Comparative effect of salinity on growth, grain yield, water use efficiency, δ(13)C and δ(15)N of landraces and improved durum wheat varieties

Polyphenols, Flavonoids, and Antioxidant Activity Involved in Salt Tolerance in Wheat, Aegilops cylindrica and Their Amphidiploids

Aegilops spp. is the closest genus to wheat (Triticum spp.), which makes Aegilops great candidates to exhibit precursors of wheat features. Aegilops cylindrica Host displays excellent salt tolerance. In the current study, biochemical and phytochemical compounds in the leaves of two wheat cultivars, one hyper-salt tolerant Ae. cylindrica genotype and their amphidiploids (derived from "Chinese Spring" × Ae. cilindrica and "Roshan" × Ae. cylindrica), grown under control and saline field conditions, were assessed. These compounds included total protein content, proline content, electrolyte leakage, total flavonoid content, total phenolic content, DPPH radical scavenging activity, and reducing power. In addition, phenolic components were also identified using HPLC analysis. Chlorogenic acid, ellagic acid, ferulic acid, syringic acid, vanillic acid, p-coumaric acid, caffeic acid, and gallic acid were the most abundant phenolic acids. Luteolin, apigenin, and rutin were the most abundant flavonoids in the leaves. Salt stress significantly increased all biochemical variables, with the exceptions of reducing power and p-coumaric acid. Interestingly, amphidiploid genotypes exhibited intermediate levels of most of the detected phenolic compounds between the two parental species. As demonstrated by bivariate correlations luteolin, chlorogenic acid, caffeic acid and apigenin could predict inhibition percentage by DPPH assay, suggesting a possible role in the cellular defense against oxidative stress in wheat. The amphidiploids and their wild parent performed significantly better than wheat cultivars on phenolic constituents, flavonoids, and maintaining redox homeostasis under salt stress conditions.

Morphological, Physiological and Molecular Markers for Salt-Stressed Plants

Plant growth and development is adversely affected by different kind of stresses. One of the major abiotic stresses, salinity, causes complex changes in plants by influencing the interactions of genes. The modulated genetic regulation perturbs metabolic balance, which may alter plant's physiology and eventually causing yield losses. To improve agricultural output, researchers have concentrated on identification, characterization and selection of salt tolerant varieties and genotypes, although, most of these varieties are less adopted for commercial production. Nowadays, phenotyping plants through Machine learning (deep learning) approaches that analyze the images of plant leaves to predict biotic and abiotic damage on plant leaves have increased. Here, we review salinity stress related markers on molecular, physiological and morphological levels for crops such as maize, rice, ryegrass, tomato, salicornia, wheat and model plant, Arabidopsis. The combined analysis of data from stress markers on different levels together with image data are important for understanding the impact of salt stress on plants.

Comparative Study of the Effects of Salinity on Growth, Gas Exchange, N Accumulation and Stable Isotope Signatures of Forage Oat (Avena sativa L.) Genotypes

Identifying suitable salt stress-tolerant phenotypes based on their agronomic and physiological traits remains a herculean task in forage-type oat (Avena sativa L.) breeding. This study examined the responses of six forage-type oat cultivars under four levels of saline stress over the vegetative growth cycle. Crop growth, water status-related traits and nitrogen status-related traits were analyzed in different plant parts to evaluate effective approaches for identifying salt tolerance. Plant biomass, height, tiller number and culm thickness changed substantially during salinity, but they were not precise enough for use in estimating genotypic salinity tolerance during long-term stress. Genotypes bearing larger numbers of tillers showed greater sensitivity to salinity due to its effects on biomass loss. Tolerant genotypes exhibited higher relative shoot biomass together with higher water use efficiency. The concentrations of Na⁺, K⁺ and their ratio, combined with the δ¹³C in shoots and roots were effective indicators for estimating tolerant genotypes through better water maintenance. N concentrations of shoots were the most efficient for evaluating genotypic tolerance. Low nitrate reductase (NR) and glutamine synthetase (GS) activity might be key factors limiting N accumulation. Chlorophyll (Chl) content and net photosynthetic rate, as well as stomatal conductance and evaporation, were useful for identifying salinity tolerance physiological mechanisms, but the effectiveness was low for genotypic tolerance testing for forage type oats due to the interaction between genotypes and salinity levels. The selection of high salinity-tolerant genotypes should focus on genotypes with photosynthetic resilience to salt, followed by high N metabolism (higher NR and GS activities) to ensure accumulation of more N in the shoot dry matter.

Identification of Phenotypic and Physiological Markers of Salt Stress Tolerance in Durum Wheat (Triticum Durum Desf.) through Integrated Analyses

Salinity is one of the most important stresses that reduces plant growth and productivity in several parts of the world. Nine Tunisian durum wheat genotypes grown under hydroponic conditions were subjected to two levels of salt stress (100 and 170 mM NaCl) for 21 days. An integrative analysis revealing the impact of salinity on key phenotypic and physiological marker traits was then conducted. Principal component analysis grouped these traits into three different clusters corresponding to the absence of salt stress and the two levels of salt stress. This analysis also allowed the identification of genotypes exhibiting various levels of tolerance to NaCl. Among the nine genotypes of Triticum durum Desf., cultivar Om Rabiaa was the most tolerant whereas cultivar Mahmoudi genotype was the most sensitive. Following the multivariate analysis of the examined phenotypic and physiological traits, we found that shoot length, shoot fresh weight, leaf area, the whole-plant stable isotope ratios of nitrogen (δ15N), shoot ammonium and proline contents, and shoot glutamine synthetase activity could be used as markers for the selection of salt-tolerant wheat genotypes.

Shoot δ13 C values as an indicator of cumulative stress: The role of re-watering during drought and salinity stress

RATIONALE

The carbon stable isotope composition (δ¹³ C value) of a plant can reflect prolonged drought and salinity, as different isotopic signals resulting from drought and salinity can be retained in plant tissue. Commonly, drought and salinity are interrupted by intermittent precipitation or irrigation. It remains unclear whether the δ¹³ C values reflect the cumulative duration of intermittent drought or salinity stress.

METHODS

Drought (5% and 10% polyethylene glycol) and salinity (35 mM and 85 mM NaCl) were imposed on annual ryegrass consistently or cyclically; throughout the treatments, the stress duration for cyclic drought/salinity was half that of the corresponding prolonged stress treatment. The shoot δ¹³ C values were measured using isotope ratio mass spectrometry.

RESULTS

Prolonged drought restrained growth and increased shoot δ¹³ C values relative to the control group. However, the shoot biomass was even lower under cyclic drought than under prolonged drought. Furthermore, the shoot δ¹³ C value under cyclic drought was close to that of the control group. The low NaCl concentration treatment actually enhanced shoot growth. The shoot δ¹³ C value varied with both duration and intensity of salinity across all groups.

CONCLUSIONS

The shoot δ¹³ C value in annual ryegrass did indicate cumulative stress from cyclic low salinity, but not that from cyclic drought, in a manner that was mediated by the effect of re-watering on the mass and allocation of the photosynthates produced during stress.

Comparisons of WUE in twelve genotypes of winter wheat and the relationship between δ 13C and WUE

Twelve winter wheat (Triticum aestivum) genotypes were examined for differences in grain yield, water use efficiency (WUE), and stable carbon isotope composition (δ13C) in flag leaves. The plants were subjected to rain-fed treatment and supplemental irrigation at the jointing and anthesis stages, during the 2015–2016 and 2016–2017 winter wheat growing seasons. The relationships between δ13C with grain yield and WUE were analyzed under two different water environments. The results indicated that there were significant differences in δ13C, grain yield, and WUE among wheat genotypes both under rain-fed and supplemental irrigation conditions. The δ13C values increased with grain-filling proceeding, the δ13C being lower under supplemental irrigation treatment than that under rain-fed treatment. The relationships between the average of δ13C with grain yield and WUE were significantly positive during three measurement periods (R2 = 0.5785 − 0.8258), whether under rain-fed or irrigation environments. This suggests that δ13C might be associated with the grain yield and WUE in winter wheat under rain-fed and supplemental irrigation conditions in the climate region of the northwest Huang-Huai-Hai Plain of China.

Oxygen isotope enrichment in rice (Oryza sativa L.) grain organic matter captures signature of relative humidity

The oxygen isotopic composition (δ¹⁸O) of plant organic matter (OM) is primarily governed by the δ¹⁸O of source water (δ¹⁸O_SW) and climatic factor of relative humidity (RH). Among the cereals, the growth of rice plants is critically dependent on the water availability in the growth-environment. In the present study, we investigated the sensitivity of δ¹⁸O in the bulk organic matter of rice grains to RH of their growth-environment. Our experimental setup consisted of both glasshouse and field experiments, where eight genotypes were grown at RH levels ranging from 67% to 87%. The δ¹⁸O measured in bulk grain OM and source water was used to calculate the net oxygen isotopic enrichment (Δ¹⁸O_OM). Regression analysis of Δ¹⁸O_OM with RH demonstrated a significant relationship (r² = 0.96; p < 0.0001), thereby implying that the isotopic signature of evaporative conditions gets recorded in the rice grain OM. In addition, our study involved a separate experiment that monitored the degree of oxygen isotope enrichment in water samples extracted from different parts of the rice plant. For this purpose, we sampled four of the above eight genotypes along with three other rice genotypes that were grown in both open cultivation fields and glasshouse. Water present in the culms, leaves, and grains were extracted quantitatively. Isotopic analyses revealed progressive ¹⁸O enrichment of the water in the culms and leaves and intermediate enrichment values of that in the grains. Based on the isotope data, we validated mechanistic models for prediction of δ¹⁸O of the leaf water and that of the plant carbohydrates. The model predictions were in close agreement with the experimental observations. The study provides insights into the rice plant's oxygen isotope systematics that build the foundation for future applications of the stable isotope technique to study the interactions between rice and environment.

Characterising variation in wheat traits under hostile soil conditions in India

Intensive crop breeding has increased wheat yields and production in India. Wheat improvement in India typically involves selecting yield and component traits under non-hostile soil conditions at regional scales. The aim of this study is to quantify G*E interactions on yield and component traits to further explore site-specific trait selection for hostile soils. Field experiments were conducted at six sites (pH range 4.5-9.5) in 2013-14 and 2014-15, in three agro-climatic regions of India. At each site, yield and component traits were measured on 36 genotypes, representing elite varieties from a wide genetic background developed for different regions. Mean grain yields ranged from 1.0 to 5.5 t ha-1 at hostile and non-hostile sites, respectively. Site (E) had the largest effect on yield and component traits, however, interactions between genotype and site (G*E) affected most traits to a greater extent than genotype alone. Within each agro-climatic region, yield and component traits correlated positively between hostile and non-hostile sites. However, some genotypes performed better under hostile soils, with site-specific relationships between yield and component traits, which supports the value of ongoing site-specific selection activities.

Exploring the heat-responsive chaperones and microsatellite markers associated with terminal heat stress tolerance in developing wheat

Global warming is a major threat for agriculture and food security, and in many cases the negative impacts are already apparent. Wheat is one of the most important staple food crops and is highly sensitive to the heat stress (HS) during reproductive and grain-filling stages. Here, whole transcriptome analysis of thermotolerant wheat cv. HD2985 was carried out at the post-anthesis stage under control (22 ± 3 °C) and HS-treated (42 °C, 2 h) conditions using Illumina Hiseq and Roche GS-FLX 454 platforms. We assembled ~24 million (control) and ~23 million (HS-treated) high-quality trimmed reads using different assemblers with optimal parameters. De novo assembly yielded 52,567 (control) and 59,658 (HS-treated) unigenes. We observed 785 transcripts to be upregulated and 431 transcripts to be downregulated under HS; 78 transcripts showed >10-fold upregulation such as HSPs, metabolic pathway-related genes, etc. Maximum number of upregulated genes was observed to be associated with processes such as HS-response, protein-folding, oxidation-reduction and photosynthesis. We identified 2008 and 2483 simple sequence repeats (SSRs) markers from control and HS-treated samples; 243 SSRs were observed to be overlying on stress-associated genes. Polymorphic study validated four SSRs to be heat-responsive in nature. Expression analysis of identified differentially expressed transcripts (DETs) showed very high fold increase in the expression of catalytic chaperones (HSP26, HSP17, and Rca) in contrasting wheat cvs. HD2985 and HD2329 under HS. We observed positive correlation between RNA-seq and qRT-PCR expression data. The present study culminated in greater understanding of the heat-response of tolerant genotype and has provided good candidate genes for the marker development and screening of wheat germplasm for thermotolerance.