Effect of salt stress on lipid peroxidation and superoxide dismutase and peroxidase activities of Lycopersicon esculentum and L. pennellii

In this study, a relationship between lipid peroxidation, the antioxidant defense system and salt stress in salt-sensitive cultivated tomato (Lycopersicon esculentum) and its salt-tolerant wild relative (L. pennellii) was established. Superoxide dismutase (SOD) activities were significantly higher in the leaves of L. pennellii than those of L. esculentum after 12 and 84 d. POX activity showed a gradual increase in both cultivars under 70 mM NaCl. POX activity in L. pennellii significantly increased after 6 and 84 d whereas showed no remarkable change in leaves of L. esculentum under 140 mM NaCl. A higher salinity tolerance of L. pennellii was also correlated with a lower lipid peroxidation, which might be due to a higher content of antioxidant enzymes studied.     

Osmotic adjustment in Lycopersicon esculentum and L. Pennellii under NaCl and polyethylene glycol 6000 iso–osmotic stresses

Changes in leaf solute contents in response to saline (NaCl) and osmotic (polyethylene glycol, PEG, 6000) stresses were measured in three different salt tolerant cultivars of Lycopersicon esculentum (L.) Mill. (Pera, P-73 and Volgogradskij), and its wild relative L. pennellii (Correll) D'Arcy accession PE-47. Iso-osmotic stresses (–0. 5 MPa) of NaCl (140 mM) and PEG 6000 (150 g l^-1) were applied to one-month old plants for 3 weeks. Decreasing leaf dry weight was similar in L. pennellii or L. esculentum cv. P-73 and Volgogradskij under both stresses, while leaf dry weight of L. esculentum cv. Pera decreased more under PEG stress than under NaCl stress. Water contents decreased in all the PEG treated populations, while their calculated solute potential (Ψ_s increased. Under osmotic stress, the total ion contents decreased in relation to control, whereas organic solutes (sugars, amino acids and organic acids) markedly increased in both tomato species, specially in the tomato cultivars, where these solutes represented 50% of the Ψ₅ calculated. Soluble sugar increase was three times higher in leaves of L. esculentum than in the leaves of L. pennellii. Free proline increased under both stresses and its content was highest in L. esculentum and in L. pennellii, respectively, under NaCl and PEG stresses. Nevertheless, the contribution of this metabolite to Ψ_s did not exceed 5%, irrespective of treatment and species. The greater organic solute accumulation in L. esculentum than in L. pennellii– which was not reflected in their Ψ₅ values – was not correlated with the tolerances of the two species to osmotic stress. Therefore, osmotic adjustment may not be the only process influencing salt and drought tolerances in tomato; the ability of plants to regulate their metabolic and physiological functions could also play an important role under these harmful conditions. The possible roles of inorganic solutes and metabolites in osmotic adjustment, energetic metabolism and redox regulation are discussed     

Salt tolerance in <Emphasis Type="Italic">Solanum pennellii</Emphasis>: antioxidant response and related QTL

Background  

Excessive soil salinity is an important problem for agriculture, however, salt tolerance is a complex trait that is not easily bred into plants. Exposure of cultivated tomato to salt stress has been reported to result in increased antioxidant content and activity. Salt tolerance of the related wild species, Solanum pennellii, has also been associated with similar changes in antioxidants. In this work, S. lycopersicum M82, S. pennellii LA716 and a S. pennellii introgression line (IL) population were evaluated for growth and their levels of antioxidant activity (total water-soluble antioxidant activity), major antioxidant compounds (phenolic and flavonoid contents) and antioxidant enzyme activities (superoxide dismutase, catalase, ascorbate peroxidase and peroxidase) under both control and salt stress (150 mM NaCl) conditions. These data were then used to identify quantitative trait loci (QTL) responsible for controlling the antioxidant parameters under both stress and nonstress conditions.     

Responses to NaCl stress of cultivated and wild tomato species and their hybrids in callus cultures

Summary If in vitro culture is to be used for evaluating the salt tolerance of tomato hybrids and segregant populations in a breeding programme, it is previously necessary to get quick and reliable traits. In this work, growth and physiological responses to salinity of two interspecific hybrids between the cultivated tomato (Lycopersicon esculentum Mill) and its wild salt-tolerant species L pennellii are compared to those of their parents. The leaf callus of the first subculture was grown on media amended with 0, 35, 70, 105, 140, 175 and 210 mM NaCl for 40 days. Relative fresh weight growth of callus in response to increased salinity in the culture medium was much greater in L pennellii than in the tomato cultivars, and greater in the hybrids than in the wild species. Moreover, the different salt tolerance degree of hybrids was related to that of female parents. At high salt levels, only Cl^– accumulation was higher in L pennellii than in tomato cultivars, whereas in the hybrids both Cl^–, and Na⁺ accumulation were higher than in their parents. Proline increased with salinity in the callus of all genotypes; these increases were much higher in the tomato cultivars than in L pennellii, and the hybrids showed a similar response to that of the wild species. Salt-treated callus of the tomato cultivars showed significant increases in valine, isoleucine and leucine contents compared to control callus tissue. In contrast, these amino acids in callus tissues of the wild species and hybrids showed a tendency to decrease with increasing salinity.     

Short-term salt tolerance mechanisms in differentially salt tolerant tomato species

The physiological changes induced by a daily increase of NaCl level, over a period of 4 d, were studied in leaves of the salt-sensitive cultivated tomato species Lycopersicon esculentum and its wild salt-tolerant relative Lycopersicon pennellii. A higher solute contribution to the osmotic adjustment was observed in NaCl-treated leaves of L. pennellii than in those of L. esculentum. This response together with the higher accumulation of inorganic solutes in the wild species and of organic solutes in the cultivated species verified the different salt tolerance mechanisms operating in the two species in the short-term. With regard to the changes induced by salt stress on the free polyamine levels, the putrescine and spermine levels increased with salinity, whereas the spermine levels decreased in both tomato species; nevertheless, the main difference between the two species lays in an earlier and greater accumulation of putrescine induced by salinity in L. pennellii than in L. esculentum. The changes in putrescine levels were associated to changes in amino acids related to its synthesis, and the changes were different in both species. In L. esculentum, the high concentrations of some intermediate compounds (glutamate and arginine) were related to the low accumulation rate of both proline and putrescine. In contrast, in L. pennellii, important reductions in glutamate and arginine levels were found at the end of the salinization period. Moreover, in this last situation, a decline in the putrescine level ran parallel to a high proline accumulation, which suggests that the higher the stress level, the higher the deviation of glutamate to proline occurring in the salt tolerant species. It could be concluded that an early accumulation of the diamine putrescine seems to be associated with salt tolerance in the short-term.     

The Effect of Ventilation on in vitro Response of Seedlings of the Cultivated Tomato and its Wild Salt-tolerant Relative Lycopersicon pennellii to Salt Stress

Organs or plants grown in vitro do not always exhibit the same responses to salinity as the whole plant of same species grown ex vitro. The response to salinity (100 mM NaCl) of seedlings of the wild tomato species Lycopersicon pennellii acc. Atico (Lpa) and of the cultivated tomato L. esculentum cv. M82 (Lem), the former is known as salt tolerant and the second as relatively salt sensitive under ex vitro conditions, was compared under in vitro conditions with three different ventilation regimes. It was found that under salinity shoots of the wild species accumulated the same or even more dry biomass than the control (roots somewhat less) under all ventilation levels. Growth of shoots and roots of the cultivated species was inhibited under the same conditions especially under the high ventilation. Ventilation reduced some abnormalities of leaf development related to hyperhydricity and consequently ventilated leaves exhibited a more compounded structure, increased area, increased resistance to water loss and stomata functioning. Ventilation increased K⁺, Na⁺ and Cl⁻ accumulation in shoots of both tomato species. This was more pronounced under salinity and in Lpa. This work indicates that differences that characterize whole plants of these species in response to salinity under ex vitro conditions are exhibited also in whole plants grown in vitro under high ventilation. It is suggested that ventilation is needed to evaluate well the response of whole plants to salt stress applied in vitro.     

A comparative study of the genetic bases of natural variation in tomato leaf,sepal, and petal morphology

In an effort to better understand the dramatic differences in vegetative and floral morphology that differentiate species within the genus Lycopersicon, quantitative trait loci (QTL) for leaflet and perianth size and shape characters were mapped in an interspecific F₂ population of tomato (Lycopersicon esculentum × L. pennellii). Thirty-six highly significant (P0.001) QTL were associated with 18 separate traits. QTL for correlated traits were generally not colocalized in the genome unless there was a clear codependence between the traits (e.g., organ length and area). Little or no overlap in QTL positioning between different organs was observed, suggesting that the genes determining the size and shape of leaflets, sepals, and petals are organ specific. Thus, while leaves are considered the developmental and evolutionary precursors to floral organs, genes acting late in development to determine certain aspects of morphology (namely shape and size) must have specialized to exert control over individual organs. Five of the leaflet-trait QTL map to analogous regions in the genome of eggplant, and therefore it appears there has been some conservation in the genes controlling leaf morphology within the Solanaceae.     

QTLs mapping of morphological traits related to salt tolerance in <Emphasis Type="Italic">Medicago truncatula</Emphasis>

To understand the complex inheritance of tolerance to salt stress in Medicago truncatula, quantitative trait loci (QTLs) analysis was performed using a set of recombinant inbred lines (RILs) derived from a cross between the tolerant line Jemalong A17 and susceptible line F83005.5. The RILs and parental lines were grown in individual pots filled with sterilized sand in a greenhouse under 0 and 50 mM NaCl. Plants were harvested after a period of 60 days. Fourteen quantitative traits related to aerial and root growths were measured. Broad-sense heritability of measured traits ranged from 0.21 to 0.83 and from 0.05 to 0.62 in control and in salt-stressed conditions, respectively. Established correlations between measured traits are dependent on treatment effect. We identified and mapped 10 QTLs in control conditions and 19 in salt stress. No major QTL was identified indicating that tolerance to salt stress is governed by several genes with low effects. The QTLs detected under control and under salt-stressed conditions almost did not share the same map locations suggesting that the loci that are not stable across treatments reflect adaptation to this constraint. The maximum of QTLs was observed on the chromosome 8. The usefulness of these QTLs, identified in greenhouse conditions, for marker-assisted selection should therefore be evaluated under field conditions, and validated in other genetic backgrounds.     

Molecular analysis of the extent of asymmetry in two asymmetric somatic hybrids of tomato

Summary Two somatic hybrid plants generated from a single fusion event between Lycopersicon esculentum and irradiated L. pennellii protoplasts have been analyzed at the molecular level. Over 30 loci have been analyzed using isozymes and RFLPs. All loci tested on chromosomes 2–10 were heterozygous, while those loci on chromosome 12 were homozygous L. pennellii in both somatic hybrids. In one of the somatic hybrids, 2850, loci on chromosome 1 were also homozygous L. pennellii. The other somatic hybrid, 28F5, was heterozygous at all chromosome 1 loci tested, but exhibited altered stoichiometry of parental bands as compared to the sexual hybrid. Loci on chromosome 2 from both somatic hybrids have altered stoichiometry, with L. pennellii alleles being four times more abundant than expected. Both somatic hybrids contain the L. esculentum chloroplast genome, while only L. pennellii polymorphisms have been detected in the mitochondrial genome.     

fw 2.2:a major QTL controlling fruit weight is common to both red- and green-fruited tomato species

We have shown that a major QTL for fruit weight (fw2.2) maps to the same position on chromosome 2 in the green-fruited wild tomato species, Lycopersicon pennellii and in the red-fruited wild tomato species, L. pimpinellifolium. An introgression line F₂ derived from L. esculentum (tomato) x L. pennellii and a backcross 1 (BC₁) population derived from L. esculentum x L. pimpinellifolium both place fw2.2 near TG91 and TG167 on chromosome 2 of the tomato highdensity linkage map. fw2.2 accounts for 30% and 47% of the total phenotypic variance in the L. pimpinellifolium and L. pennellii populations, respectively, indicating that this is a major QTL controlling fruit weight in both species. Partial dominance (d/a of 0.44) was observed for the L. pennellii allele of fw 2.2 as compared with the L. esculentum allele. A QTL with very similar phenotypic affects and gene action has also been identified and mapped to the same chromosomal region in other wild tomato accessions: L. cheesmanii and L. pimpinellifolium. Together, these data suggest that fw2.2 represents an orthologous QTL (i.e., derived by speciation as opposed to duplication) common to most, if not all, wild tomato species. High-resolution mapping may ultimately lead to the cloning of this key locus controlling fruit development in tomato.     

QTL analysis of drought-related traits and grain yield in relation to genetic variation for leaf abscisic acid concentration in field-grown maize

Abscisic acid (ABA) concentration is a quantitatively inherited trait which plays a pivotal role in the response of plants to drought stress. A recent study identified 17 quantitative trait loci (QTLs) controlling bulk-leaf ABA concentration (L-ABA) in a maize (Zea mays L.) population of 80 F4 random families tested for two years under droughted field conditions. Sixteen of the QTL regions influencing L-ABA also harboured QTLs for one or more of the following traits: stomatal conductance, a drought sensitivity index, leaf temperature, leaf relative water content, anthesis-silking interval, and grain yield. The analysis of the effects of each QTL region on the investigated traits indicated that L-ABA mainly represented an indicator of the level of drought stress experienced by the plant at the time of sampling because an increase in L-ABA was most commonly associated with a decrease in both stomatal conductance and grain yield as well as an increase in leaf temperature. Opposite results were observed at one QTL region on chromosome 7 near the RFLP locus asg8. A model is presented to interpret these contrasting results in terms of pleiotropic effects.Key words: Abscisic acid, ABA, drought stress, quantitative trait locus (QTL), molecular markers, Zea mays.      

Using QTL mapping to investigate the relationships between abiotic stress tolerance (drought and salinity) and agronomic and physiological traits

Background

Drought and salinity are two major abiotic stresses that severely limit barley production worldwide. Physiological and genetic complexity of these tolerance traits has significantly slowed the progress of developing stress-tolerant cultivars. Marker-assisted selection (MAS) may potentially overcome this problem. In the current research, seventy two double haploid (DH) lines from a cross between TX9425 (a Chinese landrace variety with superior drought and salinity tolerance) and a sensitive variety, Franklin were used to identify quantitative trait loci (QTL) for drought and salinity tolerance, based on a range of developmental and physiological traits.

Results

Two QTL for drought tolerance (leaf wilting under drought stress) and one QTL for salinity tolerance (plant survival under salt stress) were identified from this population. The QTL on 2H for drought tolerance determined 42% of phenotypic variation, based on three independent experiments. This QTL was closely linked with a gene controlling ear emergency. The QTL on 5H for drought tolerance was less affected by agronomic traits and can be effectively used in breeding programs. A candidate gene for this QTL on 5H was identified based on the draft barley genome sequence. The QTL for proline accumulation, under both drought and salinity stresses, were located on different positions to those for drought and salinity tolerance, indicating no relationship with plant tolerance to either of these stresses.

Conclusions

Using QTL mapping, the relationships between QTL for agronomic and physiological traits and plant drought and salinity tolerance were studied. A new QTL for drought tolerance which was not linked to any of the studied traits was identified. This QTL can be effectively used in breeding programs. It was also shown that proline accumulation under stresses was not necessarily linked with drought or salinity tolerance based on methods of phenotyping used in this experiment. The use of proline content in breeding programs can also be limited by the accuracy of phenotyping.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1243-8) contains supplementary material, which is available to authorized users.     

Examination of genome stability in cultured Lycopersicon

The genetic stability of plants regenerated from either mesophyll protoplasts or leaf slices of the F1 hybrid between Lycopersicon esculentum and L. pennellii was assayed by comparing the ploidy level, leaf morphology and isozyme patterns of the regenerants with their somatic parents. Regenerants from protoplasts were predominantly tetraploid, regenerants from leaf slices were predominantly diploid; both classes of regenerants had isozyme patterns identical to those of the parent plant. Callus was analyzed that grew up from cultures containing fused protoplasts from either irradiated or untreated protoplasts of L. esculentum and L. pennellii. The L. pennellii cell line used was 18 months old and could no longer regenerate. Out of 75 calli scored at 3 isozyme loci, 51 were heterozygous at only one or two of the loci. Irradiation of the two parental lines was not necessary to produce fusion products exhibiting asymmetric expression of parental genes.Abbreviations Got-2 glutamate oxaloacetate transaminase-2 - Pgi-1 phosphoglucoisomerase-1 - Pgm-2 phosphoglucomutase-2     

Introgressions fromLycopersicon pennellii can improve the soluble-solids yield of tomato hybrids

RFLP-defined chromosome segments covering the entire tomato genome were introgressed from the wild green-fruited speciesLycopersicon pennellii into the cultivated tomato (L. esculentum cv M82; Eshed et al. 1992). SixL. pennellii chromosome segments were selected for a detailed evaluation based on previous observations of their effects on the two yield components, fresh tomato yield and total soluble-solids content (Brix). Differences in the quantitative traits measured between M82 and the introgression lines, or their hybrids with different inbred parents, can be attributed to the alien chromosome segments. Replicated field trials, grown at wide and dense spacing, identified three quantitative trait loci (QTLs) for solublesolids content on chromosomes 1, 5 and 7. In plants heterozygous for the chromosome-5 locus there was a 50% increase in soluble-solids yield in wide but not in dense spacing. Plants heterozygous for the chromosome-1 QTL/s were tested over a 2-year period, in three genetic backgrounds, and showed a significant 16% elevation in soluble-solids yield only in dense spacing. These results demonstrate that wild tomato germplasm can be used to improve the yield of the cultivated crop.     

Does Seed Priming Induce Changes in the Levels of Some Endogenous Plant Hormones in Hexaploid Wheat Plants Under Salt Stress？

In order to assess whether salt tolerance could be Improved In spring wheat （Triticum aestivum L.）, the present study was performed by soaking the seeds of two cultlvars, namely MH-97 （salt sensitive） and Inqlab-91 （salt tolerant）, for 12 h In distilled water or 100 mol/m^3 CaCl2, KCI, or NaCI. Primed seeds from each treatment group and non-primed seeds were sown In a field In which NaCI salinity of 15 dS/m was developed. Priming of seeds with CaCl2, followed by priming with KCI and NaCI, was found to be effective In alleviating the adverse effects of salt stress on both wheat cultivars In terms of shoot fresh and dry weights and grain yield. Priming with CaCl2 alleviated the adverse effects of salt stress on hormonal balance In plants of both cultlvars. In MH-97 plants, CaCl2 pretreatment considerably reduced leaf absclslc acid （ABA） concentrations and Increased leaf free salicylic acid （SA） concentrations under both saline and non-saline conditions. In contrast, In the Inqlab-91 plant, CaCl2 Increased free Indoleacetic acid （IAA） and indolebutyrlc acid （IBA） content. However, priming of seeds with CaCl2 did not alter free polyamlne levels in either cultlvar, although spermldlne levels were considerably lower In plants raised from seeds treated with CaCl2 for both cultlvars under saline conditions. Priming with KCI Increased growth In Inqlab-91 plants, but not In MH-97 plants, under saline conditions. The salinity Induced reducUon In auxins （IAA and IBA） was alleviated by NaCI priming In both cultlvars under saline conditions. However, NaCI Increased leaf free ABA content and lowered leaf SA and putresclne levels In Inqlab-91 plants under saline conditions. In conclusion, although all three priming agents （I.e. CaCl2, KCI, and NaCI） were effective In alleviating the adverse effects of salt stress on wheat plants, their effects on altering the levels of different plant hormones were different In the two cuItlvars.     

Genetic analysis of Na+ and K+ concentrations in leaf and stem as physiological components of salt tolerance in Tomato

The sodium and potassium concentrations in leaf and stem have been genetically studied as physiological components of the vegetative and reproductive development in two populations of F₈ lines, derived from a salt sensitive genotype of Solanum lycopersicum cv. Cerasiforme, as female parent, and two salt tolerant lines, as male parents, from S. pimpinellifolium, the P population (142 lines), and S. cheesmaniae, the C population (116 lines). Genetic parameters of ten traits under salinity and five of them under control conditions were studied by ANOVA, correlation, principal component and QTL analysis to understand the global response of the plant. Two linkage maps including some tomato flowering time and salt tolerance candidate genes encoding for SlSOS1, SlSOS2, SlSOS3, LeNHX1, LeNHX3, were used for the QTL detection. Thirteen and 20 QTLs were detected under salinity in the P and C populations, respectively, and four under control conditions. Highly significant and contributing QTLs (over 40%) for the concentrations of Na⁺ and K⁺ in stems and leaves have been detected on chromosome 7 in both the populations. This is the only genomic position where the concentration QTLs for both the cations locate together. The proportion of QTLs significantly affected by salinity was larger in the P population (64.3%, including all QTLs detected under control) than in the C population (21.4%), where the estimated genetic component of variance was larger for most traits. A highly significant association between the leaf area and fruit yield under salinity was found only in the C population, which is supported by the location of QTLs for these traits in a common region of chromososome C1. As far as breeding for salt tolerance is concerned, only two sodium QTLs (lnc1.1 and lnc8.1) map in genomic regions of C1 and C8 where fruit yield QTLs are also located but in both the cases the profitable allele corresponds to the salt sensitive, cultivated species. One of those QTLs, lnc1.1 might involve LeNHX3.     

Advanced backcross QTL analysis of a<Emphasis Type="Italic"> Lycopersicon esculentum</Emphasis> ×<Emphasis Type="Italic"> L</Emphasis>.<Emphasis Type="Italic"> pennellii</Emphasis> cross and identification of possible orthologs in the Solanaceae

In this study, the advanced backcross QTL (AB-QTL) mapping strategy was used to identify loci for yield, processing and fruit quality traits in a population derived from the interspecific cross Lycopersicon esculentum E6203 × Lycopersicon pennellii accession LA1657. A total of 175 BC₂ plants were genotyped with 150 molecular markers and BC₂F₁ plots were grown and phenotyped for 25 traits in three locations in Israel and California, U.S.A. A total of 84 different QTLs were identified, 45% of which have been possibly identified in other wild-species-derived populations of tomato. Moreover, three fruit-weight/size and shape QTLs (fsz2b.1, fw3.1/fsz3.1 and fs8.1) appear to have putative orthologs in the related solanaceous species, pepper and eggplant. For the 23 traits for which allelic effects could be deemed as favorable or unfavorable, 26% of the identified loci had L. pennellii alleles that enhanced the performance of the elite parent. Alleles that could be targeted for further introgression into cultivated tomato were also identified.Communicated by G. Wenzel     

Trichome-borne and artificially applied acylsugars of wild tomato deter feeding and oviposition of the leafminer Liriomyza trifolii

Oviposition and adult feeding of the leafminer Liriomyza trifollii (Burgess) (Diptera, Agromyzidae) on Lycopersicon pennellii (Corr.) D'Arcy and its F₁ hybrid with Lycopersicon esculentum (Mill.) was significantly less than that on the cultivated tomato, L. esculentum. The resistance of L. pennellii and the F₁ was reduced following rinsing of foliage with ethanol. Resistant attributes of L. pennellii were transferred to L. esculentum through appression of L. pennellii foliage to L. esculentum leaflets. Application of purified 2,3,4-tri-O-acylglucoses (the principal component of type IV glandular trichome exudate of L. pennellii) to L. esculentum significantly decreased feeding and oviposition on L. esculentum leaflets by 61–99%. Therefore the principal mechanism of resistance to this leafminer by L. pennellii is the secretion of these acylglucoses. Dose response analysis of acylglucoses applied to L. esculentum shows that dosages as low as 10% those found on L. pennellii provide large reductions (91%) in leaf punctures and mines.     

QTL analysis of fruit antioxidants in tomato using Lycopersicon pennellii introgression lines

Antioxidants present in fruits and vegetables may help prevent some chronic diseases such as cancer, arthritis, and heart disease. Tomatoes provide a major contribution to human dietary nutrition because of their widespread consumption in fresh and processed forms. A tomato introgression line population that combines single chromosomal segments introgressed from the wild, green fruited species Lycopersicon pennellii in the background of the domesticated tomato, Lycopersicon esculentum, was used to identify quantitative trait loci (QTL) for nutritional and antioxidant contents. The concentration of ascorbic acid, total phenolics, lycopene and β-carotene, and the total antioxidant capacity of the water-soluble fraction (TACW) were measured in the ripe fruits. A total of 20 QTL were identified, including five for TACW (ao), six for ascorbic acid (aa), and nine for total phenolics (phe). Some of these QTL (ao6-2, ao6-3, ao7-2, ao10-1, aa12-4, phe6-2, and phe7-4) increased levels as compared to the parental line L. esculentum. For lycopene content, we detected four QTL, but none increased levels relative to L. esculentum. The two QTL (bc6-2 and bc6-3) detected for β-carotene increased its levels. The traits studied displayed a strong environmental interaction as only 35% of the water-soluble antioxidant QTL (including TACW, ascorbic, and phenolic contents) were consistent over at least two seasons. Also, only two QTL for phenolics were observed when plants were grown in the greenhouse and none was detected for ascorbic or TACW. The analysis demonstrates that the introgression of wild germplasm may improve the nutritional quality of tomatoes; however regulation appears to be complex with strong environmental effects. M. Cecilia Rousseaux and Carl M. Jones contributed equally to this work     

Changes in water relations,photosynthetic activity and proline accumulation in one-year-old olive trees (<Emphasis Type="Italic">Olea europaea</Emphasis> L. cv. Chemlali) in response to NaCl salinity

The comparative responses of young olive trees (Olea europaea L. cv “Chemlali”) to different NaCl salinity levels were investigated over 11 months. One-year-old own rooted plants were grown in 10-L pots containing sand and perlite mixture (1:3 v/v). Trees were subjected to three irrigation treatments: CP (control plants that were irrigated with fresh water); SS1 (salt stressed plants irrigated with water containing 100 mM NaCl) and SS2 plants (salt stressed plants irrigated with water containing 200 mM NaCl). Shoot elongation rate, relative water content, leaf water potential and net carbon dioxide exchange rates decreased significantly with increased NaCl salinity level. Under stressed conditions, the increase of Na⁺ and Cl⁻ ions in both leaves and roots was accompanied with that of proline and soluble sugars. The above results show that the accumulation of proline and sugars under stressed conditions could play a role in salt tolerance. The absence of toxicity symptoms under both stress treatments and the superior photosynthetic activity recorded in SS1-treated plants suggest that cv Chemlali is better able to acclimatize to 100 mM NaCl than at 200 mM NaCl. Our findings indicate that saline water containing 100 mM NaCl, the most available water in arid region in Tunisia, can be recommended for the irrigation of cv Chemlali in the arid south of Tunisia.