Salt-tolerant Rice Cultivars Research Articles

Optimizing seedlings number and spacing to harness productivity potential of salt tolerant rice cultivars in salt affected soils

Optimizing seedlings number and spacing to harness productivity potential of salt tolerant rice cultivars in salt affected soils

Green remediation of saline–sodic Pb-factored soil by growing salt-tolerant rice cultivar along with soil applied inorganic amendments

In Pb-factored soils, soil application of appropriate inorganic amendment along with cultivation of salt-tolerant crop species/genotypes for Pb immobilization can be a good choice. Hence, in saline-sodic and non-saline/sodic Pb-factored soils, Pb immobilization was observed as influenced by exogeneously applied inorganic amendments. Salt-tolerant rice cultivar Shaheen basmati was grown in present study. The current pot study consists of two factors: three inorganic amendments (i.e., gypsum, rock phosphate and di-ammonium phosphate) each with their three increasing rates along with uncontaminated and contaminated controls, and two types of Pb-factored soils (non-saline/sodic and saline–sodic). At harvest maturity, crop was reaped and straw, paddy yields and height of plant were noted. The results showed that Pb induced decrease in rice growth and physiological attributes (i.e., transpiration rate, photosynthetic rate, stomatal conductance, chlorophyll a, b and carotenoids) were significantly (p ≤ 0.05) counteracted by exogeneously applied inorganic amendments. Among the tested amendments, the highest gypsum application rate of 9 me Ca 100 g−1 soil was proved the most effective to improve rice growth, yield, physiological functions, and to reduce Pb concentration in rice both in saline-sodic and non-saline/sodic Pb-factored soils.

Alleviation of Salt Stress in Upland Rice (Oryza sativa L. ssp. indica cv. Leum Pua) Using Arbuscular Mycorrhizal Fungi Inoculation.

Arbuscular mycorrhizal fungi (AMF) symbionts not only promote the growth of host plant but also alleviate abiotic stresses. This study aimed to investigate the putative role of AMF in salt stress regulation of upland pigmented rice cv. Leum Pua (LP) comparing with Pokkali salt tolerant (positive check). In general, LP is a variety of glutinous rice that contains anthocyanin pigment in the black pericarp, due to which it possesses high antioxidant activities compared to non-pigmented rice. Pot experiment was conducted to evaluate the impact of inoculated AMF, Glomus etunicatum (GE), Glomus geosporum (GG), and Glomus mosseae (GM) strains, in the LP plantlets subjected to 0 (control) or 150 mM NaCl (salt stress) for 2 weeks in comparison with Pokkali (a salt tolerant rice cultivar), which was maintained as a positive check. Root colonization percentage under NaCl conditions ranged from 23 to 30%. Na+ content in the flag leaf tissues was increased to 18–35 mg g–1 DW after exposure to 150 mM NaCl for 14 days in both inoculated and un-inoculated LP plants, whereas Na:K ratio was very low in cv. Pokkali. Interestingly, sucrose content in the flag leaf tissues of un-inoculated LP plants under salt stress was increased significantly by 50 folds over the control as an indicator of salt stress response, whereas it was unchanged in all AMF treatments. Fructose and free proline in GE inoculated plants under salt stress were accumulated over control by 5.75 and 13.59 folds, respectively, for osmotic adjustment of the cell, thereby maintaining the structure and functions of chlorophyll pigments, Fv/Fm, ΦPSII, and stomatal function. Shoot height, flag leaf length, number of panicles, panicle length, panicle weight, and 100-grain weight in GE inoculated plants of cv. LP under salt stress were maintained similar to cv. Pokkali. Interestingly, cyanidin-3-glucoside (C3G) and peonidin-3-glucoside (P3G) in the pericarp of cv. LP were regulated by GE inoculation under salt stress conditions. In summary, AMF-inoculation in rice crop is a successful alternative approach to reduce salt toxicity, maintain the yield attributes, and regulate anthocyanins enrichment in the pericarp of grains.

Tissue Tolerance Coupled With Ionic Discrimination Can Potentially Minimize the Energy Cost of Salinity Tolerance in Rice.

Salinity is one of the major constraints in rice production. To date, development of salt-tolerant rice cultivar is primarily focused on salt-exclusion strategies, which incur greater energy cost. The present study aimed to evaluate a balancing strategy of ionic discrimination vis-à-vis tissue tolerance, which could potentially minimize the energy cost of salt tolerance in rice. Four rice genotypes, viz., FL478, IR29, Kamini, and AC847, were grown hydroponically and subjected to salt stress equivalent to 12 dS m–1 at early vegetative stage. Different physiological observations (leaf chlorophyll content, chlorophyll fluorescence traits, and tissue Na+ and K+ content) and visual scoring suggested a superior Na+-partitioning strategy operating in FL478. A very low tissue Na+/K+ ratio in the leaves of FL478 after 7 days of stress hinted the existence of selective ion transport mechanism in this genotype. On the contrary, Kamini, an equally salt-tolerant genotype, was found to possess a higher leaf Na+/K+ ratio than does FL478 under similar stress condition. Salt-induced expression of different Na+ and K+ transporters indicated significant upregulation of SOS, HKT, NHX, and HAK groups of transporters in both leaves and roots of FL478, followed by Kamini. The expression of plasma membrane and vacuolar H+ pumps (OsAHA1, OsAHA7, and OsV-ATPase) were also upregulated in these two genotypes. On the other hand, IR29 and AC847 showed greater salt susceptibility owing to excess upward transport of Na+ and eventually died within a few days of stress imposition. But in the “leaf clip” assay, it was found that both IR29 and Kamini had high tissue-tolerance and chlorophyll-retention abilities. On the contrary, FL478, although having higher ionic-discrimination ability, showed the least degree of tissue tolerance as evident from the LC50 score (amount of Na+ required to reduce the initial chlorophyll content to half) of 336 mmol g–1 as against 459 and 424 mmol g–1 for IR29 and Kamini, respectively. Overall, the present study indicated that two components (ionic selectivity and tissue tolerance) of salt tolerance mechanism are distinct in rice. Unique genotypes like Kamini could effectively balance both of these strategies to achieve considerable salt tolerance, perhaps with lesser energy cost.

Improvement of salinity tolerance in rice by efficient management of potassium and zinc fertilizers

Appropriate nutrient management could increase crop productivity in saline areas by reducing the harmful effects of soil salinity. A field experiment was carried out at farmer’s field of Botiaghata, Khulna to investigate the mitigation of soil salinity by efficient management of potassium and zinc fertilizers in rice. BRRI dhan53, a salt-tolerant rice cultivar during aman season, was used as a test crop. The experiment was laid out in a randomized complete block design with three replications where sixteen treatment combinations were used in a factorial arrangement. Potassium and zinc nutrients were supplied from potassium sulphate and zinc sulphate, respectively and they were applied in two splits, first split during final land preparation and second split at maximum tillering stage. Recommended doses of N, P and S fertilizers were applied to all the experimental plots. Results revealed that plant height, panicle length, number of effective tillers and grains per panicle increased significantly due to application of K and Zn fertilizers. All the yield contributing parameters showed higher values in T15 (K200Zn200) treatment compared to other treatments. Grain and straw yields of BRRI dhan53 responded significantly to the different treatment combinations. The highest grain yield (4.46 t/ha) was obtained in T15 (K200Zn200) treatment and the highest straw yield (6.27 t/ha) was also obtained in the same treatment. Higher doses of potassium and zinc also increased nutrient uptake (N, P, S and Zn) by BRRI dhan53. The K+/Na+ ratio was also found higher in grain (0.319) and straw (0.301) in T15 treatment. Therefore, result of the experiment indicated that application of higher doses of K and Zn fertilizers could alleviate the adverse effects of salinity in rice production by increasing nutrient uptake and maintaining higher K+/Na+ ratio.
 Asian Australas. J. Biosci. Biotechnol. 2019, 4 (3), 154-161

Genomic and transcriptomic analysis reveal molecular basis of salinity tolerance in a novel strong salt-tolerant rice landrace Changmaogu

BackgroundSalt stress is an important factor that limits rice yield. We identified a novel, strongly salt tolerant rice landrace called Changmaogu (CMG) collected from a coastal beach of Zhanjiang, Guangdong Province, China. The salt tolerance of CMG was much better than that of the international recognized salt tolerant rice cultivar Pokkali in the germination and seedling stages.ResultsTo understand the molecular basis of salt tolerance in CMG, we performed BSA-seq for two extreme bulks derived from the cross between CMG and a cultivar sensitive to salt, Zhefu802. Transcriptomic sequencing was conducted for CMG at the germination and young seedling stages. Six candidate regions for salt tolerance were mapped on Chromosome 1 by BSA-seq using the extreme populations. Based on the polymorphisms identified between both parents, we detected 32 genes containing nonsynonymous coding single nucleotide polymorphisms (SNPs) and frameshift mutations in the open reading frame (ORF) regions. With transcriptomic sequencing, we detected a large number of differentially expressed genes (DEGs) at the germination and seedling stages under salt stress. KEGG analysis indicated two of 69 DEGs shared at the germination and seedling stages were significantly enriched in the pathway of carotenoid biosynthesis. Of the 169 overlapping DEGs among three sample points at the seedling stage, 13 and six DEGs were clustered into the pathways of ABA signal transduction and carotenoid biosynthesis, respectively. Of the 32 genes carrying sequence variation, only OsPP2C8 (Os01g0656200) was differentially expressed in the young seedling stage under salt stress and also showed sequence polymorphism in the ORFs between CMG and Zhefu802.ConclusionOsPP2C8 was identified as the target candidate gene for salinity tolerance in the seedling stage. This provides an important genetic resource for the breeding of novel salt tolerant rice cultivars.

Performance of salt-tolerant rice cultivars under different soil salinity levels in Central Vietnam

The objective of this study was to determine the effects of different soil salinity levels on the agronimic traits and yield of four newly introduced salt-tolerant rice cultivars in the Thua Thien Hue province, Central Vietnam. Three field experiments were conducted in 2018 summer-autumn crop season at three locations with different soil salinity levels of EC 4.1, 6.4 and 9.0 dS/m. Yield per plant and some agronomic traits including of plant height, panicle length and number of filled grains per panicle were measured. The cultivars of MNR3, OM5629 and OM2395 showed significantly higher yield per plant than that of the commonly used cultivar KD. As soil salinity increased from 4.1 to 6.4 dS/m, 6.4 to 9.0 dS/m, and 4.1 to 9.0 dS/m, yield per plant decreased 18.2, 16.0 and 31.3%, respectively. Therefore, it could be concluded that these cultivars were suitable for cultivation on saline soils in the summer-Vautumn crop season at soil with EC≤T6.4 dS/m in Central Vietnam.

Evaluation of the effectiveness of zinc oxide nano particles on growth and yield of rice (Oryza sativa L.)

The objective of this study was to determine the effects of different soil salinity levels on the agronimic traits and yield of four newly introduced salt-tolerant rice cultivars in the Thua Thien Hue province, Central Vietnam. Three field experiments were conducted in 2018 summer-autumn crop season at three locations with different soil salinity levels of EC 4.1, 6.4 and 9.0 dS/m. Yield per plant and some agronomic traits including of plant height, panicle length and number of filled grains per panicle were measured. The cultivars of MNR3, OM5629 and OM2395 showed significantly higher yield per plant than that of the commonly used cultivar KD. As soil salinity increased from 4.1 to 6.4 dS/m, 6.4 to 9.0 dS/m, and 4.1 to 9.0 dS/m, yield per plant decreased 18.2, 16.0 and 31.3%, respectively. Therefore, it could be concluded that these cultivars were suitable for cultivation on saline soils in the summer Vautumn crop season at soil with EC T6.4 dS/m in Central Vietnam.

Comparison of Cd subcellular distribution and Cd detoxification between low/high Cd-accumulative rice cultivars and sea rice

Salt-tolerant rice cultivar (sea rice) is a research hotspot worldwide due to its high yield in high salinity soil. However, knowledge regarding the cadmium (Cd) effects on the growth of sea rice is limited. To determine the short-term and long-term impact of Cd stress, relatively low/high Cd-accumulative rice cultivars and sea rice were grown to compare their growth responses to Cd stress over time. The results showed that sea rice presented the highest Cd concentrations in the root, stem, and leaves under 32-days of Cd stress. Cd stress shortened and thickened the rice root, and decreased the proportion of root diameters in the 0–0.2 mm range. Cd stress remarkably increased the Cd and Fe concentration in dithionite–citrate–bicarbonate (DCB) extracts, and the DCB-Cd and DCB-Fe concentrations were the highest in sea rice. The subcellular distribution of Cd in the rice roots indicated that Cd accumulated the most in the soluble fraction and cell wall. The contents of pectin and hemicellulose 2 in the root cell wall of the low-Cd accumulative rice variety CL755 were higher than those in MXZ and sea rice. Collectively, this work provides a general understanding of the Cd effects on sea rice growth and indicates that sea rice has a relatively high Cd accumulation compared with the other two rice cultivars. However, the specifically-related mechanism remains to be further studied.

Path analysis for agronomic traits and yield of salt tolerant rice cultivars under moderate salinity condition in Central Vietnam

This study was done with the aims to determine: (i) the correlation between agronomic traits and yield and (ii) the direct and indirect effects of agronomic traits on salt-tolerant rice yield. The field experiment was conducted directly on moderate salinity level of EC= 6.35 dS m-1 during the 2017 winter-spring cropping season in Central Vietnam. Ten salt-tolerant rice cultivars were studied. Results showed that yields of salt-tolerant rice cultivars had a positive correlation with traits of plant height, panicles per plant, panicle weight, and dry biomass, r = 0.3624*, 0.7019***, 0.4530** and 0.7837***, respectively. Total panicles per plant, panicle weight, and the number of grains per panicle directly affected rice yield with coefficients of dC = 0.5524, 0.8294 and 0.4355, respectively. Therefore, these traits should be used as good indicator traits for selecting salt-tolerant rice cultivars for the moderate salinity soil in Central Vietnam.

Optimizing Seedling Number and Hill Spacing: A Way Forward to Harness Productivity Potential of Salt-Tolerant Rice Cultivars in Salt-Affected Soils

Harnessing the potential of sodic soils in the Indo-Gangetic plains necessitates the development of salt-tolerant varieties and matching management practices as the management practices required for rice production in salt-affected soils are entirely different from those in normal soils. Field experiments with the main plots comprising two treatments T1:2 seedlings and T2:4 seedlings hill−1, subplot three hill spacing treatments S1: 15 × 15 cm, S2: 15 × 20 cm, S3: 20 cm × 20 cm and sub–subplot with two salt-tolerant varieties V1: CSR 36, V2: CSR 43 were conducted at the Indian Council of Agricultural Research-Central Soil Salinity Research Institute (ICAR-CSSRI), Regional Research Station, Lucknow, Uttar Pradesh, India, during 2011, 2012 and 2013 kharif seasons to develop matching management practices for salt-tolerant varieties through optimizing the number of seedlings hill−1 and hill density to enhance productivity and profitability in salt-affected soils. The experiment was set up in split plot design replicated thrice. The results revealed that transplanting of 4 seedlings hill−1 at a hill spacing of 15 cm × 20 cm proved better crop establishment and produced significantly higher grain yield over rest of the treatments. Planting of 4 seedlings hill−1 resulted in higher gross and net returns than planting of 2 seedlings hill−1. Transplanting of CSR 36 with 4 seedlings hill−1 at a hill spacing of 15 × 20 cm found superior in terms of grain yield, gross and net returns over CSR 43 with rest of the spacing treatments.

Comparative Analysis of the Expression of Candidate Genes Governing Salt Tolerance and Yield Attributes in Two Contrasting Rice Genotypes, Encountering Salt Stress During Grain Development

The rice grain filling process is of inordinate importance as it is directly associated with productivity and rice quality. Salt stress occurring during early grain development hinders seed development, resulting in yield penalty. To dissect transcriptional responses and to identify promising candidate genes, comparative expression profiling of key stress-responsive and yield-related genes was performed in developing (10 DAP, 20 DAP, and 30 DAP) and matured grains of salt-sensitive (IR-64) and salt-tolerant (Nonabokra) rice cultivars under salt stress (250 mM NaCl) along with the analyses of grain yield parameters. The phenotypic values of most of the tested yield attributes were significantly reduced under salt stress and the effect of stress was more pronounced in IR-64. Gene expression through semi-quantitative reverse transcriptase-polymerase chain reaction followed by statistical analyses identified that members of the TFs and LEA family (that is, TRAB-1, RITA-1, RISBZ1, WRKY-21, and Osem), osmolytes and polyamine metabolic genes (BADH1 and SAMDC) as well as the yield-related gene GIF1, were significantly induced by salt stress. Statistical analyses further revealed a significant correlation between the expression of these genes and grain yield under salt stress. In IR-64, the TRAB-1, RITA-1, and Osem transcripts were more up regulated during the early to mid-phase of seed development, suggesting an adaptive response of the sensitive cultivar to salt stress. The TFs along with BADH1, SAMDC, and GIF1 transcripts were mostly up regulated in Nonabokra during the early phase, and the level was maintained even after the mid-phase under stress. The heat map analysis also revealed the differential expression of genes between the two cultivars throughout the seed developmental stages. Our result indicated a possible interplay between ABA-inducible TFs and grain filling-related genes, allowing Nonabokra to maintain the grain filling process under stress condition. This is also evident by comparatively lower reduction of grain weight and filled-grain number in Nonabokra under stress. The role of different TFs in ABA-signaling in matured grains is clear by the accumulation of transcripts, especially in dry and ABA-imbibed seeds. Overall, our data established the correlation of grain yield with tolerance or susceptibility, accompanied by the expression of effector or regulatory genes.

Reactive oxygen species dynamics in roots of salt sensitive and salt tolerant cultivars of rice

Salinity stress is one of the major constraints for growth and survival of plants that affects rice productivity worldwide. Hence, in the present study, roots of two contrasting salinity sensitive cultivars, IR64 (IR64, salt sensitive) and Luna Suvarna (LS, salt tolerant) were compared with regard to the levels of reactive oxygen species (ROS) to derive clues for their differential salt stress adaptation mechanisms. In our investigation, the tolerant cultivar exhibited longer primary roots, more lateral roots, higher root number leading to increased root biomass, with respect to IR64. It was observed that LS roots maintained higher level of H2O2 in comparison to IR64. The activities of various enzymes involved in enzymatic antioxidant defense mechanism (SOD, CAT, GPX, DHAR and MDHAR) were found to be greater in LS roots. Further, the higher transcript level accumulation of genes encoding ROS generating (RbohA, RbohD and RbohE) and scavenging enzymes (Fe-SOD, Chloroplastic Cu/Zn-SOD, CAT and DHAR) were noticed in the roots of tolerant cultivar, LS. Moreover, the content of other stress markers such as total protein and proline were also elevated in LS roots. While, the expression of proline biosynthesis gene (P5CS) and proline catabolism gene (PDH) was observed to be lower in LS.

The influence of host genotype and salt stress on the seed endophytic community of salt-sensitive and salt-tolerant rice cultivars

BackgroundInherent characteristics and changes in the physiology of rice as it attains salt tolerance affect the colonizing bacterial endophytic communities of the rice seeds. These transmissible endophytes also serve as a source of the plant’s microbial community and concurrently respond to the host and environmental conditions. This study explores the influence of the rice host as well as the impact of soil salinity on the community structure and diversity of seed bacterial endophytes of rice with varying tolerance to salt stress. Endophytic bacterial diversity was studied through culture-dependent technique and Terminal-Restriction Fragment Length Polymorphism (T-RFLP) analysis.ResultsResults revealed considerably diverse communities of bacterial endophytes in the interior of rice seeds. The overall endophytic bacterial communities of the indica rice seeds based on 16S rRNA analysis of clones and isolates are dominated by phylum Proteobacteria followed by Actinobacteria and Firmicutes. Community profiles show common ribotypes found in all cultivars of the indica subspecies representing potential core microbiota belonging to Curtobacterium, Flavobacterium, Enterobacter, Xanthomonas, Herbaspirillum, Microbacterium and Stenotrophomonas. Clustering analysis shows that the host genotype mainly influences the seed endophytic community of the different rice cultivars. Under salt stress conditions, endophytic communities of the salt-sensitive and salt-tolerant rice cultivars shift their dominance to bacterial groups belonging to Flavobacterium, Pantoea, Enterobacter, Microbacterium, Kosakonia and Curtobacterium.ConclusionThe endophytic communities of rice indica seeds are shaped by the hosts’ genotype, their physiological adaptation to salt stress and phylogenetic relatedness. Under salt stress conditions, a few groups of bacterial communities become prominent causing a shift in bacterial diversity and dominance.

Tương quan giữa độ mặn đất và các đặc điểm nông sinh học của một số giống lúa chịu mặn

The purposes of this research were to evaluate the effects of different soil salinity levels to the performance and correlations between agro-biological traits of some salt-tolerant rice cultivars. Two experiments were conducted on saline soils with two different salinity levels of medium (6.35 dS/m) and high (9.90 dS/m), in the winter-spring of 2017, at Thua Thien Hue province. 10 different salt-tolerant rice cultivars were used in the experiment. Agro-biological traits such as plant height, yields, and yield’s components were studied. The results showed that the growth, yields, and yield’s components of the salt-tolerant rice cultivars were poor, especially at the high soil salinity level of 9.90 dS/m. Yields per plant decreased by 14.8% as salinity increased to 3.55 units (from 6.35 dS/m to 9.90 dS/m). To increase the yield per plant at the medium soil salinity level of 6.35 dS/m, the best approach is to find out solutions to increase plant height, total panicle, panicle’s weight and dry biomass of plants. However, at high soil salinity level of 9.90 dS/m, in order to increase the yields per plant, it needs to find out solutions to increase the traits of panicle’s weight, total seeds/panicle, full-seeds/panicle and total dry biomass of plants.

Seed pre-treatment with spermidine alleviates oxidative damages to different extent in the salt (NaCl)-stressed seedlings of three indica rice cultivars with contrasting level of salt tolerance

The effect of seed pre-treatment with the triamine, spermidine (Spd), in mitigating the detrimental effect of NaCl stress in rice is poorly explored. Due to limited available reports, such an investigation was carried out in the seedlings of three indica rice cultivars, IR-64 (salt-sensitive), Nonabokra (salt-tolerant) and Gobindobhog (aromatic and salt-sensitive). The lethal effect of NaCl was particularly noteworthy in the two susceptible cultivars IR-64 and Gobindobhog, as evidenced by extensive tissue-growth inhibition, oxidative damages and chlorophyll degeneration. Seed pre-treatment with Spd could remarkably alleviate stress injury, especially in IR-64 and Gobindobhog, by reverting back from growth retardation and oxidative damages to near-normal conditions. Spd pre-treatment also promoted the levels of osmolytes, particularly proline in Gobindobhog, concomitant with enhanced anthocyanin, cysteine and polyphenol oxidase, but lowered total phenolics and reducing power in the susceptible cultivars. However, the antioxidant enzyme activities were more enhanced in salt-stressed Nonabokra seedlings with Spd, as means of ameliorating cellular NaCl toxicity. A clear-cut variation in GPX, APX, CAT and SOD isozyme profile was discernible among the three cultivars during NaCl stress, with specific isoform(s) being up regulated or down regulated with Spd pre-treatment. Our results indicated that seed treatment with Spd at the pre-sowing stage can promote NaCl tolerance with varying degrees in salt-sensitive and salt-tolerant rice cultivars by alleviating oxidative damages, triggering the antioxidants and osmolytes, and activating the antioxidative enzymes.

Irrigation Water Management of Some Salt Tolerant Rice Cultivars for Higher Yield

Irrigation Water Management of Some Salt Tolerant Rice Cultivars for Higher Yield

Association mapping validates previously identified quantitative trait loci for salt tolerance in rice (Oryza sativa L.)

Salinity is the main abiotic stress that limits rice (Oryza sativa L.) production worldwide. An association mapping project was designed to validate quantitative trait loci (QTLs) in rice associated with Na+, K+ and Ca++ accumulation traits identified in our previous study of linkage mapping. Twenty four varieties/lines of rice were phenotyped for biochemical and yield traits. Among these varieties/lines, two mapping parents, Pokkali and IR-36, of our previous linkage mapping study were also included. For marker-trait assessments, both general linear model (GLM) and mixed linear model (MLM) analyses were performed. Thirteen significant marker-trait associations at P ≤ 0.001 were identified. Associated markers for these marker-trait associations were RM503, RM225, RM152, and RM254 located on chromosomes 3, 6, 8, and 11, respectively. Previously identified QTLs in linkage mapping study for Na+ uptake, Ca++ uptake, total cations uptake, Ca++ uptake ratio, K+ uptake ratio, and Na+/K+ uptake were validated in this study. Heritability values for these traits ranged from 1.00e-05 to 1. Linked markers for these validated QTLs were RM140, RM243, RM203, RM480, RM137, and RM254 located on chromosomes 1, 1, 3, 5, 8, and 11, respectively. These markers will be a valuable resource for marker-assisted breeding (MAB) approach to develop elite salt tolerant rice cultivars. This study demonstrates the potential of association mapping approach to validate previously identified QTLs.

Reactive oxygen species generating system and brassinosteroids are linked to salt stress adaptation mechanisms in rice

ABSTRACTSalinity stress is one of the major environmental challenges which adversely affects plant growth and productivity. The acquisition of salinity stress tolerance has been an interesting area of investigation for plant abiotic stress management. Recently, we investigated the interdependency of reactive oxygen species (ROS) generating and scavenging system for offering salt stress adaptation in rice. In continuation to our earlier findings, in the present study we analyzed the transcript level expression of different respiratory burst oxidase homologs (Rbohs) genes in salt sensitive and salt tolerant cultivars of rice to corroborate this result with their activities. Brassinosteroid (BR) is known to confer abiotic stress tolerance by modulating ROS machinery, and hence in the present study, the expression of key genes associated in brassinosteroid biosynthesis and signaling in salt sensitive and tolerant cultivar of rice was also conducted. In the present investigation, the other stress markers involving proline catabolism and anabolism along with chlorophyllase has been analyzed to get a better insights to our understanding of salt stress adaptation mechanisms in rice.

Interdependency of Reactive Oxygen Species generating and scavenging system in salt sensitive and salt tolerant cultivars of rice.

BackgroundSalinity stress is a major constrain in the global rice production and hence serious efforts are being undertaken towards deciphering its remedial strategies. The comparative analysis of differential response of salt sensitive and salt tolerant lines is a judicious approach to obtain essential clues towards understanding the acquisition of salinity tolerance in rice plants. However, adaptation to salt stress is a fairly complex process and operates through different mechanisms. Among various mechanisms involved, the reactive oxygen species mediated salinity tolerance is believed to be critical as it evokes cascade of responses related to stress tolerance. In this background, the present paper for the first time evaluates the ROS generating and the scavenging system in tandem in both salt sensitive and salt tolerant cultivars of rice for getting better insight into salinity stress adaptation.ResultsComparative analysis of ROS indicates the higher level of hydrogen peroxide (H2O2) and lower level of superoxide ions (O2-) in the salt tolerant as compared to salt sensitive cultivars. Specific activity of ROS generating enzyme, NADPH oxidase was also found to be more in the tolerant cultivars. Further, activities of various enzymes involved in enzymatic and non enzymatic antioxidant defence system were mostly higher in tolerant cultivars. The transcript level analysis of antioxidant enzymes were in alignment with the enzymatic activity. Other stress markers like proline were observed to be higher in tolerant varieties whereas, the level of malondialdehyde (MDA) equivalents and chlorophyll content were estimated to be more in sensitive.ConclusionThe present study showed significant differences in the level of ROS production and antioxidant enzymes activities among sensitive and tolerant cultivars, suggesting their possible role in providing natural salt tolerance to selected cultivars of rice. Our study demonstrates that the cellular machinery for ROS production and scavenging system works in an interdependent manner to offer better salt stress adaptation in rice. The present work further highlights that the elevated level of H2O2 which is considered as a key determinant for conferring salt stress tolerance to rice might have originated through an alternative route of photocatalytic activity of chlorophyll.