Drought Stress Tolerance In Wheat Research Articles

Deciphering the genetic landscape of seedling drought stress tolerance in wheat (Triticum aestivum L.) through genome-wide association studies.

Wheat is an important cereal crop constrained by several biotic and abiotic stresses including drought stress. Understating the effect of drought stress and the genetic basis of stress tolerance is important to develop drought resilient, high-yielding wheat cultivars. In this study, we investigated the effects of drought stress on seedling characteristics in an association panel consisting of 198 germplasm lines. Our findings revealed that drought stress had a detrimental effect on all the seedling characteristics under investigation with a maximum effect on shoot length (50.94% reduction) and the minimum effect on germination percentage (7.9% reduction). To gain a deeper understanding, we conducted a genome-wide association analysis using 12,511 single nucleotide polymorphisms (SNPs), which led to the identification of 39 marker-trait associations (MTAs). Of these 39 MTAs, 13 were particularly noteworthy as they accounted for >10% of the phenotypic variance with a LOD score >5. These high-confidence MTAs were further utilized to extract 216 candidate gene (CGs) models within 1 Mb regions. Gene annotation and functional characterization identified 83 CGs with functional relevance to drought stress. These genes encoded the WD40 repeat domain, Myb/SANT-like domain, WSD1-like domain, BTB/POZ domain, Protein kinase domain, Cytochrome P450, Leucine-rich repeat domain superfamily, BURP domain, Calmodulin-binding protein60, Ubiquitin-like domain, etc. Findings from this study hold significant promise for wheat breeders as they provide direct assistance in selecting lines harboring favorable alleles for improved drought stress tolerance. Additionally, the identified SNPs and CGs will enable marker-assisted selection of potential genomic regions associated with enhanced drought stress tolerance in wheat.

Unraveling the regulatory role of MYC2 on ASMT gene expression in wheat: Implications for melatonin biosynthesis and drought tolerance.

Recognized for its multifaceted functions, melatonin is a hormone found in both animals and plants. In the plant kingdom, it plays diverse roles, regulating growth, development, and stress responses. Notably, melatonin demonstrates its significance by mitigating the effects of abiotic stresses like drought. However, understanding the precise regulatory mechanisms controlling melatonin biosynthesis genes, especially during monocots' response to stresses, requires further exploration. Seeking to understand the molecular basis of drought stress tolerance in wheat, we analyzed RNA-Seq libraries of wheat exposed to drought stress using bioinformatics methods. In light of our findings, we identified that the Myelocytomatosis oncogenes 2 (MYC2) transcription factor is a hub gene upstream of a main melatonin biosynthesis gene, N-acetylserotonin methyltransferase (ASMT), in the wheat drought response-gene network. Promoter analysis of the ASMT gene suggested that it might be a target gene of MYC2. We conducted a set of molecular and physiochemical assays along with robust machine learning approaches to elevate those findings further. MYC2 and ASMT were co-regulated under Jasmonate, drought, and a combination of them in the leaf tissues of wheat was detected. A meaningful correlation was observed among gene expression profiles, melatonin contents, photosynthetic activities, antioxidant enzyme activities, H2 O2 levels, and plasma membrane damage. The results indicated an evident relationship between jasmonic acid and the melatonin biosynthesis pathway. Moreover, it seems that the MYC2-ASMT module might contribute to wheat drought tolerance by regulating melatonin contents.

The wheat VQ motif-containing protein TaVQ4-D positively regulates drought tolerance in transgenic plants.

VQ motif-containing proteins play important roles in plant abiotic and biotic stresses. In this study, we cloned the VQ-protein gene TaVQ4-D that is induced by drought stress. Arabidopsis and wheat plants overexpressing TaVQ4-D showed increased tolerance to drought stress. In contrast, wheat lines in which TaVQ4-D expression had been silenced showed decreased drought tolerance. Under drought stress conditions, the contents of superoxide dismutase and proline increased and the content of malondialdehyde decreased in transgenic wheat plants overexpressing TaVQ4-D compared with WT. At the same time, the expression of ROS scavenging-related genes and stress-related genes was up-regulated. However, plants of TaVQ4-D-silenced wheat lines showed decreased activities of antioxidant enzymes and reduced expression of some stress-related and antioxidant-related genes. In addition, the TaVQ4-D protein physically interacts with two mitogen-activated protein kinases (MPK3 and MPK6) and plays a role in plant drought stress as the phosphorylated substrates of MPK3 and MPK6. In summary, the results of our study suggest that TaVQ4-D can positively regulate drought stress tolerance in wheat.

Retraction: Exogenous salicylic acid-induced drought stress tolerance in wheat (Triticum aestivum L.) grown under hydroponic culture.

Retraction: Exogenous salicylic acid-induced drought stress tolerance in wheat (Triticum aestivum L.) grown under hydroponic culture.

Zinc-Regulated P5CS and Sucrose Transporters SUT1B Expression to Enhance Drought Stress Tolerance in Wheat

Zinc-Regulated P5CS and Sucrose Transporters SUT1B Expression to Enhance Drought Stress Tolerance in Wheat

Volatile compounds of Bacillus pseudomycoides induce growth and drought tolerance in wheat (Triticum aestivum L.)

The plant growth-boosting biofilm-forming bacteria Bacillus pseudomycoides is able to promote growth and drought stress tolerance in wheat by suppressing the MYB gene, which synthesizes Myb protein (TaMpc1-D4) through secreted volatile compounds. In the present study, Triticum aestivum seeds were inoculated with five distinct bacterial strains. The growth, germination rate, root-shoot length, RWC, and chlorophyll content of seedlings were investigated. Furthermore, the levels of soluble sugars, proteins, H2O2, NO, cell death, and antioxidant enzymes (CAT, SOD, POD, and APX) were observed throughout the growth stage. All of the results showed that B. pseudomycoides had a substantially higher ability to form biofilm and promote these traits than the other strains. In terms of molecular gene expression, B. pseudomycoides inoculation strongly expressed the Dreb1 gene by silencing the expression of MYB gene through secreted volatile compounds. For identifying the specific volatile compound that silenced the MYB gene, molecular docking with Myb protein was performed. Out of 45 volatile compounds found, 2,6-ditert-butylcyclohexa-2,5-diene-1,4-dione and 3,5-ditert-butylphenol had a binding free energy of − 6.2 and − 6.5, Kcal/mol, respectively, which predicted that these compounds could suppress this protein's expression. In molecular dynamics simulations, the RMSD, SASA, Rg, RMSF, and hydrogen bonding values found assured the docked complexes' binding stability. These findings suggest that these targeted compounds may be suppressing Myb protein expression as well as the expression of Dreb1 and other drought response genes in wheat. More research (field trial) into plant growth and drought stress is needed to support the findings of this study.

The C2H2 zinc finger protein TaZFP13D increases drought stress tolerance in wheat

Wheat is one of the most cultivated crops, and its production is greatly affected by abiotic stresses such as drought. Transcription factors that regulate multiple downstream genes have a good potential to improve stress tolerance due to their ability to modulate various response pathways. Many members of the C1-2i C2H2 zinc finger protein (ZFP) sub-family are up-regulated in response to abiotic stress and specific members were shown to improve oxidative and abiotic stress tolerance in different plant species. Our previous work demonstrated that the most up-regulated TaZFP, TaZFP1B, improves drought tolerance and oxidative stress protection. Based on their strong response to different abiotic stresses, five additional candidate TaZFPs were selected for functional characterization by reverse genetics in three wheat lines, using the four-component Barley Stripe Mosaic Virus system. Of the five candidates studied, TaZFP13D was the only gene that increased drought stress tolerance (resistance to wilting and improved relative water content) in three different wheat lines and significantly improved antioxidant enzymes activities resulting in lower accumulation of superoxide and hydrogen peroxide. Moreover, TaZFP13D down-regulation decreased drought stress tolerance suggesting that this gene does not have a redundant function within the TaZFPs family.

Association Mapping of Drought Tolerance Indices in Ethiopian Durum Wheat (Triticum turgidum ssp. durum).

Ethiopia is a major producer of durum wheat in sub-Saharan Africa. However, its production is prone to drought stress as it is fully dependent on rain, which is erratic and unpredictable. This study aimed to detect marker-trait associations (MTAs) and quantitative trait loci (QTLs) related to indices. Six drought tolerance indices, i.e., drought susceptibility index (DSI), geometric mean productivity (GMP), relative drought index (RDI), stress tolerance index (STI), tolerance index (TOL), and yield stability index (YSI) were calculated from least-square means (lsmeans) of grain yield (GY) and traits significantly (p < 0.001) correlated with grain yield (GY) under field drought stress (FDS) and field non-stress (FNS) conditions. GY, days to grain filling (DGF), soil plant analysis development (SPAD) chlorophyll meter, seeds per spike (SPS), harvest index (HI), and thousand kernel weight (TKW) were used to calculate DSI, GMP, RDI, STI, TOL, and YSI drought indices. Accessions, DW084, DW082, DZ004, C037, and DW092 were selected as the top five drought-tolerant based on DSI, RDI, TOL, and YSI combined ranking. Similarly, C010, DW033, DW080, DW124-2, and C011 were selected as stable accessions based on GMP and STI combined ranking. A total of 184 MTAs were detected linked with drought indices at –log10p ≥ 4.0,79 of which were significant at a false discovery rate (FDR) of 5%. Based on the linkage disequilibrium (LD, r2 ≥ 0.2), six of the MTAs with a positive effect on GY-GMP were detected on chromosomes 2B, 3B, 4A, 5B, and 6B, explaining 14.72, 10.07, 26.61, 21.16, 21.91, and 22.21% of the phenotypic variance, respectively. The 184 MTAs were clustered into 102 QTLs. Chromosomes 1A, 2B, and 7A are QTL hotspots with 11 QTLs each. These chromosomes play a key role in drought tolerance and respective QTL may be exploited by marker-assisted selection for improving drought stress tolerance in wheat.

Inducing Drought Tolerance in Wheat through Exopolysaccharide-Producing Rhizobacteria

Wheat is the main staple food in the world, so it is the backbone of food security. Drought not only affects growth and development but also ultimately has a severe impact on the overall productivity of crop plants. Some bacteria are capable of producing exopolysaccharides (EPS) as a survival mechanism, along with other metabolites, which help them survive in stressful conditions. The present study was conducted with the aim of inducing drought stress tolerance in wheat through EPS-producing plant growth-promoting rhizobacteria (PGPR). In this regard, a series of laboratory bioassays were conducted with the aim to isolating, characterizing, and screening the EPS-producing PGPR capable of improving wheat growth under limited water conditions. Thirty rhizobacterial strains (LEW1–LEW30) were isolated from the rhizosphere of wheat. Ten isolates with EPS-producing ability were quantitatively tested for EPS production and IAA production ability. Four of the most efficient EPS-producing strains (LEW3, LEW9, LEW16, and LEW28) were evaluated for their drought tolerance ability along with quantitative production of EPS and IAA under polyethylene glycol (PEG-6000)-induced drought stress. The jar experiment was conducted under gnotobiotic conditions to examine the drought-tolerant wheat genotypes, and two wheat varieties (Johar-16, and Gold-16) were selected for further experiments. The selected varieties were inoculated with EPS-producing rhizobacterial strains and grown under control conditions at different stress levels (0, 2, 4, and 6% PEG-6000). The strain LEW16 showed better results for improving root morphology and seedling growth in both varieties. The maximum increase in germination, growth parameters, percentage, root diameter, root surface area, and root colonization was recorded in Johar-16 by inoculating LEW16 at 6% PEG-6000. Plant growth-promoting traits were tested on the top-performing strains (LEW3, LEW9, and LEW16). Through 16S rRNA sequencing, these strains were identified as Chryseobacterium sp. (LEW3), Acinetobacter sp. (LEW9), and Klebsiella sp. (LEW16), and they showed positive results for phosphorous and zinc solubilization as well as hydrogen cyanide (HCN) production. The partial sequencing results were submitted to the National Center for Biotechnology Information (NCBI) under the accession numbers MW829776, MW829777, and MW829778. These strains are recommended for their evaluation as potential bioinoculants for inducing drought stress tolerance in wheat.

Role of Water Soluble Carbohydrates in Improving Drought Stress Tolerance in Wheat: An Overview

Abiotic factors such as drought and heat stress impairs photosynthetic assimilates, shortening the carbon supply to the developing grains leads to yield loss. Under water stress, stem water-soluble carbohydrates (WSCs) mainly fructans, play an important role in buffering yield during the grain filling period in wheat. The stem WSCs may contribute up to 20% of the total dry weight of grain under irrigated conditions and upto 70% of grain dry matter under drought stress. Additionally, it maintains physiological balance under water-stressed conditions by acting as signalling molecules to various phytochemicals and hormones. Therefore, this drought adaptive trait can be a potential breeding target for sustainable wheat production, especially for water limiting conditions. Despite the proven contribution of stem WSCs to water-stress tolerance in wheat and compensating grain yield, a comprehensive review on this trait is still missing in the literature. With this review, efforts are made to compile the available information on the physiological, genetic and molecular aspects of accumulation and remobilisation of stem WSCs to bring more attention of plant scientists to this trait. Furthermore, effective molecular marker systems such as KASP to target stable loci identified using GWAS, QTL or meta-QTL studies may bring precision to the selection and accelerate the WSCs based wheat breeding program.

Exogenous salicylic acid-induced drought stress tolerance in wheat (Triticum aestivum L.) grown under hydroponic culture.

Wheat is an important cereal crop, which is adversely affected by water deficit stress. The effect of induced stress can be reduced by the application of salicylic acid (SA). With the objective to combat drought stress in wheat, an experiment was conducted in greenhouse under hydroponic conditions. The treatments consisted of (a) no drought (DD0 = 0 MPa), mild drought (DD1 = -0.40 MPa) and severe drought (DD2 = -0.60 MPa) by applying PEG-8000, (b) two contrasting wheat varieties Barani-17 (drought tolerant) and Anaj-17 (drought-sensitive), and (c) foliar treatments of salicylic acid (0, 50 mM, 75 mM, and 100 mM). Evaluation of wheat plants regarding biochemical, physiological, and morphological attributes were rendered after harvesting of plants. Statistically, maximum shoot and root fresh and dry weights (18.77, 11.15 and 1.99, 1.81 g, respectively) were recorded in cultivar Barani-17 under no drought condition with the application of SA (100 mM). While, minimum shoot and root fresh and dry weights (6.65, 3.14 and 0.73, 0.61 g, respectively) were recorded in cultivar Anaj-2017 under mild drought stress without SA application. The maximum shoot length (68.0 cm) was observed in cultivar Barani-2017 under no drought condition with the application of SA (100 mM). While, maximum root length (59.67 cm) was recorded in cultivar Anaj-17 under moderate drought stress without application of SA. Further, minimum shoot length (28.67 cm) was recorded in Anaj-17 under moderate drought stress without SA application. Minimum root length (38.67 cm) was recorded in cultivar Barani-17 under no drought condition without SA application. Furthermore, maximum physio-biochemical traits, including membrane stability index (MSI), chlorophyl content, photosynthetic rates, stomatal conductance, antioxidant enzymatic activities and relative water content (RWC) were found highest in cultivar Barani-17 under no drought stress and SA application at 100 mM. However, minimum values of these traits were recorded in cultivar Anaj-17 under severe drought stress without SA application. Our results also demonstrated that under severe drought, application of SA at 100 mM significantly increased leaf nitrogen (N), phosphrus (P) and potassium (K) contents and cultivar Barani-17 demonstrated significantly higher values than Anaj-17. The obtained results also indicated that the cultivation of wheat under drought stress conditions noticeably declines the morphological, physiological, and biochemical attributes of the plants. However, the exogenous application of SA had a positive impact on wheat crop for enhancing its productivity.

Nucleoredoxin Gene TaNRX1 Positively Regulates Drought Tolerance in Transgenic Wheat (Triticum aestivum L.).

Drought is the main abiotic stress factor limiting the growth and yield of wheat (Triticum aestivum L.). Therefore, improving wheat tolerance to drought stress is essential for maintaining yield. Previous studies have reported on the important role of TaNRX1 in conferring drought stress tolerance. Therefore, to elucidate the regulation mechanism by which TaNRX1 confers drought resistance in wheat, we generated TaNRX1 overexpression (OE) and RNA interference (RNAi) wheat lines. The results showed that the tolerance of the OE lines to drought stress were significantly enhanced. The survival rate, leaf chlorophyll, proline, soluble sugar content, and activities of the antioxidant enzymes (catalase, superoxide dismutase, and peroxidase) of the OE lines were higher than those of the wild type (WT); however, the relative electrical conductivity and malondialdehyde, hydrogen peroxide, and superoxide anion levels of the OE lines were lower than those of the WT; the RNAi lines showed the opposite results. RNA-seq results showed that the common differentially expressed genes of TaNRX1 OE and RNAi lines, before and after drought stress, were mainly distributed in the plant–pathogen interaction, plant hormone signal transduction, phenylpropane biosynthesis, starch and sucrose metabolism, and carbon metabolism pathways and were related to the transcription factors, including WRKY, MYB, and bHLH families. This study suggests that TaNRX1 positively regulates drought stress tolerance in wheat.

H2O2 signaling regulates seed germination in ZnO nanoprimed wheat (Triticum aestivum L.) seeds for improving plant performance under drought stress

Nanopriming has proved to be an effective technique to protect plants from various stresses. The aim of the present work is to investigate the underlying mechanism of zinc oxide (ZnO) nanopriming in imparting drought stress tolerance in wheat. The changes in primed and unprimed wheat plants associated during drought stress were studied by monitoring their physiological and biochemical performance. Results showed that zinc oxide nanoparticles (ZnO NPs) pre-treatment prevented chlorophyll degradation under drought condition thereby improving overall photosynthetic performance and overall plant growth. Study of Chl a fluorescence induction kinetics showed a drastic increase in various photosynthetic parameters in primed drought stressed plants. Nanopriming seems to have protected the photosynthetic apparatus of plant by improving the efficiency of primary photochemistry of PSII under drought stress conditions. Furthermore, the activity of antioxidant enzymes such as catalase (CAT), peroxidase (POD), superoxide dismutase (SOD) and glutathione reductase (GR) as well as malondialdehyde (MDA) content were decreased significantly in nanoprimed drought stressed (NP + DS) plants as compared to unprimed drought stressed (UP + DS) plants. Generation of more reactive oxygen species (ROS) mainly hydrogen peroxide (H2O2) was observed in nanoprimed germinating seeds. We propose role of H2O2 to act as signaling molecule in improving seed germination and vigor by enhancing activity of α-amylase. Lower levels of reactive oxygen species (ROS) production in NP + DS plants was observed which indicates better tolerance to drought stress in nanoprimed plants. It is concluded that nanopriming facilitates improved seed germination and increased seedling vigor through H2O2 signaling networks.

Sorghum Water Extract Application Mediates Antioxidant Defense and Confers Drought Stress Tolerance in Wheat

Drought is the most threatening abiotic constraint, affecting more than 43% of the cropped area around the globe. The use of allelopathic hormesis offers a pragmatic solution for mitigating the negative effects of drought on field crops. The present study evaluated the potential of sorghum water extract in enhancing drought tolerance in wheat and examined the possible underlying mechanisms. The experiment comprised of three factors viz. drought with three levels (100%, 60% and 30% field capacity; FC), sorghum water extracts with eight levels (control, water spray, 0.5%, 1.0%, 1.5%, 2.0%, 2.5% and 3.0% of sorghum water extract) and two wheat cultivars Ihsan-2016 (drought tolerant) and Galaxy-2013 (drought-sensitive). Drought stress, particularly at 30% FC, profoundly decreased the morpho-physiological attributes of both wheat cultivars; nevertheless, the application of sorghum water extract at 2.0% effectively enhanced the tolerance against drought stress. Compared with control, application of 2.0% sorghum water extract increased the morphological attributes such as shoot and root length as well as fresh and dry weight of both wheat cultivars in the range of 3–146% under 30% field capacity. In addition, 2.0% sorghum water extract triggered (9–165%) the activities of superoxide dismutase, catalase, and peroxidase, decreased the hydrogen peroxide contents (42–48%), and enhanced the contents of chlorophyll a, b, and carotenoid (6–151%) as compared to control in both wheat cultivars under 30% field capacity suggesting that these measures helped to reduce the drought-induced oxidative stress. Vigorous growth and higher drought tolerance derived from sorghum water extract was related to improved chlorophyll contents and a better antioxidant defense system in wheat.

Validation of molecular markers linked with QTLs for heat and drought stress tolerance in wheat

Global climatic changes affect the production and productivity of wheat around the globe. Increasing heat and drought are the most important abiotic stress factors that hinders productivity. To produce sufficient wheat there is ardent need to develop heat and drought tolerant wheat cultivars; therefore, identification of genetic diversity present among available wheat genotypes using SSRs markers is of prime importance. The allelic variation present among wheat genotypes can be exploited in breeding heat and drought tolerant cultivars. A set of 36 wheat genotypes was evaluated for evaluating genetic diversity for heat and drought tolerance among wheat genotypes using already reported SSR markers. A total of 24 SSR markers were analysed and out of them 19 were found polymorphic. Using SSR markers data cluster analysis was carried out to classify the 34 wheat cultivars for genetic variation in heat tolerance. The dandrogram constructed using SSR markers data assigned the 34 wheat cultivars into three broad clusters. The polymorphic SSRs thus identified could be used to evaluate genetic diversity present among wheat genotypes and the wheat cultivars thus identified genetically diverse could be exploited in wheat breeding programs.

Expansin gene TaEXPA2 positively regulates drought tolerance in transgenic wheat (Triticum aestivum L.)

Expansins loosen plant cell walls and are involved in cell enlargement and various abiotic stresses. In previous studies, we cloned the expansin gene TaEXPA2 from the wheat cultivar HF9703. Here, we studied its function and regulation in wheat drought stress tolerance. The results indicated that TaEXPA2-overexpressing wheat plants (OE) exhibited drought tolerant phenotypes, whereas down-regulation of TaEXPA2 by RNA interference (RNAi) resulted in elevated drought sensitivity, as measured by survival rate, photosynthetic rate and water containing ability under drought stress. Overexpression of TaEXPA2 enhanced the antioxidant capacity in wheat plants, via elevation of antioxidant enzyme activity and the increase of the transcripts of some ROS scavenging enzyme-related genes. Further investigation revealed that TaEXPA2 positively influenced lateral root formation under drought conditions. A MYB transcription factor of wheat named TaMPS activates TaEXPA2 expression directly by binding to its promoter. Overexpression of TaMPS in Arabidopsis conferred drought tolerance associated with improved lateral root number, and the close homolog genes of TaEXPA2 were up-regulated in Arabidopsis roots overexpressing TaMPS, which suggest that TaMPS may function as one of the regulator of TaEXPA2 gene expression in the root lateral development under drought stress. These findings suggest that TaEXPA2 positively regulates drought stress tolerance in wheat.

Transcription factor TabHLH49 positively regulates dehydrin WZY2 gene expression and enhances drought stress tolerance in wheat

BackgroundAs functional proteins, dehydrins are found in many maturing seeds and vegetable tissues under adverse environmental conditions. However, the regulation of dehydrin expression remains unclear.ResultsIn this study, a novel drought stress-related bHLH transcription factor, TabHLH49, was isolated from a wheat cDNA library treated with the drought and cold stress by using yeast one-hybrid system. TabHLH49 protein possesses a typical conserved bHLH domain and is a Myc-type bHLH transcription factor. TabHLH49 was detected in the nucleus of tobacco epidermal cells, and the amino acid sequences at the C-terminus (amino acids 323–362) is necessary for its transactivation activity. Real-time PCR analyses revealed the tissue-specific expression and drought stress-responsive expression of TabHLH49 in wheat. In addition, the verification in Y1H and electrophoretic mobility shift assays illustrated that TabHLH49 protein can bind and interact with the promoter of the wheat WZY2 dehydrin. Furthermore, the dual-luciferase assays showed that TabHLH49 can positively regulate the expression of WZY2 dehydrin. The transient expression and BSMV-mediated gene silencing of TabHLH49 also showed that TabHLH49 positively regulates the expression of WZY2 dehydrin and improves drought stress resistance in wheat.ConclusionsThese results provide direct evidences that TabHLH49 positively regulates expression level of dehydrin WZY2 gene and improves drought tolerance of wheat.

Drought Stress Tolerance in Wheat and Barley: Advances in Physiology, Breeding and Genetics Research.

Climate change is a major threat to most of the agricultural crops grown in tropical and sub-tropical areas globally. Drought stress is one of the consequences of climate change that has a negative impact on crop growth and yield. In the past, many simulation models were proposed to predict climate change and drought occurrences, and it is extremely important to improve essential crops to meet the challenges of drought stress which limits crop productivity and production. Wheat and barley are among the most common and widely used crops due to their economic and social values. Many parts of the world depend on these two crops for food and feed, and both crops are vulnerable to drought stress. Improving drought stress tolerance is a very challenging task for wheat and barley researchers and more research is needed to better understand this stress. The progress made in understanding drought tolerance is due to advances in three main research areas: physiology, breeding, and genetic research. The physiology research focused on the physiological and biochemical metabolic pathways that plants use when exposed to drought stress. New wheat and barley genotypes having a high degree of drought tolerance are produced through breeding by making crosses from promising drought-tolerant genotypes and selecting among their progeny. Also, identifying genes contributing to drought tolerance is very important. Previous studies showed that drought tolerance is a polygenic trait and genetic constitution will help to dissect the gene network(s) controlling drought tolerance. This review explores the recent advances in these three research areas to improve drought tolerance in wheat and barley.

Genome-wide association analyses for yield and yield-related traits in bread wheat (Triticum aestivum L.) under pre-anthesis combined heat and drought stress in field conditions.

Understanding the genetic basis of heat and drought stress tolerance in wheat is prerequisite for wheat breeding program. In the present study, a wheat panel comprising of 192 elite bread wheat genotypes was phenotyped in eight environments for yield and related traits in field conditions. Four stress environments were created by implying four different treatments differing in sowing date and water availability, panel was evaluated for two years in field conditions. The panel was genotyped with 15K Illumina chip and 9236 polymorphic markers concentrated on B genome were employed in GWAS analysis. Consistent, fast LD decay was observed on D genome and structure analysis germplasm divided panel into three major populations. GWAS was performed using BLUEs values of combined environment data in R package GAPIT using log10(P) = 3.96 as significance threshold. The significance of association was further checked using FDR<0.05 threshold. The GWAS identified 487 loci associated with the traits and were significant at log10(p) threshold out of these 350 loci were significant at FDR threshold. For two stress indices 108 associations were significant at FDR threshold. Nine genomic regions were shared among all treatment, while multiple pleiotropic regions were present on chromosome 7D followed by unmapped chromosome. The present study validated many marker trait associations for yield and other traits, MTAs significant under combined drought and heat stress were novel. These regions are important and can be used for fine mapping and marker assisted selection to discover new genes responsible for heat and drought tolerance in wheat.

WHEAT (TRITICUM AESTIVUM L.) PRODUCTION UNDER DROUGHT AND HEAT STRESS – ADVERSE EFFECTS, MECHANISMS AND MITIGATION: A REVIEW

Heat and drought stresses are the most important abiotic factors that reduce crops productivity by affecting various physiological and biochemical processes. Thus, selecting cultivars with better drought or heat stress tolerance or breeding for stress tolerance will be helpful in enhancing crop productivity under harsh environments. This review elaborates the physiological basis of high temperature and drought stress tolerance in wheat which can be used as selection criteria in wheat breeding program. In addition, some agronomic selection criteria which are valid and useful in selecting stress tolerant wheat species and cultivars. The review also discussed the valid usage of stress tolerance indices (such as mean productivity (MP), geometric mean productivity (GMP), yield index (YI), yield stability index (YSI), relative productivity (RP%), stress susceptibility index (SSI), and the tolerance index (TOL)) to scan the genotypes against drought and heat stress. Beside these, exogenous application of stress signaling compounds, osmolytes, or certain inorganic salts play a vital role for alleviating adverse effects of abiotic stresses for sustainable wheat production. In addition, applications for soil amendments will also helpful in increasing wheat crop productivity under stressful conditions. All these strategies may be helpful to meet the food demands of the increasing population.