Sodium and Chloride Sensitivity in Alfalfa (Medicago sativa L.): Growth,Photosynthesis, and Tissue Ion Regulation in Contrasting Genotypes

Alfalfa (Medicago sativa L.) is a moderately salt-tolerant plant. This study was conducted to evaluate responses of two contrasting alfalfa genotypes (OMA-84-salt sensitive and OMA-285-salt-tolerant) to components (Na⁺, and/or Cl^?) of salt stress. Alfalfa genotypes were exposed to Na⁺???salts (without chloride), Cl^????salts (without sodium), and NaCl (sodium chloride) stresses with two concentrations (30 and 150 mM). The treatments, involving macronutrients, with the same osmotic potentials, were taken as control. Salt stress, irrespective of type and intensity, caused a significant reduction in plant biomass, physiological (net photosynthetic rate, photosystem II efficiency, chlorophyll fluorescence, water use efficiency, maximum yield of primary photochemistry, and electron transport rate), and shoot mineral (calcium, magnesium, phosphorus, and potassium) contents compared to control; however, this reduction was in the order of NaCl (150 mM)?>?Na⁺ (150 mM)?>?Cl^? (150 mM). The alfalfa genotype OMA-285 sustained growth under both types of salt stresses than the genotype OMA-84 due to less accumulation of Na⁺ and Cl^? ions, maintenance of higher K⁺/Na⁺ ratio, and better photosynthetic activities. In conclusion, salt stress caused a significant reduction in alfalfa growth, this reduction was more under NaCl stress and the effect was mainly additive. The alfalfa genotype OMA-285 sustained growth under salt stresses than the genotype OMA-84 due to ionic homeostasis. However, the tested genotypes were more sensitive to Na⁺ toxicity than the Cl^? toxicity, and the contrasting genotypes differed in tissue tolerance of high Na⁺ and Cl^?. Further research is needed to evaluate tissue tolerance in a diverse and large group of alfalfa genotypes to elucidate the general salt tolerance mechanism in alfalfa.

     

Is salinity tolerance related to Na accumulation in Upland cotton (Gossypium hirsutum) seedlings?

Physiological responses to salt stress were studied in two cotton cultivars previously selected on the basis of growth under salinity. Plants were grown in nutrient solutions under controlled conditions. In the first experiment, the genotypes were grown at different salt concentrations (0, 100 and 200 mt M NaCl) and growth rates, water contents and ion accumulation were determined. In a second experiment, both genotypes were grown at the same salt concentration (200 mt M NaCl). Dry matter partitioning in individual leaves, stem and roots, water contents, specific leaf area (SLA), ion accumulation (K⁺, Na⁺, Cl^–) and leaf water potentials were measured. Finally, an experiment with low salt levels (2.7 and 27 mt M NaCl) was run to compare K and Na⁺ uptake and distribution.There were no differences in growth between the cultivars in the absence of salt stress, whereas under stress genotype Z407 had higher leaf area and dry matter accumulation than P792. Leaf water potential and leaf water content were lower in cv P792 than in cv Z407. There were no significant differences in the levels of Cl^– accumulation between genotypes. The main feature of the tolerant genotype (Z407) was a higher accumulation of Na⁺ in leaves and an apparent capacity for K⁺ redistribution to younger leaves.We postulate that the higher tolerance in Z407 is the result of several traits such as a higher Na⁺ uptake and water content. Adaptation through adequate, but tightly controlled ion uptake, typical of some halophytes, matched with efficient ion compartmentation and redistribution, would result in an improved water uptake capacity under salt stress and lead to maintenance of higher growth rates.     

Effect of salt stress on photosynthesis and physiological parameters of three contrasting barley genotypes

In order to understand the physiological traits important in conferring salt tolerance in three barley genotypes, this study was performed under field conditions with three water salinity levels (2, 10, and 18 dS m–1). High salinity decreased net photosynthetic rate, transpiration rate, and stomatal conductance, K⁺ concentration, K⁺:Na⁺ ratio, and grain yield, but increased electrolyte leakage and Na⁺ content. Under 10 and 18 dS m–1 salinity, Khatam (salt-tolerant) had the maximum stomatal conductance, K⁺, K⁺:Na⁺ ratio, and the grain yield, and a minimum Na⁺ content and electrolyte leakage, whereas Morocco (salt-sensitive) had the lowest net photosynthetic rate, stomatal conductance, K⁺ content, K⁺:Na⁺ ratio, and grain yield, and the highest Na⁺ content and electrolyte leakage. This study showed that tolerant genotypes of barley may avoid Na⁺ accumulation in aboveground parts, facilitating a higher photosynthetic rate and higher grain yield.     

Growth,Na, K,osmolyte accumulation and lipid membrane peroxidation of two provenances of Cakile maritima during water deficit stress and subsequent recovery

The effects of water deficit stress on growth, Na⁺, K⁺ and osmolyte accumulation in the halophyte species Cakile maritima were investigated. Two Tunisian provenances, Tabarka and Chaffar, belonging to different bioclimatic stages, humid and arid, respectively, were compared. After germination, thirty-day-old seedlings were cultivated for 4 weeks under optimal or limiting water supply, at 100% and 25% of field capacity (FC), respectively. A subset of stressed plants was thereafter rehydrated. The final harvest was carried out after 60 days of treatment. Upon water deficit stress, Chaffar provenance showed significantly lower reduction in biomass production, net CO₂ assimilation and stomatal conductance as well as of leaf water content. Leaf malondialdehyde (MDA) content was significantly increased in the two provenances but this effect was more pronounced in Tabarka plants than in Chaffar ones. Several criteria seem to be associated with the relative tolerance of Chaffar to water deficit: a slow growth rate, a greater ability to control photosynthetic gas exchange, a high ability to preferentially allocate photoassimilates to its roots, and a greater capacity for osmotic adjustment ensured by K⁺ and some compatible solutes such as proline and glycine betaine, but not soluble sugars. The superiority of Chaffar provenance also appeared at the level of its ability to recover after a severe water deficit stress (irrigation at 25% FC only during one month). The data suggest that compatible osmolytes (proline and glycine betaine) accumulated upon water deficit stress play important roles in this halophyte, being involved not only in osmotic adjustment but probably serving also in preservation of the structural and functional integrity at the cellular level during water deficit.     

Co‐expression of tonoplast Cation/H+ antiporter and H+‐pyrophosphatase from xerophyte Zygophyllum xanthoxylum improves alfalfa plant growth under salinity,drought and field conditions

Salinity and drought are major environmental factors limiting the growth and productivity of alfalfa worldwide as this economically important legume forage is sensitive to these kinds of abiotic stress. In this study, transgenic alfalfa lines expressing both tonoplast NXH and H⁺‐PPase genes, ZxNHX and ZxVP1‐1 from the xerophyte Zygophyllum xanthoxylum L., were produced via Agrobacterium tumefaciens‐mediated transformation. Compared with wild‐type (WT) plants, transgenic alfalfa plants co‐expressing ZxNHX and ZxVP1‐1 grew better with greater plant height and dry mass under normal or stress conditions (NaCl or water‐deficit) in the greenhouse. The growth performance of transgenic alfalfa plants was associated with more Na⁺, K⁺ and Ca²⁺ accumulation in leaves and roots, as a result of co‐expression of ZxNHX and ZxVP1‐1. Cation accumulation contributed to maintaining intracellular ions homoeostasis and osmoregulation of plants and thus conferred higher leaf relative water content and greater photosynthesis capacity in transgenic plants compared to WT when subjected to NaCl or water‐deficit stress. Furthermore, the transgenic alfalfa co‐expressing ZxNHX and ZxVP1‐1 also grew faster than WT plants under field conditions, and most importantly, exhibited enhanced photosynthesis capacity by maintaining higher net photosynthetic rate, stomatal conductance, and water‐use efficiency than WT plants. Our results indicate that co‐expression of tonoplast NHX and H⁺‐PPase genes from a xerophyte significantly improved the growth of alfalfa, and enhanced its tolerance to high salinity and drought. This study laid a solid basis for reclaiming and restoring saline and arid marginal lands as well as improving forage yield in northern China.     

Differential stress responses to NaCl salt application in early- and late-maturing diploid potato (Solanum sp.) clones

Cultivated tetraploid potatoes (Solanum tuberosum L.) are moderately salt sensitive but greater stress tolerance exists in diploid wild types. However, little work has been published on salt-tolerance in diploid potato. This study utilized sensitive and tolerant diploid potatoes as well as a commercially cultivated potato to investigate mechanisms of stress tolerance. Stem cuttings from salt-tolerant (T) and sensitive (S) clones of early-maturing (EM) and late-maturing (LM) diploid potato clones were stressed for 5 days at the tuber initiation stage with 150 mmol NaCl in a hydroponic sand culture under greenhouse conditions. The stress responses of the early- and late-maturing potato clones were distinctly different. Under stress, early-maturing clones accumulated Na⁺ in the leaf tissues while late-maturing clones generally excluded Na⁺ from the leaf tissues. Salt tolerant clones of both maturity types were able to tolerate high levels of Na⁺ in the leaf tissues. The lower leaves accumulated more Na⁺ than the upper leaves in both maturity types. The potassium to sodium ratio was significantly greater in the leaves of the late-maturing types, reflecting differences in Na⁺ accumulation rather than alterations in K⁺ levels. Proline levels increased upon salt exposure but were not clearly associated with salinity tolerance. Tolerance was manifested in maintenance of vegetative growth, tuber yield, and reduced leaf necrosis. These responses require efficient uptake of water and source–sink translocation. Maintenance of stomatal conductance under stress was not associated with these responses but tuber yield was related to lower-leaf osmotic potential (OP) in both early- and late-maturity types. Salt tolerant clones of both maturity types also had less negative tuber OP under salt stress than sensitive types. High yielding EMT and LMT clones either minimized tuber yield loss or even increased yield after exposure to salt stress. Mechanistic studies and screening experiments for salt tolerant clones should consider maturity type, leaf position and source–sink relationships enhancing tuber yield.     

The influence of salinity on cell ultrastructures and photosynthetic apparatus of barley genotypes differing in salt stress tolerance

A hydroponic experiment was conducted to elucidate the difference in growth and cell ultrastructure between Tibetan wild and cultivated barley genotypes under moderate (150 mM NaCl) and high (300 mM NaCl) salt stress. The growth of three barley genotypes was reduced significantly under salt stress, but the wild barley XZ16 (tolerant) was less affected relative to cultivated barley Yerong (moderate tolerant) and Gairdner (sensitive). Meanwhile, XZ16 had lower Na⁺ and higher K⁺ concentrations in leaves than other two genotypes. In terms of photosynthetic and chlorophyll fluorescence parameters, salt stress reduced maximal photochemical efficiency (F _v/F _m), net photosynthetic rate (Pn), stomatal conductance (Gs), and intracellular CO₂ concentration (Ci). XZ16 showed relatively smaller reduction in comparison with the two cultivated barley genotypes. The observation of transmission electron microscopy found that fundamental cell ultrastructure changes happened in both leaves and roots of all barley genotypes under salt NaCl stress, with chloroplasts being most changed. Moreover, obvious difference could be detected among the three genotypes in the damage of cell ultrastructure under salt stress, with XZ16 and Gairdner being least and most affected, respectively. It may be concluded that high salt tolerance in XZ16 is attributed to less Na⁺ accumulation and K⁺ reduction in leaves, more slight damage in cell ultrastructure, which in turn caused less influence on chloroplast function and photosynthesis.     

Biomass accumulation and allocation in soybean associated with genotypic differences in tolerance of nitrogen fixation to water deficits

Nitrogen fixation in soybean (Glycine max [L.] Merr.) is more sensitive to water deficits than many physiological processes and may therefore limit yield under nonirrigated conditions. Tolerance of nitrogen fixation to water deficits has been observed in the cultivar Jackson, however, the physiological basis for this is unclear. It was hypothesized that genotypes that could continue biomass production on limited soil water would prolong nitrogen fixation by continued photosynthate allocation to nodules. An initial greenhouse experiment compared biomass and N accumulation in six genotypes over an 8 d water deficit. Low stress intensity minimized genotypic expression of water-deficit tolerance; nevertheless, Jackson was clearly one of the most tolerant genotypes. In a second experiment, Jackson was compared to SCE82-303 at more severe stress levels. Biomass and N accumulation continued during water deficits for Jackson but ceased in SCE82-303. Individual nodule mass tended to increase during water deficits in Jackson and tended to decrease in SCE82-303, indicating greater allocation of photosynthate to Jackson's nodules in response to water deficits. Biomass accumulation of Jackson was contrasted with the USDA plant introduction (PI) 416937, which also has demonstrated tolerance to water deficits. For water-deficit treatments, total biomass accumulation was negligible for PI416937, but biomass accumulation continued at approximately 64% of the control treatment for Jackson. Transpirational losses for Jackson and PI416937 were approximately the same for the water-deficit treatment, indicating that Jackson had higher water use efficiency (WUE). Isotopic discrimination of ¹³C relative to¹² C also indicated that Jackson had superior WUE during water deficits. Carbon-14 allocation in Jackson was compared to KS4895, a cultivar that was identified as sensitive to water deficits in an initial experiment. The comparison of water-deficit treatments of Jackson with KS4895 indicated that Jackson exported significantly greater amounts of¹⁴ C from labeled leaves and allocated approximately four times greater amounts of ¹⁴C per g of nodule. Results indicated that Jackson's sustained biomass production during water deficits resulted in the continued allocation of photosynthate to nodules and prolonged nitrogenase activity.     

Effect of saline irrigation on plant water traits,photosynthesis and ionic balance in durum wheat genotypes

In the era of climate change, decreased precipitation and increased evapo-transpiration hampers the yield of several cereal crops along with the soil salinity and poor ground water resource. Wheat being the moderately tolerant crop face many challenges in the arid and semi-arid regions under irrigated agriculture. In view of this, the study was planned to explore the potential of durum wheat genotypes under salinity on the basis of physiological traits. Experiment was designed as RBD in three replications to evaluate 15 wheat genotypes with moderate saline irrigation (EC_iw – 6 dS m⁻¹) and extreme saline irrigation (EC_iw – 10 dS m⁻¹) along with one set of control (Best available water). Different physiological traits such as water potential (ψ_p), osmotic potential (ψ_s), relative water content (RWC), Na⁺ and K⁺ content were recorded in roots as well as shoots at the reproductive stage whereas photosynthetic rate and chlorophyll content were measured in the flag leaves. A significant variability (p < 0.001) was noted among the genotypes under different stress environments and it was observed that durum genotype HI 8728 and HI 8737 showed less reduction in plant water traits (RWC, ψ_p and ψ_s) than the salinity tolerant checks of bread wheat KRL 99 and KRL 3–4. HD 4728 and HI 8708 maintained higher photosynthetic rate as well as higher chlorophyll content under the extreme salinity level of EC_iw – 10 dSm⁻¹. No significant differences were found in root Na⁺ in genotypes KRL 99 (3.17^g), KRL 3–4 (3.34^g) and HI 8737 (3.41^g) while in shoots, lowest accumulation was seen in KRL 99, MACS 3949 and KRL 3–4 at EC_iw – 10 dSm⁻¹. The mean range of K⁺ content was 7.60–9.74% in roots and 4.21–6.61% in shoots under control environment which decreased to 50.77% in roots and 46.05% in shoots under extreme salinity condition of EC_iw – 10 dSm⁻¹. At EC_iw – 10 dSm⁻¹, KRL 99 maintained highest K^+/Na⁺ in both root and shoot followed by KRL 3–4, HI 8737, MACS 3949, HD 4728 in roots and MACS 3949, KRL 3–4, MACS 4020, HD 4758, MACS 3972 and HI 8713 in shoots. The differential response of durum wheat genotypes under salinity particularly for physiological traits, confer their adaptability towards stress environments and exhibit their potential as genetic sources in breeding programs for improving salt stress tolerance.     

Effect of salt stress on cucumber: Na+–K+ ratio, osmolyte concentration, phenols and chlorophyll content

A pot experiment with 17 diverse genotypes of cucumber with four levels of salt stress viz., 0, 2, 4 and 6 dS m^?1 was carried out during 2006. ANOVA revealed significant differences amongst genotypes and genotype × salt stress interaction indicating the genetic variability and differential response of the genotypes to different salt stress levels. The salt stress adversely affected the biochemical parameters; effects were severe under 4 dS m^?1. No genotype could survive at 6 dS m^?1. Sodium content, Na⁺–K⁺ ratio, proline, reducing sugars, phenol and yield reduction (%) increased significantly as the salt stress increased. Potassium, chlorophyll, membrane stability index and fruit yield decreased significantly under salt stress in all genotypes. However, the genotypes CRC-8, CHC-2 and G-338 showed lower accumulation of sodium, lesser depletion of potassium, lower Na⁺–K⁺ ratio and higher accumulation of proline, reducing sugars, phenols, better membrane stability and lower yield reduction (%) under salt stress, while CH-20 and DC-1 were sensitive to salt stress. Thus, a combination of traits such as higher membrane stability, lower Na⁺–K⁺ ratio, higher osmotic concentration and selective uptake of useful ions and prevention of over accumulation of toxic ions contribute to salt stress tolerance in cucumber. These traits would be useful selection criteria during salt stress breeding in cucumber.     

Differential responses of antioxidant system and photosynthetic characteristics in four rice cultivars differing in sensitivity to sodium chloride stress

To keep pace with ever growing global population, progressive and sustained increase in rice production is necessary, especially in areas with extremely variable climatic conditions, where rice crop suffers from numerous abiotic stresses including salinity. Designing an effective phenotyping strategy requires thorough understanding of plant survival under stress. The investigation was carried out with four rice cultivars namely FR13A, IR42, Rashpanjor, and Pokkali that differed in salinity tolerance. The study showed that a genotype with initial vigour had some advantage in preserving shoot biomass under salt stress. Though both FR13A and IR42 showed sensitivity to salinity, FR13A with higher initial biomass maintained greater dry weight under saline condition. Increase of Na⁺:K⁺ ratio under salinity, due to accelerated absorption of Na⁺ and lesser absorption of K⁺ compared to control, was considerably higher in susceptible (118–200 %) than in tolerant (33–48 %) genotypes. While Na⁺ concentration in shoot increased significantly in both tolerant and susceptible genotypes, decrease in shoot K⁺ content was noticed only in susceptible genotypes. The imbalance of Na⁺ and K⁺ contents led to increased H₂O₂ production, causing greater peroxidation of membrane lipids and reduction in chlorophyll content and CO₂ photosynthetic rate. Certain chlorophyll fluorescence parameters could distinguish between salinity tolerant and sensitive genotypes. To protect the plant from oxidative damage, several enzymatic and nonenzymatic antioxidants such as ascorbate were involved. The genotypes with capacity to assemble antioxidant enzymes in time could detoxify the reactive oxygen species more efficiently, leading to greater protection and reduced impact of salt stress.     

Comparative performance of δ13C,ion accumulation and agronomic parameters for phenotyping durum wheat genotypes under various irrigation water salinities

The use of efficient selection traits for screening under contrasting irrigation water salinity is a challenge for breeders. To identify patterns, grain yield (GY) and yield components (kernels m^?2, thousand kernels weight), growth traits (plant height, biomass), flag leaf ion accumulation (Na⁺ and K⁺), carbon isotope composition (δ¹³C_grain) and nitrogen concentration (N_grain) of grains were assessed on 25 durum wheat genotypes (G) in two consecutive growing seasons (2010 and 2011), in three semi‐arid locations in Tunisia. Each location differed in their irrigation water salinity as measured by electrical conductivity: Echbika (S1, 6 dS m^?1), Barrouta (S2, 12 dS m^?1) and Sidi Bouzid (S3, 18 dS m^?1). GY was shown to be negatively correlated to N_grain as well as to δ¹³C_grain. This is confirmed by a multiple linear regression analysis that showed that both δ¹³C_grain and N_grain were the major determinant components for GY variability under S3. A high genotypic variability was observed and the improved genotype Maali exhibited the most stable GY under the three irrigation water salinities and the two cropping seasons. Maali showed the lowest δ¹³C_grain. This indicates that tolerance in durum wheat is likely to be correlated to the ability of maintaining a high stomatal conductance. According to our data suggests δ¹³C_grain can be used for an efficient screening of salt tolerant durum wheat. Under our experimental conditions, N_grain was shown to be highly correlated to δ¹³C_grain and can therefore be easier‐to‐use trait to assess the tolerance to salinity.     

Eco-physiological response to water stress of drought-tolerant and drought-sensitive tomato genotypes

Water stress is an increasing environmental constraint affecting tomato growth and yield in Mediterranean areas. Solanum pennellii is a wild tomato species that exhibits a higher water use efficiency compared with cultivated S. lycopersicum. In particular, a cultivated line carrying a small S. pennellii region on chromosome 9 (IL 9-2-5) was identified as more tolerant to water deficit. In this work, the tolerant (IL 9-2-5) and the susceptible (M82) genotypes were subjected to three different water regimes: irrigation with 100% (V1), 50% (V2) and 25% (V3) field capacity. To evaluate the physiological response of IL 9-2-5 and M82 to water deficit, leaf functional traits, plant biomass production and maximal PSII photochemical efficiency were measured together with photosynthetic pigments and phenolic compounds. The higher tolerance to water deficiency of IL 9-2-5 was associated with the development of a better antioxidant system, especially in treatment V3. In addition, IL 9-2-5 had higher values of sclerophylly and leaf dry matter content thus confirming that the tolerance of IL 9-2-5 can be attributed to traits related to leaf morphology and physiology. In future, identification of polymorphisms in key-genes controlling these traits can guide breeding efforts aimed at improving susceptible genotypes.     

Response of Contrasting Rice Genotypes to Zinc Sources under Saline Conditions

Abiotic stresses are among the major limiting factors for plant growth and crop productivity. Among these, salinity is one of the major risk factors for plant growth and development in arid to semi-arid regions. Cultivation of salt tolerant crop genotypes is one of the imperative approaches to meet the food demand for increasing population. The current experiment was carried out to access the performance of different rice genotypes under salinity stress and Zinc (Zn) sources. Four rice genotypes were grown in a pot experiment and were exposed to salinity stress (7 dS m⁻¹), and Zn (15 mg kg⁻¹ soil) was applied from two sources, ZnSO₄ and Zn-EDTA. A control of both salinity and Zn was kept for comparison. Results showed that based on the biomass accumulation and K⁺/Na⁺ ratio, KSK-133 and BAS-198 emerged as salt tolerant and salt sensitive, respectively. Similarly, based on the Zn concentration, BAS-2000 was reported as Zn-in-efficient while IR-6 was a Zn-efficient genotype. Our results also revealed that plant growth, relative water content (RWC), physiological attributes including chlorophyll contents, ionic concentrations in straw and grains of all rice genotypes were decreased under salinity stress. However, salt tolerant and Zn-in-efficient rice genotypes showed significantly higher shoot K⁺ and Zn concentrations under saline conditions. Zinc application significantly alleviates the harmful effects of salinity by improving morpho-physiological attributes and enhancing antioxidant enzyme activities, and the uptake of K and Zn. The beneficial effect of Zn was more pronounced in salt-tolerant and Zn in-efficient rice genotypes as compared with salt-sensitive and Zn-efficient genotypes. In sum, our results confirmed that Zn application increased overall plant’s performance under saline conditions, particularly in Zn in-efficient and tolerant genotypes as compared with salt-sensitive and Zn efficient rice genotypes.     

Variability in the response of six genotypes of N<Subscript>2</Subscript>-fixing <Emphasis Type="Italic">Medicago ciliaris</Emphasis> to NaCl

Genotypic variability was assessed within six Medicago ciliaris genotypes growing symbiotically with Sinorhizobium medicae in order to identify physiological criteria (growth, ion content, and plant health) associated with salt tolerance. Response to salt stress depended on the line and the level of salt. Two lines with lower dry biomass under non-saline conditions (TNC 1.8 from a semi-arid area and TNC 10.8 from a sub-humid area), were more tolerant to NaCl, whereas the most productive lines (TNC 11.5 and TNC 11.9 from a humid bioclime) were more sensitive in terms of growth and nitrogen fixation. Susceptibility of symbiotic nitrogen fixation to saline stress was not associated with a higher accumulation of Na⁺ in nodules, since the most tolerant lines TNC 1.8 and TNC 10.8 accumulated the highest Na⁺ amount in nodules. Leaf area and net photosynthate assimilation rate were conserved in line TNC 1.8 and to a lesser extent in line TNC 10.8 potentially owing to a greater ability to protect aerial organs and nodules from Na⁺ damage and to insure a better supply of leaves with nitrogen. Our results suggest that nodule growth and number and nodule Na⁺ content should not be used as selection tools for tolerance or susceptibility, since two of the tested lines maintained consistent growth in spite of reduced nodule and high Na⁺ content. Instead, the most reliable physiological indicators for tolerance appear to be consistent growth (i.e., no growth changes) and reduced leaf Na⁺ accumulation with increasing concentrations of NaCl.     

Molecular,Physiological and Biochemical Responses of Theobroma cacao L. Genotypes to Soil Water Deficit

Six months-old seminal plants of 36 cacao genotypes grown under greenhouse conditions were subjected to two soil water regimes (control and drought) to assess, the effects of water deficit on growth, chemical composition and oxidative stress. In the control, soil moisture was maintained near field capacity with leaf water potentials (ΨWL) ranging from −0.1 to −0.5 MPa. In the drought treatment, the soil moisture was reduced gradually by withholding additional water until ΨWL reached values of between −2.0 to −2.5 MPa. The tolerant genotypes PS-1319, MO-20 and MA-15 recorded significant increases in guaiacol peroxidase activity reflecting a more efficient antioxidant metabolism. In relation to drought tolerance, the most important variables in the distinguishing contrasting groups were: total leaf area per plant; leaf, stem and total dry biomass; relative growth rate; plant shoot biomass and leaf content of N, Ca, and Mg. From the results of these analyses, six genotypes were selected with contrasting characteristics for tolerance to soil water deficit [CC-40, C. SUL-4 and SIC-2 (non-tolerant) and MA-15, MO-20, and PA-13 (tolerant)] for further assessment of the expression of genes NCED5, PP2C, psbA and psbO to water deficit. Increased expression of NCED5, PP2C, psbA and psbO genes were found for non-tolerant genotypes, while in the majority of tolerant genotypes there was repression of these genes, with the exception of PA-13 that showed an increased expression of psbA. Mutivariate analysis showed that growth variables, leaf and total dry biomass, relative growth rate as well as Mg content of the leaves were the most important factor in the classification of the genotypes as tolerant, moderately tolerant and sensitive to water deficit. Therefore these variables are reliable plant traits in the selection of plants tolerant to drought.     

Phylogenetic relationship of salt tolerance in early Green Revolution CIMMYT wheats

Twenty-five genotypes of early CIMMYT hexaploid wheat (Triticum aestivum L.) were screened for salt tolerance in a glasshouse experiment at 150 mol m⁻³ NaCl in sand culture. The genotypes Na(20)TPP, Penjamo 62, and Inia 66 exceeded all the lines in grain yield per plant under salt stress, whereas Nainari 60 and Norin 10 were the lowest of all genotypes. However, Jaral 66 and Yaqui 54 were the lowest of all the genotypes in all growth and yield attributes. Considerable variation in accumulation of Na⁺ and Cl⁻ in different plant parts of 25 genotypes of early CIMMYT wheat under salt stress was observed. The genotype Noreste 66 was the lowest in leaf Na⁺ and Cl⁻, and it had highest leaf K/Na ratio and K versus Na selectivity of all the genotypes, but in terms of growth and grain yield, it was moderately tolerant. The other genotype Norin 10 was the highest in leaf Na⁺ and Cl⁻ of all genotypes, but its leaf K/Na ratio and K versus Na selectivity were considerably low. However, in shoot biomass it was the highest and in grain yield the lowest of all genotypes. In view of phylogenetic lineage of the genotypes, most of the genotypes have evolved from Norin 10, so the trait of high uptake of Na⁺ and Cl⁻ in most genotypes may have been inherited from Norin 10. The ion exclusion trait in the moderately salt tolerant genotype Noreste 66 was possibly inherited from Yaqui 50 as it was the only among all putative parents which showed low uptake of toxic ions. Overall, owing to the complex nature of the salt tolerance trait being controlled by polygenes, it was not easy to draw relationships between degree of salt tolerance and pattern of uptake of toxic ions and maintenance of leaf K/Na ratios. However, from the phylogenetic lineage of the 25 genotypes it was possible to draw relationships between degree of salt tolerance and mechanism of ion uptake between parents and progeny.     

Prospects of Inducing Resistance in Fodder Species against Toxic Ions and Metals

ABSTRACT

Experiments were carried out with various salts and their combinations to ascertain the impact of these salts on seedling traits of fodder species and to identify tolerant species. Length-based traits showed a repressed effect, whereas weight-based traits were increased under salt stress. Furthermore, accumulation of Na⁺, Ca²⁺, and Cl^? ions and metals (Cu²⁺, Fe²⁺, and Al³⁺) increased in various organs of seedlings due to various salt treatments. Contrastingly, K⁺, K⁺/Na⁺, and Ca²⁺/Cl^? decreased, showing priority for specific salts. Seedling traits, such as shoot length sensitivity and shoot biomass, provide an effective mean of selection for tolerant or susceptible genotypes. Diverse types of tolerance mechanisms were present in cultivars to detoxify the effect of ions and metals. Cultivars that showed low susceptibility index, high shoot biomass, and high metal concentration were salt includers and could be utilized for bioremediation of the affected areas, whereas tolerant cultivars that showed low susceptibility index, metals concentration, and comparable shoot biomass to that of the control were salt excluders and could be utilized for fodder purposes.