Growth and inorganic composition of ‘Nova’ mandarin plants grafted on two commercial rootstocks in response to salinity and silicon

The effects of salinity and its combination with silicon (Si) were studied in ‘Nova’ mandarin plants grafted on Citrus aurantium L. or Swingle Citrumelo to determine: (1) which combination is more tolerant to salt stress and (2) the impact of Si in limiting the harmful effects of salinity. Six groups of plants were grown in a greenhouse for 120 days and irrigated with: (1) 50 % Hoagland’s solution (Control), (2) 50 % Hoagland’s solution plus 80 mM NaCl (NaCl), and (3) 50 % Hoagland’s solution plus 80 mM NaCl plus 0.5 mM Si (NaCl + Si). Grafted plants exhibited accumulation of Na and Cl in their tissues following exposure to salinity. The ability of S. Citrumelo to retain the toxic ions in the roots in corroboration with the observation that the dry weights (DWs) of S. Citrumelo tissues were not influenced by NaCl treatment indicates that this rootstock is more tolerant to salinity. Silicon supplementation into the saline medium promoted the accumulation of toxic ions, whereas, when compared to NaCl treatment, it increased the DW of S. Citrumelo roots. Mineral concentrations were significantly affected by rootstock, treatment, and their interaction with S. Citrumelo, which presented better nutrient status than Sour Orange; and Si which differed depending on citrus tissue. It appears that S. Citrumelo rootstock is the most tolerant for ‘Nova’ mandarin plants under salinity, whereas salt tolerance in grafted citrus plants is not improved by Si application, indicating that the beneficial role of Si depends on the cultivar or rootstock–scion combinations.     

Effect of zinc nutrition on salinity-induced oxidative damages in wheat genotypes differing in zinc deficiency tolerance

Zinc deficiency and salinity are well-documented soil problems and often occur simultaneously in cultivated soils. Usually, plants respond to environmental stress factors by activating their antioxidative defense mechanisms. The antioxidative response of wheat genotypes to salinity in relation to Zn nutrition is not well understood. So, we investigated the effect of Zn nutrition on the growth, membrane permeability and sulfhydryl group (–SH groups) content of root cells and antioxidative defense mechanisms of wheat plants exposed to salt stress. In a hydroponic experiment, three bread wheat genotypes (Triticum aestivum L. cvs. Rushan, Kavir, and Cross) with different Zn-deficiency tolerance were exposed to adequate (1 μM Zn) and deficient (no Zn) Zn supply and three salinity levels (0, 60, and 120 mM NaCl). The results obtained showed that adequate Zn nutrition counteracted the detrimental effect of 60 mM NaCl level on the growth of all three wheat genotypes while it had no effect on the root and shoot growth of ‘Rushan’ and ‘Kavir’ at the 120 mM NaCl treatment. At the 0 and 60 mM NaCl treatments, Zn application decreased root membrane permeability while increased –SH group content and root activity of catalase (CAT) and superoxide dismutase (SOD) in ‘Rushan’ and ‘Kavir’. In contrast, Zn had no effect on the root membrane permeability and –SH group content of ‘Rushan’ and ‘Kavir’ exposed to the 120 mM NaCl treatment. At all salinity levels, ‘Cross’ plants supplied with Zn had lower root membrane permeability and higher –SH group content compared to those grown under Zn-deficient conditions. At the 0 and 60 salinity levels, Zn-deficient roots of Kavir and Rushan genotype leaked significantly higher amounts of Fe and K than the Zn-sufficient roots. In contrast, at the 120 mM treatment, Zn application had no effect or slightly increased Fe and K concentration in the root ion leakage of these wheat genotypes. For ‘Cross’, at all salinity levels, Zn-deficient roots leaked significantly higher amounts of Fe and K compared with the Zn-sufficient roots. The differential tolerance to salt stress among wheat genotypes examined in this study was related to their tolerance to Zn-deficiency, –SH group content, and root activity of CAT and SOD. Greater tolerance to salinity of Zn-deficiency tolerant genotype ‘Cross’ is probably associated with its greater antioxidative defense capacity.     

硅对干旱胁迫下玉米水分代谢的影响

利用盆栽试验研究了施硅(K2SiO3)对玉米植株水分代谢的影响.结果表明:施硅降低了干旱胁迫下玉米植株的气孔导度,降低了干旱胁迫早期到中期的蒸腾速率,保持了干旱胁迫后期较高的蒸腾速率,从而导致施硅玉米植株的叶片含水量和水势高于对照.由于植株的水分状况改善,施硅玉米植株生物量高于对照.硅增强玉米植株的抗旱性,而提高植株保水能力是硅提高抗旱性的重要原因.     

Silicon Application to Rice Root Zone Influenced the Phytohormonal and Antioxidant Responses Under Salinity Stress

Silicon (Si) application shows beneficial effects on plant growth; however, its effects on the phytohormone and enzymatic antioxidant regulation have not been fully understood. We studied the effects of short-term (6, 12, and 24 h) silicon (0.5, 1.0, and 2.0 mM) application on salinity (NaCl)-induced phytohormonal [abscisic acid (ABA), jasmonic acid (JA), and salicylic acid (SA)] and antioxidant regulation in Oryza sativa. The results showed that Si treatments significantly increased rice plant growth compared to controls under salinity stress. Si treatments reduced the sodium accumulation resulting in low electrolytic leakage and lipid peroxidation compared to control plants under salinity stress. Enzymatic antioxidant (catalase, peroxidase and polyphenol oxidase) responses were more pronounced in control plants than in Si-treated plants under salinity stress. Stress- and defense-related phytohormones like JA were significantly downregulated and SA was irregular after short-term Si applications under salinity stress compared to control. Conversely, ABA was significantly higher after 6 and 12 h but insignificant after 24 h in Si-treated plants under salinity stress. After 6 and 12 h, Si and salinity stress resulted in upregulation of zeaxanthin epoxidase and 9-cis-epoxycarotenoid dioxygenase 1 and 4 (NCED1 and 4), whereas 24-h treatments significantly downregulated the expressions of these genes compared to those in the control. NCED3 expression increased after 6 and 24 h but it was insignificant after 12 h of Si application compared to control. The current findings indicate that increasing the Si concentrations for longer periods of time can regulate the salinity-induced stress by modulating phytohormonal and enzymatic antioxidants’ responses.     

Separate and combined effects of silicon and selenium on salt tolerance of wheat plants

Soil salinity is the leading global abiotic stress which limits agricultural production with an annual increment of 10%. Therefore; a pot experiment was conducted with the aim to alleviate the salinity effects on wheat seedlings through exogenous application of silicon (Si) and selenium (Se). Treatments included in the study were viz. (Ck) control (no NaCl nor Si and Se added), only salinity (50 mM NaCl), salinity + Si (50 mM NaCl with 40 mM Si), salinity + Se (50 mM NaCl with 40 mM Se) and salinity + Si + Se (50 mM NaCl + 40 mM Si + 40 mM Si). The salt stress impaired the growth (root and shoot dry weight, root: shoot ratio, seedlings biomass), water relations, photosynthetic attributes, transpiration rate and chlorophyll contents of wheat seedlings. Nonetheless, the foliar application of Si and Se alone and in combination improved the growth, water relations, photosynthetic attributes, transpiration rate and chlorophyll contents of wheat seedlings under stressed conditions. Moreover, an increase in antioxidant enzyme activity and accumulation of osmo-protectants (proline, soluble protein and soluble sugar) was noted under stressed conditions, which was more pronounced in wheat seedling which experienced combined application of Si and Se. To conclude that, foliar application of Si alone mitigated the adverse effect of salinity, while the combined application of Si and Se was proved to be even more effective in alleviating the toxic effects of salinity stress on wheat seedlings.     

Alleviation of detrimental effects of NaCl by silicon nutrition in salt-sensitive and salt-tolerant genotypes of sugarcane (Saccharum officinarum L.)

Salt stress is a major environmental factor which adversely affects the crop yield and quality. However, adequate regulation of mineral nutrients may ameliorate the deleterious effects of salts and help to sustain crop productivity under salt stress. Salt-sensitive (SPF 213) and salt-tolerant (HSF 240) sugarcane genotypes were grown in gravel at 0 and 100 mM NaCl by supplying 0, 1.4 mM, 2.1 mM and 2.8 mM of Si as calcium silicate. Results revealed that plants treated with NaCl alone showed a significant (P?≤?0.05) reduction in dry matter production, K⁺ concentration, cane yield and juice quality in both genotypes but the magnitude of reduction was relatively more in salt-sensitive genotype than salt-tolerant. Addition of Si significantly (P?≤?0.05) reduced the uptake and translocation of Na⁺ but increased K⁺ concentrations particularly in shoots of both sugarcane genotypes. Cane yield and yield attributes were significantly (P?≤?0.05) higher where Si was added. Juice quality characteristics were significantly (P?≤?0.05) improved in salt-sensitive and salt-tolerant sugarcane genotypes with the application of Si. The results suggested that added Si interacted with Na⁺, reduced its uptake and transport to shoots and consequently improved cane yield and juice quality in salt-sensitive and salt-tolerant sugarcane genotypes under salt stress.     

Sensitivity of different flax (Linum usitatissimum L.) genotypes to salinity determined by GE biplot

Plants respond differently to salt stress depending on their genetic structure and the severity of the stress. Salinity reduces seed germination, delays plant emergence, and inhibits seedling growth. The selection of the tolerant genotypes, however, plays a vital role in increasing agricultural output since various genotypes greatly vary for their tolerance to salinity. Therefore, this study determined the impact of five different NaCl levels (i.e., 0, 50, 100, 150 and 200 mM) on seed germination and growth attributes of 10 flax (Linum usitatissimum L.) genotypes. The germination and growth characteristics of the genotypes under study were examined using the biplot approach at varied salt levels. The results indicated that individual and interactive effects of genotypes and salinity levels significantly (p ≤ 0.01 or p ≤ 0.05) affected several seed germination traits. The relations of genotype × germination traits indicated that ‘G4′ and ‘G6′ were the most stable genotypes with the highest performance regarding seed germination characteristics. The genotype ‘G2′ was associated with shoot length, while ‘G7′ was linked with salinity tolerance index. The biplot divided the germination characteristics into five different groups according to sector analysis. Most of the germination parameters had higher values under 100 mM, while some of the parameters had better values under 0, 50 and 200 mM NaCl levels. The tested genotypes varied for their seed germination and growth response depending on the NaCl levels. The genotypes ‘G4′, ‘G5′ and ‘G6′ proved more tolerant to high NaCl levels. Therefore, these genotypes can be used to improve flax productivity under saline soils.     

Effects of silicon on photosynthesis,water relations and nutrient uptake of <Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> under NaCl stress

A greenhouse experiment was conducted to investigate the effects of silicon application on Phaseolus vulgaris L. under two levels of salt stress (30 and 60 mM NaCl in the irrigation water). Salinity significantly reduced growth, stomatal conductance and net photosynthetic rate, and increased Na⁺ and Cl⁻ content mainly in roots. Silicon application enhanced growth of salt stressed plants, significantly reduced Na⁺ content especially in leaves and counterbalanced the effects of NaCl on gas exchange; the effect was more evident at 30 mM NaCl. Cl⁻ content in shoots and roots was not significantly modified by silicon application; the drop in K⁺ content caused by salinity was partially counterbalanced by silicon, especially in roots.     

Silicon increases salt tolerance by influencing the two-phase growth response to salinity in wheat (Triticum aestivum L.)

Salt usually stresses plants in two ways, osmotic stress and ion toxicity. Plant responds to salinity in two distinct phases through time. It is known that silicon (Si) could alleviate salt stress by decreasing the Na⁺ accumulated in the leaf. In order to determine the function of Si in the two-phase growth response (osmotic and ion toxicity) to salinity, we selected the wheat cultivar “Changwu 134” out of 10 wheat cultivars, and confirmed that it responds to salinity in two distinct phases through time. The fresh weight, leaf area, and leaf Na⁺ concentration were measured during 31 days of 120 mM NaCl supplemented with 1 mM Si treatment. The results revealed that the growth of plants under salinity conditions both with and without Si application were in accordance with the two-phase growth model. Si alleviated the salt stress in the both two-phase growth, but the alleviative effects were more pronounced in the osmotic stress phase than ion toxicity phase. These results clearly showed that Si can enhance plant salt tolerance by alleviating the salt-induced osmotic stress.     

Comparative physiological and biochemical evaluation of salt and nickel tolerance mechanisms in two contrasting tomato genotypes

Plant tolerance against a combination of abiotic stresses is a complex phenomenon, which involves various mechanisms. Physiological and biochemical analyses of salinity (NaCl) and nickel (Ni) tolerance in two contrasting tomato genotypes were performed in a hydroponics experiment. The tomato genotypes selected were proved to be tolerant (Naqeeb) and sensitive (Nadir) to both salinity and Ni stress in our previous experiment. The tomato genotypes were exposed to combinations of NaCl (0, 75 and 150 mM) and Ni (0, 15, and 20 mg l⁻¹) for 28 days. The results revealed that the tolerant and sensitive tomato genotypes showed similar response to NaCl and Ni stress; however, the level of response was significantly different in both genotypes. The tolerant tomato genotype showed less reduction in growth than the sensitive genotype against both NaCl and Ni stress. Root and shoot ionic analysis showed a decrease in Na and increase in K concentration by increasing Ni levels in the growth medium. Moreover, accumulation of Na and Ni in tissues showed a decrease in membrane stability index and an increase in malondialdehyde contents. The activity of superoxide dismutase, catalase, peroxidase and glutathione reductase under NaCl and Ni stress was significantly higher in the tolerant compared to the sensitive genotype. Enhanced activity of many antioxidant enzymes in Naqeeb under stress conditions is among the other mechanisms that enabled the genotype to better detoxify reactive oxygen species and therefore Naqeeb tolerated the stresses better than Nadir.     

Modulation in growth,photosynthetic efficiency,activity of antioxidants and mineral ions by foliar application of glycinebetaine on pea (Pisum sativum L.) under salt stress

A pot experiment was carried out to explore the role of glycinebetaine (GB) as foliar spray foliar on two pea (Pisum sativum L.) varieties (Pea 09 and Meteor Fsd) under saline and non-saline conditions. Thirty-two-day-old plants were subjected to two levels 0 and 150 mM of NaCl stress. Salt treatment was applied in full strength Hoagland’s nutrient solution. Three levels 0, 5 and 10 mM of GB were applied as foliar treatment on 34-day-old pea plants. After 2 weeks of foliar treatment with GB data for various growth and physiochemical attributes were recorded. Rooting-medium applied salt (150 mM NaCl) stress decreased growth, photosynthesis, chlorophyll, chlorophyll fluorescence and soluble protein contents, while increasing the activities of enzymatic (POD and CAT) and non-enzymatic (ascorbic acid and total phenolics) antioxidant enzymes. Foliar application of GB decreased root and shoot Na⁺ under saline conditions, while increasing shoot dry matter, root length, root fresh weight, stomatal conductance (g _s), contents of seed ascorbic acid, leaf phenolics, and root and shoot Ca²⁺ contents. Of three GB (0, 5, 10 mM) levels, 10 mM proved to be more effective in mitigating the adverse effects of salinity stress. Overall, variety Pea 09 showed better performance in comparison to those of var. Meteor Fsd under both normal and salinity stress conditions. GB-induced modulation of seed ascorbic acid, leaf phenolics, g _s, and root Ca²⁺ values might have contributed to the increased plant biomass, reduction of oxidative stress, increased osmotic adjustment and better photosynthetic performance of pea plants under salt stress.     

Silicon supply in soilless cultivations of zucchini alleviates stress induced by salinity and powdery mildew infections

In the present study, the hypothesis was tested as to whether silicon supplied via the nutrient solution is capable of enhancing the tolerance of hydroponically grown zucchini squash (Cucurbita pepo L. cv. ‘Rival’) to salinity and powdery mildew infections. Two experiments were conducted involving a low (2.2 dS m^?1, 0.8 mM NaCl) and a high salinity level (6.2 dS m^?1, 35 mM NaCl) in combination with a low (0.1 mM) and a high (1.0 mM) Si level in the nutrient solution supplied to the crop. The exposure of the plants to high external salinity restricted significantly the vegetative growth as well as the fruit yield of zucchini due to a reduction of both the number of fruits per plant and the mean fruit weight. However, the inclusion of 1 mM of Si in the salinized nutrient solution mitigated the salinity-associated suppression of both growth and yield. Part of the growth and fruit yield suppression at high salinity was due to restriction of net photosynthesis. The stomatal conductance was also restricted by salinity, whereas the substomatal CO₂ concentration was not affected by the NaCl or Si treatments. The supply of 1 mM of Si via the nutrient solution mitigated the inhibitory effect of salinity on net photosynthesis and this effect was associated with lower Na and Cl translocation to the epigeous plant tissues. Furthermore, the supply of Si via the nutrient solution suppressed appreciably the expansion of a powdery mildew (Podosphaera xanthii) infection in the leaves at both salinity levels. These results indicate that the supply of at least 1 mM of Si via the nutrient solution is capable of enhancing both tolerance to salinity and resistance to powdery mildew in soilless cultivations of zucchini squash.     

Application of chlorophyll fluorescence to screen eggplant (Solanum melongena L.) cultivars for salt tolerance

The objective of this study was to investigate the relative salt tolerance of four eggplant cultivars (Solanum melongena L.) by studying chlorophyll (Chl) fluorescence parameters during the vegetative growth stage under increasing salinity levels. The plants were grown in pots filled with peat under controlled conditions and were subjected to the salt stress ranging from 0 (control), 20, 40, 80, and 160 mM NaCl for 25 days. The results showed that the increasing NaCl concentration affected hardly the maximum quantum yield of photosystem (PS) II. The quantum yield of PSII (Φ_PSII) decreased significantly in ‘Adriatica’ and ‘Black Beauty’ under the salt stress. The photochemical quenching decreased in ‘Black Beauty’ and nonphotochemical quenching increased in ‘Adriatica’ under the salt stress. The Chl fluorescence parameters did not change significantly under the salt stress in ‘Bonica’ and ‘Galine’, revealing their tolerance to salinity. After 25 days of the salt stress, the plant growth was reduced in all cultivars, however, this decline was more pronounced in ‘Adriatica’ and ‘Black Beauty’. Additionally, a significant correlation between the biomass and Φ_PSII was observed in ‘Adriatica’ and ‘Black Beauty’. Our results suggest that Φ_PSII can be used as a diagnostic tool to identify salt-tolerant egg-plant cultivars.     

The role of arbuscular mycorrhizal fungi in alleviating salt stress in Medicago sativa L. var. icon

Medicago sativa L. is the most important forage crop in arid and semi-arid areas, where increased salinity is a major factor limiting plant growth and crop productivity. The role of arbuscular mycorrhizal (AM) fungus Glomus viscosum H.T. Nicolson strain A6 in protecting alfalfa plants from salt stress, induced by sodium chloride (NaCl), was studied in two ways. Firstly, the root systems of 3-month old M. sativa plants, both mycorrhizal (AM+) and non-mycorrhizal (non-AM) (M. sativa L. var. icon), were placed in solutions of increasing salt concentrations (0, 50, 100, 150, 200 mM NaCl) to study the wilting response. G. viscosum improved the tolerance to salinity stress and the benefit was expressed in terms of the time required to reach the T4 stage in the wilting experiment. Secondly, to evaluate the ability of the Glomus-alfalfa symbiosis to tolerate salt, a pot experiment was set up in a glasshouse in which 3-month old alfalfa plants (M. sativa var. icon) were grown in a peat substratum at three salinity levels (0, 100, 150 mM NaCl). The AM symbiosis stimulated plant height, leaf area, root density, fresh and dry plant weight under saline conditions. Furthermore, proline accumulation was higher in mycorrhizal M. sativa plants than in non-mycorrhizal plants under conditions of salt stress. These and other results indicated that the micropropagated selected clone of M. sativa var. icon, when in symbiosis with G. viscosum H.T. Nicolson strain A6, exhibited better growth and physiological activities under saline conditions than non-AM plants. The AM+ plants also had lower sodium and chloride concentrations in tissues than non-AM plants.     

Influence of silicon and chitosan on growth and physiological attributes of maize in a saline field

Soil salinity is the main constraint for crop productivity in many parts of the world. Application of silicon (Si) and chitosan (Chi) can improve crop growth under saline soil conditions. The current study was aimed to examine the effects of Si and Chi on mitigation of salinity, morphological and physiological attributes as well as the antioxidant system of maize (Zea mays L.) under saline soil conditions. A field experiment was conducted that comprised of nine treatments as follows: (i) Control (no amendment), (ii) Silicon 40 kg ha⁻¹ (Si1), (iii) Chitosan 15 kg ha⁻¹ (Chi1), (iv) Si1 + Chi1, (v) Silicon 80 kg ha⁻¹ (Si2), (vi) Chitosan 30 kg ha⁻¹ (Chi2), (vii) Si2 + Chi2, (viii) Si1 + Chi2 and (ix) Si2 + Chi1. Application of Si and Chi substantially improved the morphological and physiological attributes as well as antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) of maize plants, and combined application of Si and Chi was more effective when compared with Si and Chi treatments separately. Membrane stability index was improved by 25%, relative water content by 26%, chlorophyll a by 69% and b by 56% with combined application of Si and chitosan (Si2 + Chi2) compared with control. The SOD, POD and CAT increased by 36%, 38% and 65% with Si2 + Chi2 compared with control. The results suggest that Si and Chi application is the possible option for alleviating salinity stress in maize plant. Further research is suggested to examine Si and Chi effects on various crop''s growth.     

Silicon alleviates simulated acid rain stress of <Emphasis Type="BoldItalic">Oryza sativa</Emphasis> L. seedlings by adjusting physiology activity and mineral nutrients

Silicon (Si) has been a modulator in plants under abiotic stresses, such as acid rain. To understand how silicon made an effect on rice (Oryza sativa L.) exposed to simulated acid rain (SAR) stress, the growth, physiologic activity, and mineral nutrient content in leaves of rice were investigated. The results showed that combined treatments with Si (1.0, 2.0, or 4.0 mM) and SAR (pH 4.0, 3.0, or 2.0) obviously improved the rice growth compared with the single treatment with SAR. Incorporation of Si into SAR treatment decreased malondialdehyde (MDA) content; increased soluble protein and proline contents; promoted CAT, POD, SOD, and APX activity; and maintained the K, Ca, Mg, Fe, Zn, Cu content balance in leaves of rice seedlings under SAR stress. The moderate concentration of Si (2.0 mM) was better than the low and high concentration of Si (1.0 and 4.0 mM). Therefore, application of Si could be a better strategy for maintaining the crop productivity in acid rain regions.     

Investigation of the salt tolerance of new Polish bread and durum wheat cultivars

In some regions of the world, low annual precipitation necessitates irrigation of crop plants which usually leads to soil salinity. Due to climatic changes this effect is also expected in the countries of Central Europe, and so in Poland. The aim of the study was (1) to compare tolerance to salt stress of Polish Triticum aestivum cvs. ‘Bogatka’ and ‘Banderola’ with T. durum cv. ‘Komnata’ and breeding line 121, and (2) to indicate the physiological parameter/parameters most suitable for such comparison. The investigation was performed in two experiments. In the first one, the germination ability of caryopses and coleoptiles’ growth were estimated at 0–250 mM of NaCl. The second experiment was conducted on plants grown in a glasshouse in saline soil at 0–150 mM of NaCl for 6 weeks. Salt tolerance was evaluated on the basis of following parameters: chlorophyll fluorescence, net photosynthesis rate (P _N), transpiration rate (E), stomatal conductance (g _s), cell membrane permeability (EL), proline content, fresh weight (FW), dry weight (DW), and relative water content (RWC). Highest germination of caryopses of durum cultivars was recorded at all the salinity levels; however, their coleoptiles were shorter than coleoptiles of bread wheat cultivars. Analysis of chlorophyll fluorescence showed that applied salt doses did not disturb the light phase of photosynthesis in all cultivars under study. Plants of durum wheat showed the higher dissipation of energy excess at the level of the antenna chlorophyll (DIo/CSm) under salinity as compared to plants of bread wheat. Both ‘Komnata’ and line 121 showed stronger P _N reduction as an effect of salinity. A decline of P _N was closely connected with a decrease in g _s. The P _N correlated with a decrease in DW in all studied cultivars except ‘Bogatka’. Control plants of ‘Komnata’ and line 121 were characterized by higher EL and proline level than bread wheat cultivars. An increasing cell membrane permeability correlated with a decrease of RWC in ‘Banderola’ and ‘Komnata’. The content of proline under the increasing salinity correlated with changes of RWC in ‘Banderola’, ‘Komnata’ and line 121, which indicate protectoral role of proline against dehydration of tissue. Dry weight and RWC seem to be the parameters most useful in the salt-tolerance estimation of wheat plants. Taking into account the studied parameters ‘Banderola’ could be recognized as more salt tolerant, the degree of salinity tolerance of ‘Bogatka’ is the same as line 121, while ‘Komnata’ seems to be the most salt sensitive. The salt tolerance of T. aestivum and T. durum depends on the cultivar rather than the wheat species.     

Salicylic Acid Induces Salinity Tolerance in Tomato (Lycopersicon esculentum cv. Roma): Associated Changes in Gas Exchange, Water Relations and Membrane Stabilisation

The present study investigates the role of salicylic acid (SA) in inducing plant tolerance to salinity. The application of 0.1 mM SA to tomato [Lycopersicon esculentum Mill.] plants via root drenching provided protection against 150 mM or 200 mM NaCl stress. SA treated plants had greater survival and relative shoot growth rate compared to untreated plants when exposed to salt stress. At 200 mM salt, shoot growth rates were approximately 4 times higher in SA treated plants than untreated plants. Application of SA increased photosynthetic rates in salt stressed plants and may have contributed to the enhanced survival. Transpiration rates and stomatal conductance were also significantly higher in SA treated plants under saline stress conditions. SA application reduced electrolyte leakage by 44% in 150 mM NaCl and 32% in 200 mM NaCl, compared to untreated plants, indicating possible protection of integrity of the cellular membrane. Beneficial effects of SA in saline conditions include sustaining the photosynthetic/transpiration activity and consequently growth, and may have contributed to the reduction or total avoidance of necrosis. SA, when used in appropriate concentrations, alleviates salinity stress without compromising the plants ability for growth under a favourable environment.     

The effectiveness of grafting to improve salt tolerance in tomato when an ‘excluder’ genotype is used as scion

If the main effect of long-term exposure of tomato plants to salinity is the accumulation of toxic concentrations of Na⁺ and Cl⁻ in the leaves, then the selection of ‘excluder’ rootstocks should increase tolerance to salinity in grafted tomato plants, independently of the genotype used as the scion. The question addressed in this study is whether shoot genotypes with an ‘excluder’ character are able to increase their salt tolerance when grafted onto rootstocks of the same characteristics. Moneymaker (with excluder character) was grafted onto two root genotypes, Radja and Pera, selected for their very different ability to regulate the transport of saline ions to the shoot over time. Grafting onto either Pera or Radja improved fruit yield compared to the self-grafted plants of Moneymaker (M/M) when the plants were grown at 50 mM NaCl, whereas there was no effect of either rootstock or of grafting per se (M/M) on fruit yield in the absence of or at 25 mM NaCl. The relationship between the salt responses to mid- and long-term depended on the stress level; after 27 d of 150 mM NaCl treatment, both graft combinations enhanced similarly their salt tolerances as did in the long-term experiment. Moreover, the tolerance induced by rootstock was related to the low rates of saline ion accumulation in their leaves. However, the positive effect of rootstock was only observed with rootstock Pera when the grafted plants were grown at 50 mM NaCl (the same salt level used in the long-term experiment) for 35 d. According to the physiological changes induced by rootstock in the leaves, the different salt responses seem to be due to the fact that the osmotic effect predominated on the toxic effect under these last conditions. Consequently, in order to select rootstocks care must be taken in the timing of any selection process: the stress level and length of exposure to salinity must be sufficient for the true differences in salt tolerance for toxicity to be shown. Taken together, these results show the effectiveness of grafting to enhance fruit yield in tomato and provide evidence that the positive effect induced by rootstock is related to the re-establishment of ionic homeostasis.