Drought-tolerant Cultivars Research Articles

Evaluation of water stress tolerance, dry forage yield and biochemical traits of five alfalfa cultivars

One of the important activities to achieve drought tolerant cultivars is screening and selection of cultivars based on yield and biochemical characteristics. A split-plot experiment arranged in a randomized complete blocks design with three replications was carried out in Safiabad Agricultural Research Center during two growing seasons (2017-19). Main plots consisted of different irrigation regimes based on crop’s water requirement (25%, 50%, 75% and 100%) and sub plots included five levels of alfalfa cultivars (Baghdadi, Nikshahri, Yazdi, Omid and american Mesa-Sirsa). Results showed that drought stress due to irrigation regimes led to significantly reduce of forage dry matter yield and significantly changes of soluble sugar, glutation peroxidase and catalase in alfalfa leaves but it did not have significantly effect on total protein. For forage dry matter yield, the highest statistical class belonged to Baghdadi cultivar under 100% water requirement supply treatment (2.824 t.ha-1). The lowest statistical class for forage dry matter yield was observed in Yazdi and Mesa-Sirsa cultivars under 25% water requirement supply treatment (0.598 and 0.546 t.ha-1), respectively. Among the cultivars that are examined in this experiment, Yazdi was identified as a drought tolerant cultivar due to the stability of dry forage yield and also high leaf antioxidants content.

Genome-Wide Association Mapping for Yield and Related Traits Under Drought Stressed and Non-stressed Environments in Wheat.

Understanding the genetics of drought tolerance in hard red spring wheat (HRSW) in northern USA is a prerequisite for developing drought-tolerant cultivars for this region. An association mapping (AM) study for drought tolerance in spring wheat in northern USA was undertaken using 361 wheat genotypes and Infinium 90K single-nucleotide polymorphism (SNP) assay. The genotypes were evaluated in nine different locations of North Dakota (ND) for plant height (PH), days to heading (DH), yield (YLD), test weight (TW), and thousand kernel weight (TKW) under rain-fed conditions. Rainfall data and soil type of the locations were used to assess drought conditions. A mixed linear model (MLM), which accounts for population structure and kinship (PC+K), was used for marker–trait association. A total of 69 consistent QTL involved with drought tolerance-related traits were identified, with p ≤ 0.001. Chromosomes 1A, 3A, 3B, 4B, 4D, 5B, 6A, and 6B were identified to harbor major QTL for drought tolerance. Six potential novel QTL were identified on chromosomes 3D, 4A, 5B, 7A, and 7B. The novel QTL were identified for DH, PH, and TKW. The findings of this study can be used in marker-assisted selection (MAS) for drought-tolerance breeding in spring wheat.

Identification of Main-Effect and Environmental Interaction QTL and Their Candidate Genes for Drought Tolerance in a Wheat RIL Population Between Two Elite Spring Cultivars.

Understanding the genetics of drought tolerance can expedite the development of drought-tolerant cultivars in wheat. In this study, we dissected the genetics of drought tolerance in spring wheat using a recombinant inbred line (RIL) population derived from a cross between a drought-tolerant cultivar, ‘Reeder’ (PI613586), and a high-yielding but drought-susceptible cultivar, ‘Albany.’ The RIL population was evaluated for grain yield (YLD), grain volume weight (GVW), thousand kernel weight (TKW), plant height (PH), and days to heading (DH) at nine different environments. The Infinium 90 k-based high-density genetic map was generated using 10,657 polymorphic SNP markers representing 2,057 unique loci. Quantitative trait loci (QTL) analysis detected a total of 11 consistent QTL for drought tolerance-related traits. Of these, six QTL were exclusively identified in drought-prone environments, and five were constitutive QTL (identified under both drought and normal conditions). One major QTL on chromosome 7B was identified exclusively under drought environments and explained 13.6% of the phenotypic variation (PV) for YLD. Two other major QTL were detected, one each on chromosomes 7B and 2B under drought-prone environments, and explained 14.86 and 13.94% of phenotypic variation for GVW and YLD, respectively. One novel QTL for drought tolerance was identified on chromosome 2D. In silico expression analysis of candidate genes underlaying the exclusive QTLs associated with drought stress identified the enrichment of ribosomal and chloroplast photosynthesis-associated proteins showing the most expression variability, thus possibly contributing to stress response by modulating the glycosyltransferase (TraesCS6A01G116400) and hexosyltransferase (TraesCS7B01G013300) unique genes present in QTL 21 and 24, respectively. While both parents contributed favorable alleles to these QTL, unexpectedly, the high-yielding and less drought-tolerant parent contributed desirable alleles for drought tolerance at four out of six loci. Regardless of the origin, all QTL with significant drought tolerance could assist significantly in the development of drought-tolerant wheat cultivars, using genomics-assisted breeding approaches.

Genome-wide investigation on transcriptional responses to drought stress in wild and cultivated rice

Whole transcriptomic sequencing of the drought-tolerant (DT) and drought-sensitive (DS) accessions of cultivated and wild rice under drought treatments was performed to uncover the mechanism of plant adaptation to drought and to facilitate the development of drought-tolerant cultivars in crops. By analyzing the differentially expressed genes (DEGs) between the drought-treated and untreated samples and their co-expressed pattern, we revealed distinct susceptibilities of different samples to the stress treatments and identified some specific transcription factors (TFs) and genes that play critical roles in rice adaptation to drought. Some drought-responsive genes or pathways unique to the wild rice were also detected, highlighting the importance of wild rice resources in developing elite cultivars. Furthermore, we showed that the DEGs in the DT accessions were enriched in the genome as clusters or hotspots in which previously identified drought-associated quantitative trait loci (QTLs) were overrepresented. The finding that a single hotspot contained up to 52 QTLs and involved as many as 20 traits implicates the complicated genetic architecture underlying the DT traits. These results provide new insights into the understanding of plant adaptation to drought and help effective manipulation of specific genes or gene cluster in crop breeding.

English

Improving crop productivity under drought conditions contributes largely to the sustainable agriculture globally. In this study, the agronomic traits and physiological processes related to osmolyte accumulation and reactive oxygen species (ROS) homeostasis during late growth stage in wheat under drought stress were studied. Three cultivars viz., Shimai 22 (drought tolerant), Zhongxinmai 99 (median drought-tolerant, control), and Shi 4185 (drought sensitive) sharing contrasting drought tolerance were grown under normal irrigation (NI: with irrigations prior to sowing, and at jointing and flowering stages) and deficit irrigation (DI, with irrigations prior to sowing and at jointing) conditions. Data regarding yields, osmolyte (i.e., proline and soluble sugar) contents, and antioxidant enzyme activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), and malondialdehyde (MDA) contents were recorded. Under deficit irrigation, the cultivars displayed modified agronomic and physiological traits. Among cultivars, Shimai 22 showed best agronomic traits (6.47 to 7.23% higher yield than control), osmolyte contents and AE activities (10.12 to 22.18% higher than control), and least MDA accumulation (12.30 to 17.06% lower than control). In contrast, Shi 4185 cultivar performed worst regarding above said traits. The transcripts of the genes in ��1-Pyrroline-5-carboxylate synthetase (P5CS) family that regulates proline biosynthesis and those in AE families that modulate ROS homeostasis were evaluated. Results revealed that the P5CS genes TaP5CS2 and TaP5CS5 and the AE ones TaSOD3, TaCAT2 and TaCAT5 were modified on transcripts across the cultivars under DI condition, showing to be significant upregulated compared with NI. These results suggested the essential roles of osmolyte accumulation and AE proteins in improving the drought tolerance of wheat during late growth stages. In addition, this study suggested that the elevated transcription efficiencies of distinct P5CS and AE family genes under water deprivation contribute to the enhanced drought tolerance in drought-tolerant cultivars. © 2021 Friends Science Publishers

Comparative analysis of alfalfa (Medicago sativa L.) seedling transcriptomes reveals genotype-specific drought tolerance mechanisms

Drought is one of the main abiotic factors that affect alfalfa yield. The identification of genes that control this complex trait can provide important insights for alfalfa breeding. However, little is known about how alfalfa responds and adapts to drought stress, particularly in cultivars of differing drought tolerance. In this study, the drought-tolerant cultivar Dryland ‘DT’ and the drought-sensitive cultivar WL343HQ ‘DS’ were used to characterize leaf and root physiological responses and transcriptional changes in response to water deficit. Under drought stress, Dryland roots (DTR) showed more differentially expressed genes than WL343HQ roots (DSR), whereas WL343HQ leaves (DSL) showed more differentially expressed genes than Dryland leaves (DTL). Many of these genes were involved in stress-related pathways, carbohydrate metabolism, and lignin and wax biosynthesis, which may have improved the drought tolerance of alfalfa. We also observed that several genes related to ABA metabolism, root elongation, peroxidase activity, cell membrane stability, ubiquitination, and genetic processing responded to drought stress in alfalfa. We highlighted several candidate genes, including sucrose synthase, xylan 1,4-beta-xylosidase, primary-amine oxidase, and alcohol-forming fatty acyl-CoA reductase, for future studies on drought stress resistance in alfalfa and other plant species. In summary, our results reveal the unique drought adaptation and resistance characteristics of two alfalfa genotypes. These findings, which may be valuable for drought resistance breeding, warrant further gene functional analysis to augment currently available information and to clarify the drought stress regulatory mechanisms of alfalfa and other plants.

Water deficit in the soybean breeding

The climate unpredictability causes long periods of drought, becoming the main risk factor in soybeans production fields and consequent losses to farmers in Brazil and worldwide. As sessile organisms, plants are constantly challenged by a wide range of environmental stresses, including drought. Growth constraints and stress due to these environmental changes result in reduced yield and significant harvesting losses. The response to abiotic stresses is a very complex phenomenon, since several stages of plant development can be affected by a particular stress and often several stresses affect the plant simultaneously. In order to mitigate the damages caused by the climate, new soybean cultivars adapted to the drought and the diversified climate are necessary, as well as technological advances in the production of soybeans that must advance with the increase of cultivated area. Therefore, the mechanisms underlying tolerance and adaptation to stress have been the focus of intensive research. In this sense, the objective of this review is to provide an overview of the evolution of genetic improvement regarding the search for more drought-tolerant cultivars, as well as to verify which strategies are used in the genetic improvement of soybean in the search of these genotypes.

Analysis of DNA Polymerase λ Activity and Gene Expression in Response to Salt and Drought Stress in Oryza sativa Indica Rice Cultivars

The plants are constantly subjected to varying degree of environmental stress. These stresses results in severe damage to the DNA of the plants, which if not repaired can lead to the impairment of their genetic material, and can prove fatal for the plants. The present work studies the damage to the genomic DNA in response to salinity and drought stress on the indica rice cultivars. The comet assay results showed that maximum DNA damage was seen in the IR29 cultivar, whereas, the Nonabokra cultivar showed minimal DNA damage. The gene expression profiling of DNA polymerase λ (OsPolλ), the only X family DNA polymerase in rice which is involved in the repair of DNA damage, shows that the gene is up-regulated in all the rice cultivars irrespective of their degree of tolerance to the environmental stresses. Further the enzymatic activity of the OsPolλ protein was studied in the three rice cultivars and it was revealed that the OsPolλ activity increases in response to stresses in all the rice cultivars, however, the salinity-susceptible IR29 showed a more prominent increases in the activity of OsPolλ than Nonabokra (salinity tolerant) and N22 (drought tolerant) cultivars. The study on the upstream regions of the OsPolλ gene to identify the different cis acting upstream elements effecting the gene expression showed the presence of unique stress responsive regulatory elements was detected in the upstream region of OsPolλ gene. The present study suggest that the OsPolλ gene expression and enzymatic activity is enhanced in response to these abiotic stress, thus, playing an important role in the repair of salinity and drought induced DNA damages in indica rice cultivars.

Absence of Nanoparticle-Induced Drought Tolerance in Nutrient Sufficient Wheat Seedlings.

Strategies to reduce crop losses due to drought are needed as climate variability affects agricultural productivity. Wheat (Triticum aestivum var. Juniper) growth in a nutrient-sufficient, solid growth matrix containing varied doses of CuO, ZnO, and SiO2 nanoparticles (NPs) was used to evaluate NP mitigation of drought stress. NP amendments were at fertilizer levels, with maxima of 30 Cu, 20 Zn, and 200 Si (mg metal/kg matrix). Seeds of this drought-tolerant cultivar were inoculated with Pseudomonas chlororaphis O6 (PcO6) to provide a protective root microbiome. An 8 day drought imposed on 14 day-old wheat seedlings decreased shoot and root mass, shoot water content, and the quantum yield of photosystem II when compared to watered plants. PcO6 root colonization was not impaired by drought or NPs. A dose-dependent increase in the Cu, Zn, and Si from the NPs was observed from analysis of the rhizosphere solution, and this process was not affected by drought. Consequently, fertilizer concentrations of the NPs did not further improve drought tolerance in wheat seedlings under the growth conditions of adequate mineral nutrition and the presence of a beneficial microbiome. These findings suggest that potential NP benefits in promoting plant drought tolerance occur only under certain environmental conditions.

Transcriptome and Co-expression Network Analyses Reveal Differential Gene Expression and Pathways in Response to Severe Drought Stress in Peanut (Arachis hypogaea L.).

Drought is one of the major abiotic stress factors limiting peanut production. It causes the loss of pod yield during the pod formation stage. Here, one previously identified drought-tolerant cultivar, “L422” of peanut, was stressed by drought (35 ± 5%) at pod formation stage for 5, 7, and 9 days. To analyze the drought effects on peanut, we conducted physiological and transcriptome analysis in leaves under well-watered (CK1, CK2, and CK3) and drought-stress conditions (T1, T2, and T3). By transcriptome analysis, 3,586, 6,730, and 8,054 differentially expressed genes (DEGs) were identified in “L422” at 5 days (CK1 vs T1), 7 days (CK2 vs T2), and 9 days (CK3 vs T3) of drought stress, respectively, and 2,846 genes were common DEGs among the three-time points. Furthermore, the result of weighted gene co-expression network analysis (WGCNA) revealed one significant module that was closely correlated between drought stress and physiological data. A total of 1,313 significantly up-/down-regulated genes, including 61 transcription factors, were identified in the module at three-time points throughout the drought stress stage. Additionally, six vital metabolic pathways, namely, “MAPK signaling pathway-plant,” “flavonoid biosynthesis,” “starch and sucrose metabolism,” “phenylpropanoid biosynthesis,” “glutathione metabolism,” and “plant hormone signal transduction” were enriched in “L422” under severe drought stress. Nine genes responding to drought tolerance were selected for quantitative real-time PCR (qRT-PCR) verification and the results agreed with transcriptional profile data, which reveals the reliability and accuracy of transcriptome data. Taken together, these findings could lead to a better understanding of drought tolerance and facilitate the breeding of drought-resistant peanut cultivars.

Expression pattern of GmLAX genes under different stresses in soybean drought sensitive cultivar and tolerant cultivar

Auxin has been reported to regulate plant growth and development, as well as to mediate plant adaption to abiotic stresses, including drought. AUX/LAX family displays auxin uptake functions and comprises four highly conserved genes AUX1 and LIKE AUX1 (LAX1, LAX2, and LAX3) in Arabidopsis. There are fifteen GmLAX family genes in the soybean genomes and several members were regulated by dehydration stress. In this study, the sequence differences and expression pattern of GmLAXs-I were analyzed under stress treatment between the soybean drought-tolerant Jindou 21 and drought-sensitive varieties Zhongdou 33. Five homologous genes of AUX1 were all responsive to PEG, salt, ABA and IAA stimuli. There were two SNPs in the promoter region of GmLAX4 gene, and this gene was differentially expressed in two cultivars. Moreover, our results showed YFP-GmLAXs are predominantly localized in plasma membrane. Taken together, our results suggest that GmLAXs are involved in abiotic response, which can provide theoretical and technical support for the genetic improvement of soybean drought tolerance.

Dissection of Drought Tolerance in Upland Cotton Through Morpho-Physiological and Biochemical Traits at Seedling Stage.

Cotton is an important fiber and cash crop. Extreme water scarceness affects the growth, quality, and productivity of cotton. Water shortage has threatened the future scenario for cotton growers, so it is imperative to devise a solution to this problem. In this research, we have tried to machinate a solution for it. 23 genotypes have been screened out against drought tolerance at the seedling stage by evaluating the morphological, physiological, and biochemical traits in a triplicate completely randomized design plot experiment with two water regimes [50 and 100% field capacity]. Genotypic differences for all the morphological and physiological traits revealed highly significant differences except transpiration rate (TR). Moreover, the interaction between genotype and water regime (G × W) was highly significant for root length (RL, 5.163), shoot length (SL, 11.751), excised leaf water loss (ELWL, 0.041), and stomatal conductance (SC, 7.406). A positively strong correlation was found in TR with relative water content (RWC; 0.510) and SC (0.584) and RWC with photosynthesis (0.452) under drought conditions. A negative correlation was found in SC with SL (−0.428) and photosynthesis (−0.446). Traits like RL, SL, SC, photosynthesis, proline, catalase, and malondialdehyde were visible indicators, which can differentiate drought-tolerant genotypes from the susceptible ones. A wide range of diversity was found in all the morpho-physiological traits with the cumulative variance of four principal components (PCs) 83.09% and three PCs 73.41% under normal and water-stressed conditions, respectively, as per the principal component analysis. Hence, selection criteria can be established on the aforementioned traits for the development of drought-tolerant cultivars. Moreover, it was found that out of 23 experimental varieties, NIAB-135, NIAB-512, and CIM-554 could be used to devise breeding strategies for improving drought tolerance in cotton.

Allele mining for a drought responsive gene DRO1 determining root growth angle in donors of drought tolerance in rice (Oryza sativa L.).

The online version of this article (10.1007/s12298-021-00950-2).

QTL mapping of PEG-induced drought tolerance at the early seedling stage in sesame using whole genome re-sequencing.

Improvement in sesame drought tolerance at seedling stage is important for yield stability. Genetic approaches combing with conventional breeding is the most effective way to develop drought-tolerant cultivars. In this study, three traits and their relative values, including seedling weight (SW), shoot length (SL) and root length (RL), were evaluated under control and osmotic conditions in a recombinant inbred line (RIL) population derived from cross of Zhushanbai and Jinhuangma. Significant variation and high broad sense heritability were observed for all traits except SW under stress condition in the population. With this population, a high-density linkage map with 1354 bin markers was constructed through whole genome re-sequencing (WGS) strategy. Quantitative trait loci (QTL) mapping was performed for all the traits. A total of 34 QTLs were detected on 10 chromosomes. Among them, 13 stable QTLs were revealed in two independent experiments, eight of them were associated with traits under water stress condition. One region on chromosome 12 related to RL under osmotic condition and relative RL had the highest LOD value and explained the largest phenotypic variation among all the QTLs detected under water stress condition. These findings will provide new genetic resources for molecular improvement of drought tolerance and candidate gene identification in sesame.

Characterization on the physiological traits of plants and yield formation capacity upon water- and N-saving conditions in wheat (T. aestivum L.)

Improving water and nitrogen (N) use efficiencies of the Triticum aestivum species contributes to the sustainable agriculture worldwide. In this study, we investigated the physiological traits of plants and the yield formation capacity of winter wheat treated with deficit irrigation together with N-saving condition. Compared with OI-ON (optimum irrigation, OI together with optimum nitrogen, ON), treatment DI-DN (deficit irrigation, DI combined with deficient N (DN, N120) led to decreased contents of chlorophyll, nitrogen (N), and osmolytes, Pn, and the activities of SOD and POD in leaves at various stages together with reduced yields in Jimai 585 and Shimai 22, two cultivars with contrast drought stress responses. The moisture contents in soil profile planted by tested cultivars showed significant reduction under OI-ON with respect to those under DI-DN, suggesting the positive impact of elevated soil water consumption on plant physiological and agronomic traits. The drought-tolerant cultivar Shimai 22 displayed much more improvement on the physiological and agronomic traits, WUE, and NUE than drought-sensitive cultivar Jimai 585 under DI-DN, due to effective usage for soil water and N storage. Yields and grain weights under DI-DN were positively correlated with chlorophyll and osmolytes contents, Pn, and antioxidant enzyme activities, suggesting that the improved physiological traits under DI-DN contributed to the elevated yield for the drought-tolerant cultivar. Two nitrate transporter (NRT) family ones TaNRT2.1 and TaNRT2.2 and TaPYR3 and TaPYR6, two abscisic acid receptor (PYR) family genes exhibited induced transcripts upon DI-DN in wheat cultivars, with more abundance in Shimai 22 than in Jimai 585. Transgenic analysis on the differential genes confirmed their functions in mediating plant drought and N deprivation responses, suggesting that distinct PYR and NRT family members mediate drought and N deprivation adaptation in wheat plants. Our investigation provided insights into high WUE and NUE cultivation of winter wheat under the limited-water and N-saving management.

Peroxidase activity and operation of photo-protective component of NPQ play key roles in drought tolerance of mung bean [Vigna radiata (L.) Wilcziek

Developing drought-tolerant cultivars is mainly restricted due to poor knowledge of the mechanism behind drought tolerance. In the present work, available germplasm of Vigna radiata (mung bean) was screened for drought tolerance using multiple agronomic and physiological parameters and used to selected one drought-tolerant (NM-13-1) and one drought-sensitive (NM-54) cultivar for further studies. Plant water status and PSII activity were found to be potential physiological discriminating traits. Changes in PSII and PSI activity, accumulation of proline, oxidative damage, and antioxidants were further assessed in selected drought-sensitive and drought-tolerant cultivars. Drought stress reduced PSII efficiency and electron transport in both mung bean cultivars. Drought increased NPQ and Y(NPQ), a greater increase in NPQ and Y(NPQ) was found in the drought-tolerant cv NM-13-1, indicating that the drought-tolerant cultivar managed over-excitation of PSII by safe heat dissipation via photo-protective component of NPQ. A decrease in PSI efficiency with an increase in donor end limitation of PSI in both mung bean cultivars further confirmed that the electron transport through PSII became down-regulated. However, the drought-sensitive cv. NM-54 had poor ability to manage over-excitation of PSII through buildup of Y(NPQ) thereby causing greater oxidative stress. Mung bean cultivars counteracted oxidative stress by accumulation of proline and increasing POD activities. Drought-tolerant cv. NM-13-1 had higher proline accumulation and antioxidant potential than in the drought-sensitive cultivar. Overall, drought tolerance in the mung bean cultivars can be related to plant water status, PSII activity, Y(NPQ), and POD activity, which can be effectively used for selecting mung bean cultivars for drought tolerance.

Transcriptomic analysis reveals key transcription factors associated to drought tolerance in a wild papaya (Carica papaya) genotype.

Most of the commercial papaya genotypes show susceptibility to water deficit stress and require high volumes of irrigation water to yield properly. To tackle this problem, we have collected wild native genotypes of Carica papaya that have proved to show better physiological performance under water deficit stress than the commercial cultivar grown in Mexico. In the present study, plants from a wild Carica papaya genotype and a commercial genotype were subjected to water deficit stress (WDS), and their response was characterized in physiological and molecular terms. The physiological parameters measured (water potential, photosynthesis, Fv/Fm and electrolyte leakage) confirmed that the papaya wild genotype showed better physiological responses than the commercial one when exposed to WDS. Subsequently, RNA-Seq was performed for 4 cDNA libraries in both genotypes (susceptible and tolerant) under well-watered conditions, and when they were subjected to WDS for 14 days. Consistently, differential expression analysis revealed that after 14 days of WDS, the wild tolerant genotype had a higher number of up-regulated genes, and a higher number of transcription factors (TF) that were differentially expressed in response to WDS, than the commercial genotype. Thus, six TF genes (CpHSF, CpMYB, CpNAC, CpNFY-A, CpERF and CpWRKY) were selected for further qRT-PCR analysis as they were highly expressed in response to WDS in the wild papaya genotype. qRT-PCR results confirmed that the wild genotype had higher expression levels (REL) in all 6 TF genes than the commercial genotype. Our transcriptomic analysis should help to unravel candidate genes that may be useful in the development of new drought-tolerant cultivars of this important tropical crop.

Deciphering novel QTL for spectral reflectance indices in spring wheat

Drought is a common abiotic stress factor that seriously affects wheat production in many parts of the world. To identify stable QTLs associated with three morphophysiological traits and four spectral reflectance indices (SRIs) in F6 (previous research) and F7 generations, recombinant inbred line (RIL) population from the cross between drought-sensitive (Yecora Rojo) and drought-tolerant (Pavon 76) cultivars was used in a study conducted under two irrigation regimes at the King Saud University Agricultural, Research Station. The parents and RILs were genotyped using a set of microsatellite loci. The composite interval mapping (CIM) analysis detected 53 QTLs for the three morphophysiological traits and four SRIs. The phenotypic variance (PV) explained varied from 3 to 44%. Twelve co-located QTLs were identified on chromosomes: 1B, 1D, 2A, 2D, 3A, 3B, 4B, 5B and 5D. The highest number of co-located QTLs was identified on chromosomes 5B. The QTL on chromosome 5B flanked by barc109–barc59 showed significant effects for the morphophysiological traits and SRIs under the two irrigation regimes. This QTL explained the highest proportion of PV (14.0–44.0%) with LOD score (3.2–13.2). Seven stable QTLs were identified in both F6 and F7 generations. Of these QTLs, QWc.li-5B co-localized with QNdvi.li-5B and flanked by markers Barc109 and Barc59 was identified in F6 and F7 generations under reduced irrigation. QWc.li-5B explained the highest PV (43 and 44%) for relative water content in F6 and F7 RIL, respectively. The novel and consistent QTLs obtained can be used in marker-assisted selection to improve drought tolerance 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.

Assimilate limitation compensating factors under environmental stresses in wheat

In recent years, considerable efforts have been made to understand the factors controlling grain weight in wheat. In addition to sink capacity, the supply of assimilates for developing grain determines the weight of the grain. The current photosynthesis of the flag leaf is the most important source of assimilation, and the onset and rate of senescence are important factors for determining grain yield. Hence stress induced leaf senescence can reduce the supply of assimilates for grains. Under such conditions, assimilate contributions of stored non structural carbohydrates in stem and photosynthesis of non foliar parts of the plant such as spike are crucial for grain development. Non structural carbohydrates in wheat stem have been estimated and efforts have been made to reveal the mechanisms of assimilate partitioning. The hormone levels and activities of enzymes involved in assimilate partitioning and carbohydrate metabolism in wheat stem and grains have been significantly correlated with grain filling in wheat. Remobilization efficiency of stem reserves is increased under heat or drought stress along with increase in the proteins associated with senescence and ROS handling in the tolerant cultivars. The heat and drought tolerant wheat cultivars have a higher WSC content in stem, higher mobilization efficiency, longer duration of grain filling and stronger sink activity. However, some of the key issues such as intra-spike assimilation distribution have not been sufficiently addressed. This review has been compiled for information related to assimilate supply to the developing wheat grain under stress conditions and also enlists opportunities to translate this knowledge into traits for improvement of climate resilience in wheat.