Paclobutrazol improves salt tolerance in quinoa: Beyond the stomatal and biochemical interventions

Quinoa is gaining importance on global scale due to its excellent nutritious profile and environmental stress‐enduring potential. Its production decreases under high salt stress but can be improved with paclobutrazol application. This study showed involvement of some potential protective mechanisms in root and leaf tissues of quinoa plants treated with paclobutrazol (PBZ) against high salinity. The treatment levels were based on preliminary experiments, and it was found that salt stress (400 mm NaCl) markedly reduced growth and photosynthetic pigments while PBZ (20 mg/L) application significantly improved these attributes. Stomata density and aperture declined on adaxial and abaxial surfaces of leaves due to salinity. Paclobutrazol application significantly improved the stomatal density on both surfaces of leaves. Concentration of proline and soluble sugars increased in root and leaf tissues under salinity, which was more obvious in PBZ‐treated plants. Salinity stress induced the oxidative damage by increasing lipid peroxidation (MDA) level in roots and more specifically in leaf tissues. However, PBZ treatments ameliorated the drastic effects of salinity and markedly reduced oxidative damage in salt‐stressed quinoa plants. Enhanced activity of enzymatic antioxidants such as superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) was triggered by PBZ application, more pronounced in leaf than root tissues. Based on these findings, we conclude that PBZ application improves the salt tolerance in quinoa by activation of the above‐mentioned physiological and biochemical mechanisms specifically in leaves.     

Antioxidant Activity in Salt‐Stressed Barley Leaves: Evaluating Time‐ and Age‐Dependence and Suitability for the Use as a Biochemical Marker in Breeding Programs

Soil salinity disturbs the equilibrium between reactive oxygen species (ROS) production and removal, leading to a dramatic increase in ROS concentration and oxidative damage. Enzymatic scavenging is one of the two main mechanisms involved in ROS detoxification in plants. This study has investigated the role of major antioxidant (AO) enzymes in mitigating salinity‐induced oxidative stress in plant shoots. Firstly, two barley varieties were used to evaluate the activity of major AO enzymes in different leaves and at different times after salt treatment. Our results showed that AO enzyme activities had strong tissue and time specificity. A further study was conducted using six barley varieties contrasting in salinity tolerance. AO enzyme activities and proline contents were measured in the third leaves of seedlings after plants were treated with 240 mm NaCl for 10 days. No significant correlation was revealed between leaf AO activity and either plant grain yield or plant survival rate under salt stress. In contrast, a significant increase in leaf proline content under salt stress was found in all sensitive varieties, while in most tolerant varieties, salt stress did not change leaf proline level. It is concluded that although salinity induces changes in leaf AO enzyme activities, the changes cannot be used as biochemical indicators in breeding for salinity tolerance.     

Improved Cold and Drought Tolerance of Doubled Haploid Maize Plants Selected for Resistance to Prooxidant tert‐Butyl Hydroperoxide

To improve the abiotic stress tolerance of maize (Zea mays L.), doubled haploid (DH) plants were produced by in vitro selection of microspores exposed to tert‐butyl hydroperoxide (t‐BuOOH) as a powerful prooxidant This study investigated the tolerance of the progenies of t‐BuOOH‐selected DH lines to oxidative stress, cold and drought in controlled environment pot experiments by analyses of photosynthetic electron transport and CO₂ assimilation processes, chlorophyll bleaching and lipid peroxidation of leaves. Our results demonstrated that the t‐BuOOH‐selected DH plants exhibited enhanced tolerance not only to oxidative stress‐induced by t‐BuOOH but also to cold and drought stresses. In addition, they showed elevated activities of antioxidant enzymes such as superoxide dismutase, ascorbate peroxidase, catalase, glutathione reductase and glutathione S‐transferase when compared with the DH lines derived from microspores that were not exposed to t‐BuOOH and to the original hybrid plants. The results suggest that the simultaneous up‐regulation of several antioxidant enzymes may contribute to the oxidative and cold stress tolerance of the t‐BuOOH‐selected DH lines, and that the in vitro microspore selection represents a potential way to improve abiotic stress tolerance in maize.     

Leaf Cell‐Wall Components as Influenced in the First Phase of Salt Stress in Three Maize (Zea mays L.) Hybrids Differing in Salt Resistance

The leaf cell wall (CW) chemical composition of three maize (Zea mays L.) hybrids (salt‐resistant SR 03 and SR 12, salt‐sensitive Pioneer 3906) was investigated in the first phase of salt stress (100 mm NaCl) compared with the control (1 mm NaCl) treatment to investigate whether changes in CW composition were responsible for shoot growth reduction. Salt treatment caused a strong inhibition in shoot growth with a concomitant increase in the ratio between CW dry mass (DM) and shoot fresh mass (FM) and a decrease in CW cellulose concentrations in all hybrids. NaCl caused a large increase in the concentrations of total and non‐methylated uronic acid (UA) in salt‐sensitive Pioneer 3906 and salt‐resistant SR 12. The onset of the accumulation of non‐methylated UA was delayed in SR 12, which indicates that this may be one reason for the better growth performance of this hybrid under salt stress compared with Pioneer 3906. It is concluded that a low accumulation of non‐methylated UA in leaf CW may, among other mechanisms, contribute to salt resistance in the first phase of salt stress.     

Na+ Retention in the Root is a Key Adaptive Mechanism to Low and High Salinity in the Glycophyte,Talinum paniculatum (Jacq.) Gaertn. (Portulacaceae)

Talinum paniculatum is an important leafy vegetable and medicinal plant, used in many parts of South America, Africa and Asia. Its adaptation to abiotic stress has received little attention and therefore worthy of interest, especially as environmental conditions are rendering arable lands increasingly unfavourable for agriculture. Therefore, this study was undertaken to examine the influence of salt stress on the vegetative growth of the plant by subjecting seedlings to 0, 25, 50, 100, 200 and 300 mm NaCl stress for 10 days. The dry weight, ion concentrations, relative water content, oxidative damage, proline, osmotic potential and some antioxidants were determined. The plants were found to retain Na⁺ mainly in the root, with less affected leaf K⁺ concentration, and consequently very low shoot Na⁺/K⁺ ratios (<0.2) under all the stress treatments. The proline content significantly increased under the 100–300 mm treatments (18‐ to 244‐fold), with a corresponding significant reduction in osmotic potential and hence high osmotic adjustment. The antioxidant enzyme activities and non‐enzyme antioxidants showed significant increase only under the highest salinity. Taken together, these results suggest that shoot Na⁺ exclusion is characteristic of this plant and is mainly responsible for its adaptation to low salinity.     

Genetic variation in root development responses to salt stresses of quinoa

Soil salinity has become a serious environmental abiotic stress limiting crop productivity and quality. The root system is the first organ sensing the changes in salinity. Root development under elevated salinity is therefore an important indicator for saline tolerance in plants. Previous studies focused on varietal differences in morphological traits of quinoa under saline stresses; however, variation in root development responses to salinity remains largely unknown. To understand the genetic variation in root development responses to salt stress of quinoa, we conducted a preliminary screening for salinity response at two salinity levels of a diverse set of 52 quinoa genotypes and microsatellite markers were used to link molecular variation to that in root development responses to salt stresses of represented genotypes. The frequency distribution of saline tolerance index showed continuous variation in the quinoa collection. Cluster analysis of salinity responses divided the 52 quinoa genotypes into six major groups. Based on these results, six genotypes representative of groups I to VI including Black quinoa, 2-Want, Atlas, Riobamba, NL-6 and Sayaña, respectively, were selected to evaluate root development under four saline stress levels: 0, 100, 200 and 300 mM NaCl. Contrasts in root development responses to saline stress levels were observed in the six genotypes. At 100 mM NaCl, significant differences were not observed in root length development (RLD) and root surface development (RSAD) of most genotypes except Black quinoa; a significant reduction was observed in this genotype as compared to controls. At 200 mM NaCl, significant reduction was detected in RLD and RSAD in all genotypes showing this as the best concentration to discriminate among genotypes. The strongest inhibition of root development was found for all genotypes at 300 mM NaCl as compared to lower saline levels. Among genotypes, Atlas of group III shows as a saline-tolerant genotype confirming previous reports. Variation in root responses to salinity stresses is also discussed in relation to climate conditions of origins of the genotypes and reveal interesting guidelines for further studies exploring the mechanisms behind this aspect of saline adaptation.     

Saponin seed priming improves salt tolerance in quinoa

Quinoa (Chenopodium quinoa Willd.) is a facultative halophyte of great value, and World Health Organization has selected this crop, which may assure future food and nutritional security under changing climate scenarios. However, germination is the main critical stage of quinoa plant phenology affected by salinity. Therefore, two experiments were conducted to improve its performance under salinity by use of saponin seed priming. Seeds of cv. Titicaca were primed in seven different solutions with varying saponin concentrations (i.e. 0%, 0.5%, 2%, 5%, 10%, 15%, 25% and 35%), and then, performances of primed seeds were evaluated based on mean germination time and final germination percentage in germination assays (0 and 400 mM NaCl stress). Saponin solutions of 10%, 15% and 25% concentration were found most effective priming tools for alleviating adverse effects of salt stress during seed germination. Performances of these primed seeds were further evaluated in pot study. At six‐leaf stage, plants were irrigated with saline water having either 0 or 400 mM NaCl. The results indicated that saline irrigation significantly decreased the growth, physiology and yield of quinoa, whereas saponin priming found operative in mitigating the negative effects of salt stress. Improved growth, physiology and yield performance were linked with low ABA concentration, better plant water (osmotic and water potential) and gas relations (leaf photosynthetic rate, stomatal conductance), low Na⁺ and high K⁺ contents in leaves. Our results suggest that saponin priming could be used as an easy‐operated and cost‐effective technology for sustaining quinoa crop growth on salt‐affected soils.     

Morphological and biochemical responses of Balanites aegyptiaca to drought stress and recovery are provenance‐dependent

Balanites aegyptiaca is a drought‐tolerant tree naturally distributed in Africa and has a high potential for biofuel production and livelihood. To understand the plant tolerance to drought stress, B. aegyptiaca plants collected from five provenances were subjected for 4 weeks to drought stress through different regimes of soil volumetric water content (VWC, i.e. 25% control, 15% as moderate and 5% as a severe drought stress) followed by 2‐week recovery. Morpho‐physiological responses as well as the changes in antioxidant defences under water stress and recovery were investigated. Drought stress significantly reduced plant biomass‐related parameters, stomatal conductance, quantum efficiency and increased leaf temperature. Each provenance showed specific patterns of stress response reactions that were detected in a cluster analysis. The large leaf area and a high level of lipid peroxidation in Cairo provenance increased its sensitivity to severe drought. For provenances El‐Kharga and Yemen, the highest tocopherol contents and the highest catalytic activities of ascorbate peroxidase (SOD), catalase (CAT), glutathione reductase (GR) and dehydroascorbate reductase (DHAR) were recorded. These traits contributed to the high drought tolerance of these two provenances in comparison with the other provenances. All plants recovered from stress and showed specifically increased activity of glutathione‐S‐transferase (GST) as a repair mechanism. Results showed that the drought tolerance level in B. aegyptiaca is provenance‐dependent.     

Changes in Hormonal Balance: A Possible Mechanism of Pre‐Sowing Chilling‐Induced Salt Tolerance in Spring Wheat

There is a lack of knowledge about factors contributing to the chilling‐induced alleviatory effects on growth of plants under salt stress. Thus, the primary objective of the study was to determine whether chilling‐induced changes in endogenous hormones, ionic partitioning within shoots and roots and/or gaseous exchange characteristics is involved in salt tolerance of two genetically diverses of wheat crops. For this purpose, the seeds of two spring wheat (Triticum aestivum) cultivars, MH‐97 (salt intolerant) and Inqlab‐91 (salt tolerant) were chilled at 3°C for 2 weeks. The chilled, hydroprimed and non‐primed (control) seeds of the two wheat cultivars were sown in both Petri dishes in a growth room and in the field after treatment with 15 dS m^?1 NaCl salinity. Chilling was very effective in increasing germination rate and subsequent growth when compared with hydropriming and control under salt stress. Results from field experiments clearly indicated the efficacy of chilling over hydropriming in improving shoot dry biomass and grain yield in either cultivar, particularly under salt stress. This increase in growth and yield was related to increased net photosynthetic rate, greater potential to uptake and accumulate the beneficial mineral elements (K⁺ and Ca²⁺) in the roots and reduced uptake and accumulation of toxic mineral element (Na⁺) in the shoots of both wheat cultivars when grown under salt stress. Salt‐stressed plants of both wheat cultivars raised from chilled seed had greater concentrations of indoleacetic acid, abscisic acid, salicylic acid and spermine when compared with hydropriming and control. Therefore, induction of salt tolerance by pre‐sowing chilling treatment in wheat could be attributed to its beneficial effects on ionic homeostasis and hormonal balance. The results presented are also helpful to understand the chilling‐induced cross adaptation of plants in natural environments. Moreover, efficacy of pre‐sowing chilling treatment over hydropriming suggested its commercial utilization as a low risk priming treatment for better wheat crop production under stressful environments.     

Role of Arbuscular Mycorrhizae in the Alleviation of Ionic, Osmotic and Oxidative Stresses Induced by Salinity in Cajanus cajan (L.) Millsp. (pigeonpea)

Salinity stress causes ion toxicity and osmotic imbalances, leading to oxidative stress in plants. Arbuscular mycorrhizae (AM) are considered bio‐ameliorators of saline soils and could develop salinity tolerance in crop plants. Pigeonpea exhibits strong mycorrhizal development and has a high mycorrhizal dependency. The role of AM in enhancing salt tolerance of pigeonpea in terms of shoot and root dry weights, phosphorus and nitrogen contents, K⁺ : Na⁺, Ca²⁺ : Na⁺ ratios, lipid peroxidation, compatible solutes (proline and glycine betaine) and antioxidant enzyme activities was examined. Plants were grown and maintained at three levels of salt (4, 6 and 8 dSm^?1). Stress impeded the growth of plants, led to weight gain reductions in shoots as well as roots and hindered phosphorus and nitrogen uptake. However, salt‐stressed mycorrhizal plants produced greater root and shoot biomass, had higher phosphorus and nitrogen content than the corresponding uninoculated stressed plants. Salt stress resulted in higher lipid peroxidation and membrane stability was reduced in non‐AM plants. The presence of fungal endophyte significantly reduced lipid peroxidation and membrane damage caused by salt stress. AM plants maintained higher K⁺ : Na⁺ and Ca²⁺ : Na⁺ ratios than non‐AM plants under stressed and unstressed conditions. Salinity induced the accumulation of both proline and glycine betaine in AM and non‐AM plants. The quantum of increase in synthesis and accumulation of osmolytes was higher in mycorrhizal plants. Antioxidant enzyme activities increased significantly with salinity in both mycorrhizal and non‐mycorrhizal plants. In conclusion, pigeonpea plants responded to an increased ion influx in their cells by increasing the osmolyte synthesis and accumulation under salt stress, which further increased with AM inoculation and helped in maintaining the osmotic balance. Increase in the antioxidant enzyme activities in AM plants under salt stress could be involved in the beneficial effects of mycorrhizal colonization.     

Growth and Physiological Responses of Quinoa to Drought and Temperature Stress

Quinoa (Chenopodium quinoa Willd.), traditionally called the mother of grains, has the potential to grow under high temperatures and drought, tolerating levels regarded as stresses in other crop species. A pot experiment was conducted in a climate chamber to investigate the potential of quinoa tolerance to increasing drought and temperature. Quinoa plants were subjected to three irrigation and two temperature regimes. At low temperature, the day/night climate chamber temperature was maintained at 18/8 °C and 25/20 °C for high temperature throughout the treatment period. The irrigation treatments were full irrigation (FI), deficit irrigation (DI) and alternate root‐zone drying (ARD). FI plants were irrigated daily to the level of the pot's water‐holding capacity. In DI and ARD, 70 % water of FI was applied either to the whole pot or to one side of the pot alternating, respectively. The results indicated that plant height and shoot dry weight significantly decreased by ARD and DI compared to FI treatment both at low and at high temperatures. However, plants in ARD treatment showed significantly higher plant height and shoot dry weight compared to DI especially at higher temperature, which is linked to increased xylem ion content. Higher quinoa plant growth in ARD was associated with increase in water‐use efficiency (WUE_i) due to higher abscisic acid concentration and higher nutrient contents compared to DI. From results, it can be concluded that quinoa plant growth is favoured by high temperature (25/20 °C) and ARD is an effective irrigation strategy to increase WUE in drought prone areas.     

Induction of Drought Tolerance in Maize (Zea mays L.) due to Exogenous Application of Trehalose: Growth,Photosynthesis, Water Relations and Oxidative Defence Mechanism

The present investigation was conducted to assess the ameliorative effects of foliar‐applied trehalose on growth, photosynthetic attributes, water relation parameters and oxidative defence mechanism in two maize cultivars under field water deficit conditions. Various components of the experiment comprised two maize cultivars (EV‐1098 and Agaiti‐2002), two water‐stress levels (irrigation after 2 weeks and irrigation after 3 weeks during the entire period of growth), and two levels of trehalose (0 and 30 mm ) and four replicates of each treatment. Water stress significantly reduced the plant biomass production, photosynthetic attributes and water relation parameters in both maize cultivars. In contrast, water stress considerably increased the leaf malondialdehyde (MDA) contents, the activities of antioxidant enzymes such as peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT), and the levels of non‐enzymatic compounds such as ascorbic acid and tocopherols. In contrast, water stress caused a marked reduction in leaf phenolic contents. Foliar‐applied trehalose significantly increased plant biomass production, and improved some key photosynthetic attributes and plant–water relation parameters. The ameliorative effect of exogenously applied trehalose was also observed on the activities of some key antioxidant enzymes (POD and CAT) and non‐enzymatic compounds (tocopherols and phenolics). Overall, exogenously applied trehalose considerably improved drought tolerance of maize plants by up‐regulating photosynthetic and water relation attributes as well as antioxidant defence mechanism.     

The Effects of Foliar Application of Ascorbic Acid (Vitamin C) on Antioxidant Enzymes Activities, Lipid Peroxidation and Proline Accumulation of Canola (Brassica napus L.) under Conditions of Salt Stress

The effects of salt stress on protein (PROT) content, lipid peroxidation, proline accumulation, chlorophyll (Chl) content, and superoxide dismutase (SOD; EC 1.15.1.1), catalase (EC 1.11.1.6) and peroxidase (EC 1.11.1.7) activity were studied in the leaves and roots of canola (Brassica napus L. cv. Okapi). Four weeks after sowing (at the V₄ stage), plants were exposed to salt stress by the application of NaCl solution (200 mm ) for 6 days daily, After 6 days followed by foliar application of ascorbic acid (AsA) solution (25 mm ). The activity of all the antioxidant enzymes assayed (except SOD in the roots) was increased significantly in the plants under conditions of salt stress. The application of AsA decreased enzyme activity in the leaves, but it had no effect on enzyme activity in the roots. The total PROT content of the leaves and roots decreased under the conditions of high salinity. AsA treatment of plants under salt stress increased the total PROT content significantly in both leaves and roots. Measurement of the malondialdehyde content of leaves and roots showed that lipid peroxidation was increased by interaction with damaging reactive oxygen species during salt stress, and that application of AsA reduced lipid peroxidation only in the leaves. The Chl content was also affected by salt stress. There was significant difference between the controls and salt‐stress treatments in Chl content. The results of the present study indicate that usage of AsA reduces the harmful effects of salinity and increases resistance to salinity in canola plant.     

Growth and Ionic Content of Quinoa Under Saline Irrigation

Drought and salinity are the most important abiotic stresses that affect plant's growth and productivity. The aim of the present work was to evaluate the effect of salt and water deficit on water relations, growth parameters and capacity to accumulate inorganic solutes in quinoa plants. An irrigation experiment was carried out in 2009 and 2010 in the Volturno river plain. Three treatments irrigated with fresh water (Q100, Q50 and Q25) and three irrigated with saline water (Q100S, Q50S and Q25S) were tested. For saline irrigation, water with an electrical conductivity of 22 dS m^?1 was used. Actual evapotranspiration (ET_a), water productivity (WP), biomass allocation, relative growth rate (RGR), net assimilation rate (NAR), specific leaf area, leaf area ratio and ions accumulation of quinoa plants were evaluated. WP and plant growth were not influenced by saline irrigation, as quinoa plants incorporated salt ions in the tissues (stems, roots, leaves) preserving seed quality. Treatment with a reduction in the irrigation water to 25 % of full irrigated treatment (Q25) caused an increase in WP and a reduced dry matter accumulation in the leaves. Quinoa plants (Q25) were initially negatively affected by severe drought with RGR and NAR reduction, and then, they adapted to it. Quinoa could be considered a drought tolerant crop that adapt photosynthetic rate to compensate for a reduced growth.     

Physiological processes associated with salinity tolerance in an alfalfa half‐sib family

We previously reported an alfalfa half‐sib family, HS‐B, with improved salt tolerance, compared to parental plants, P‐B. In this study, we conducted additional experiments to address potential physiological mechanisms that may contribute to salt tolerance in HS‐B. Vegetatively propagated HS‐B and P‐B plants were treated with a nutrient solution (control) or a nutrient solution containing NaCl (EC = 12 dS/m). Shoots and roots were harvested at various time points after treatment for quantification of proline, soluble sugar, and H₂O₂ using spectrophotometers. Subcellular localization and quantification of Na in roots were conducted using a Na⁺‐specific dye under a confocal microscope. HS‐B produced 86 and 89% greater shoot and root dry biomass, respectively, compared to parental plants, P‐B, under salinity in the greenhouse. Under saline conditions the HS‐B shoots accumulated 115% and roots 55% more soluble sugars than P‐B counterparts. The non‐saline HS‐B shoots, however, showed 72% less soluble sugars than the non‐saline P‐B plants. Under saline conditions HS‐B accumulated 39% less proline in shoots, while roots accumulated 56% more proline, compared to their P‐B parents. HS‐B plants also showed a greater reduction of stomatal conductance under mild saline stress. HS‐B shoots and roots contained 3–4 times less reactive oxygen species (H₂O₂) after salt treatment compared to P‐B plants. Sodium localization and distribution analysis using Na⁺‐specific dye revealed HS‐B plants accumulated 88% and 48% less Na⁺ in stele and xylem vessels compared to P‐B. The study provides insights into the potential mechanisms that may contribute to salt tolerance in HS‐B: maintaining RWC by accumulating soluble sugars while reducing transpiration, maintaining healthy status by reducing oxidative stresses, and preventing salt toxicity by reducing accumulation of Na⁺ inside root cells and xylem.     

Identification of molecular markers linked to salt‐tolerant genes at germination stage of rice

An F_2 : 4 population derived from the cross between salt‐tolerant variety ‘Gharib’ (indica) and salt‐sensitive variety Sepidroud (indica) was used to determine the germination traits. The seeds were treated with 80 mm NaCl (salt stress), and 11 traits were determined as indicators for salt‐tolerant including germination rate, germination percentage, radicle length, plumule length, coleoptile length, plumule fresh and dry weight, radicle fresh and dry weight and coleoptile fresh and dry weight. A linkage map of 2475.7 cM with an average interval of 10.48 cM was constructed using 105 amplified fragment length polymorphism (AFLP) markers and 131 SSR markers. As many as that 17 quantitative trait loci (QTLs) were detected related to germination traits under salt stress condition; some of them are being reported for first time. Also, overlapping of QTLs related to salt tolerance was observed in this study. The identification of genomic regions associated with salt‐tolerant and its components under salt stress will be useful for marker‐based approaches to improve salt‐tolerant for farmers in salt‐prone rice environments.     

Influence of the root endophyte Piriformospora indica on the plant water relations,gas exchange and growth of Chenopodium quinoa at limited water availability

This study aimed to evaluate the ability of Piriformospora indica to colonize the root of Chenopodium quinoa and to verify whether this endosymbiont can improve the growth, performance and drought resistance of this species. The study delivered, for the first time, evidence for successful colonization of P. indica in quinoa. Hence, pot experiment was conducted in the greenhouse, where inoculated and non‐inoculated plants were subjected to ample (40%–50% WHC) and deficit (15%–20%WHC) irrigation treatments. Drought adversely influenced the plant growth, leading to decline the total plant biomass by 74%. This was linked to an impaired photosynthetic activity (caused by lower g_s and C_i/C_a ratio; stomatal limitation of photosynthesis) and a higher risk of ROS production (enhanced ETR/A_gross ratio). P. indica colonization improved quinoa plant growth, with total biomass increased by 8% (controls) and 76% (drought‐stressed plants), confirming the growth‐promoting activity of P. indica. Fungal colonization seems to diminish drought‐induced growth hindrance, likely, through an improved water balance, reflected by the higher leaf ψ_w and g_s. Additionally, stomatal limitation of photosynthesis was alleviated (indicated by enhanced C_i/C_a ratio and A_net), so that the threat of oxidative stress was minimized (decreased ETR/A_gross). These results infer that symbiosis with P. indica could negate some of the detrimental effects of drought on quinoa growth, a highly desired feature, in particular at low water availability.     

Genomewide association analysis of salt tolerance in soybean [Glycine max (L.) Merr.]

Salinity is a common abiotic stress causing soybean [Glycine max (L.) Merr.] yield loss worldwide. The use of tolerant cultivars is an effective and economic approach to coping with this stress. Towards this, research is needed to identify salt‐tolerant germplasm and better understand the genetic and molecular basis of salt tolerance in soybean. The objectives of this study were to identify salt‐tolerant genotypes, to search for single‐nucleotide polymorphisms (SNPs) and QTLs associated with salt tolerance. A total of 192 diverse soybean lines and cultivars were screened for salt tolerance in the glasshouse based on visual leaf scorch scores after 15–18 days of 120 mM NaCl stress. These genotypes were further genotyped using the SoySNP50K iSelect BeadChip. Genomewide association mapping showed that 62 SNP markers representing six genomic regions on chromosomes (Chr.) 2, 3, 5, 6, 8 and 18, respectively, were significantly associated with salt tolerance (p < 0.001). A total of 52 SNP markers on Chr. 3 are mapped at or near the major salt tolerance QTL previously identified in S‐100 (Lee et al., 2014). Three SNPs on Chr. 18 map near the salt tolerance QTL previously identified in Nannong1138‐2 (Chen, Cui, Fu, Gai, & Yu, 2008). The other significant SNPs represent four putative minor QTLs for salt tolerance, newly identified in this study. The results above lay the foundation for fine mapping, cloning and molecular breeding for soybean salt tolerance.     

Accession Variation for Salt Tolerance in Proso Millet (Panicum miliaceum L.) Using Leaf Proline Content and Activities of Some Key Antioxidant Enzymes

Inter‐accession variation for salt tolerance of Panicum miliaceum (proso millet) was appraised using leaf proline content and activities of antioxidant enzymes as selection criteria. Eighteen accessions of proso millet were grown under control conditions and after 14 days subjected to saline (120 mm NaCl) stress for 4 weeks. Salt stress substantially decreased relative water content (RWC), while increased leaf free proline and malondialdehyde (MDA) and activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) of all accessions of proso millet. The difference among the accessions of P. miliaceum was significant in yield as well as in the activities of antioxidant enzymes analyses. On the basis of seed yield (expressed as per cent of control), of 18 accessions, three were categorised as salt‐tolerant (008211, 008214 and 008226), seven as moderately tolerant (008210, 008213, 008216, 008220, 008222, 008223 and 008242) and eight as salt‐sensitive (008208, 008215, 008217, 008218, 008221, 008225, 008230 and 008236). Of all P. miliaceum accessions, 008211, 008226, 008215 and 008218 were relatively higher in proline, 008214 and 008221 in MDA contents, 00812, 008225, 008236, 008222 and 008242 in SOD activity and 008218, 008220, 008211 and 008226 in POD and CAT enzyme activities. Thus, because of differential response of high or low seed yielded accessions in accumulation of proline and antioxidant enzyme activities, these variables were not found effective criteria for discriminating the P. miliaceum accessions for salt tolerance.