Development Of Drought Tolerance Research Articles

Developing Drought Tolerance in Field Crops towards Current Century: An Integrated Bio-Molecular Approach

Drought stresses are foremost threat to plant growth, productivity as well as sustainability towards agriculture through worldwide. Some of the classical breeding approaches have been attempted to develop crop performance towards stress without significant success and so therefore, recently genetic engineering in crop plants is recognized as an alternative strategy to generate drought tolerant crop plants. Various integrated biological approaches have been undertaken to overcome such drought hurdles in achieving the full potentiality of the plant growth and production as well as improving the drought tolerance in different field crops. Some approaches are commonly used to identify genes related to drought tolerance and genes to be identified which are involved in processes known to be critical for drought tolerance; whose expression is regulated by drought stress and that consists in the identification of drought tolerance determinants based on functionality. Plant researchers have developed several spurts of biological novel ‘Omics’ technologies viz. genomics, transcriptomics, proteomics and metabolomics etc to engineer plant stress tolerance. In this review, an attempt has been made to summarize the current information based on recent literature towards recent understanding as well as latest advancement related to the adverse effect of plant under drought and their adaptations or tolerance towards such abiotic stress with a focus on the identification of drought tolerance mechanisms by soil management practices, crop establishment and exogenous application of growth regulators by regulating an appropriate level of water due to osmotic adjustment and stomatal performance etc at an integrated biological level of approach.

The combined application of rutin and silicon alleviates osmotic stress in maize seedlings by triggering accumulation of osmolytes and antioxidants’ defense mechanisms

Silicon (Si) has been shown to improve plant defenses against a variety of stresses. However, how rutin (Rut) affects stress factors is yet to be fully explored. Moreover, their combined role in osmotic stress response remains unclear. The current study was performed to determine how the use of Rut and Si, both separately and in combination, improved the physiological resilience of maize seedlings to two levels of osmotic stress (induced by polyethylene glycol (PEG) 6000). We aimed to enhance osmotic stress tolerance with the simultaneous use of Rut and Si. First, we selected the best water status and the lowest membrane damage enhancing concentration of Rut (60 ppm) and Si (1 mM) to research their tolerance and resistance to osmotic stress (moderate: 10% PEG, severe: 15% PEG). The application of Rut and Si separately and together reduced oxidative stress by decreasing the reactive oxygen species and improved the relative water content, osmoprotectants (proline, total soluble sugar, and glycine-betaine), ascorbate level, and some antioxidant defense-related enzyme activities and their gene expression in maize seedlings under osmotic stress. However, these effects were more promising under moderate stress. As a result, findings from the study indicate the synergistic effect of combined Rut and Si on osmotic stress tolerance in maize seedlings. Overall, the combination of Rut and Si was more effective than independent Rut and Si in reducing osmotic stress in maize seedlings. Here, it was clear that Rut played an active role in alleviating stress. This combined application can be useful for developing drought tolerance in crops for the agriculture sector.

Effects of drought stress on growth, physiological and biochemical parameters of two Ethiopian red pepper (Capsicum annum L.) cultivars

Drought is the most predominant abiotic factor that affects plant growth and development. The present research examined at how drought stress affected the growth, physiological, and biochemical responses of Local and Markofana red pepper (Capsicum annum L.) cultivars. Five-week-old cultivars were exposed to well-watered, low, moderate, and severe drought conditions, kept at 100, 80, 60 and 40% of field capacity, respectively. Nine-week-old cultivars were sampled to analyze the effects of the stress on different parameters of both cultivars. Compared with the control group, drought stress caused a reduction in growth, physiological and biochemical parameters; nevertheless, adverse effects of the stress were more noticeable in the Local cultivar. Severe drought stress significantly reduced shoot length in Markofana (53.71 %) compared to the control group. Significant variation was observed in relative water content in the Local cultivar (20.26 %) exposed to drought. In the Local cultivar, the total chlorophyll content and chlorophyll fluorescence declined significantly by 77.28 and 3.33 %, respectively. Therefore, the cultivar Markofana was relatively less affected by drought stress. In general, these differences in cultivar responses to drought stress may aid in developing drought tolerance genotypes that can withstand drought stress conditions with minimal yield losses.

Herbivoría y sequía en el Monte: Factores de estrés que afectan el crecimiento y el ataque de insectos en hojas y semillas de una especie forrajera

Plants in arid environments are exposed to drought stress but also may suffer herbivory by large mammals. Since this may affect plant fitness, plants may display different responses and/or defences, developing tolerance and resistance mechanisms. In this work, we experimentally investigated how drought and herbivory affect seedling growth of a forage species, Atriplex lampa, from Patagonian Monte Desert. In addition, we evaluated in a greenhouse whether simulated herbivory stress affects the presence of aphids, and in the field whether herbivory by large mammals affects insect granivory in this species. We found that drought did not affect the species growth, suggesting toleration or adaptation to drought condition, while herbivory reduced its growth. In addition, we found that a higher level of stress on seedlings and, to minor extent, on parent (seed origin) is related to a lower presence of aphids on the seedlings growth in the greenhouses. However, at field conditions, we observed that the higher the stocking rate, the higher the insect granivory. The results from the greenhouse experiment suggest that this species develops some kind of defences or a decrease in aphid attraction caused by drought stress and the simulated herbivory. In contrast, field results imply that this species does not develop any defences or that they are mainly found in stems and leaves, but not in fruits. Our results show that A. lampa has developed drought tolerance strategies but is vulnerable to herbivory. These stress factors could be exerting selection pressures on A. lampa that affect evolutionary and ecological processes and, consequently, its ecosystem services as a key forage species in the Monte Region.

EVALUATION OF COTTON GENOTYPES SEEDLINGS FOR DROUGHT STRESS TOLERANCE

The present studies clearly indicated that expressivity of some of the genes was changed due to the simulated drought conditions. The root increases in length in response to drought thus utilizes more photosynthates changing the sink and ultimately reducing the shoot growth. The shift due to drought indicated that the growth and morphological development of root system are under genetic control but may be modified by environmental influences. To screen out drought tolerant and drought susceptible genotypes on the basis of morphological seedling traits such as root characters and root / shoot length ratio. After screening, three drought tolerant genotypes namely BH-124,149-F and DPL-26 and three drought susceptible genotypes i.e. CIM-446, FH-945 and VH-28 were identified which may be used in further hybridization programme to develop drought tolerance varieties and hybrids.

Abiotic stress tolerance in wheat with emphasis on drought

Environmental change presents a significant hazard to most tropical and subtropical crops across the world. Drought stress is among the negative repercussions of environmental modification that affects agricultural development and output. It has a significant influence on the vegetative and propagative phases of plants. Considering the current and prospective nutrition demands of a growing populace, it is critical to target crop production in drought-prone rainfed areas. Crops respond to drought stress in various manners, including structural, physio-chemical, and molecular responses. Drought tolerance encompasses processes that operate at several geographical and temporal dimensions, ranging from immediate stomatal closure to crop production management. There are multiple genes in wheat that are responsible for drought resistance and generate various enzymes and proteins under drought conditions. This review focusses the current advances in wheat physio-chemical, and molecular adaptation to drought tolerance. The experimental data revealed that drought stress negatively impacts multiple physiological processes that occur in wheat plants during their various growth phases, including germination, vegetative growth, reproductive development, and maturity. Therefore, studying the drought-induced damage in wheat plants, as well as strategies for boosting drought tolerance, is critical for increasing wheat output. Furthermore, molecular genetics and breeding strategies for developing drought tolerance in wheat to boost yield and quality are discussed

Influence of Ascophyllum nodosum Extract Foliar Spray on the Physiological and Biochemical Attributes of Okra under Drought Stress.

Drought stress restricts the growth of okra (Abelmoschus esculentus L.) primarily by disrupting its physiological and biochemical functions. This study evaluated the role of Ascophyllum nodosum extract (ANE) in improving the drought tolerance of okra. Drought stress (3 days (control), 6 days (mild stress), and 9 days (severe stress)) and 4 doses of ANE (0, 0.1%, 0.2%, and 0.3%) were imposed after 30 days of cultivation. The results indicate that drought stress decreases the chlorophyll content (total chlorophyll, chlorophyll a, chlorophyll b, and carotenoid) but increases the activity of anthocyanin, proline, and antioxidant enzymes such as ascorbate peroxidase (APX), peroxidase (POD), and catalase (CAT). Physiological and biochemical plant disturbances and visible growth reduction in okra under drought stress were significantly decreased by the application of ANE foliar spray. ANE spray (0.3%) significantly increased the chlorophyll abundance and activity of anthocyanin, proline, and antioxidants (APX, POD, and CAT). ANE regulated and improved biochemical and physiological functions in okra under both drought and control conditions. The results of the current study show that ANE foliar spray may improve the growth performance of okra and result in the development of drought tolerance in okra.

Differential Response of Two Tomato Genotypes, Wild Type cv. Ailsa Craig and Its ABA-Deficient Mutant flacca to Short-Termed Drought Cycles.

Two tomato genotypes with constitutively different ABA level, flacca mutant and wild type of Ailsa Craig cv. (WT), were subjected to three repeated drought cycles, with the aim to reveal the role of the abscisic acid (ABA) threshold in developing drought tolerance. Differential responses to drought of two genotypes were obtained: more pronounced stomatal closure, ABA biosynthesis and proline accumulation in WT compared to the mutant were compensated by dry weight accumulation accompanied by transient redox disbalance in flacca. Fourier-transform infrared (FTIR) spectra analysis of isolated cell wall material and morphological parameter measurements on tomato leaves indicated changes in dry weight accumulation and carbon re-allocation to cell wall constituents in flacca, but not in WT. A higher proportion of cellulose, pectin and lignin in isolated cell walls from flacca leaves further increased with repeated drought cycles. Different ABA-dependent stomatal closure between drought cycles implies that acquisition of stomatal sensitivity may be a part of stress memory mechanism developed under given conditions. The regulatory role of ABA in the cell wall restructuring and growth regulation under low leaf potential was discussed with emphasis on the beneficial effects of drought priming in developing differential defense strategies against drought.

Genotypic selection approach made successful advancement in developing drought tolerance in perennial tree crop coconut

Coconut (Cocos nucifera L.) is a major plantation crop in humid tropics that affects the socio-economic life of several developing countries. Being a rainfed crop, coconut is highly prone to drought and breeding for drought tolerance has become a high priority research. We have identified that selection within populations as the way forward to improve drought tolerance. The current study evaluates the comparative performance of Ambakelle special (AS), a progeny of a within population selection with unselected CRIC60 to identify stable higher yielding palms for future breeding programs. Six-year yield data (2014-2019) from 110 palms in each group were evaluated. Results revealed variety, year and interaction have significant impact on annual yield (P<0.05) however, variety x year showed a non-cross-over interaction. AS recorded significant higher mean annual yield (101 nuts/palm/year) compared to CRIC60 (90 nuts/palm/year). Due to low rainfall condition prevailed from July 2016; lower nut yields were recorded for both varieties in 2017 and 2018. However, AS maintained its superiority indicating a better adaptation than CRIC60 under low rainfall conditions. Regression coefficient (bi) and mean annual yield were used in stability analysis and selected 45 palms as stable and higher yielding genotypes. Out of these 45 palms, thirty-three palms (73.3%) were from AS progeny further indicating the adaptability of AS to varying environmental conditions. Twenty palms (16 AS and 4 CRIC60) were further selected using variance of deviations from the regression (S2di) and mean kernel weight to be used in the future breeding programs for drought tolerance in coconut.

Spermine: Its Emerging Role in Regulating Drought Stress Responses in Plants

In recent years, research on spermine (Spm) has turned up a lot of new information about this essential polyamine, especially as it is able to counteract damage from abiotic stresses. Spm has been shown to protect plants from a variety of environmental insults, but whether it can prevent the adverse effects of drought has not yet been reported. Drought stress increases endogenous Spm in plants and exogenous application of Spm improves the plants’ ability to tolerate drought stress. Spm’s role in enhancing antioxidant defense mechanisms, glyoxalase systems, methylglyoxal (MG) detoxification, and creating tolerance for drought-induced oxidative stress is well documented in plants. However, the influences of enzyme activity and osmoregulation on Spm biosynthesis and metabolism are variable. Spm interacts with other molecules like nitric oxide (NO) and phytohormones such as abscisic acid, salicylic acid, brassinosteroids, and ethylene, to coordinate the reactions necessary for developing drought tolerance. This review focuses on the role of Spm in plants under severe drought stress. We have proposed models to explain how Spm interacts with existing defense mechanisms in plants to improve drought tolerance.

Understanding Transcription Factors in Plant Response to Drought Stress

Increasing sensitivity of plants to abiotic and biotic stress such as drought, salt and extreme temperatures poses a worldwide peril to sustained growth and productivity of crops. Decrease in crop produce corresponds to increase in food prices and lower monetary return for farmers. In view of this, developing drought tolerance cultivars arises as the most viable solution toward enhancing crop productivity in adverse environment conditions. Therefore, it is imperative to identify the key regulators of water stress in plants and develop new varieties with improved drought stress tolerance. Drought tolerance is now well understood to be regulated by multiple genes, including transcription factors (TFs) that enable plants to tolerate harsh conditions and these genes remain viable genetic options for crop breeding. Plants have evolved various mechanisms to respond to various stressors which involve many transcription factors (TFs) like WRKY, TCP, DOF, HSF and NF-Ys. They participate in activation of various signalling pathways that protect cells against the damages caused by both abiotic and biotic stress. This review summarizes the role of such TF families in drought stress and provides insights for development of stress-tolerance in plants.

A regression model to depict the influence of physiological and agronomic traits on yield of wheat cultivars under water stress in Tigray, Ethiopia

Although developing drought tolerance is the major objective of plant breeders, it is hampered by the lack of effective selection criteria. Most plant breeders use the single trait approach in identifying the crop response to drought condition, and little priority is given to the physiological traits. Thus, all the possible traits have not been critically evaluated, and correlation among the different traits and their relation to drought has not yet been critically examined. With those facts field and greenhouse, experiments were conducted at Mekelle University to determine the relationship among the different physiological, agronomic, yield and yield component of wheat genotype under water stress. The experiment was laid out in Randomized Complete Block Design using six wheat genotypes and three water regimes with three replications. Pearson’s correlation coefficient at 5% indicated that yield was positively and significantly correlated with relative water content, excised leaf water retention, spike length, number of seed per spike, and seed weight in contrast stress susceptibility index and rate of water loss were negatively associated with yield. Regression analysis also showed the rate of water loss, excised leaf water retention, and relative water content explain more of the variation (90%) in grain yield under different water stress regimes. Hence plant breeders should incorporate these physiological traits as a selection criterion in their breeding program for screening water stress on wheat cultivars.

Biotechnology and Drought Stress Tolerance in Plants

Drought stress in plants has become one of the major abiotic stress that limits the growth and development of plants which also contributes to low yields. Biotechnology which has new and emerging techniques can be use to solve the problem of drought stress in plants. This review aimed at identifying drought stress tolerance in plants at different stages, how plants respond to drought stress using different methods and the application of different biotechnology methods to improve drought tolerance in plants. Some important parameters about drought stress in plants such as drought tolerance mechanisms, plants responses to drought stress, gene regulation for drought stress tolerance in plants, effects of drought stress at different stages of plant growth and biotechnology methods in developing drought tolerance in plants was reviewed. The use of biotechnology methods such as classical breeding, use of genetic manipulation, genes from resurrection plants and Protoplast fusion was discussed. Drought stress affects our plants seriously and it leads to wilts, reduction of yields and death of plants at different developmental stages. Plants have developed different mechanisms to respond to drought stress but these mechanisms are not sufficient enough without the application of biotechnology to greatly improve the growth, development and increase yield in pants. The use of biotechnology greatly improves plants ability to tolerate drought stress depending on the plant species and period of exposure. The use of biotechnology methods has become very vital in improving plants drought stress so as to overcome the major problems of plants which includes increase in population and climatic change.

Tinkering Cis Motifs Jigsaw Puzzle Led to Root-Specific Drought-Inducible Novel Synthetic Promoters.

Following an in-depth transcriptomics-based approach, we first screened out and analyzed (in silico) cis motifs in a group of 63 drought-inducible genes (in soybean). Six novel synthetic promoters (SynP14-SynP19) were designed by concatenating 11 cis motifs, ABF, ABRE, ABRE-Like, CBF, E2F-VARIANT, G-box, GCC-Box, MYB1, MYB4, RAV1-A, and RAV1-B (in multiple copies and various combination) with a minimal 35s core promoter and a 222 bp synthetic intron sequence. In order to validate their drought-inducibility and root-specificity, the designed synthetic assemblies were transformed in soybean hairy roots to drive GUS gene using pCAMBIA3301. Through GUS histochemical assay (after a 72 h 6% PEG6000 treatment), we noticed higher glucuronidase activity in transgenic hairy roots harboring SynP15, SynP16, and SynP18. Further screening through GUS fluorometric assay flaunted SynP16 as the most appropriate combination of efficient drought-responsive cis motifs. Afterwards, we stably transformed SynP15, SynP16, and SynP18 in Arabidopsis and carried out GUS staining as well as fluorometric assays of the transgenic plants treated with simulated drought stress. Consistently, SynP16 retained higher transcriptional activity in Arabidopsis roots in response to drought. Thus the root-specific drought-inducible synthetic promoters designed using stimulus-specific cis motifs in a definite fashion could be exploited in developing drought tolerance in soybean and other crops as well. Moreover, the rationale of design extends our knowledge of trial-and-error based cis engineering to construct synthetic promoters for transcriptional upgradation against other stresses.

A QTL hot spot region on chromosome 1B for nine important traits under terminal drought stress conditions in wheat

Drought tolerance is a polygenic trait and is considered as one of the most important limiting factors to productivity of wheat and other crops around the world. Identifying drought-responsive genes using quantitative trait loci (QTL) and association analysis is one of the ways of developing drought tolerance cultivars. In order to detect QTLs for terminal drought tolerance in wheat, QTL analyses were conducted using an F12 recombinant inbred line population. A total of 53 main effects QTLs on 15 different chromosomes and 12 QTL by QTL (QQ) interactions on 13 different chromosomes were detected for yield, yield components and some agronomic traits using composite interval mapping and mixed-model based composite interval mapping analysis. The most significant QTL for grain yield was QYld.1A1 on 1A1, explaining 19.7% of the phenotypic variance under terminal drought stress. In addition, a QTL hot-spot region including important QTLs for grain yield, biological yield, grain number per spike, thousand grain weight, spike length, spike weight, stem weight and plant height was identified in the same region on chromosome 1B and clustered within the marker interval between wpt-3465 and wpt-2019. The DArT marker Wpt-5801 at the position of 67.7 cM showed linkage with all traits using single marker regression analysis. The BLAST search of markers sequences on the wheat genome identified 390 gene stable identifiers. Gene ontology analysis showed that the most dominant terms were ‘binding’ and ‘single-organism catabolic process’ for molecular function and biological process categories, respectively. This QTL hot-spot region with nine important QTLs could be used to improve drought tolerance after validation.

In silico identification and evaluation of Bacillus subtilis cold shock protein B (cspB)-like plant RNA chaperones

Cold shock domain (CSD) proteins with nucleic acid binding properties are well conserved from bacteria to higher organisms. In bacteria, the cold shock proteins (CSPs) are single domain RNA chaperones, whereas in animals and plants, CSDs are accompanied by additional domains with roles in transcription regulation. Bacterial CSPs (Escherischia coli-cspA and Bacilus subtilis-cspB) have successfully imparted drought tolerance in transgenic plants; however, these cannot be deployed in food crops due to their low public acceptance of transgenics with bacterial genes. Therefore, this study aimed to identify CSPB-like proteins from plants that can be used for developing drought tolerant transgenic crops. Twelve single domain plant CSPs presenting >40% sequence identity with CSPB were identified. All 12 plant CSPs were modeled by homology modeling and refined by molecular dynamics simulation for 10 ns. Selected plant CSPs and CSPB exhibited high structural similarity (Tm-score: 0.63–0.86). Structure based phylogenetic analysis revealed that Triticum aestivum-csp1 and Aegilops tauschii-cspE are structurally closer to CSPB compared to their orthologs and paralogs. Molecular docking with three RNA molecules (5U, UC3U, and C2UC) indicates that Ricinus communis-csd1 and T. aestivum-csp1 have a binding pattern and docking scores similar to those of CSPB. Furthermore, MD simulations for 20 ns and analysis of RMSD, RMSF, Rg as well as the number of hydrogen bonds in all the three complexes revealed that plant CSP-RNA complexes behave in a similar manner to that of the CSPB-RNA complex, making them highly potential candidate genes for developing drought tolerance in transgenic plants. Communicated by Ramaswamy H. Sarma

Selecting Traits for Drought Tolerance Screening in Rice

Drought is one of major constrains for rice production in Indonesia. Development of drought tolerant rice variety is believed as an efficien and effective strategy to face the challange. Nevertheless, drought is a complex trait thus many approach had been implemented in the selection of drought tolerant rice genotypes. This study aimed to search traits correlated with drought tolerance in rice plant. Two screening methods, i.e. seedling box and mini pot methods was conducted into 60 rice genotypes. The experiments were conducted during dry season 2016. The results showed that based on % recovery, TIL24 had the highest (82.5 %) while number of green leaves had strong positive correlation with root length, root number in zone 1 (horizontal), 2 (medium), and 3 (vertical), total root number, leaf rolling, and plant recovery. Nevertheless, proportion of root in zone 3 negatively correlated with shoot length, green leaf number, root number in zone 1 and 2, total root number, and plant recovery. It seem that proportion of vertical root compensate with other traits in developing drought tolerance, while number of green leaf under stress and root number in zone 2 correlated more with traits supporting drought tolerant in rice.

Resurrection plants: Imperative resources in developing strategies to drought and desiccation pressure

Resurrection plants are the vital assets of nature that have amazing mechanism to restrict the negative impacts of drought or desiccation stress by diminishing cell damage. These surprising plants are in minority on this planet but have the potential to serve as a powerful resource for developing new strategies for major crop plants that are unable to adapt well to the arid climate. In this review, an attempt is made to highlight the potential aspects of these resurrection plants especially the genetic engineering facet which has been done to develop drought tolerance in economically important plants.

Stomatal response in soybean during drought improves leaf-scale and field-scale water use efficiencies

Diminishing water resources and an expected increase in frequency of extreme water stress events necessitate tools to diagnose and improve the drivers of variability in agronomic water use efficiency. The objective of this study was to determine if leaf-scale water use efficiency (measured as intrinsic water use efficiency and transpiration efficiency) is expressed at the field scale as yield or agronomic water use efficiency variability. We measured grain yield, total aboveground biomass, and carbon isotope discrimination and estimated evapotranspiration using a mass balance approach for field-grown Glycine max (soybean) over five years. We found that the high agronomic water use efficiency in years characterized by high vapor pressure deficit was caused by a large reduction in evapotranspiration and a relatively smaller reduction in yield. This has implications for developing drought tolerance in soybeans without compromising yield. We observed a positive relationship between transpiration efficiency and agronomic water use efficiency, with the leaf scale explaining 68% of the variability at the field scale. Through this analysis, we infer that increasing transpiration efficiency at the leaf scale will likely improve agronomic water use efficiency at the field scale in rain-fed soybean systems.

Identification of Drought Tolerant Mutant Lines of Tef [Eragrostis Tef (Zucc.) Trotter

Introduction: Tef [Eragrostis tef (Zucc.) Trotter] is the major food crop in Ethiopia where it is annually cultivated on about 30% of the total area allocated to cereals. The productivity of tef is, however, significantly reduced by drought which can occur at either the early or the late developmental stage of the crop. Methodology: A total of 10,000 EMS (ethyl methane sulfonate) mutagenized M2 tef populations were screened first for early and second for terminal drought tolerance. The performance of candidate lines was investigated using diverse agronomical and physiological parameters. Results and discussion: Several promising lines were obtained for both early and terminal drought tolerance. Among these, genotypes with outstanding performance were found for two drought tolerant tef lines targeting early drought tolerance (dtt2 and dtt13) and three terminal drought tolerant lines targeting terminal drought tolerance (tdt9, tdt15 and tdt19). Conclusions: Candidate lines for both early and terminal drought tolerance will play vital roles in developing drought tolerance in tef improvement.