Diverse Traits Contribute to Salinity Tolerance of Wild Tomato Seedlings from the Galapagos Islands

Association analysis provides insights into molecular evolution in salt tolerance during tomato domestication

Salt stress impairs plant growth and development, generally resulting in crop failure. Tomato domestication gave rise to a dramatic decrease in salt tolerance caused by the genetic variability of the wild ancestors. However, the nature of artificial selection in reducing tomato salt tolerance remains unclear. Here, we generated and analyzed datasets on the survival rates and sodium (Na+) and potassium (K+) concentrations of hundreds of tomato varieties from wild ancestors to contemporary breeding accessions under high salinity. Genome-wide association studies revealed that natural variation in the promoter region of the putative K+ channel regulatory subunit-encoding gene KSB1 (potassium channel beta subunit in Solanum lycopersicum) is associated with the survival rates and root Na+/K+ ratios in tomato under salt stress. This variation is deposited in tomato domestication sweeps and contributes to modified expression of KSB1 by a salt-induced transcription factor SlHY5 in response to high salinity. We further found that KSB1 interacts with the K+ channel protein KSL1 to maintain cellular Na+ and K+ homeostasis, thus enhancing salt tolerance in tomato. Our findings reveal the crucial role of the SlHY5-KSB1-KSL1 module in regulating ion homeostasis and salt tolerance during tomato domestication, elucidating that selective pressure imposed by humans on the evolutionary process provides insights into further crop improvement.

Characterisation of a major QTL for sodium accumulation in tomato grown in high salinity

Soil salinity is a serious concern for tomato culture, affecting both yield and quality parameters. Although some genes involved in tomato salt tolerance have been identified, their genetic diversity has been rarely studied. In the present study, we assessed salt tolerance-related traits at juvenile and adult stages in a large core collection and identified salt tolerance quantitative trait loci (QTLs) by genome-wide association study (GWAS). The results suggested that a major QTL is involved in leaf sodium accumulation at both physiological stages. We were able to identify the underlying candidate gene, coding for a well-known sodium transporter, called SlHKT1.2. We showed that an eQTL for the expression of this gene in roots colocalized with the above ground sodium content QTL. A polymorphism putatively responsible for its variation was identified in the gene promoter. Finally, to extend the applicability of these results, we carried out the same analysis on a test-cross panel composed of the core collection crossed with a distant line. The results indicated that the identified QTL retained its functional impact even in a hybrid genetic context: this paves the way for its use in breeding programs aimed at improving salinity tolerance in tomato cultivars.

Association of Seedling Vigour and Salinity Tolerance in Field Pea

Soil salinity results in reduced productivity in field peas, making soil salinity tolerance a critical breeding objective. In this study, four pot experiments were carried out in semi-controlled environments over four consecutive years to assess the contribution of seedling vigour to salinity tolerance at the seedling stage. Split-plot designs were used to assess the effect of salt stress (sodium chloride solution at 16 dSm-1) and control conditions. Extensive sets of advanced breeding lines were used in 2018-2020 to assess growth differences in relation to the treatment, with elemental analysis used on a subset of 15 lines in 2021. A salt tolerance index (STI) was defined as a proportion of shoot biomass under salt stress (DWstress) relative to the shoot dry weight under control (DWctrl). Visual scores of salt stress were recorded on a 1-10 scale (1 = tolerant, 10 = susceptible) from salt stress treatments. The consistent positive and significant correlations (p < 0.01) between shoot DWctrl and DWstress indicated that vigorous genotypes maintained higher shoot DWstress. Both the shoot DWctrl and shoot DWstress had negative and significant (p < 0.01) correlations with visual scores of salt stress. Shoot DWstress showed strong positive correlations with STI (p < 0.01). Both the shoot DWctrl and Shoot DWstress had negative correlations (p < 0.01) with shoot Na+ whereas shoot DWstress had a positive correlation (p < 0.05) with root Na+ concentration. The results indicated that seedling vigour (measured as shoot DWctrl) contributed to salinity tolerance by maintaining improved shoot DWstress, limiting Na+ deposition in shoot and enduring less tissue damage in field pea seedlings. Additional field evaluations are required to establish the correlations of tolerance at seedling stage with yield under saline conditions. The insights obtained from this study may assist field pea breeders in identifying salt-tolerant parent plants, offspring, and breeding lines during the initial growth phases.

Mitigating Salt Stress with Biochar: Effects on Yield and Quality of Dwarf Tomato Irrigated with Brackish Water

The increase in the frequency and magnitude of environmental stresses poses a significant risk to the stability of food supplies. In coastal areas of the Mediterranean, brackish water has long been considered a limitation on horticultural production. In this scenario, the use of biochar in agriculture could be considered a valuable tool to cope with the deleterious effects of salt stress. This work aimed to investigate, in a protected environment, the effects of different concentrations of biochar (0, 1, and 2% v/v) obtained from poplar (Populus L.) biomass on the yield and quality of dwarf San Marzano ecotype tomatoes irrigated with saline water at different concentrations of NaCl (0, 40 and 80 mM). The increase in salt concentration from 0 to 80 mM NaCl reduced the total yield (-63%) and the number of fruits (-25%), but improved the main quality parameters such as dry matter (+75%), total soluble solids (+56%), and polyphenol content (+43%). Compared to control conditions, biochar supplementation improved the total yield (+23%) and number of fruits (+26%) without altering the functional and organoleptic characteristics of the fruits. The promising results underscore the potential of biochar as a sustainable solution to amend soils in order to improve tomato production under unfavorable conditions such as high salinity. However, there is a need to clarify which adaptation mechanisms triggered by biochar amending improve production responses even and especially under suboptimal growing conditions.

Combined salt and low nitrate stress conditions lead to morphophysiological changes and tissue-specific transcriptome reprogramming in tomato

Despite intense research towards the understanding of abiotic stress adaptation in tomato, the physiological adjustments and transcriptome modulation induced by combined salt and low nitrate (low N) conditions remain largely unknown. Here, three traditional tomato genotypes were grown under long-term single and combined stresses throughout a complete growth cycle. Physiological, molecular, and growth measurements showed extensive morphophysiological modifications under combined stress compared to the control, and single stress conditions, resulting in the highest penalty in yield and fruit size. The mRNA sequencing performed on both roots and leaves of genotype TRPO0040 indicated that the transcriptomic signature in leaves under combined stress conditions largely overlapped that of the low N treatment, whereas root transcriptomes were highly sensitive to salt stress. Differentially expressed genes were functionally interpreted using GO and KEGG enrichment analysis, which confirmed the stress and the tissue-specific changes. We also disclosed a set of genes underlying the specific response to combined conditions, including ribosome components and nitrate transporters, in leaves, and several genes involved in transport and response to stress in roots. Altogether, our results provide a comprehensive understanding of above- and below-ground physiological and molecular responses of tomato to salt stress and low N treatment, alone or in combination.

De novo domestication in the Solanaceae: advances and challenges

The advent of highly efficient genome editing (GE) tools, coupled with high-throughput genome sequencing, has paved the way for the accelerated domestication of crop wild relatives. New crops could thus be rapidly created that are well adapted to cope with drought, flooding, soil salinity, or insect damage. De novo domestication avoids the complexity of transferring polygenic stress resistance from wild species to crops. Instead, new crops can be created by manipulating major genes in stress-resistant wild species. However, the genetic basis of certain relevant domestication-related traits often involve epistasis and pleiotropy. Furthermore, pan-genome analyses show that structural variation driving gene expression changes has been selected during domestication. A growing body of work suggests that the Solanaceae family, which includes crop species such as tomatoes, potatoes, eggplants, peppers, and tobacco, is a suitable model group to dissect these phenomena and operate changes in wild relatives to improve agronomic traits rapidly with GE. We briefly discuss the prospects of this exciting novel field in the interface between fundamental and applied plant biology and its potential impact in the coming years.

Deciphering salt stress responses in Solanum pimpinellifolium through high-throughput phenotyping

Soil salinity is a major environmental stressor affecting agricultural productivity worldwide. Understanding plant responses to salt stress is crucial for developing resilient crop varieties. Wild relatives of cultivated crops, such as wild tomato, Solanum pimpinellifolium, can serve as a useful resource to further expand the resilience potential of the cultivated germplasm, S. lycopersicum. In this study, we employed high-throughput phenotyping in the greenhouse and field conditions to explore salt stress responses of a S. pimpinellifolium diversity panel. Our study revealed extensive phenotypic variations in response to salt stress, with traits such as transpiration rate, shoot mass, and ion accumulation showing significant correlations with plant performance. We found that while transpiration was a key determinant of plant performance in the greenhouse, shoot mass strongly correlated with yield under field conditions. Conversely, ion accumulation was the least influential factor under greenhouse conditions. Through a Genome Wide Association Study, we identified candidate genes not previously associated with salt stress, highlighting the power of high-throughput phenotyping in uncovering novel aspects of plant stress responses. This study contributes to our understanding of salt stress tolerance in S. pimpinellifolium and lays the groundwork for further investigations into the genetic basis of these traits, ultimately informing breeding efforts for salinity tolerance in tomato and other crops.

A natural variation in SlSCaBP8 promoter contributes to the loss of saline-alkaline tolerance during tomato improvement

Saline-alkaline stress is a worldwide problem that threatens the growth and yield of crops. However, how crops adapt to saline-alkaline stress remains less studied. Here we show that saline-alkaline tolerance was compromised during tomato domestication and improvement, and a natural variation in the promoter of SlSCaBP8, an EF-hand Ca2+ binding protein, contributed to the loss of saline-alkaline tolerance during tomato improvement. The biochemical and genetic data showed that SlSCaBP8 is a positive regulator of saline-alkaline tolerance in tomato. The introgression line Pi-75, derived from a cross between wild Solanum pimpinellifolium LA1589 and cultivar E6203, containing the SlSCaBP8LA1589 locus, showed stronger saline-alkaline tolerance than E6203. Pi-75 and LA1589 also showed enhanced saline-alkaline-induced SlSCaBP8 expression than that of E6203. By sequence analysis, a natural variation was found in the promoter of SlSCaBP8 and the accessions with the wild haplotype showed enhanced saline-alkaline tolerance compared with the cultivar haplotype. Our studies clarify the mechanism of saline-alkaline tolerance conferred by SlSCaBP8 and provide an important natural variation in the promoter of SlSCaBP8 for tomato breeding.

Heat and salinity stress on the African eggplant F1 Djamba, a Kumba cultivar

Climate change is expected to increase soil salinity and heat-wave intensity, duration, and frequency. These stresses, often present in combination, threaten food security as most common crops do not tolerate them. The African eggplant (Solanum aethiopicum L.) is a nutritious traditional crop found in sub-Saharan Africa and adapted to local environments. Its wider use is, however, hindered by the lack of research on its tolerance. This project aimed to describe the effects of salinity (100 mM NaCl solution) combined with elevated temperatures (27/21°C, 37/31°C, and 42/36°C). High temperatures reduced leaf biomass while cell membrane stability was reduced by salinity. Chlorophyll levels were boosted by salinity only at the start of the stress with only the different temperatures significantly impacted the levels at the end of the experiment. Other fluorescence parameters such as maximum quantum yield and non-photochemical quenching were only affected by the temperature change. Total antioxidants were unchanged by either stress despite a decrease of phenols at the highest temperature. Leaf sodium concentration was highly increased by salinity but phosphorus and calcium were unchanged by this stress. These findings shed new light on the tolerance mechanisms of the African eggplant under salinity and heat. Further research on later developmental stages is needed to understand its potential in the field in areas affected by these abiotic stresses.

B. subtilis CNBG-PGPR-1 induces methionine to regulate ethylene pathway and ROS scavenging for improving salt tolerance of tomato

Soil salinity severely threatens plant growth and crop yields. The utilization of PGPR is an effective strategy for enhancing plant salt tolerance, but the mechanisms involved in this process have rarely been reported. In this study, we investigated the effects of Bacillus subtilis CNBG-PGPR-1 on improving plant salt tolerance and elucidated the molecular pathways involved. The results showed that CNBG-PGPR-1 significantly improved the cellular homeostasis and photosynthetic efficiency of leaves and reduced ion toxicity and osmotic stress caused by salt in tomato. Transcriptome analysis uncovered that CNBG-PGPR-1 enhanced plant salt tolerance through the activation of complex molecular pathways, with plant hormone signal transduction playing an important role. Comparative analysis and pharmacological experiments confirmed that the ethylene pathway was closely related to the beneficial effect of CNBG-PGPR-1 on improving plant salt tolerance. Furthermore, we found that methionine, a precursor of ethylene synthesis, significantly accumulated in response to CNBG-PGPR-1 in tomato. Exogenous L-methionine largely mimicked the beneficial effects of CNBG-PGPR-1 and activated the expression of ethylene pathway-related genes, indicating CNBG-PGPR-1 induces methionine accumulation to regulate the ethylene pathway in tomato. Finally, CNBG-PGPR-1 reduced salt-induced ROS by activating ROS scavenger-encoding genes, mainly involved in GSH metabolism and POD-related genes, which were also closely linked to methionine metabolism. Overall, our studies demonstrate that CNBG-PGPR-1-induced methionine is a key regulator in enhancing plant salt tolerance through the ethylene pathway and ROS scavenging, providing a novel understanding of the mechanism by which beneficial microbes improve plant salt tolerance.

Regulation of ethylene metabolism in tomato under salinity stress involving linkages with important physiological signaling pathways

The tomato is well-known for its anti-oxidative and anti-cancer properties, and with a wide range of health benefits is an important cash crop for human well-being. However, environmental stresses (especially abiotic) are having a deleterious effect on plant growth and productivity, including tomato. In this review, authors describe how salinity stress imposes risk consequences on growth and developmental processes of tomato through toxicity by ethylene (ET) and cyanide (HCN), and ionic, oxidative, and osmotic stresses. Recent research has clarified how salinity stress induced-ACS and - β-CAS expressions stimulate the accumulation of ET and HCN, wherein the action of salicylic acid (SA),compatible solutes (CSs), polyamines (PAs) and ET inhibitors (ETIs) regulate ET and HCN metabolism. Here we emphasize how ET, SA and PA cooperates with mitochondrial alternating oxidase (AOX), salt overly sensitive (SOS) pathways and the antioxidants (ANTOX) system to better understand the salinity stress resistance mechanism. The current literature evaluated in this paper provides an overview of salinity stress resistance mechanism involving synchronized routes of ET metabolism by SA and PAs, connecting regulated network of central physiological processes governing through the action of AOX, β-CAS, SOS and ANTOX pathways, which might be crucial for the development of tomato.

Untargeted Metabolomics of Alternaria solani-Challenged Wild Tomato Species Solanum cheesmaniae Revealed Key Metabolite Biomarkers and Insight into Altered Metabolic Pathways

Untargeted metabolomics of moderately resistant wild tomato species Solanum cheesmaniae revealed an altered metabolite profile in plant leaves in response to Alternaria solani pathogen. Leaf metabolites were significantly differentiated in non-stressed versus stressed plants. The samples were discriminated not only by the presence/absence of specific metabolites as distinguished markers of infection, but also on the basis of their relative abundance as important concluding factors. Annotation of metabolite features using the Arabidopsis thaliana (KEGG) database revealed 3371 compounds with KEGG identifiers belonging to biosynthetic pathways including secondary metabolites, cofactors, steroids, brassinosteroids, terpernoids, and fatty acids. Annotation using the Solanum lycopersicum database in PLANTCYC PMN revealed significantly upregulated (541) and downregulated (485) features distributed in metabolite classes that appeared to play a crucial role in defense, infection prevention, signaling, plant growth, and plant homeostasis to survive under stress conditions. The orthogonal partial least squares discriminant analysis (OPLS-DA), comprising a significant fold change (≥2.0) with VIP score (≥1.0), showed 34 upregulated biomarker metabolites including 5-phosphoribosylamine, kaur-16-en-18-oic acid, pantothenate, and O-acetyl-L-homoserine, along with 41 downregulated biomarkers. Downregulated metabolite biomarkers were mapped with pathways specifically known for plant defense, suggesting their prominent role in pathogen resistance. These results hold promise for identifying key biomarker metabolites that contribute to disease resistive metabolic traits/biosynthetic routes. This approach can assist in mQTL development for the stress breeding program in tomato against pathogen interactions.

Use of a Biostimulant to Mitigate the Effects of Excess Salinity in Soil and Irrigation Water in Tomato Plants

Global warming is linked to progressive soil salinisation, which reduces crop yields, especially in irrigated farmland on arid and semiarid regions. Therefore, it is necessary to apply sustainable and effective solutions that contribute to enhanced crop salt tolerance. In the present study, we tested the effects of a commercial biostimulant (BALOX^®) containing glycine betaine (GB) and polyphenols on the activation of salinity defense mechanisms in tomato. The evaluation of different biometric parameters and the quantification of biochemical markers related to particular stress responses (osmolytes, cations, anions, oxidative stress indicators, and antioxidant enzymes and compounds) was carried out at two phenological stages (vegetative growth and the beginning of reproductive development) and under different salinity conditions (saline and non-saline soil, and irrigation water), using two formulations (different GB concentrations) and two doses of the biostimulant. Once the experiments were completed, the statistical analysis revealed that both formulations and doses of the biostimulant produced very similar effects. The application of BALOX^® improved plant growth and photosynthesis and assisted osmotic adjustment in root and leaf cells. The biostimulant effects are mediated by the control of ion transport, reducing the uptake of toxic Na⁺ and Cl^- ions and favoring the accumulation of beneficial K⁺ and Ca²⁺ cations, and a significant increase in leaf sugar and GB contents. BALOX^® significantly reduced salt-induced oxidative stress and its harmful effects, as evidenced by a decrease in the concentration of oxidative stress biomarkers, such as malondialdehyde and oxygen peroxide, which was accompanied by the reduction of proline and antioxidant compound contents and the specific activity of antioxidant enzymes with respect to the non-treated plants.

Crop Wild Relatives: A Valuable Source of Tolerance to Various Abiotic Stresses

Global climate change is one of the major constraints limiting plant growth, production, and sustainability worldwide. Moreover, breeding efforts in the past years have focused on improving certain favorable crop traits, leading to genetic bottlenecks. The use of crop wild relatives (CWRs) to expand genetic diversity and improve crop adaptability seems to be a promising and sustainable approach for crop improvement in the context of the ongoing climate challenges. In this review, we present the progress that has been achieved towards CWRs exploitation for enhanced resilience against major abiotic stressors (e.g., water deficiency, increased salinity, and extreme temperatures) in crops of high nutritional and economic value, such as tomato, legumes, and several woody perennial crops. The advances in -omics technologies have facilitated the elucidation of the molecular mechanisms that may underlie abiotic stress tolerance. Comparative analyses of whole genome sequencing (WGS) and transcriptomic profiling (RNA-seq) data between crops and their wild relative counterparts have unraveled important information with respect to the molecular basis of tolerance to abiotic stressors. These studies have uncovered genomic regions, specific stress-responsive genes, gene networks, and biochemical pathways associated with resilience to adverse conditions, such as heat, cold, drought, and salinity, and provide useful tools for the development of molecular markers to be used in breeding programs. CWRs constitute a highly valuable resource of genetic diversity, and by exploiting the full potential of this extended allele pool, new traits conferring abiotic-stress tolerance may be introgressed into cultivated varieties leading to superior and resilient genotypes. Future breeding programs may greatly benefit from CWRs utilization for overcoming crop production challenges arising from extreme environmental conditions.

Climate change challenges, plant science solutions

Climate change is a defining challenge of the 21st century, and this decade is a critical time for action to mitigate the worst effects on human populations and ecosystems. Plant science can play an important role in developing crops with enhanced resilience to harsh conditions (e.g. heat, drought, salt stress, flooding, disease outbreaks) and engineering efficient carbon-capturing and carbon-sequestering plants. Here, we present examples of research being conducted in these areas and discuss challenges and open questions as a call to action for the plant science community.

Evaluation of eleven kiwifruit genotypes for bicarbonate tolerance and characterization of two tolerance-contrasting genotypes

Screening bicarbonate-tolerant genotypes is an environmentally-friendly and long-term effective strategy to cope with bicarbonate-induced chlorosis in fruit crops grown on calcareous soils. We investigated eleven genotypes from four kiwifruit species (Actinidia chinensis, A. macrosperma, A. polygama, and A. valvata) for differences in bicarbonate tolerance. We also characterized the physiological and molecular differences in two contrasting genotypes of this group. In the first experiment, bicarbonate-treated plantlets were irrigated with 3.0 g L^-1 CaCO₃ and 5.04 g L^-1 NaHCO₃ in peat and perlite medium culture. Based on principal component analysis, weight-based membership function method and cluster analysis, the tested genotypes were classified into three groups: (1) tolerant, including YX, Av-1, Acd, Ap, Av-2, and QM; (2) moderately tolerant, including Av-3, Am, Av-4, and HWD; and (3) sensitive, including only QH. In the second experiment, QH (bicarbonate-sensitive) and YX (bicarbonate-tolerant) were grown in sand culture with 4.0 g L^-1 CaCO₃ and 0.84 g L^-1 or 1.26 g L^-1 NaHCO₃. Compared with QH, YX showed a better ability to take up iron (Fe) by roots and to transport Fe from roots to shoots in the bicarbonate treatments, probably due to a better capacity to protect from oxidative damage and to excrete protons, and a differential expression of genes associated with Fe uptake and translocation, including HA8, IRT1, YSL3 and NRAMP3. The results can facilitate identifying potential resources for bicarbonate tolerance and breeding new rootstocks, and contribute to the elucidation of the bicarbonate tolerance mechanisms in the genus Actinidia.

Quantitative proteomics analysis of tomato root cell wall proteins in response to salt stress

Cell wall proteins perform diverse cellular functions in response to abiotic and biotic stresses. To elucidate the possible mechanisms of salt-stress tolerance in tomato. The 30 d seedlings of two tomato genotypes with contrasting salt tolerances were transplanted to salt stress (200 mM NaCl) for three days, and then, the cell wall proteins of seedling roots were analyzed by isobaric tags for relative and absolute quantification (iTRAQ). There were 82 and 81 cell wall proteins that changed significantly in the salt-tolerant tomato IL8-3 and the salt-sensitive tomato M82, respectively. The proteins associated with signal transduction and alterations to cell wall polysaccharides were increased in both IL8-3 and M82 cells wall in response to salt stress. In addition, many different or even opposite metabolic changes occurred between IL8-3 and M82 in response to salt stress. The salt-tolerant tomato IL8-3 experienced not only significantly decreased in Na⁺ accumulation but also an obviously enhanced in regulating redox balance and cell wall lignification in response to salt stress. Taken together, these results provide novel insight for further understanding the molecular mechanism of salt tolerance in tomato.

Tomato salt tolerance mechanisms and their potential applications for fighting salinity: A review

One of the most significant environmental factors affecting plant growth, development and productivity is salt stress. The damage caused by salt to plants mainly includes ionic, osmotic and secondary stresses, while the plants adapt to salt stress through multiple biochemical and molecular pathways. Tomato (Solanum lycopersicum L.) is one of the most widely cultivated vegetable crops and a model dicot plant. It is moderately sensitive to salinity throughout the period of growth and development. Biotechnological efforts to improve tomato salt tolerance hinge on a synthesized understanding of the mechanisms underlying salinity tolerance. This review provides a comprehensive review of major advances on the mechanisms controlling salt tolerance of tomato in terms of sensing and signaling, adaptive responses, and epigenetic regulation. Additionally, we discussed the potential application of these mechanisms in improving salt tolerance of tomato, including genetic engineering, marker-assisted selection, and eco-sustainable approaches.

Silicon Nanoparticle-Induced Regulation of Carbohydrate Metabolism, Photosynthesis, and ROS Homeostasis in Solanum lycopersicum Subjected to Salinity Stress

Agricultural crops are facing major restraints with the rapid augmentation of global warming, salt being a major factor affecting productivity. Tomato (Solanum lycopersicum) plant has immense nutritional significance; however, it can be negatively influenced by salinity stress. Nanoparticles (NPs) have excellent properties, due to which these particles are used in agriculture to enhance various growth parameters even in the presence of abiotic stresses. The objective of this study was to investigate the effects of silicon NPs (Si-NPs) through root dipping and foliar spray on tomato in the presence/absence of salt stress. Plant root and leaf were used for the measurements of morphological, physiological, and biochemical parameters treated with Si-NPs under salt stress. At 45 days after sowing, the activity of antioxidant enzymes, photosynthesis, mineral concentration, chlorophyll index, and growth attributes of tomato plants were measured. The developmental processes of tomato plants were severely slowed down by salt stress upto 35.8% (shoot dry mass), 44.3% (root dry mass), 51% (shoot length), and 62% (root length), but this reduction was mitigated by the treatment of Si-NPs. Application of Si-NPs significantly increased the growth attributes (height and dry weight), mineral content [magnesium (Mg), potassium (K), copper (Cu), iron (Fe), manganese (Mn), zinc (Zn)], photosynthesis [net photosynthetic rate (P _N), stomatal conductance (gs), transpiration rate (E), internal CO₂ concentration (Ci)], and activity of antioxidative enzymes including superoxide dismutase and catalase in salt stress. Foliar application of Si-NPs in tomato plants appears to be more effective over root dipping and alleviates the salt stress by increasing the plant's antioxidant enzyme activity.

Enhancing drought stress tolerance in Camelina (Camelina sativa L.) through exogenous application of potassium

The current study was performed under controlled conditions to study the effects of exogenous potassium application on carotenoid contents and drought tolerance in Camelina. Water deficit levels such as 100% FC (control) and 40% FC (drought stress) were imposed after germination of Camelina plants grown to maturity, and different treatments of exogenous K+ were applied at the vegetative stage. We have reported 17 traits of plant growth, physiology, antioxidant enzyme activity, focusing on carotenoids in Camelina to explore their potential yield and yield components. For this purpose, we used multivariate analysis techniques (descriptive statistics, correlation matrix, analysis of variance [ANOVA] and principal components analysis [PCA] to determine the best relation between potassium and studied traits). The results showed a large number of variations in the studied trait under control and water deficit condition. Plant fresh weight (g) was negatively correlated with shoot length and SOD insignificantly correlated with plant fresh weight (g) under water deficit conditions. Potassium loading predicted that foliar application (3 mM K₂ SO₄ ), foliar application (6 mM KNO₃ ), foliar application (12 mM KNO₃ ) and foliar application (12 mM K₂ SO₄ ) are the important doses that contribute the most to enhance the growth, physiological and biochemical activities and carotenoids to improve the Camelina yield under water deficit condition. These doses should be considered in the future to improve the Camelina yield under semi-arid conditions with increased genetic diversity (varietal selection).

Selection strategies to introgress water deficit tolerance derived from Solanum galapagense accession LA1141 into cultivated tomato

Crop wild relatives have been used as a source of genetic diversity for over one hundred years. The wild tomato relative Solanum galapagense accession LA1141 demonstrates the ability to tolerate deficit irrigation, making it a potential resource for crop improvement. Accessing traits from LA1141 through introgression may improve the response of cultivated tomatoes grown in water-limited environments. Canopy temperature is a proxy for physiological traits which are challenging to measure efficiently and may be related to water deficit tolerance. We optimized phenotypic evaluation based on variance partitioning and further show that objective phenotyping methods coupled with genomic prediction lead to gain under selection for water deficit tolerance. The objectives of this work were to improve phenotyping workflows for measuring canopy temperature, mapping quantitative trait loci (QTLs) from LA1141 that contribute to water deficit tolerance and comparing selection strategies. The phenotypic variance attributed to genetic causes for canopy temperature was higher when estimated from thermal images relative to estimates based on an infrared thermometer. Composite interval mapping using BC₂S₃ families, genotyped with single nucleotide polymorphisms, suggested that accession LA1141 contributed alleles that lower canopy temperature and increase plant turgor under water deficit. QTLs for lower canopy temperature were mapped to chromosomes 1 and 6 and explained between 6.6 and 9.5% of the total phenotypic variance. QTLs for higher leaf turgor were detected on chromosomes 5 and 7 and explained between 6.8 and 9.1% of the variance. We advanced tolerant BC₂S₃ families to the BC₂S₅ generation using selection indices based on phenotypic values and genomic estimated breeding values (GEBVs). Phenotypic, genomic, and combined selection strategies demonstrated gain under selection and improved performance compared to randomly advanced BC₂S₅ progenies. Leaf turgor, canopy temperature, stomatal conductance, and vapor pressure deficit (VPD) were evaluated and compared in BC₂S₅ progenies grown under deficit irrigation. Progenies co-selected for phenotypic values and GEBVs wilted less, had significantly lower canopy temperature, higher stomatal conductance, and lower VPD than randomly advanced lines. The fruit size of water deficit tolerant selections was small compared to the recurrent parent. However, lines with acceptable yield, canopy width, and quality parameters were recovered. These results suggest that we can create selection indices to improve water deficit tolerance in a recurrent parent background, and additional crossing and evaluation are warranted.

Role of mineral nutrients, antioxidants, osmotic adjustment and PSII stability in salt tolerance of contrasting wheat genotypes

Global food production is threatened due to increasing salinity and can be stabilized by improving salt tolerance of crops. In the current study, salt tolerance potential of 40 local wheat cultivars against 150 mM NaCl stress was explored. Salt treatment at seedling stage caused less reduction in biomass, K⁺ and P while more decline of Na⁺ in tolerant cultivars due to reduced translocation and enhanced exclusion of Na⁺ from leaves. Principal component analysis based selected S-24, LU-26S, Pasban-90 (salt tolerant) and MH-97, Kohistan-97, Inqilab-91 and Iqbal-2000 (salt sensitive) cultivars were evaluated at adult stage applying 150 mM salinity. Osmotic adjustment by accumulation of soluble sugars and proline and accelerated antioxidant enzymes activities caused efficient scavenging of reactive oxygen species making S-24 and LU-26S tolerant while in MH-97 and Kohistan-97, high MDA represent greater membrane damage due to oxidative stress making them salt sensitive. Chlorophyll a fluorescence transients confirmed better efficiency of photosystem II in S-24 and LU-26S based on energy fluxes (ABS/RC, TRo/RC, ETo/RC and DIo/RC), performance index (PI_ABS) and maximum quantum yield (Fv/Fm). These findings can be correlated using molecular techniques to identify genes for salt exclusion, osmotic adjustment and photosynthetic activity for use in molecular breeding programs.

How Could the Use of Crop Wild Relatives in Breeding Increase the Adaptation of Crops to Marginal Environments?

Alongside the use of fertilizer and chemical control of weeds, pests, and diseases modern breeding has been very successful in generating cultivars that have increased agricultural production several fold in favorable environments. These typically homogeneous cultivars (either homozygous inbreds or hybrids derived from inbred parents) are bred under optimal field conditions and perform well when there is sufficient water and nutrients. However, such optimal conditions are rare globally; indeed, a large proportion of arable land could be considered marginal for agricultural production. Marginal agricultural land typically has poor fertility and/or shallow soil depth, is subject to soil erosion, and often occurs in semi-arid or saline environments. Moreover, these marginal environments are expected to expand with ongoing climate change and progressive degradation of soil and water resources globally. Crop wild relatives (CWRs), most often used in breeding as sources of biotic resistance, often also possess traits adapting them to marginal environments. Wild progenitors have been selected over the course of their evolutionary history to maintain their fitness under a diverse range of stresses. Conversely, modern breeding for broad adaptation has reduced genetic diversity and increased genetic vulnerability to biotic and abiotic challenges. There is potential to exploit genetic heterogeneity, as opposed to genetic uniformity, in breeding for the utilization of marginal lands. This review discusses the adaptive traits that could improve the performance of cultivars in marginal environments and breeding strategies to deploy them.

HKT1;1 and HKT1;2 Na+ Transporters from Solanum galapagense Play Different Roles in the Plant Na+ Distribution under Salinity

Salt tolerance is a target trait in plant science and tomato breeding programs. Wild tomato accessions have been often explored for this purpose. Since shoot Na⁺/K⁺ is a key component of salt tolerance, RNAi-mediated knockdown isogenic lines obtained for Solanum galapagense alleles encoding both class I Na⁺ transporters HKT1;1 and HKT1;2 were used to investigate the silencing effects on the Na and K contents of the xylem sap, and source and sink organs of the scion, and their contribution to salt tolerance in all 16 rootstock/scion combinations of non-silenced and silenced lines, under two salinity treatments. The results show that SgHKT1;1 is operating differently from SgHKT1;2 regarding Na circulation in the tomato vascular system under salinity. A model was built to show that using silenced SgHKT1;1 line as rootstock would improve salt tolerance and fruit quality of varieties carrying the wild type SgHKT1;2 allele. Moreover, this increasing effect on both yield and fruit soluble solids content of silencing SgHKT1;1 could explain that a low expressing HKT1;1 variant was fixed in S. lycopersicum during domestication, and the paradox of increasing agronomic salt tolerance through silencing the HKT1;1 allele from S. galapagense, a salt adapted species.

Salt tolerance mechanisms in the Lycopersicon clade and their trade-offs

Salt stress impairs growth and yield in tomato, which is mostly cultivated in arid and semi-arid areas of the world. A number of wild tomato relatives (Solanum pimpinellifolium, S. pennellii, S. cheesmaniae and S. peruvianum) are endemic to arid coastal areas and able to withstand higher concentration of soil salt concentrations, making them a good genetic resource for breeding efforts aimed at improving salt tolerance and overall crop improvement. However, the complexity of salt stress response makes it difficult to introgress tolerance traits from wild relatives that could effectively increase tomato productivity under high soil salt concentrations. Under commercial production, biomass accumulation is key for high fruit yields, and salt tolerance management strategies should aim to maintain a favourable plant water and nutrient status. In this review, we first compare the effects of salt stress on the physiology of the domesticated tomato and its wild relatives. We then discuss physiological and energetic trade-offs for the different salt tolerance mechanisms found within the Lycopersicon clade, with a focus on the importance of root traits to sustain crop productivity.

A Simple and Effective Bioassay Method Suitable to Comparative In Vitro Study of Tomato Salt Tolerance at Early Development Stages

In vitro evaluation of tomato seeds and seedlings for salt tolerance has undoubted advantages (high productivity, as well as stability and reproducibility of the obtained experimental data due to the maintenance of constant controlled conditions) in comparison with open-field system and pot experiments. However, even high-quality seeds greatly differ in the uniformity of germination capacity and germination energy. Heterogeneous germination in the habit and developmental stage of plant material significantly distorts the obtaining of relevant experimental data suitable for correct interpretation. In our study, we propose a simple and effective bioassay method suitable to comparative in vitro study of tomato salt tolerance using shoot apex of seedlings at the early first-true-leaf stage. Shoot apexes cultured the on the root induction medium (RIM) supplemented with 0.2 mg/L indole-3-butyric acid (IBA) and NaCl at different concentrations (0–250 mM NaCl) revealed significant differences between two tomato genotypes (line YaLF and cv. Rekordsmen) at the organismal (measurements of CO₂ gas exchange), organ (rhizogenesis frequency; number and length of de novo regenerated roots; root fresh (RFW) and dry (RDW) weights; shoot fresh (SFW) and dry (SDW) weights), tissue (the average cross-sectional area of epidermal and mesophylls cotyledonary cells) and cellular (ultrastructure of chloroplast and nuclear compartments) development levels. In addition, a quantitative comparison of proline and photosynthetic pigments contents under 75 and 150 mm NaCl treatments showed a different response between two tomato genotypes. The proposed methodological approach can be used for other plants with a high response to auxin-induced rhizogenesis in vitro, as well as for the comparative in vitro assessment of other abiotic stresses.

Salt stress proteins in plants: An overview

Salinity stress is considered the most devastating abiotic stress for crop productivity. Accumulating different types of soluble proteins has evolved as a vital strategy that plays a central regulatory role in the growth and development of plants subjected to salt stress. In the last two decades, efforts have been undertaken to critically examine the genome structure and functions of the transcriptome in plants subjected to salinity stress. Although genomics and transcriptomics studies indicate physiological and biochemical alterations in plants, it do not reflect changes in the amount and type of proteins corresponding to gene expression at the transcriptome level. In addition, proteins are a more reliable determinant of salt tolerance than simple gene expression as they play major roles in shaping physiological traits in salt-tolerant phenotypes. However, little information is available on salt stress-responsive proteins and their possible modes of action in conferring salinity stress tolerance. In addition, a complete proteome profile under normal or stress conditions has not been established yet for any model plant species. Similarly, a complete set of low abundant and key stress regulatory proteins in plants has not been identified. Furthermore, insufficient information on post-translational modifications in salt stress regulatory proteins is available. Therefore, in recent past, studies focused on exploring changes in protein expression under salt stress, which will complement genomic, transcriptomic, and physiological studies in understanding mechanism of salt tolerance in plants. This review focused on recent studies on proteome profiling in plants subjected to salinity stress, and provide synthesis of updated literature about how salinity regulates various salt stress proteins involved in the plant salt tolerance mechanism. This review also highlights the recent reports on regulation of salt stress proteins using transgenic approaches with enhanced salt stress tolerance in crops.

Analysis of Salinity Tolerance in Tomato Introgression Lines Based on Morpho-Physiological and Molecular Traits

The development of salt-tolerant tomato genotypes is a basic requirement to overcome the challenges of tomato production under salinity in the field or soil-free farming. Two groups of eight tomato introgression lines (ILs) each, were evaluated for salinity tolerance. Group-I and the group-II resulted from the following crosses respectively: Solanum lycopersicum cv-6203 × Solanum habrochaites and Solanum lycopersicum M82 × Solanum pennellii. Salt tolerance level was assessed based on a germination percentage under NaCl (0, 75, 100 mM) and in the vegetative stage using a hydroponic growing system (0, 120 mM NaCl). One line from group I (TA1648) and three lines from group II (IL2-1, IL2-3, and IL8-3) were shown to be salt-tolerant since their germination percentages were significantly higher at 75 and 100 mM NaCl than that of their respective cultivated parents cvE6203 and cvM82. Using the hydroponic system, IL TA1648 and IL 2-3 showed the highest value of plant growth traits and chlorophyll concentration. The expression level of eight salt-responsive genes in the leaves and roots of salt-tolerant ILs (TA1648 and IL 2-3) was estimated. Interestingly, SlSOS1, SlNHX2, SlNHX4, and SlERF4 genes were upregulated in leaves of both TA1648 and IL 2-3 genotypes under NaCl stress. While SlHKT1.1, SlNHX2, SlNHX4, and SlERF4 genes were upregulated under salt stress in the roots of both TA1648 and IL 2-3 genotypes. Furthermore, SlSOS2 and SlSOS3 genes were upregulated in TA1648 root and downregulated in IL 2-3. On the contrary, SlSOS1 and SlHKT1.2 genes were upregulated in the IL 2-3 root and downregulated in the TA1648 root. Monitoring of ILs revealed that some of them have inherited salt tolerance from S. habrochaites and S. pennellii genetic background. These ILs can be used in tomato breeding programs to develop salt-tolerant tomatoes or as rootstocks in grafting techniques under saline irrigation conditions.

Identification of novel source of salt tolerance in local bread wheat germplasm using morpho-physiological and biochemical attributes

Salt tolerant wheat cultivars may be used as genetic resource for wheat breeding to ensure yield stability in future. The study was aimed to select salt tolerant cultivar(s) to identify novel source of salt tolerance in local wheat germplasm. Initially, 40 local wheat cultivars were screened at 150 mM NaCl stress at seedling stage. Selected salt-tolerant (three; S-24, LU-26S and Pasban-90) and salt-sensitive (four; MH-97, Kohistan-97, Inqilab-91 and Iqbal-2000) wheat cultivars were further evaluated using growth, yield, biochemical and physiological attributes. Growth and yield of selected cultivars were reduced under salt stress due to decline in plant water status, limited uptake of macronutrients (N, P and K), reduced K⁺/Na⁺ ratio, photosynthetic pigments and quantum yield of PSII. Wheat plants tried to acclimate salt stress by osmotic adjustment (accumulation of total soluble sugars, proline and free amino acids). Degree of salinity tolerance in cvs. S-24 and LU-26S found to be associated with maintenance of K⁺/Na⁺ ratio, osmo-protectant and photosynthetic activity and can be used as donor for salt tolerance in wheat breeding program at least in Pakistan. These cultivars can be further characterized using molecular techniques to identify QTLs/genes for salt exclusion, osmo-protectant and photosynthetic activity for molecular breeding.

Early Growth Stage Characterization and the Biochemical Responses for Salinity Stress in Tomato

Salinity is one of the most significant environmental stresses for sustainable crop production in major arable lands of the globe. Thus, we conducted experiments with 27 tomato genotypes to screen for salinity tolerance at seedling stage, which were treated with non-salinized (S1) control (18.2 mM NaCl) and salinized (S2) (200 mM NaCl) irrigation water. In all genotypes, the elevated salinity treatment contributed to a major depression in morphological and physiological characteristics; however, a smaller decrease was found in certain tolerant genotypes. Principal component analyses (PCA) and clustering with percentage reduction in growth parameters and different salt tolerance indices classified the tomato accessions into five key clusters. In particular, the tolerant genotypes were assembled into one cluster. The growth and tolerance indices PCA also showed the order of salt-tolerance of the studied genotypes, where Saniora was the most tolerant genotype and P.Guyu was the most susceptible genotype. To investigate the possible biochemical basis for salt stress tolerance, we further characterized six tomato genotypes with varying levels of salinity tolerance. A higher increase in proline content, and antioxidants activities were observed for the salt-tolerant genotypes in comparison to the susceptible genotypes. Salt-tolerant genotypes identified in this work herald a promising source in the tomato improvement program or for grafting as scions with improved salinity tolerance in tomato.

De novo domestication of wild species to create crops with increased resilience and nutritional value

Creating crops with resistance to drought, soil salinity and insect damage, that simultaneously have higher nutritional quality, is challenging to conventional breeding due to the complex and diffuse genetic basis of those traits. Recent advances in gene editing technology, such as base editors and prime-editing, coupled with a deeper understanding of the genetic basis of domestication delivered by the analysis of crop 'pangenomes', open the exciting prospect of creating novel crops via manipulation of domestication-related genes in wild species. A de novo domestication platform may allow rapid and precise conversion of crop wild relatives into crops, while retaining many of the valuable resilience and nutritional traits left behind during domestication and breeding. Using the Solanaceae family as case in point, we discuss how such a knowledge-driven pipeline could be exploited to contribute to food security over the coming decades.

A Review on the Beneficial Role of Silicon against Salinity in Non-Accumulator Crops: Tomato as a Model

Salinity is an abiotic stress that affects agriculture by severely impacting crop growth and, consequently, final yield. Considering that sea levels rise at an alarming rate of >3 mm per year, it is clear that salt stress constitutes a top-ranking threat to agriculture. Among the economically important crops that are sensitive to high salinity is tomato (Solanum lycopersicum L.), a cultivar that is more affected by salt stress than its wild counterparts. A strong body of evidence in the literature has proven the beneficial role of the quasi-essential metalloid silicon (Si), which increases the vigor and protects plants against (a)biotic stresses. This protection is realized by precipitating in the cell walls as opaline silica that constitutes a mechanical barrier to the entry of phytopathogens. With respect to Si accumulation, tomato is classified as a non-accumulator (an excluder), similarly to other members of the nightshade family, such as tobacco. Despite the low capacity of accumulating Si, when supplied to tomato plants, the metalloid improves growth under (a)biotic stress conditions, e.g., by enhancing the yield of fruits or by improving vegetative growth through the modulation of physiological parameters. In light of the benefits of Si in crop protection, the available literature data on the effects of this metalloid in mitigating salt stress in tomato are reviewed with a perspective on its use as a biostimulant, boosting the production of fruits as well as their post-harvest stability.

Emerging Technologies to Enable Sustainable Controlled Environment Agriculture in the Extreme Environments of Middle East-North Africa Coastal Regions

Despite global shifts in attitudes toward sustainability and increasing awareness of human impact on the environment, projected population growth and climate change require technological adaptations to ensure food and resource security at a global scale. Although desert areas have long been proposed as ideal sites for solar electricity generation, only recently have efforts shifted toward development of specialized and regionally focused agriculture in these extreme environments. In coastal regions of the Middle East and North Africa (MENA), the most abundant resources are consistent intense sunlight and saline sea water. MENA coastal regions hold incredible untapped potential for agriculture driven by the combination of key emerging technologies in future greenhouse concepts: transparent infrared collecting solar panels and low energy salt water cooling. These technologies can be combined to create greenhouses that drive regionally relevant agriculture in this extreme environment, especially when the target crops are salt-tolerant plants and algal biomass. Future controlled environment agriculture concepts will not compete for municipal fresh water and can be readily integrated into local human/livestock/fisheries food chains. With strategic technological implementation, marginal lands in these environments could participate in production of biomass, sustainable energy generation, and the circular carbon economy. The goal of this perspective is to reframe the idea of these environments as extreme, to having incredible untapped development potential.