Terminal Drought Research Articles

Evaluating stress tolerance indices for their comparative validity to access terminal heat stress and heat drought tolerance of winter wheat (Triticum aestivum L.) genotypes

Evaluating stress tolerance indices for their comparative validity to access terminal heat stress and heat drought tolerance of winter wheat (Triticum aestivum L.) genotypes

Agronomic adaptations to heat stress: Sowing summer crops earlier

CONTEXTSummer crops are exposed to heat and drought stresses at critical stages during and after flowering, and their intensity and frequency are likely to increase with climate change. Agronomic stress avoidance offers the opportunity to temporally separate critical crop stages from heat and drought events. However, it might require sowing cold-sensitive summer crops earlier into colder than recommended soil temperatures. There is a need to understand how cold is too cold to sow summer crops early in late winter as well as what are the yield benefits and risks. OBJECTIVEHere, we quantify the likely benefits and trade-offs of sowing sorghum, a summer cereal, earlier to adapt to the increased frequency and intensity of heat and water stresses during flowering and grain filling. METHODSTwo years of multi-environment (n=32) genotype by management trials were conducted across the main sorghum growing regions of Australia. Environments (E) consisted of the combination of years, sites, three times of sowing (early, spring, and summer), and the use of supplementary irrigation. At each E a factorial combination of four plant populations (M) and eight commercial sorghum hybrids (G) were sown with three replications. Crop growth and yield components were measured, and the APSIM model was used to simulate all trials and treatments to quantify risks and derive insights into functional relationships between simulated and measured environmental covariates, and measured crop traits. RESULTSThe tested hybrids showed small differences in cold tolerance during crop establishment. Across the tested environments, the G×M combinations produced up to 60% variation in treatment yields across environment yields, which varied between <0.5 to about 10t ha-1; this translated into a ~5.5-fold variation in water use efficiency. Significant G×E and M×E interactions were observed for grain yield components. No G×M or G×E×M interactions were observed on yield or yield components. Early sowing was associated with a reduced risk of heat stress and water use transfer from vegetative to reproductive stages. Early sowing in late winter or early spring resulted in no significant yield gain or loss when all sites and years were included in the analysis. However, early sowing yielded between 1-2 t ha-1 more when the hottest sites and years were considered separately. This resulted from both the avoidance of heat stresses and milder or no terminal drought stresses. CONCLUSIONSEarly sowing of sorghum can reduce the likelihood of heat stresses around flowering as well as the likelihood of terminal drought stresses. Advantages include reduced yield losses in the hottest years and a transfer of water use to grain filling stages, resulting in increased grain yield and improved grain quality parameters. IMPLICATIONSEarly sowing, an agronomic adaptation, offers the opportunity to quickly adapt to the increase in the frequency and intensity of extreme hot events during critical crop stages. However, for the practice to be de-risked, there is a need to increase cold and chilling tolerance in sorghum and/or identify interventions that enhance seed germination and seedling vigour when the crop is sown early into cold soils.

Impact of supplemental irrigation and organic manure on growth and yield performance of rice variety BRRI dhan103 under terminal drought condition in Aman season

BRRI dhan103 is a transplanting Aman (T. Aman) rice variety that demands sufficient organic manure and supplemental irrigation to ensure successful production. Seven treatments, viz., T1= rainfed control; T2= one supplemental irrigation at 80 days after transplanting (DAT); T3= two supplemental irrigations at 70 and 80 DAT; T4= additional 5 t ha-1 poultry compost under rainfed condition; T5= additional 10 t ha-1 poultry compost under rainfed condition; T6= additional 2.5 t ha-1 biochar under rainfed condition; and T7= additional 5 t ha-1 biochar under rainfed condition, were evaluated against BRRI dhan103 to assess the impact of supplemental irrigation and manuring under terminal drought conditions. It was revealed that supplemental irrigation and manuring significantly improved all growth parameters and yield attributes compared to the rainfed control. Notably, T5 treatment provided its greatest performance statistically in respect of SPAD value (36.13), root dry weight (12.43 g), number of tillers hill-1 (13.22), panicle length (28.87 cm), panicles hill-1 at harvest (9.13), total spikelet (194.53), spikelet panicle-1 (197.63), filled spikelet panicle-1 (197.63), thousand grain weight (33.78 g), grain weight panicle-1 (28.70 g), grain yield hill-1 (31.97 g), and above-ground biological yield (3043.35 g m-2). The highest tiller hill-1 at harvest (9.53) was achieved when an additional 10 t ha-1 of poultry compost was applied under rainfed conditions. This study suggested that additional 10 t ha-1 poultry compost under rainfed conditions performed best to enhance the growth and yield of BRRI dhan103.

UAV-Based Phenotyping: A Non-Destructive Approach to Studying Wheat Growth Patterns for Crop Improvement and Breeding Programs

Rising food demands require new techniques to achieve higher genetic gains for crop production, especially in regions where climate can negatively affect agriculture. Wheat is a staple crop that often encounters this challenge, and ideotype breeding with optimized canopy traits for grain yield, such as determinate tillering, synchronized flowering, and stay-green (SG), can potentially improve yield under terminal drought conditions. Among these traits, SG has emerged as a key factor for improving grain quality and yield by prolonging photosynthetic activity during reproductive stages. This study aims to highlight the importance of growth dynamics in a wheat mapping population by using multispectral images obtained from uncrewed aerial vehicles as a high-throughput phenotyping technique to assess the effectiveness of using such images for determining correlations between vegetation indices and grain yield, particularly regarding the SG trait. Results show that the determinate group exhibited a positive correlation between NDVI and grain yield, indicating the effectiveness of these traits in yield improvement. In contrast, the indeterminate group, characterized by excessive vegetative growth, showed no significant NDVI–grain yield relationship, suggesting that NDVI values in this group were influenced by sterile tillers rather than contributing to yield. These findings provide valuable insights for crop breeders by offering a non-destructive approach to enhancing genetic gains through the improved selection of resilient wheat genotypes.

Agronomic and morpho‐physiological response of Andean genotypes of common bean to terminal drought

AbstractDrought is a major production constraint of common bean (Phaseolus vulgaris L.) worldwide. The objectives of this study were to (i) assess the agronomic and morpho‐physiological response of Andean genotypes to terminal drought, and (ii) identify Andean genotypes with an ideal combination of agronomic and morpho‐physiological traits for enhanced drought tolerance. Twenty Andean genotypes and seven checks were evaluated for drought tolerance in three field trials conducted in three locations. Agronomic and morpho‐physiological traits including seed yield, seed weight, shoot dry weight, pod number, pod harvest index, harvest index, and carbon isotope discrimination (CID) were measured. Strong positive correlations were observed between seed yield, and partitioning efficiency metrics and CID (r = 0.57***) under drought, which suggested the important role of assimilate partitioning and water use efficiency in the observed drought tolerance. The heritability estimates for pod harvest index (H2 = 0.88) and harvest index (H2 = 0.87) were higher than for seed yield (H2 = 0.43) and other morpho‐physiological traits, thus they can be used to indirectly select for drought tolerance. Based on the relationship between seed yield and CID under drought stress, 12 genotypes were identified as drought tolerant with high water use efficiency. Among these, three were classified as water savers, while nine as water spenders. Genotypes with an ideal combination of superior shoot dry weight, partition efficiency, water use efficiency, and superior seed yield under both drought stress and non‐stress conditions were identified. The identified genotypes can be used for genetic improvement of drought tolerance in the Andean gene pool of common bean.

Assessing the impact of turnip yellows virus infection and drought on canola performance: implications under a climate change scenario

IntroductionCanola (Brassica napus L.) is one of the most important crops worldwide. Turnip yellows virus (TuYV), transmitted by aphids, is one of the most damaging viruses affecting canola crops and is challenging to control. With the prediction of more intense and prolonged drought events due to future climate change, an additional factor may extensively impact the epidemiology of plant diseases. This study aimed to understand the impact of drought on canola plants infected with TuYV and to explore the relationship between virus infection and drought.MethodsTwo glasshouse experiments were conducted: 1. Competition: Four plants (two infected, two non-infected) were grown in the same pot. 2. No Competition: One plant was grown per pot. In both experiments, infected and non-infected canola plants were exposed to well-watered conditions, water stress (simulated drought), and terminal drought. Various plant traits were recorded, including biomass, leaf area, height, number of leaves, chlorophyll content, water use efficiency, and virus symptom expression.ResultsBoth virus infection and water stress reduced dry biomass, leaf area, and height. Virus infection alone reduced canola biomass by up to 49% compared to non-infected, well-watered controls. Under water stress or terminal drought, the biomass of TuYV-infected plants was further reduced by up to 71% and 65%, respectively. Virus infection also reduced the number of leaves, although water treatment alone did not. Chlorophyll content was higher in water-stressed and terminal drought plants compared to well-watered ones, while virus infection reduced chlorophyll content. The impact of drought and virus infection was more pronounced when plants were under competition.DiscussionGiven the expected increase in prolonged and frequent droughts in many canola-growing regions due to climate change, a significant detrimental effect on canola production due to the combined influence of drought and TuYV is anticipated. This study underscores the need for developing mitigation strategies to protect canola production in a changing climate.

Phenotyping for Effects of Drought Levels in Quinoa Using Remote Sensing Tools

Drought is a principal limiting factor in the production of agricultural crops; however, quinoa possesses certain adaptive and tolerance factors that make it a potentially valuable crop under drought-stress conditions. Within this context, the objective of the present study was to evaluate morphological and physiological changes in ten quinoa genotypes under three irrigation treatments: normal irrigation, drought-stress followed by recovery irrigation, and terminal drought stress. The experiments were conducted at the UNSA Experimental Farm in Majes, Arequipa, Peru. A series of morphological, physiological, and remote measurements were taken, including plant height, dry biomass, leaf area, stomatal density, relative water content, selection indices, chlorophyll content via SPAD, multispectral imaging, and reflectance measurements via spectroradiometry. The results indicated that there were numerous changes under the conditions of terminal drought stress; the yield variables of total dry biomass, leaf area, and plant height were reduced by 69.86%, 62.69%, and 27.16%, respectively; however, under drought stress with recovery irrigation, these changes were less pronounced with a reduction of 21.10%, 27.43%, and 17.87%, respectively, indicating that some genotypes are adapted or tolerant of both water-limiting conditions (Accession 50, Salcedo INIA and Accession 49). Remote sensing tools such as drones and spectroradiometry generated reliable, rapid, and precise data for monitoring stress and phenotyping quinoa and the optimum timing for collecting these data and predicting yield impacts was from 79–89 days after sowing (NDRE and CREDG r Pearson 0.85).

Sweet Immunity in Action: Unlocking Stem Reserves to Improve Yield and Quality. A Potential Key Role for Jasmonic Acid.

Common agronomic practices such as stem topping, side branch removal, and girdling can induce wound priming, mediated by jasmonic acid (JA). Low light conditions during greenhouse tomato production make the leaves more sensitive to the application of exogenous sugar, which is perceived as a "danger" in accordance with the concept of "Sweet Immunity". Consequently, source-sink balances are altered, leading to the remobilization of stem starch reserves and enabling the redirection of more carbon toward developing fruits, thereby increasing tomato yield and fruit quality. Similarities are drawn with the mobilization of fructans following defoliation of fodder grasses (wounding) and the remobilization of fructan and starch reserves under terminal drought and heat stress in wheat and rice (microwounding, cellular leakage). A central role for JA signaling is evident in all of these processes, closely intertwining with sugar signaling pathways. Therefore, JA signaling, associated with wounding and sugar priming events, offers numerous opportunities to alter source-sink balances across a broader spectrum of agricultural and horticultural crops, for instance, through the exogenous application of JA and fructans or a combination. This may entail reconfiguring and reversing phloem connections, potentially leading to an enhanced yield and product quality. Such processes may also disengage the growth-defense trade-off in plants.

Screening New Mungbean Varieties for Terminal Drought Tolerance

Rainfed mungbean crops in Queensland Australia frequently experience terminal drought (drought stress in the final stages of reproductive development), highlighting the importance of drought-tolerant varieties for sustainable mungbean production. Given there is limited information on the relative drought tolerance of current mungbean varieties in Australia, the study of genetic variations and mechanisms of drought tolerance in summer mungbean can provide a basis for developing drought-tolerant mungbean varieties. This study evaluated the physiological, biochemical, and phenological traits underpinning yield attributes associated with drought tolerance in selected mungbean varieties. Four new mungbean varieties (AVTMB#1 to 4) and the Australian commercial line (Jade-AU) were grown in tall (75 cm) polyvinyl chloride (PVC) lysimeters where drought stress was imposed at the early flowering stage (R1) and maintained until maturity. Drought stress significantly impacted all the varieties. Averaged across all the varieties, drought stress was associated with a reduction in stomatal conductance (gs) and photosynthetic rate (Asat) by 78% and 86%, respectively, compared to well-watered plants. Internal carbon dioxide concentration (Ci), the effective quantum yield of photosystem II (ΦPSII) and maximum light-use efficiency of light-acclimated photosystem II (PSII) centres (Fv’/Fm’) were also decreased, while excitation pressure (1-qP) increased with drought treatment. A positive correlation (r = 0.60) existed between seed yield and ΦPSII assessed at R1, while a weak correlation with Fv’/Fm’ (r = 0.24) was observed. Excitation pressure (1-qP) at the R1 stage was negatively correlated with seed yield (r = −0.66). Therefore, leaf fluorescence measures, viz., 1-qP and ΦPSII, were recommended for use in screening mungbean varieties for drought tolerance. The varieties, AVTMB#1 and AVTMB#4, respectively achieved 39 and 38% greater seed yields relative to the commercial variety, Jade-AU, under terminal drought conditions.

Stable hydrogen isotope evidence of late-Holocene precipitation variability on the Caribbean slope of the Cordillera Central, Costa Rica

In Central America and the Caribbean, periods of increased aridity that correspond to the Terminal Classic Drought (TCD; 1200–850 cal yr BP) and the Little Ice Age (LIA; 500–100 cal yr BP) have been documented in many paleoclimate records. Compound-specific hydrogen (δDalkane) and carbon (δ13Calkane) isotopic compositions of n-alkanes in lake sediment can be used to interpret changes in paleoprecipitation and terrestrial paleovegetation, respectively. To assess the climate forcing mechanisms that drove the TCD and LIA, we established a multidecadal to centennial-scale late-Holocene reconstruction of precipitation variability and vegetation change at mid-elevation on the Caribbean slope of Costa Rica, developed from new δDalkane, δ13Calkane, and geochemical analyses and previous pollen and microscopic charcoal analyses from a sediment core from Laguna María Aguilar. Laguna María Aguilar is a freshwater lake located at 770 m elevation on the Caribbean slope of the Cordillera Central. During the TCD, δDalkane data for María Aguilar indicate relatively wet conditions compared to the mean δDalkane value for the entire record. Other proxy records for the TCD indicate that the Pacific slope of Costa Rica and sites above 3400 m near the continental divide experienced generally drier conditions than mid- and low-elevations on the Caribbean slope. We conclude that the TCD may have been driven by both Pacific and Atlantic climate-forcing mechanisms. During the LIA, the Laguna María Aguilar δDalkane record indicates an increase in hydroclimate variability, with some of the highest recorded δDalkane values (driest conditions) during the earliest portions of the LIA, but conditions were not persistently dry for the entirety of the LIA. Based on regional paleoclimate records overall, the LIA drought appears to be more clearly expressed on the Caribbean slope than on the Pacific slope of Costa Rica, indicating that the LIA was perhaps driven primarily by Atlantic Ocean conditions and climate dynamics.

Sorghum landraces perform better than a commonly used cultivar under terminal drought, especially on sandy soil

Landraces of sorghum [Sorghum bicolor (L.) Moench] have a high potential for drought adaptations to increasingly extreme climates. We investigated the performance of five sorghum genotypes (four landraces and one commonly grown elite line) under water-limited conditions. Plants were grown until maturity in field-like columns on soils of four textures (silty clay, sandy loam, loamy sand, sand), which were dried during flowering stage down to 30 % usable field capacity. Plant transpiration, physiological characteristics, and yield were measured. For most of the measured parameters, the interaction between genotypes and soils was statistically significant. Alongside the gradient in available water between soils, plants had the highest total transpiration, transpiration efficiency (TE), harvest index (HI), and nutrient uptake in silty clay, steadily reduced towards soils with higher sand content. Especially in sandy soil, all measured plant performance parameters were significantly reduced compared to the other soils. There was a significant negative relationship between later flowering time and HI. While the elite cultivar M35–1 showed the highest TE, it suffered from late flowering and yield loss on all soils, especially when growing on sandy soil. The landraces IS 29914 and IS 8348 had a stable HI irrespective of their lowest TE. The shorter the plant, the better it coped with water and nutrient limitation and high transpiration efficiency was not connected to water conservation. The study overall emphasizes the high potential of sorghum landraces to overcome more extreme droughts as imposed by climate change. It also underlines the importance and strong interaction effect of soil texture on plant performance and transpiration efficiency, which is crucial to be considered in crop production. This outlines that specifically regions with sandy soils, characterized by low water-holding capacities, need genotypes that efficiently utilize the limited available water and nutrient resources – a genetic potential hidden in many landraces.

Integrating high-throughput phenotyping and genome-wide association studies for enhanced drought resistance and yield prediction in wheat.

Drought, especially terminal drought, severely limits wheat growth and yield. Understanding the complex mechanisms behind the drought response in wheat is essential for developing drought-resistant varieties. This study aimed to dissect the genetic architecture and high-yielding wheat ideotypes under terminal drought. An automated high-throughput phenotyping platform was used to examine 28 392 image-based digital traits (i-traits) under different drought conditions during the flowering stage of a natural wheat population. Of the i-traits examined, 17 073 were identified as drought-related. A genome-wide association study (GWAS) identified 5320 drought-related significant single-nucleotide polymorphisms (SNPs) and 27 SNP clusters. A notable hotspot region controlling wheat drought tolerance was discovered, in which TaPP2C6 was shown to be an important negative regulator of the drought response. The tapp2c6 knockout lines exhibited enhanced drought resistance without a yield penalty. A haplotype analysis revealed a favored allele of TaPP2C6 that was significantly correlated with drought resistance, affirming its potential value in wheat breeding programs. We developed an advanced prediction model for wheat yield and drought resistance using 24 i-traits analyzed by machine learning. In summary, this study provides comprehensive insights into the high-yielding ideotype and an approach for the rapid breeding of drought-resistant wheat.

Assessing the impact of early and terminal droughts on root growth, grain yield and yield stability in old and modern wheat cultivars on the Loess Plateau

Understanding changes in root traits of high-yielding genotypes that consistently perform during different drought periods is crucial for improving wheat production and yield stability. A 2-year field trial and a pot experiment were conducted to determine the response of root growth and grain yield to early and terminal droughts in old and modern cultivars (FC3: 1960s and CH1: 2010s) under rainfed and irrigated conditions in the field. Rainfed wheat faced terminal drought in 2015–2016 and early drought in 2016–2017. Plants in the pot experiment were exposed to terminal drought, early drought, and well-watered. Both field and pot experiments showed higher grain yield in modern cultivar CH1 compared to FC3. Early and terminal droughts reduced grain yield in both cultivars, with a greater reduction in FC3. CH1 exhibited higher yield stability under drought conditions and experienced less reduction in early drought. Compared to FC3, CH1 produced more root biomass in the early growth stage. At anthesis, CH1 had significantly lower root biomass and root length density in the topsoil layer (00.2 m) and higher in the subsoil layer (0.21.0 m) than FC3, respectively. At maturity, the retention rate of subsoil root biomass in CH1 was higher, especially under early drought (80.2 % in field and 93.9 % in pot experiments). Both cultivars consumed similar seasonal water use, but CH1 reduced pre-anthesis water use and consumed more water after anthesis. This study indicates that modern cultivar had vigorous root growth at early stage. A higher proportion of root biomass preserved in deep soil after anthesis enhanced post-anthesis water use and photosynthetic rate, improved post-anthesis dry matter accumulation, and thus resulted in higher thousand kernel weight. These factors ensure higher yield and yield stability under both early and terminal drought stress.

Supplemental Sodium Nitroprusside and Spermidine Regulate Water Balance and Chlorophyll Pigments to Improve Sunflower Yield under Terminal Drought.

Drought is an inevitable environmental stress that drastically hampers the growth, productivity, and quality of food crops. Exogenous sodium nitroprusside and spermidine have decisive functions in the growth enhancement of plants; nevertheless, their specific role in mediating stress responses to improve drought tolerance in sunflowers at the reproductive stage (terminal drought) remains largely unknown. In the present study, we explored the positive effects of sodium nitroprusside and spermidine on physiological responses to increase in sunflower yield during periods of terminal drought. Initially, various doses (50, 100, 150, 200, 400 μM) for each sodium nitroprusside or spermidine were foliar sprayed to improve water content, chlorophylls, and biomass accumulation in sunflower seedlings under control (100% FC) and drought (60% FC) conditions. Optimized rates (100 μM for sodium nitroprusside) and (100 μM for spermidine) were further tested alone and in combination to assess drought tolerance potential and their ultimate impact on yield under drought stress. Drought exposure caused a marked reduction in relative water content (26%) and chlorophyll a (31%) and b (35%) contents; however, sodium nitroprusside and spermidine at 100 μM significantly improved the growth of sunflower (13%). Furthermore, combined use of sodium nitroprusside and spermidine at 100 + 100 μM markedly improved the achenes per head (16%), 1000-achene weight (14%), and ultimately grain (28%) and oil (21%) yields of sunflowers under drought stress. A strong association was found between the 1000-achene weight and the achene yield of sunflower. Hence, combined sodium nitroprusside and spermidine upregulate water balance and chlorophyll contents to increase sunflower yield under terminal drought.

Delineation of loci governing an extra-earliness trait in lentil (Lens culinaris Medik.) using the QTL-Seq approach.

Developing early maturing lentil has the potential to minimize yield losses, mainly during terminal drought. Whole-genome resequencing (WGRS) based QTL-seq identified the loci governing earliness in lentil. The genetic analysis for maturity duration provided a good fit to 3:1 segregation (F2), indicating earliness as a recessive trait. WGRS of Globe Mutant (late parent), late-flowering, and early-flowering bulks (from RILs) has generated 1124.57, 1052.24 million raw and clean reads, respectively. The QTL-Seq identified three QTLs (LcqDTF3.1, LcqDTF3.2, and LcqDTF3.3) on chromosome 3 having 246244 SNPs and 15577 insertions/deletions (InDels) and 13 flowering pathway genes. Of these, 11 exhibited sequence variations between bulks and validation (qPCR) revealed a significant difference in the expression of nine candidate genes (LcGA20oxG, LcFRI, LcLFY, LcSPL13a, Lcu.2RBY.3g060720, Lcu.2RBY.3g062540, Lcu.2RBY.3g062760, LcELF3a, and LcEMF1). Interestingly, the LcELF3a gene showed significantly higher expression in late-flowering genotype and exhibited substantial involvement in promoting lateness. Subsequently, an InDel marker (I-SP-383.9; LcELF3a gene) developed from LcqDTF3.2 QTL region showed 82.35% PVE (phenotypic variation explained) for earliness. The cloning, sequencing, and comparative analysis of the LcELF3a gene from both parents revealed 23 SNPs and InDels. Interestingly, a 52 bp deletion was recorded in the LcELF3a gene of L4775, predicted to cause premature termination of protein synthesis after 4 missense amino acids beyond the 351st amino acid due to the frameshift during translation. The identified InDel marker holds significant potential for breeding early maturing lentil varieties.

Precision phenotyping of a barley diversity set reveals distinct drought response strategies.

Plants exhibit an array of drought responses and adaptations, where the trade-off between water loss and CO2 uptake for growth is mediated by regulation of stomatal aperture in response to soil water content (SWC), among other factors. For crop yield stability, the question is how drought timing and response patterns relate to post-drought growth resilience and vigor. We earlier identified, in a few reference varieties of barley that differed by the SWC at which transpiration was curtailed, two divergent water use strategies: water-saving ("isohydric") and water-spending ("anisohydric"). We proposed that an isohydric strategy may reduce risk from spring droughts in climates where the probability of precipitation increases during the growing season, whereas the anisohydric is consistent with environments having terminal droughts, or with those where dry periods are short and not seasonally progressive. Here, we have examined drought response physiology in an 81-line barley (Hordeum vulgare L.) diversity set that spans 20th century European breeding and identified several lines with a third, dynamic strategy. We found a strong positive correlation between vigor and transpiration, the dynamic group being highest for both. However, these lines curtailed daily transpiration at a higher SWC than the isohydric group. While the dynamic lines, particularly cv Hydrogen and Baronesse, were not the most resilient in terms of restoring initial growth rates, their strong initial vigor and high return to initial transpiration rates meant that their growth nevertheless surpassed more resilient lines during recovery from drought. The results will be of use for defining barley physiological ideotypes suited to future climate scenarios.

Three-dimensional image analysis specifies the root distribution for drought avoidance in the early growth stage of rice.

Root system architecture (RSA) plays a key role in plant adaptation to drought because deep rooting enables better water uptake than shallow rooting under terminal drought. Understanding RSA during early plant development is essential for improving crop yields, as early drought can affect subsequent shoot growth. Herein, we demonstrate that root distribution in the topsoil significantly impacts shoot growth during the early stages of rice (Oryza sativa) development under drought, as assessed through three-dimensional (3D) image analysis. We used 109 F12 recombinant inbred lines (RILs) obtained from a cross between shallow-rooting lowland rice and deep-rooting upland rice, representing a population with diverse RSA. We applied a moderate drought during the early development of rice grown in a plant pot (25cm height) by stopping irrigation 14 days after sowing (DAS). Time-series RSA at 14, 21, and 28 DAS was visualized by X-ray computed tomography, and subsequently compared between drought and well-watered conditions. Following this analysis, we further investigated drought-avoidant RSA by testing 20 randomly selected RILs under drought conditions. We inferred the root location that most influences shoot growth using a hierarchical Bayes approach: the root segment depth, which positively impacted shoot growth, ranged between 1.7-3.4cm under drought conditions and between 0.0-1.7cm under well-watered conditions. Drought-avoidant RILs had a higher root density in the lower layers of the topsoil compared to the others. Fine classification of soil layers using 3D image analysis revealed that increasing root density in the lower layers of the topsoil, rather than in the subsoil, is advantageous for drought avoidance during the early growth stage of rice.

Model‐based multi‐genotype characterization of drought stress Target Population of Environments for the common bean in East Africa

AbstractEfforts toward the development of common bean varieties that can perform better under the drought conditions in Eastern Africa are constrained by significant genotype–environment–management (G × E × M) interactions. To address this, an attempt was made previously to assess drought stress for Eastern Africa using the Target Population of Environments (TPE) approach, albeit by using a single cultivar. Here, we extend earlier TPE work with a larger sample of representative genotypes from East Africa including commercial and breeding lines. By using a larger genotype pool, we are able to (1) assess the extent to which TPEs identified vary across genotypes (i.e., generality of the TPEs) and (2) identify best‐performing genotypes for the various environments identified. To perform the analyses, we used the CROPGRO‐DRYBEAN cropping system model available in the Decision Support System for Agrotechnology Transfer (DSSAT) v4.7 calibrated and evaluated from field trials in Africa and Colombia with 10 genotypes. Our findings indicate that despite some level of genotype‐related variation, the dominant drought stress patterns, and their priorities—drought stress‐free conditions remain the dominant TPE, followed by terminal drought stress—remain unaltered. Moreover, we find that it is possible to reduce the extent and intensity of drought stress in various TPEs by adequately targeting genotypes from the pool considered herein. Importantly, the genotype characteristics for stress‐free, extreme terminal drought and moderate terminal drought stress are significantly different, confirming a differentiated breeding strategy is required between the TPEs. The findings from this study are useful for the modernization of the bean breeding programs in Africa.

Does late water deficit induce root growth or senescence in wheat?

In crops like wheat, terminal drought is one of the principal stress factors limiting productivity in rain-fed systems. However, little is known about root development after heading, when water uptake can be critical to wheat crops. The impact of water-stress on root growth was investigated in two wheat cultivars, Scout and Mace, under well-watered and post-anthesis water stress in three experiments. Plants were grown outside in 1.5-m long pots at a density similar to local recommended farming practice. Differences in root development were observed between genotypes, especially for water stress conditions under which Scout developed and maintained a larger root system than Mace. While under well-watered conditions both genotypes had shallow roots that appeared to senesce after heading, a moderate water stress stimulated shallow-root growth in Scout but accelerated senescence in Mace. For deep roots, post-heading biomass growth was observed for both genotypes in well-watered conditions, while under moderate water stress, only Scout maintained net growth as Mace deep roots senesced. Water stress of severe intensity affected both genotypes similarly, with root senescence at all depths. Senescence was also observed above ground. Under well-watered conditions, Scout retained leaf greenness (i.e. stay-green phenotype) for slightly longer than Mace. The difference between genotypes accentuated under moderate water stress, with rapid post-anthesis leaf senescence in Mace while Scout leaf greenness was affected little if at all by the stress. As an overall result, grain biomass per plant ('yield') was similar in the two genotypes under well-watered conditions, but more affected by a moderate stress in Mace than Scout. The findings from this study will assist improvement in modelling root systems of crop models, development of relevant phenotyping methods and selection of cultivars with better adaptation to drought.

Exogenous Application of β-aminobutyric Acid Improved Water Relations, Membrane Stability Index, and Achene Yield in Sunflower Hybrids Under Terminal Drought Stress

Exogenous Application of β-aminobutyric Acid Improved Water Relations, Membrane Stability Index, and Achene Yield in Sunflower Hybrids Under Terminal Drought Stress