Drought Stress Situations Research Articles

Identification of SbWRKY Transcription Factors in Scutellaria baicalensis Georgi under Drought Stress and Their Relationship with Baicalin

One of the most significant transcription factors in plants, WRKYs, are crucial for plant growth and stress response. In this study, we analyzed the physicochemical properties, evolutionary relationships, conservation structure, and expression of the WRKY gene family in S. baicalensis. The WRKY family has highly conserved structural domains, which have been classified into three major categories, I, II, and III, based on the number of WRKY structural domains and zinc finger structural features. SbWRKYs of the same subgroup are functionally similar and essentially contain the same motif. Additionally, different drought stress situations resulted in varying levels of SbWRKYs expression, with the majority of these factors being up-regulated in moderate drought stress settings, and fewer of them were up-regulated under severe drought stress conditions. Under moderate drought stress, the expression of key enzymes increased, while under severe drought stress, the expression of key enzymes decreased. Mild drought stress resulted in a 26.42% increase in baicalin accumulation, while severe drought stress led to a 22.88% decrease. The protein interaction analysis of key enzyme genes and SbWRKYs revealed that the expression of key enzyme genes affected the expression of SbWRKYs. We screened nine SbWRKYs with a significant relationship with baicalin accumulation, and SbWRKY8 and SbWRKY16 showed the highest correlation with the baicalin content. These findings offer a theoretical framework for more research on the roles of SbWRKYs and show that SbWRKYs can respond to drought stress in S. baicalensis.

Investigating the phytotoxic potential of Carlina acaulis essential oil against the weed Bidens pilosa through a physiological and metabolomic approach

Essential oils (EOs) are widely studied as possible candidates for new eco-friendly herbicides for weed management due to their phytotoxicity. In this study we tested the phytotoxic potential of the EO obtained from the roots of Carlina acaulis L. (Apiaceae) against the weed Bidens pilosa L. This EO, containing 98% of the polyacetylene carlina oxide, showed strong phytotoxic effects on the plant metabolism, such as leaf necrosis, reduction of relative water content and total leaf area, and an increase in the dry weight/fresh weight ratio, suggesting a water status alteration. The EO also damaged the photosynthetic machinery, as evidenced by the significant reduction of the effective quantum yield of photosystem II (ΦII) and the maximum quantum yield of photosystem II (Fv/Fm). In addition, the non-photochemical quenching (ΦNPQ) significantly increased after spraying with C. acaulis EO. Damage to photosystem II was further demonstrated through the reduction of manganese and calcium concentrations, possibly due to an alteration in the correct functionality of the Mn4Ca cluster of the PSII. Metabolomics analysis revealed an accumulation of branched-chain amino acids, such as isoleucine and valine, which is commonly related to osmotic alterations under drought stress situations and a general reduction in sugar content (fructose, glucose, mannose, among others), suggesting reduction of the photosynthetic efficiency too. Overall, these findings suggest C. acaulis EO as a promising natural product with phytotoxic potential against weeds that deserves further investigation.

Capturing Genetic Variability and Identification of Promising Drought-Tolerant Lines in Exotic Landrace Derived Population Under Reproductive Drought Stress in Rice.

Drought is one of the most predominant abiotic stresses in this century, leading to a drastic reduction in the yield of rainfed rice ecosystems. Breeding of drought-resilient rice varieties is very much in demand for sustainable rice production in drought-prone rainfed ecology. An experiment was designed under irrigated non-stress and drought-stress situations involving an exotic drought-tolerant landrace (Chao Khaw) and a high-yielding aromatic rice cultivar (Kasturi), and an F2:4 derived population of 156 breeding lines was developed at IRRI South Asia Hub, Hyderabad. The objective of the study was to assess the genetic variability, drought tolerance behavior, and identify promising breeding lines for different rice ecologies and drought breeding programs. Restricted maximum likelihood (REML) analysis using the mixed model approach revealed a considerable genetic variation in the population for yield and yield contributing traits in non-stress and drought-stress conditions. We observed very high heritability for all the selected traits under stress 2015 WS (73.8% to 85.3%) and 2016 WS (72.4% to 93.5%) and non-stress 2015 WS (68.2% To 92.9%) and 2016 WS (61.4% to 92.6%) environments, indicating possible selection for grain yield under drought stress and non-stress with the same precision level. None of the secondary traits except harvest index and biomass included in our study showed a positive association with grain yield, indicating indirect selection’s ineffectiveness in improving yield under drought. A total of 48 promising breeding lines were found to have a better yield than donor Chao Khaw (up to 38% advantage) and popular drought-tolerant cultivars Shabhagidhan (up to 48% advantage) in stress conditions and recommended for rainfed upland ecology, 34 breeding lines under the well-watered condition suited for rainfed lowland ecology. Overall, the study found 21 common breeding lines that showed their superiority in non-stress and under drought stress situations, fitting best in rainfed lowland ecology with occasional drought occurrence. The large genetic variation found in this population can be exploited further to develop a few forward breeding high-yielding lines with better drought tolerance ability and used as drought donors in drought breeding programs.

Stress indices based on cane and sugar yields: Implications in selection of sugarcane varieties for drought tolerance

Drought is a major cause of yield loss for many important crops including sugarcane. Due to increasing demand for sugar by a growing world population, it is needed to accelerate the selection of sugarcane clones/varieties that are resistant/tolerant and productive under water stress conditions. This study was conducted to assess the relative drought tolerance of diverse sugarcane clones/varieties evaluated under water stress (E2) and normal (E2) conditions for sugar and cane yields. Analysis of variance revealed significant differences among tested clones/varieties under both the water regimes. Per cent cane and sugar yield reduction in comparison to normal (E1) situation was assessed that ranged from 16.66–47.89 and 25.54–62.54 per cent, respectively under stressed (E2) conditions. Since, water deficit is the single largest abiotic stress affecting sugarcane productivity and the development of water use efficient and drought tolerant cultivars is an imperative, eleven stress indices were worked out from cane and sugar yields recorded under normal and stress conditions as reported earlier to see their effectiveness in sugarcane crop. Study is suggestive that lower score values for seven stress and stability indices viz. stress susceptibility index (SSI), stress tolerance index (STI), yield stability index (YSI), yield index (YI), drought resistance index (DI), relative drought index (RDI) and modified stress tolerance index (K1STI and K2STI) higher score for stress tolerance (TOL), mean productivity and geometric mean productivity (MP and GMP) and stress susceptibility percentage index (SSPI) categorized the clones/varieties as tolerant ones and vice versa. Further association studies showed that all the indices exhibited significant positive interaction with cane and sugar yields (CY and SY) under stress conditions except SSI and SSPI. Also inter association with different level of magnitude and significance among/between different indices were observed indicating their importance for selection of clones under drought stress situations. YI and DI had a positive correlation with RDI, GM, MP, K1 & K2 and between themselves for both cane and sugar yields indicating that they are a better predictor of potential cane and sugar yields under a stress conditions and can be useful for sugarcane researchers. Besides, clones and varieties reported in study with lowest score for SSI, STI, YSI, YI, DI, RDI and (K1STI and K2STI) and highest score for TOL, MP, GMP and SSPI be categorized for enhanced tolerance to water stress in present global warming situation in terms of their resilience to stress and production capacity to have better cane and sugar yields.

Effect of stress on the leaf anatomy of sugarcane cultivars with different drought tolerance (Saccharum officinarum, Poaceae)

ABSTRACT. Introduction: Drought is an important stress factor for sugarcane production in many areas of the world. Water proportion and moisture indices are applicable information for agronomic planning to forecast water excess or deficit during the crop cycle. Objective: Leaf anatomical features of two different sugarcane Saccharum ‘UT12’ (drought susceptible cultivar) and Saccharum ‘UT13’ (drought tolerant cultivar) were compared under early drought stress situation between 30 and 90 days after planting. Methods: Forty leaf anatomical features were investigated using peeling and free hand sectioning technique. Results: Some anatomical characteristics showed response to drought stress. Saccharum ‘UT12’ demonstrated higher sensitivity toward anatomical characteristics than Saccharum ‘UT13’. A total of 23 and 15 out of the 40 anatomical characteristics showed significance in Saccharum ‘UT12’ and Saccharum ‘UT13’, respectively. Some anatomical features such as cell wall and cuticle thickness, vascular bundle size, stomatal size and density can be used as important markers for drought stress assessment in sugarcane leaf. Conclusions: This is the first report describing comparative leaf anatomy of sugarcane Saccharum ‘UT12’ and Saccharum ‘UT13’ in Thailand under drought stress. Results will provide important information to improve adaptation mechanisms of tolerant sugarcane cultivars under initial drought stress situations.

Relationship of root aquaporin genes, OsPIP1;3, OsPIP2;4, OsPIP2;5, OsTIP2;1 and OsNIP2;1 expression with drought tolerance in rice

Aquaporins are channel proteins that facilitate the passive uptake and transport of water, ions, molecules and regulate the water balance at the plant level. Genes for aquaporins are important since they play a major role in water uptake. The present study was therefore conducted to assess the relationship of aquaporins predominantly expressed in roots in response to drought tolerance. Transcript abundance of five rice aquaporin genes (PIP2;5, PIP1;3, PIP2;4, TIP2;1 and NIP2;1) in five rice genotypes (Banglami, ARC 10372, Inglongkiri, Ranjit and IR 64) under well-watered and drought stress conditions were measured using qRT-PCR. Significant variation in PIP relative transcript abundance in roots was observed between varieties under both well-watered and drought stress conditions. In roots, the expression levels of most OsPIPs were found to be increased in drought stress conditions. OsPIP1;3, OsPIP2;5, OsTIP2;1 and OsNIP2;1 were upregulated more in upland (drought tolerant) rice and Ranjit lowland (moderately drought tolerant) genotypes than drought susceptible lowland IR-64 rice in drought stress conditions and downregulated/unchanged in well-irrigated conditions. The OsPIP genes were identified as candidate genes based on their high expression under drought stress situations and played a significant role in water uptake and root development under water stress conditions. A positive correlation was observed between fold increase in aquaporin expression and degree of drought tolerance which suggest that these aquaporins genes might play an important role in root development under water stress situation to overcome stress.

Association mapping for yield traits under drought stress in Autumn rice germplasm collection of Assam

Association mapping approach was applied to identify regions linked to SSR markers with yield and related traits in drought stress conditions using 267 autumn rice germplasm collection of Assam. The germplasm exhibited extensive phenotypic and genotypic diversity in both irrigated and artificial drought stress conditions. The drought screening in rainout shelter was successful causing a reduction of mean yield up to 65% in contrast to irrigated conditions. The grain yield showed a positive correlation with traits like productive tiller number, spikelet fertility, and relative leaf water content in drought stress situations suggesting their scope for use as an indirect selection parameter in breeding autumn rice. Many traditional autumn genotypes like ‘Koni ahu’, ‘Garam ahu 2’, ‘Bengonagutiya’, ‘Ahu Joha’ were found to be tolerant in drought stress conditions. The population structure study revealed the presence of structure in the panel dividing 203 accessions into two subgroups and leaving sixty-nine accessions under admixed ancestry. The marker-trait association (MTA) studies using structured mixed linear model (MLM) method unveiled 64 MTA for nine different traits under drought stress conditions. For grain yield, six MTA’s were reported on chromosome 2, 3, 5, 6 and 10 explaining the Phenotypic Variance in the range of 6 to 16%. Seven novel MTA were obtained for their corresponding traits and many of the identified QTL’s were reported previously. Some of the associations were also consistent with General linear model study. Candidate gene analysis of associated marker regions inferred that there are certain stress-responsive genes in its proximity. The tolerant genotypes identified can be employed in different drought breeding programs. The novel associations with major effect offer scope in the mining of new alleles for traits associated with drought tolerance for this class of rice.

The Effect of Calcium to Maize Seedlings under Drought Stress

Global warming brings a series of problems, including the worsening of drought stress worldwide. This paper aims to find optimal Calcium-using strategies in realistic events of drought stress. Maize seedlings were grown in solutions with differing Ca2+ concentrations, and PEG6000 was used to simulate drought stress. Several physiological indexes were measured to determine the effect of Calcium ions on maize seedlings under drought stress. Results show that a calcium concentration of 10 mM yields best results under both normal and drought conditions, but the lower calcium concentration of 2 mM may be more favorable in short-term drought stress situations.

Climate change determined drought stress profiles in rainfed common bean production systems in Brazil

Reductions in agricultural productivity with consequences for food security associated to climate change are expected in the absence of adaptation. For common beans, across South America, a decrease in climatic suitability has been projected, with heat and drought stresses being the key drivers for such suitability reductions. Breeding programs will play an important role in the adaptation of common beans to the changing climates. However, breeding targets may vary as climate changes during the 21st century. Here, we assess historical and future (2030) probabilities of occurrence, intensity and impact of seasonal variations of drought stress, which is the most important stress for common beans in the Goiás state. We focus on two rainfed (wet and dry) target population environments (TPEs), which encompass ca. 62% of the bean cropped area in the state for 2016, and address potential breeding implications of future projected changes. The analysis revealed two environment groups for both TPEs (highly favorable environment and favorable environment), and four drought stress profiles within these environmental groups (drought stress free, reproductive stress, terminal stress, and joint reproductive-terminal stress) across all climate and management (cultivars and sowing dates) scenarios. Results suggest that, with respect to the historical (1980–2005) period, climate change will make drought more frequent, but less severe, across the region. For the dry TPE, the probability of occurrence of drought stress situations (reproductive and/or terminal) changes from 29.6% (baseline) to ca. 70% (2030, RCP [Representative Concentrations Pathway] 8.5), whereas for the wet TPE, it increases from 16% (baseline) to ca. 43% (2030, RCP 8.5). Results are consistent across RCPs, although benefits from stringent (RCP 2.6) mitigation are evident. We conclude that drought tailoring under climate change is needed for the Embrapa dry bean breeding program.

QDTY12.1: a locus with a consistent effect on grain yield under drought in rice

BackgroundSelection for grain yield under drought is an efficient criterion for improving the drought tolerance of rice. Recently, some drought-tolerant rice varieties have been developed using this selection criterion and successfully released for cultivation in drought-prone target environments. The process can be made more efficient and rapid through marker-assisted breeding, a well-known fast-track approach in crop improvement. QTLs have been identified for grain yield under drought with large effects against drought-susceptible varieties. Most of the identified QTLs show large QTL × environment or QTL × genetic background interactions. The development of mapping populations in the background of popular high-yielding varieties, screening across environments, including the target environments, and the identification of QTLs with a consistent effect across environments can be a suitable alternative marker-assisted breeding strategy. An IR74371-46-1-1 × Sabitri backcross inbred line population was screened for reproductive-stage drought stress at the International Rice Research Institute, Philippines, and Regional Agricultural Research Station, Nepalgunj, Nepal, in the dry and wet seasons of 2011, respectively. A bulk segregant analysis approach was used to identify markers associated with high grain yield under drought.ResultsA QTL, qDTY12.1, significantly associated with grain yield under reproductive-stage drought stress was identified on chromosome 12 with a consistent effect in two environments: IRRI, Philippines, and RARS, Nepalgunj, Nepal. This QTL explained phenotypic variance of 23.8% and contributed an additive effect of 45.3% for grain yield under drought. The positive QTL allele for qDTY12.1 was contributed by tolerant parent IR74371-46-1-1.ConclusionsIn this study, qDTY12.1 showed a consistent effect across environments for high grain yield under lowland reproductive-stage drought stress in the background of popular high-yielding but drought-susceptible recipient variety Sabitri. qDTY12.1 was also reported previously [Crop Sci 47:507–516, 2007] to increase grain yield under upland reproductive-stage drought stress situations. qDTY12.1 is the only QTL reported so far in rice to have shown a large effect against multiple recipient genetic backgrounds as well as under highly diverse upland and lowland rice ecosystems. qDTY12.1 can be successfully introgressed to improve grain yield under drought of popular high-yielding but drought-susceptible lowland as well as upland adapted varieties following marker-assisted breeding.

High-yielding, drought-tolerant, stable rice genotypes for the shallow rainfed lowland drought-prone ecosystem

High and stable yield of rainfed lowland rice is important for sustainable rice production and food security. Many varieties grown on large holdings in rainfed areas provide good yield under normal water availability but suffer high losses in the event of drought. From a set of 129 genotypes tested in shallow rainfed drought-prone environments at three locations in eastern India from 2005 to 2007, a subset of 39 genotypes that were tested for two or more years under favorable irrigated, moderate reproductive-stage drought stress, and severe reproductive-stage drought stress situations in 16 environments was selected for a GGE biplot analysis to identify genotypes that provide stable yield across environments. IR74371-70-1-1 and IR74371-46-1-1 were identified as stable genotypes showing high yield under varied environments across different sites. IR36, IR64, and MTU1010, the three popular varieties grown on large holdings in rainfed areas but bred for irrigated ecosystem, as well as improved genotypes CB2-458, DGI237, R1027-2282-2-1, RR272-21, IR67469-R-1-1, and IR66873-R-11-1, and varieties PMK1 and PMK2 released for rainfed ecosystems performed well only in irrigated non-stress environments and were not found promising in drought environments. Improved genotypes ARB6, ARB2, ARB5, ARB7, ARB8, RF5329, CB0-15-24, IR72667-16-1-B-B-3, IR74371-78-1-1, and IR55419-04, and drought-tolerant released varieties Tripuradhan, Annada, and Poornima performed well only in drought-stress environments. The identification of improved genotypes with ability to provide stable high yield across variable environments and their release for cultivation by farmers will enable farmers to reap high yield and stable income.

Potential drought stress in a Swiss mountain catchment—Ensemble forecasting of high mountain soil moisture reveals a drastic decrease, despite major uncertainties

Climate change is expected to profoundly influence the hydrosphere of mountain ecosystems. The focus of current process‐based research is centered on the reaction of glaciers and runoff to climate change; spatially explicit impacts on soil moisture remain widely neglected. We spatio‐temporally analyzed the impact of the climate on soil moisture in a mesoscale high mountain catchment to facilitate the development of mitigation and adaptation strategies at the level of vegetation patterns. Two regional climate models were downscaled using three different approaches (statistical downscaling, delta change, and direct use) to drive a hydrological model (WaSiM‐ETH) for reference and scenario period (1960–1990 and 2070–2100), resulting in an ensemble forecast of six members. For all ensembles members we found large changes in temperature, resulting in decreasing snow and ice storage and earlier runoff, but only small changes in evapotranspiration. The occurrence of downscaled dry spells was found to fluctuate greatly, causing soil moisture depletion and drought stress potential to show high variability in both space and time. In general, the choice of the downscaling approach had a stronger influence on the results than the applied regional climate model. All of the results indicate that summer soil moisture decreases, which leads to more frequent declines below a critical soil moisture level and an advanced evapotranspiration deficit. Forests up to an elevation of 1800 m a.s.l. are likely to be threatened the most, while alpine areas and most pastures remain nearly unaffected. Nevertheless, the ensemble variability was found to be extremely high and should be interpreted as a bandwidth of possible future drought stress situations.

Yield and yield-attributing traits of rice ( Oryza sativa L.) under lowland drought and suitability of early vigor as a selection criterion

Fifteen experiments testing seven sets of genotypes under irrigated non-stress and drought stress situations were conducted from 2004 to 2006 with the objective to study the effect of different severity levels of drought on tolerant and susceptible advanced breeding lines, current varieties, and traditional and improved donors, and to study the effect of selection for high early vigor on yield. With the onset of drought, a yield reduction due to a decrease in biomass was observed in both susceptible and tolerant lines. However, after an initial reduction in yield, tolerant lines were able to sustain a yield loss more effectively than susceptible lines by better maintenance of biomass and higher harvest index. Under intermittent drought stress, genotypes with the ability to maintain higher biomass, reflected in terms of high early vigor recorded 3 wk after transplanting, recorded higher grain yield than genotypes with low early vigor. Lines with high early vigor yielded higher under both irrigated non-stress and intermittent drought stress situations. Under intermittent stress, plants with high vigor, low vigor, or random plants with high or low vigor coming from tolerant × susceptible crosses yielded higher than did the plants with the same vigor coming from susceptible × susceptible crosses. Under both irrigated non-stress and intermittent drought stress situations, early vigor showed significant genetic correlation with grain yield and could be included as an efficient selection criterion to improve yield in the lowlands.

A new harvest time prognosis tool for forage maize production in Germany

Optimum harvest date of silage maize is crucial for exploiting the yield and forage quality potential of the crop, and for minimising losses during silage storage and the feedout phase. Simulation models are a useful tool for determining this optimal date. While numerous models are available for yield and some for quality, no comprehensive model deals simultaneously with yield and quality. The current project aims to fill this gap by (i) adapting the grass model FOPROQ to growth and quality of silage maize, and (ii) calibrating and validating the model for dry matter (DM) yield, DM content, and starch content. This allowed subsequently (iii) to perform a long-term simulation study for quantifying the climatic risk of silage maize grown under the marginal conditions of Northern Germany. Calibration was based on a field trial conducted at four sites over 3 years (1998–2000) in Germany, including six cultivars covering a wide range of maturity classes (early to mid-late) and maturity types (normal, dry-down, stay-green). Samples were taken every 2 weeks over the vegetation period. Validation was based on an independent data set collected during two years (2001, 2002) at two sites, however, with only one cultivar. No changes of algorithms were necessary to adapt the grass model to forage maize. Calibration results showed good agreement between observed and calculated data (RMSE values of 153.8 g DM m −2 for DM yield, 26.8 g DM kg −1fresh weight for DM content, and 33.5 g kg −1 DM for starch content). For severe drought stress situations the validation revealed some discrepancies between observed and simulated starch content. Model refinements by implementing environmental response as a function of developmental stage and by broadening the calibration database are discussed. A 25-year (1979–2003) simulation study was conducted for one mid-early and two early cultivars at Kiel, Northern Germany. The simulation results were in good agreement with corresponding regional mean values for DM content and starch content of maize silage samples. A climatic risk analysis for this long-term simulation showed a substantial likelihood of failure to reach silage maturity, with failure rates between 44 and 64% depending on cultivar. The last decade (1994–2003), characterised by considerable temperature increase, showed somewhat lower failure rates. The reliable results presented in this study support current efforts to develop FOPROQ into a harvest time prognosis tool for Germany.