotypes that may not be stress tolerant in a real sense. In most plant species, salt tolerance is a genetically complex trait, often modulated by multiple biosynthetic and signaling pathways. Cross-talks among various stress-controlling pathways have been observed under salt stress, many of which are regulated by transcription factors. Thus, a comprehensive knowledge of the up- and downregulating genes under salt-stress is necessary, which would provide a better understanding of the interactions among pathways in response to salt stress. Attaining such knowledge is a good step toward successful development of salt-tolerant crop cultivars. To this end, DNA microarray technology has been employed to study expression profiles in different plant species and at varying developmental stages in response to salt stress. As a result, large-scale gene expression profiles under salt stress are now available for many plant species, including Arabidopsis, rice, barley, and ice plant. Examinations of such gene expression profiles will help understand the complex regulatory pathways affecting plant salt tolerance and potentially functional characterization of unknown genes, which may be good candidates for developing plants with field salt tolerance. In this article, we review and discuss the current knowledge of plant salt tolerance and the extent to which expression profiling has helped, or will help, a better understanding of the genetic basis of plant salt tolerance. We also discuss possible approaches to improving plant salt tolerance using various tools of biotechnology.

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

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

Isolation, identification and expression analysis of salt-induced genes in Suaeda maritima, a natural halophyte, using PCR-based suppression subtractive hybridization.

BackgroundDespite wealth of information generated on salt tolerance mechanism, its basics still remain elusive. Thus, there is a need of continued effort to understand the salt tolerance mechanism using suitable biotechnological techniques and test plants (species) to enable development of salt tolerant cultivars of interest. Therefore, the present study was undertaken to generate information on salt stress responsive genes in a natural halophyte, Suaeda maritima, using PCR-based suppression subtractive hybridization (PCR-SSH) technique.ResultsForward and reverse SSH cDNA libraries were constructed after exposing the young plants to 425 mM NaCl for 24 h. From the forward SSH cDNA library, 429 high quality ESTs were obtained. BLASTX search and TIGR assembler programme revealed overexpression of 167 unigenes comprising 89 singletons and 78 contigs with ESTs redundancy of 81.8%. Among the unigenes, 32.5% were found to be of special interest, indicating novel function of these genes with regard to salt tolerance. Literature search for the known unigenes revealed that only 17 of them were salt-inducible. A comparative analysis of the existing SSH cDNA libraries for NaCl stress in plants showed that only a few overexpressing unigenes were common in them. Moreover, the present study also showed increased expression of phosphoethanolamine N-methyltransferase gene, indicating the possible accumulation of a much studied osmoticum, glycinebetaine, in halophyte under salt stress. Functional categorization of the proteins as per the Munich database in general revealed that salt tolerance could be largely determined by the proteins involved in transcription, signal transduction, protein activity regulation and cell differentiation and organogenesis.ConclusionThe study provided a clear indication of possible vital role of glycinebetaine in the salt tolerance process in S. maritima. However, the salt-induced expression of a large number of genes involved in a wide range of cellular functions was indicative of highly complex nature of the process as such. Most of the salt inducible genes, nonetheless, appeared to be species-specific. In light of the observations made, it is reasonable to emphasize that a comparative analysis of ESTs from SSH cDNA libraries generated systematically for a few halophytes with varying salt exposure time may clearly identify the key salt tolerance determinant genes to a minimum number, highly desirable for any genetic manipulation adventure.

Molecular Analysis of Soybean Cultivars Differing in Response to Salinity Stress

Forty-seven soybean cultivars differing in response to sodium chloride were analyzed with 37 SSR markers for genetic diversity estimation. Thirty-two (86.5 %) out of 37 markers were polymorphic. The number of alleles ranged from 2–7 for different polymorphic markers, whereas the polymorphic information content (PIC) ranged from 0.061 to 0.793 with an average of 0.549. Average genetic similarity coefficient was 0.281. UPGMA based cluster analysis placed cultivars into five main clusters. In addition, the Mantel’s test for cophenetic correlation with r = 0.878 indicated good fit of the cultivars to a group in the cluster analysis. No clear pattern was observed between major clusters and place of release or targeted area of the cultivars. Genetically diverse cultivars were identified that could be potentially important sources of the germplasm for the development of salt tolerant cultivars in soybean.

The challenge of the food sufficiency through salt tolerant crops

This work is focused on deserts, as extreme environments, because the year 2006 has been declared Year of Deserts and Desertification by the United Nations (IYDD Program 2006). The loss of vital resources such as fresh water and soil, and the depletion of biodiversity are emerging hazards, able to transform beneficial situations into extreme environments. Desertification is generated by land degradation: the loss of biological productivity is caused by nature or by human-induced factors and climate change. Nearby the desertification process there is the increasing process of salinisation of soil and water, induced by irrigation itself, or by salt water ingress derived by tsunamis or hurricanes. Increased research on the development of salt-tolerant cultivars could, with appropriate management, result in the broader use of saline soils. Although careful application is necessary, the combination of sand, seawater, sun and salt-tolerant plants presents a valuable opportunity for many developing countries. Cooperation among plant ecologists, plant physiologists, plant breeders, soil scientists, and agricultural engineers could accelerate the development of economic salt tolerant crops. If saline water is available, the introduction of salt tolerant plants in poor regions can improve food or fuel supplies, increase employment, help stem desertification, and contribute to soil reclamation.

Assessment of tolerance to salt stress in Kenyan tomato germplasm

Tomato is an important vegetable crop in Kenya and the development of salt tolerant cultivars would enhance its productivity in the vast marginal areas of the country. This study was aimed at determining the magnitude of genotypic variability for salt tolerance in the Kenyan tomato germplasm. Pot experiments with 22 landraces and 9 market cultivars were laid out as a two and four replicate split-plot design in glasshouse in Experiments 1 and 2, respectively. Salt treatments in Experiment 1 were 0 and 5 g NaCl kg-1 resulting into 0.5 and 9.1 dS m-1 of the soil saturation extracts, respectively. In Experiment 2 the treatments were 0, 4, and 8 g NaCl kg-1 soil corresponding to 0.5, 7.4, and 14.2 dS m-1, respectively. Data were recorded on agronomic and biochemical parameters. The germplasm showed large variation for salt tolerance. Fruit and seed production at soil salinity of 14.2 dS m-1 demonstrated that these tomatoes are fairly tolerant of NaCl. Osmotic adjustment was achieved by higher fruit electrical conductivity, brix and total titratable acidity. Low and high contents of K+, Ca2+ and Mg2+ within tomato tissues and soil, respectively, under salt treatment, confirmed competition and antagonism involving Na+ and these cations. Low Na+ and Cl- contents in the fruit at 7.4 dS m-1 revealed their exclusion and ensured production of physiologically normal seeds and nutritionally healthy fruits. Two landraces ‘Chwerotonglo’ and ‘Nyanyandogo’ were identified as salt tolerant. Comparatively, the market cultivars showed superior fruit yields despite their susceptibility to salinity. Accordingly, tolerance of landraces in combination with superior yields of the market cultivars is suitable for tomato improvement for salt tolerance.

Salt tolerance in natural populations of Trifolium repens L.

SUMMARYThe salt tolerances of plants from natural populations of Trifolium repens L. (White Clover) growing in saline and non‐saline sites were compared by root growth tests at a range of NaCl concentrations. Plants from three salt‐marsh sites showed high or very high salt tolerance, with relatively vigorous root growth in 150–200 mM NaCl. Plants with two non‐saline inland sites showed little or no tolerance. A sea‐cliff population and plants of cv. Gwenda showed intermediate levels of tolerance at low salt concentrations. Halophytic maritime populations may‐provide material for the development of salt tolerant cultivars of T. repens, a crop plant in which most existing cultivars are thought to be salt‐sensitive.