Leaf Chloride Concentrations Research Articles

Physiological and Transcriptional Responses to Saline Irrigation of Young 'Tempranillo' Vines Grafted Onto Different Rootstocks.

The use of more salt stress-tolerant vine rootstocks can be a sustainable strategy for adapting traditional grapevine cultivars to future conditions. However, how the new M1 and M4 rootstocks perform against salinity compared to conventional ones, such as the 1103-Paulsen, had not been previously assessed under real field conditions. Therefore, a field trial was carried out in a young ‘Tempranillo’ (Vitis vinifera L.) vineyard grafted onto all three rootstocks under a semi-arid and hot-summer Mediterranean climate. The vines were irrigated with two kinds of water: a non-saline Control with EC of 0.8 dS m–1 and a Saline treatment with 3.5 dS m–1. Then, various physiological parameters were assessed in the scion, and, additionally, gene expression was studied by high throughput sequencing in leaf and berry tissues. Plant water relations evidenced the osmotic effect of water quality, but not that of the rootstock. Accordingly, leaf-level gas exchange rates were also reduced in all three rootstocks, with M1 inducing significantly lower net photosynthesis rates than 1103-Paulsen. Nevertheless, the expression of groups of genes involved in photosynthesis and amino acid metabolism pathways were not significantly and differentially expressed. The irrigation with saline water significantly increased leaf chloride contents in the scion onto the M-rootstocks, but not onto the 1103P. The limitation for leaf Cl– and Na+ accumulation on the scion was conferred by rootstock. Few processes were differentially regulated in the scion in response to the saline treatment, mainly, in the groups of genes involved in the flavonoids and phenylpropanoids metabolic pathways. However, these transcriptomic effects were not fully reflected in grape phenolic ripeness, with M4 being the only one that did not cause reductions in these compounds in response to salinity, and 1103-Paulsen having the highest overall concentrations. These results suggest that all three rootstocks confer short-term salinity tolerance to the scion. The lower transcriptomic changes and the lower accumulation of potentially phytotoxic ions in the scion grafted onto 1103-Paulsen compared to M-rootstocks point to the former being able to maintain this physiological response in the longer term. Further agronomic trials should be conducted to confirm these effects on vine physiology and transcriptomics in mature vineyards.

Co-application of Phosphorus and Sulfur Improve Yield, Quality, and Nutrients Uptake in Nicotiana tabaccum L.

A field experiment was carried out to evaluate the interactive effect of phosphorus (0, 30, 60, and 90 kg P2O5 ha-1) and sulfur (0, 15, 30, and 45 kg ha-1) on yield, quality, and uptake of nutrients by tobacco (Nicotiana tabaccum L.). The experiment was organized in a two-factorial randomized complete block design with three replications at Tobacco Research Station, Mardan, Pakistan in 2017-2018. Application of 90 kg P2O5 ha-1 improved tobacco leaf area (24.2%), green leaf weight (44.5%), cured leaf weight (44.7%), grade index (18.3%), nicotine (35.8%), sugar (12%), and P (24.5%) contents but decreased S content (35.3%) over control phosphorus plots. Similarly, application of 45 kg S ha-1 optimized leaf area (13.6%), grade index (12%), nicotine (15%), P (5.9%), and S (96%) contents over control sulfur plots. Interactively, P application antagonized leaf S content. However, it did not show any adverse effect on other agronomic and quality parameter. Both P and S application decrease leaf chloride content by 43.5% and 21.4%, respectively. Thus, 90 kg P2O5 ha-1 along with 45 kg S ha-1 is recommended for obtaining optimum yield of good quality tobacco crop.

Effect of NaCl road salt on the ionic composition of soils and Aesculus hippocastanum L. foliage and leaf damage intensity

We investigated the accumulation of sodium chloride in roadside soils and common horse chestnut Aesculus hippocastanum L. under urban conditions to evaluate changes in soil and leaf ionic content and their relationship with foliar damage, considering the visual assessment of trees of the same health status. A total of 15 field sites were assessed in late June 2016. The analysis included soil granulometric composition, pH, electrical conductivity, and the content of Cl−, Na+, K+, Ca2+, and Mg2+ ions in soil and foliage samples. The results showed increased salinity and alkalization of roadside soils together with the decreased magnesium content. Foliage samples manifested significantly higher concentrations of Na+ and Cl−. A wide range of Cl− content was noted in leaves (2.0–11.8% d.w.) regardless of their damage index. On the contrary, leaf damage was strongly correlated with increasing Na+ concentrations and decreasing K+ and Mg2+. A severe imbalance of nutrients, and therefore poor urban tree vitality, can be attributed to the excessive accumulation of de-icing salt. However, further research would be needed to clarify the discrepancy between the extent of leaf damage and chloride content.

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

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

Seedling Emergence and Seedling Growth of Mustard and Rapeseed Genotypes under Salt Stress

Core Ideas Varietal differences in salt tolerance were observed. There were differences in salt tolerance between the seedling emergence and seedling growth stages. Growth and photosynthesis decreased at high salinity, indicating osmotic stress. Chlorophyll fluorescence did not decrease at high salinity, indicating no stress on photosystem II. Leaf chloride concentrations varied among genotypes, suggesting different salt tolerance mechanisms. Salt‐tolerant energy crops can be grown on marginal lands for sustainable biofuel production without competing with food crops for arable land. However, salt tolerance is a variable trait among plant species, varieties, and growth stages. In this study, the relative salt tolerance of seven mustard (Brassica juncea) genotypes and four rapeseed (Brassica napus) genotypes was evaluated at the seedling emergence and seedling growth stages. In the first experiment, seeds were sown in a growth chamber with reverse osmosis water or saline solution at an electrical conductivity (EC) of 10 mS cm−1 for 10 d, and emergence was determined daily. In the second experiment, seedlings were grown in a greenhouse and irrigated with nutrient solution (control) with an EC of 1.5 mS cm−1 or saline solutions (EC 5 and 10 mS cm−1, respectively) for 4 wk. For the seedling emergence stage, the relative emergence percent, and emergence index showed great variation among genotypes (range, 11–112% and 7–110%, respectively). For the seedling growth stage, the saline treatments caused reductions in leaf area and fresh and dry biomass that averaged 63, 65, and 65% relative to the control, respectively. Overall, hierarchal cluster analyses showed differences in salt tolerance between the seedling emergence and seedling growth stages. Net photosynthetic rate decreased with salinity, but soil‐plant analysis development readings increased by an average of 18% in the EC10 treatment. Chlorophyll fluorescence did not change, but performance index tended to increase in response to salinity. Chloride concentrations in the leaf tissue increased with salinity and ranged from 32 to 111 mg g−1, with significant varietal differences.

Controlling salt flushing using a salinity index obtained by soil dielectric sensors improves the physiological status and quality of potted hydrangea plant

Flushing is an effective tool for controlling the concentration of salt in the growing medium, where it affects ion uptake, water flow through the root and, consequently, the quality of the plant. To avoid over-irrigation in flushing, reliable methods for monitoring soil salinity are required. This paper studies the effectiveness of an index to determine substrate salinity in potted Hydrangea macrophylla when soil moisture and electrical conductivity (EC) sensors are used. The salinity index was calculated as the average of measurements of pore water EC between two successive irrigation events, based on GS3-Decagon sensor readings and the Hilhorst Model. Three treatments were applied: GS3-treatment (saline irrigation with flushing according to the salinity index), S-treatment (saline irrigation with no flushing), and control (irrigation with fresh water and no flushing). The plants of the S-treatment exhibited lower aerial dry weight, greater flower damage, poorer appearance, higher leaf chloride content, lower photosynthesis rate, and poorer photochemical behaviour than the plants from the other treatments. The better physiological behaviour and ornamental quality of the plants of the GS3-treatment compared with that observed for the S-treatment suggest that this salinity index is a reliable indicator to control salt flushing.

Quantitative trait loci for salt tolerance in soybean

ABSTRACT Soybean [Glycine Max (L.) Merr.] growth and yield are adversely affected by soil salinity. Identification of salinity tolerance genes that improve soybean performance in saline soils is a highly effective way to use and develop soybean genotypes with high salt tolerance. The objective of this study is to identify and confirm quantitative trait loci (QTL) associated with salt tolerance using an F2:3 mapping population derived from the cross Ozark (salt-sensitive) × Jake (salt-tolerant). This population was screened in the greenhouse for salt stress using 120 mM NaCl and evaluated for leaf scorch score (LSS), percentage of dead plants (PDP), leaf chlorophyll, and leaf chloride content, and genotyped using a SoySNP 6K chip. A major QTL on chromosome 3 was confirmed, and a minor QTL on chromosome 19 and additional single nucleotide polymorphism (SNP) markers associated with salt tolerance were found in this study. These markers, once validated, will be valuable for marker-assisted selection in a soybean breeding program.

Relative Salt Tolerance of 22 Pomegranate (Punica granatum) Cultivars

A greenhouse experiment was conducted to determine the relative salt tolerance of pomegranate (Punica granatum) cultivars. Twenty-two pomegranate cultivars were irrigated weekly with a saline solution at an electrical conductivity (EC) of 10.0 dS·m–1 for 4 weeks and subsequently with a saline solution at an EC of 15.0 dS·m–1 for another 3 weeks (salt treatment). Another group of uniform plants was watered with a nutrient solution without additional salts at an EC of 1.2 dS·m–1 (control). No visual foliar salt damage (leaf burn, necrosis, or discoloration) was observed during the entire experimental period; however, salt treatment impacted pomegranate growth negatively, with a large variation among cultivars. Salt treatment reduced shoot length by 25% and dry weight (DW) by 32% on average for all cultivars. Cluster analysis classified the 22 tested pomegranate cultivars in two groups. The group consisting of ‘Arturo Ivey’, ‘DeAnda’, ‘Kazake’, ‘Russian 8’, ‘Apseronski’, ‘Purple Heart’, ‘Carolina Vernum’, ‘Chiva’, ‘Kunduzski’, ‘Larry Ceballos 1’, ‘ML’, ‘Salavatski’, ‘Spanish Sweet’, and ‘Wonderful’ was more salt tolerant than the group including ‘Al-Sirin-Nar’, ‘Kandahar’, ‘Surh-Anor’, ‘Early Wonderful’, ‘Angel Red’, ‘Ben Ivey’, ‘Utah Sweet’, and ‘Mollar’. The sodium (Na) concentration in the leaf tissue of all 22 pomegranate cultivars was less than 1 mg·g–1 on a DW basis. All pomegranate cultivars in the salt treatment had an average leaf chloride (Cl) content of 10.03 mg·g–1 DW—an increase of 17% from the control. These results indicate that pomegranate plants have a strong capability to exclude Na and Cl accumulation in leaf tissue. In conclusion, the pomegranate plant is very tolerant to saline water irrigation up to an EC of 15 dS·m–1 with little foliar salt damage and a slight growth reduction. Investigation is needed to determine the effects of saline water on the fruit yield and nutritional quality of pomegranate.

Relative Salt Tolerance of Eight Japanese Barberry Cultivars

Relative salt tolerance of eight Berberis thunbergii (japanese barberry) cultivars (B. thunbergii ‘Celeste’, ‘Kasia’, ‘Maria’, ‘Mini’, and ‘Talago’; B. thunbergii var. atropurpurea ‘Concorde’, ‘Helmond Pillar’, and ‘Rose Glow’) was evaluated in a greenhouse experiment. Plants were irrigated with nutrient solution at an electrical conductivity (EC) of 1.2 dS·m−1 (control) or saline solutions at an EC of 5.0 or 10.0 dS·m−1 (EC 5 or EC 10) once a week for 8 weeks. At 4 weeks after treatment, all barberry cultivars in EC 5 had minimal foliar damage with visual scores of 4 or greater (visual score 0: dead, 5: excellent). At 8 weeks after treatment, in EC 5, ‘Helmond Pillar’, ‘Maria’, ‘Mini’, and ‘Rose Glow’ plants exhibited slight foliar salt damage with an average visual score of 3.5, whereas ‘Celeste’, ‘Concorde’, ‘Kasia’, and ‘Talago’ had minimal foliar salt damage with an averaged visual score of 4.4. However, most barberry plants in EC 10 exhibited severe foliar salt damage 4 weeks after treatment with the exception of ‘Concorde’ and were dead 8 weeks after treatment. Compared with control, at the end of the experiment (8 weeks of treatments), shoot dry weight (DW) of ‘Celeste’, ‘Helmond Pillar’, ‘Maria’, and ‘Rose Glow’ in EC 5 was reduced by 47%, 47%, 50%, and 42%, respectively, whereas shoot DW of ‘Concorde’, ‘Kasia’, ‘Mini’, and ‘Talago’ in EC 5 did not change. In EC 10, shoot DW of ‘Celeste’, ‘Concorde’, ‘Kasia’, and ‘Talago’ was reduced by 75%, 35%, 55%, and 46%, respectively. The averaged sodium (Na) concentration of all barberry cultivars in EC 5 and EC 10 was 34 and 87 times, respectively, higher than the control, whereas leaf chloride (Cl) concentration of all barberry cultivars in EC 5 and EC 10 was 14–60 and 29–106 times, respectively, higher than the control. Growth, visual quality, and performance index (PI) were all negatively correlated with leaf Na and Cl content in all cultivars, suggesting that excessive Na and Cl accumulation in the leaf tissue led to growth reduction, salt damage, and death. In summary, ‘Concorde’, ‘Kasia’, and ‘Talago’ were relatively salt tolerant; ‘Helmond Pillar’, ‘Maria’, ‘Mini’, and ‘Rose Glow’ were relatively salt sensitive; and ‘Celeste’ was in between the two groups. Generally, barberry plants had moderate salt tolerance and can be irrigated with marginal water at an EC of 5 dS·m−1 or lower with slight foliar damage.

Mapping and confirmation of loci for salt tolerance in a novel soybean germplasm, Fiskeby III.

The confirmation of a major locus associated with salt tolerance and mapping of a new locus, which could be beneficial for improving salt tolerance in soybean. Breeding soybean for tolerance to high salt conditions is important in some regions of the USA and world. Soybean cultivar Fiskeby III (PI 438471) in maturity group 000 has been reported to be highly tolerant to multiple abiotic stress conditions, including salinity. In this study, a mapping population of 132 F2 families derived from a cross of cultivar Williams 82 (PI 518671, moderately salt sensitive) and Fiskeby III (salt tolerant) was analyzed to map salt tolerance genes. The evaluation for salt tolerance was performed by analyzing leaf scorch score (LSS), chlorophyll content ratio (CCR), leaf sodium content (LSC), and leaf chloride content (LCC) after treatment with 120mM NaCl under greenhouse conditions. Genotypic data for the F2 population were obtained using the SoySNP6K Illumina Infinium BeadChip assay. A major allele from Fiskeby III was significantly associated with LSS, CCR, LSC, and LCC on chromosome (Chr.) 03 with LOD scores of 19.1, 11.0, 7.7 and 25.6, respectively. In addition, a second locus associated with salt tolerance for LSC was detected and mapped on Chr. 13 with an LOD score of 4.6 and an R 2 of 0.115. Three gene-based polymorphic molecular markers (Salt-20, Salt14056 and Salt11655) on Chr.03 showed a strong predictive association with phenotypic salt tolerance in the present mapping population. These molecular markers will be useful for marker-assisted selection to improve salt tolerance in soybean.

Alleviatory activities in mycorrhizal tobacco plants subjected to increasing chloride in irrigation water

The effects of presence and absence of arbuscular mycorrhizal (AM+ and AM-) fungus (AMF) Glomus intraradices on agronomic and chemical characteristics of field-grown tobacco (Nicotiana tabacum L.) Virginia type (cv. K-326) plants exposed to varying concentrations of chloride 10, 40, 70 and 100 mg Cl L–1 (C1-C4) were studied over two growing seasons (2012-2013). Mycorrhizal plants had significantly higher uptake of nutrients in shoots and number of leaves regardless of intensities of chloride stress. The cured leaves yields of AM+ plants under C2-C4 chloride stressed conditions were higher than AM- plants. Leaf chloride content increased in line with the increase of chloride level, while AMF colonised plants maintained low Cl content. AM+ plants produced tobacco leaves that contained significantly higher quantities of nicotine than AM- plants. AM inoculation ameliorated the chloride stress to some extent. Antioxidant enzymes like superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase as well as non-enzymatic antioxidants (ascorbic acid and glutathione) also exhibited great variation with chloride treatment. Chloride stress caused great alterations in the endogenous levels of growth hormones with abscisic acid showing increment. AMF inoculated plants maintained higher levels of growth hormones and also allayed the negative impact of chloride. The level of 40 mg L–1 in combination with arbuscular mycorrhizal can be considered as the acceptable threshold to avoid adverse effects on Virginia tobacco.

Genome-wide association study (GWAS) of salt tolerance in worldwide soybean germplasm lines

Salt is a severe abiotic stress causing soybean yield loss in saline soils and irrigated fields. Marker-assisted selection (MAS) is a powerful genomic tool for improving the efficiency of breeding salt-tolerant soybean varieties. The objectives of this study were to uncover novel single-nucleotide polymorphisms (SNPs) and quantitative trait loci (QTLs) associated with salt tolerance and to confirm the previously identified genomic regions and SNPs for salt tolerance. A total of 283 diverse soybean plant introductions (PIs) were screened for salt tolerance in the greenhouse based on leaf chloride concentrations and leaf chlorophyll concentrations after 12–18 days of 120-mM NaCl treatment. A total of 33,009 SNPs across 283 genotypes from the Illumina Infinium SoySNP50K BeadChip database were employed in the association analysis with leaf chloride concentrations and leaf chlorophyll concentrations. Genome-wide association mapping showed that 45 SNPs representing nine genomic regions on chromosomes (Chr.) 2, 3, 7, 8, 10, 13, 14, 16, and 20 were significantly associated with both leaf chloride concentrations and leaf chlorophyll concentrations in 2014, 2015, and combined years. A total of 31 SNPs on Chr. 3 were mapped at or near the previously reported major salt tolerance QTL. The significant SNP on Chr. 2 was also in proximity to the previously reported SNP for salt tolerance. The other significant SNPs represent seven putative novel QTLs for salt tolerance. The significant SNP markers on Chr. 2, 3, 14, 16, and 20, which were identified in both general linear model and mixed linear model, were highly recommended for MAS in breeding salt-tolerant soybean varieties.

Differences in specific chloride toxicity to Diospyros kaki cv. “Rojo Brillante” grafted on D. lotus and D. virginiana

Persimmon trees grafted on D. lotus have been found to be extensively affected by leaf necrosis in the important cropping area of Valencia (E Spain). Although this problem has been attributed to chloride toxicity, this association had not been rigorously demonstrated. In addition the chloride and salinity tolerance of persimmons grafted on D. lotus has not been characterised, and neither has the performance of this rootstock been compared to D. virginiana. Two outdoors experiments, one in pots, and another one in the field were set up and conducted for three years with trees grafted on both rootstocks. Trees in the pots experiment were arranged in five groups and irrigated with waters differing in their salt and thus, Cl−, Ca2+ and Na+ water contents. Season-end leaf contents of Na, Cl, N, P, K, Ca, Mg, S, B, Cu, Fe, Mn and Zn, toxicity symptoms and fruit yields were assessed. In the field experiment, one irrigation water quality was used, and just leaf chloride contents, water potential and fruit yields were evaluated. Field toxicity symptoms were reproduced in the pots experiment in the trees on D. lotus, but not on D. virginiana, with leaf chloride contents increasing with increasing irrigation water salinity. Leaf chloride contents were much higher than either sodium or boron, and significantly more correlated with toxicity symptoms. Comparing to chloride toxicity and salinity tolerance data from similar woody crops, D. lotus was classified as sensitive to salinity with, respectively, threshold ECe and slope of 1.2dSm−1 and 22 dS−1m. D. lotus rootstocks lend persimmon trees very lower ability to avoid chloride toxicity likely because of, on the one hand, its low soil exploration capacity, and, on the other hand, its low chloride exclusion capacity. In return, however, D. lotus lends persimmon trees more productivity, which still keeps for waters with slight-to-moderate chloride contents (3–4mmol/L).

Determination of persimmon leaf chloride contents using near-infrared spectroscopy (NIRS).

Early diagnosis of specific chloride toxicity in persimmon trees requires the reliable and fast determination of the leaf chloride content, which is usually performed by means of a cumbersome, expensive and time-consuming wet analysis. A methodology has been developed in this study as an alternative to determine chloride in persimmon leaves using near-infrared spectroscopy (NIRS) in combination with multivariate calibration techniques. Based on a training dataset of 134 samples, a predictive model was developed from their NIR spectral data. For modelling, the partial least squares regression (PLSR) method was used. The best model was obtained with the first derivative of the apparent absorbance and using just 10 latent components. In the subsequent external validation carried out with 35 external data this model reached r(2) = 0.93, RMSE = 0.16% and RPD = 3.6, with standard error of 0.026% and bias of -0.05%. From these results, the model based on NIR spectral readings can be used for speeding up the laboratory determination of chloride in persimmon leaves with only a modest loss of precision. The intermolecular interaction between chloride ions and the peptide bonds in leaf proteins through hydrogen bonding, i.e. N-H···Cl, explains the ability for chloride determinations on the basis of NIR spectra.

Salt tolerance traits revealed in mandarins (Citrus reticulata Blanco) are mainly related to root-to-shoot Cl− translocation limitation and leaf detoxification processes

Mandarin is an important genetic group in citrus largely used for variety breeding programs and also to generate new rootstocks better adapted to abiotic stress. In this study, 14 mandarin accessions representative of the diversity in this group were analyzed for their salt stress tolerance properties. Physiological parameters such as gas exchange, osmotic pressure, as well as leaf and root chloride contents were measured. Samples were harvested to characterize the presence of hydrogen peroxide and to monitor the activity of enzymes involved in reactive oxygen species synthesis and detoxification processes. Very different physiological behaviors were noted among accessions. Most cultivars that are used as rootstocks such as Citrus reshni Hort. ex Tan. (‘Cleopatra’) or Citrus depressa Hayata (‘Shekwasha’), were found to be tolerant, with limited root-to-shoot chloride translocation. Also, some accessions used as varieties showed similar tolerance traits. Interestingly some accessions that presented high leaf chloride contents were not always associated with sensitivity traits. Also accessions such as ‘Willowleaf’ showed quite high leaf chloride contents that were correlated with better detoxification processes. Tolerance traits that we identified are discussed in relation to the known genetic structure in mandarins. Finally, some of the salt stress tolerant accessions that we identified could potentially be used as parents in rootstock breeding programs and others in scion variety breeding programs.

Effects of a commercial calcium protein hydrolysate on the salt tolerance of Diospyros kaki L. cv. “Rojo Brillante” grafted on Diospyros lotus L.

Diospyros lotus L. is advantageously used as rootstock for Diospyros kaki L. cv. “Rojo Brillante” in most plantations of Eastern Spain. However, one of the few drawbacks of D. lotus L. as rootstock, is the high sensitivity to soil salinity, and specifically chloride, it imparts to the scion, which is visually detected as an extensive late season leaf necrosis. Several complex mixtures of organic polymers such as calcium protein hydrolysates (CPH) have been recommended to counteract salt stress on plants. Nevertheless, the effects of these commercial complex products on tree crops, are not usually rigorously studied, nor satisfactorily explained. The effects on soil and plant of the addition of a commercial CPH in the irrigation water of a D. kaki L. cv. “Rojo Brillante” plantation grafted on D. lotus L. were studied during two successive seasons. Soil salinity and chloride contents, significantly, but slightly, increased in CPH treated subplots, while at the same time leaf chloride contents decreased. These effects suggest a lower chloride plant uptake in CPH treated subplots. The lower chloride uptake in CPH treated trees was accompanied by less leaf necrosis, and also lower leaf water potential. However, the yields of CPH treated and non-treated trees were statistically non-different. The build-up of compatible solutes, mainly proline and glycine betaine, in addition to the biosynthesis of salt-stress-response proteins, which would have been stimulated by the CPH, could explain the observed effects. However, the likely biosynthesis of all these substances may have drawn plant resources from fruit development, thus explaining why yields were the same in treated and non-treated subplots despite the trees in treated subplots showed better adaptation to soil salinity.

SALT STRESS TOLERANCE IN ACIDIC AND SWEET MANDARINS

Mandarin genotypes can be split in two main groups: the acidic and the sweet mandarins. Commonly, acidic are used as rootstocks when sweet mandarins are the varieties that are consumed as fruits. The acidic 'Cleopatra' mandarin (Citrus reshni Hort. ex Tan.) is considered to be the most salt stress tolerant rootstock since it is able to limit the absorption of chloride and sodium at root level. As a consequence, limited amount of toxic ions are translocated from root to leaves. If salt stress tolerance of 'Cleopatra' mandarin and its hybrids has been well documented, little data exist for sweet mandarins. We investigated 16 genotypes representing a large diversity in mandarins subjected to salt stress. Physiological parameters such as stomatal conductance and leaf chloride contents were analyzed. If most of the acidic varieties were tolerant, also some sweet varieties presented traits of tolerance. Taking into account the results of leaf ion contents, we observed that large leaf chloride contents were not always associated with sensitivity. (Resume d'auteur)

BEHAVIOR OF DIPLOID AND TETRAPLOID GENOTYPES OF 'CARRIZO' CITRANGE UNDER ABIOTIC STRESS

Tetraploidy is a spontaneous phenomenon in citrus and some anatomical differences have been described between tetraploid (4x) citrus plants and their corresponding diploids (2x). The choice of a suitable rootstock is often very restricted by a combination of biotic and abiotic stresses. Recent data points out that tetraploidy in citrus induces interesting phenotypes like dwarfing and tolerance to abiotic constraints. In this work we investigated the behavior of 4x and 2x 'Carrizo' citrange (Citrus sinensis X Poncirus trifoliata) subjected to the main abiotic stresses that threat Spanish citrus industry. Seedlings were exposed to salinity, drought and iron deficiency and physiological parameters were measured. Results suggest that 4x plants stressed by drought were able to maintain high leaf water potential more efficiently than 2x, thus gas exchange parameters (transpiration, stomatal conductance, and photosynthesis) were less affected. Under salt stress no difference was found in leaf chloride content neither in gas exchange parameters, but leaf burn was less severe in 4x than in 2x. Concerning iron deficiency, a better tolerance of 4x compared to 2x was supported by higher ferricchelate reductase activity, SPAD index and chlorophyll fluorescence. These preliminary results suggest that 4x 'Carrizo' citrange could be a promising rootstock, having the same general performance than the original 2x, but producing smaller trees more tolerant to abiotic stresses. (Resume d'auteur)

Genetic diversity revealed by physiological behavior of citrus genotypes subjected to salt stress

Different physiological behavior of a wide range of varieties and species belonging to the Citrus genus was analyzed when subjected to salt stress with the aim to seek new sources of tolerance that might be specie-specific. Our goal was to use physiological results obtained along a salt stress in order to clarify if it would be possible to associate them with the known citrus genetic diversity. For that purpose, we have selected 20 different genotypes representing the major species on the basis of the genetic diversity of Citrus genus complemented with one intergeneric hybrid Carrizo citrange (C. sinensis × P. trifoliata). A moderate salt stress of 75 mM of NaCl was applied for 12 weeks. For control plants, the main parameters contributing for more than 25 % to the diversity on the two axes of principal component analysis (PCA) were chlorophyll content, photosynthesis and Fv/Fm under light. However, the dispersal of species and varieties on the PCA did not show any particular structure. Under salt stress condition, four parameters (leaf chloride content, leaf chlorophyll content, photosynthesis and stomatal conductance) contributed more specifically to the dispersion on PCA representation with more than 15 % of contribution for each parameter. Large differences were observed within citrus genus: mandarin and pummelo presented good tolerance to salt stress while citron was very sensitive. Furthermore, all secondary genotypes that presented good tolerance to salt tolerance shared mandarin or pummelo as female parent.

Characterization in greenhouse conditions of two salt tolerant citrumelo (Citrus paradisi Macf. x Poncirus trifoliata (L.) Raf.) cultivars

Increasing salinity in Mediterranean soils and the wide spread of citrus tristeza virus have challenged the use of sour orange (Citrus aurantium) and have accelerated the process of seeking alternative rootstocks. In the present study, nine cultivars of citrumelo (Citrus paradisi Macf. x Poncirus trifoliata (L.) Raf.) were evaluated for salt tolerance. Two month-old seedlings were raised under greenhouse conditions and irrigated with a half strength Hoagland solution supplemented with different concentrations of NaCl, i.e., 0 mM, 35 mM and 85 mM. Tolerance was assessed after two months of stress by measuring stem growth, number of leaves, fresh and dry weight organs and leaf water, chlorophyll and chloride contents. A differential behavior was noticed among the seedlings we studied. When using increased concentration of salt in irrigation water, all the parameters were significantly reduced except for leaf chloride content which highly increased in response to stress. At 85 mM, the cultivar SC2 showed a high tolerance resulting in less apparent leaf symptoms, higher growth and higher leaf chlorophyll content when compared to other seedlings. Similarly, the cultivar C4475-C was shown to be a strong root chloride excluder with less than 2.6% DW (dry weight) chloride accumulation at leaf level. By contrast, our results suggest that C4475-A and C4475-B are salt sensitive cultivars regarding to all the parameters studied while the other citrumelos were considered as moderately tolerant.