Terminal Drought Research Articles

Early-Generation Evaluation of Marker-Assisted Transfer of bmr6 and bmr12 Alleles into Sweet and High-biomass Sorghum

The effects of transferring brown midrib (bmr) alleles in sweet and high biomass sorghums (SS/HBM) are not fully understood, and available works produced mixed results depending upon the genetic background of the recurrent parent used. Early-generation testing of the effects of the two mutations in the background of the recurrent parents can help predict the final products and make appropriate early go/no-go breeding decisions, yet, this information is missing. The present study was therefore carried out to reduce these gaps. Marker-assisted transfer of the bmr6 and bmr12 was performed using four (SSV84, ICSB474, ICSV18003, ICSV100324) SS and one (ICSV15024) HBM wild type (WT) lines as recurrent parents, and one bmr6 (N609) and two bmr12 (ICSV101039 and N600) lines as donor parents. Crossing and backcrossing techniques were used to transfer the bmr alleles to develop BC2F2 and F3 populations. Kompetitive allele-specific PCR (KASP) marker genotyping assays were performed and implemented for the indirect selection of the bmr transfer in F1 and BC_F1 populations. While the bmr6 markers were polymorphic, the bmr12 markers were monomorphic. The successful bmr6 transfer was therefore confirmed by markers in F1 and BC_F1, while for bmr12 the transfer was confirmed after segregation assessment in F2 and BC_F2 populations. The transfer of bmr12 improved the cellulose content relative to WT genotypes, and bmr12 populations were shorter-statured relative to bmr6 individuals, meaning that bmr12 gene can be considered in sorghum breeding to boost 2G bioethanol bioconversion and to control lodging, and hence favouring mechanical harvesting and limiting yield losses. The observed earliness in the bmr lines is an attractive trait conferring adaptation in the drylands, particularly in the world’s semi-arid tropics characterized by terminal drought stress. Both bmr alleles did not show any negative trade-offs relative to the must-have sorghum plant characteristics, implying that they can safely be deployed in sorghum breeding for bioenergy production purposes. The observed superior bmr lines with farmer-preferred phenotypic acceptance are candidates not only for advancement in breeding pipelines but also for subsequent pyramiding bmr6 and bmr12 in the same genetic background, further improving the bmr-conferred benefits. The successfully used molecular markers will be uploaded in the public domain and can help breed sorghum products other than SS/HBM such as high-quality forage sorghums.

Barley awn dimensions and barbs changes under terminal drought stress and its relation to grain yield and carbon isotope discrimination

Barley awn dimensions and barbs changes under terminal drought stress and its relation to grain yield and carbon isotope discrimination

Agronomic adaptations to heat stress: sowing summer crops early in late winter.

Abstract CONTEXT: Summer 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, though it might require sowing cold sensitive summer crops early in late winter 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. OBJECTIVE: Here we quantify the likely benefits and trade-offs of sowing sorghum, a summer cereal, early in late winter as an adaptation to the increased frequency and intensity of heat and water stresses during flowering and grain filling. METHODS: Two seasons of multi-environment ( n =32) genotype by management trials were conducted across sub-tropical and semi-arid regions of eastern Australia. Environments (E) consisted of the combination of seasons, 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 co-variates, and measured crop traits. RESULTS: The 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, that varied between <0.5 to about 10t ha -1 , this translated into a ~8-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 to 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 yield loss when all sites and seasons are included in the analysis, and between 1-2 t ha -1 yield gains when the hottest sites and seasons are considered separately. The likelihood and severity of terminal drought stresses was also reduced with late winter and early spring sowings, improving yield quality parameters. CONCLUSIONS: Early 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 seasons, and a transfer of water use to grain filling stages that resulted in increased grain yield and improved grain quality parameters. IMPLICATIONS: Agronomic adaptations offer 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 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.

Holocene hydroclimate in highland Costa Rica: new evidence from hydrogen and carbon isotopes in n‐alkanes of terrestrial leaf waxes in a 10 000‐year sediment profile

ABSTRACTWe conducted compound‐specific stable hydrogen (δD) and carbon (δ13C) isotope analysis on n‐alkanes from terrestrial leaf waxes preserved in a 10 000‐year sediment profile from Lago de las Morrenas 1 (9.4925° N, 83.4848° W, 3480 m), a glacial lake on the Chirripó massif of the Cordillera de Talamanca in Costa Rica. Our results demonstrate millennial‐scale variations in hydroclimate across the Holocene, with drier than average conditions in the highlands during the early Holocene, but with gradually increasing precipitation; mesic conditions during the middle Holocene with a gradual drying trend; and highly variable conditions during the late Holocene. This general pattern is punctuated by several centennial‐scale manifestations of global climate events, including dry conditions during the 8200, 5200 and 4200 cal a bp events and the Terminal Classic Drought (1200–850 cal a bp). Our δ13C analyses demonstrate that carbon isotope signals are responding to changes in hydroclimate at the site and reinforce prior interpretations of a stable páramo plant community that established following deglaciation and persisted throughout the Holocene. The shifts in hydroclimate inferred from analyses of n‐alkanes in Lago de las Morrenas 1 sediments show correspondence with charcoal records in multiple lakes, with fires most common during drier intervals.

Consistent geographical gradient of water use efficiency evidences local adaptations to drought across the complete latitudinal distribution of Quercus suber

RationaleIncreased aridity has led to drought-induced mortality or loss of health for many tree species. Of particular interest is to explore the response of the Mediterranean tree species cork oak (Quercus suber) to this declining phenomenon due to its severity and its large implications for the local economy and the provision of highly relevant ecosystem services. ApproachTo assess geographical variations in the response to water stress, we analyzed under controlled conditions the effects of four watering levels and the resistance to a terminal drought on seedlings collected from nine populations covering the complete latitudinal distribution of the species. We explored the response of a number of physiological traits and markers of oxidative stress potentially related with drought-resistance. FindingsWe found a highly plastic phenotypic response of most variables to water availability and a large influence of seedlings provenance in the drought-resistance strategies. Although the oxidative stress enzymes ruled out differential water stress throughout the distribution range, we found that seedlings from the southern limit are less vulnerable to drought than other populations. Southern seedlings adapted to xeric conditions displayed a larger sensitivity of stomata to changes in soil humidity and a higher water use efficiency. These physiological local adaptations coupled with larger acorn size in the southern populations, resulted in larger aboveground biomass and higher drought resistance at the southern distribution edge. ConclusionsOur data suggest that this evergreen tree species relies on its physiological plasticity to develop adaptative features that allows it to overcome water shortage and that southern populations hold genetic diversity that could improve the specie´s adaptation in the forecasted drought context with relevant implications for conservation programs.

Yield, lodging, and water use efficiency of Tef [Eragrostis tef (zucc) Trotter] in response to carbonized rice husk application under variable moisture condition.

Terminal drought and lodging are among the major yield-limiting factors for tef cultivation in the highly weathered soils of the Ethiopian highlands. Therefore, a study was conducted to assess the yield and lodging responses of tef to varying moisture depletion levels (MDL) and the application of carbonized rice husk (CRH). A two-year 4×4 factorial experiment with 20, 35, 55, and 75% MDL and 0, 291, 582, and 873 kg ha-1 of CRH was laid out in a split-plot design, with each treatment replicated four times. The pooled mean ANOVA showed leaf area index (LAI) and lodging index (LI) were not significantly influenced by the main and interaction effects of MDL and CRH (p > 0.05); however, individual year ANOVA showed that both LI and LAI were influenced by the interaction of MDL and CRH (p<0.05) in 2021 and 2022, respectively. The lowest LI (19.7%) was obtained from the application of 873 kg CRH ha-1, followed by 20.6% from 582 kg CRH ha-1 in 2022. A 20.7% LI reduction was recorded in 2022 compared to 2021. Tef plant height and number of tillers per plant were significantly affected by MDL at p<0.05 and p<0.01, respectively, but not by CRH and its interaction with MDL. The effect of MDL was significant on tef HI (p<0.01) but not on traits including grain yield, straw yield, and water use efficiency. In conclusion, the pooled mean analysis result showed that, though there was no significant difference in yield, tef irrigated at 55% MDL provided a maximum HI of 33.8%, which was 6.21% more than the control, and increased the level of lodging resistance with a LI of 31.9%, which was next to 75% MDL with 582 kg ha-1 CRH. The authors suggested that the research should further be verified across locations for wide application.

Organic seed priming with curtailed seed rate compensated wheat grains productivity by upgrading anti-oxidant status against terminal drought at flowering and milking

Terminal irrigation drought stress is one of the most drastic abiotic stress to diminish the wheat crop development and grains yield in arid regions of the world. The use of moringa leaf extract (MLE30) via seed priming technique is investigated as an organic and sustainable approach for the mitigation of drought stress along with curtailed seed rate in wheat crop. The study investigated the interaction of organic seed priming: control (dry seeds), hydro-priming, MLE30-priming, seed rate: recommended @ 125 kg ha−1, curtailed @ 25 kg ha−1, and terminal irrigation drought (TID): normal irrigation, mild-TID, severe-TID in wheat crop at agronomic research station, Bahawalpur, Pakistan during the wheat winter season of 2021–2022 and 2022–2023. The application of organic MLE30-priming with curtailed seed rate enhanced antioxidant enzyme activity especially total soluble proteins by 15%, superoxide dismutase by 68%, peroxidase by 16%, catalase by 70%, ascorbic acid by 17% and total protein contents by 91% under severe-TID. Yield and yield-related morphological attributes performed better in MLE30-priming as compared to hydro-priming. An effective trend was observed in the plant's chlorophyll contents, K+, and water use efficiency after being treated with MLE30-priming followed by hydro-priming under curtailed seed rate. The higher benefit–cost ratio and net income return were observed with the application of MLE30-priming with curtailed seed rate under mild-TID and severe-TID. So, it is suggested to adopt the MLE30-priming technique along with a curtailed seed rate for improving the crop establishment, stress regulation, and economic return under limited availability of irrigation water. The project findings recommended that the application of exogenous application of organic MLE30-seed priming favored and compensated the maximum wheat grains production under curtailed seed rate @ 25 kg ha−1 and induced terminal drought stress at flowering and milking conditions.

Cacao Water Use, Canopy Characteristics and Yield as Affected by Irrigation and Shade in a Rainforest Zone of Nigeria

There has been need to improve crop and water productivity considering the need for agricultural intensification in the realm of increasing water scarcity and drought in several regions of the world. Information is limited about the effects of irrigation on cacao water use (evapotranspiration) especially, during the terminal drought situation of the dry season in the rainforest agroecology of Nigeria. The effects of shade and dry season irrigation was examined on tree water use, canopy characteristics and pod and bean yields of cacao (Theobroma cacao L.). Treatments were 2 by 2 factorial combinations of irrigation intervals (5 and 10 days) and shade and no-shade (open sun) laid out in a split-plot scheme with 3 replications. Shade regimes constituted the main plots and irrigation intervals the sub-plot treatments. Irrigation water was delivered at 5-and 10-day intervals on emitter lines using gravity drip system. Irrigation combinations affected cacao canopy characteristics (leaf area index) and light integrals (photosynthetic active radiation (PAR) and canopy light attenuation (extinction coefficient, k) within the cacao field. The unshaded-irrigation had higher proportion of incident radiation (I) transmitted (Io) through the canopy (IO/I), PAR intensity, and canopy extinction coefficients (k) compared with the shaded plus irrigations at 5-and 10-day intervals. Cumulative seasonal irrigation (12119 and 8483 mm), soil moisture contents (19.6 to 13.7 %) and cacao water use (ETc: 3.8 and 3.2 mm.day-1) differed for the respective 5- and 10-day irrigation intervals. The unshaded plus 5- and 10-day irrigation intervals out-yielded the shaded-irrigation combinations for number and weights of pods and beans. Pod and bean yields were significantly different under irrigation treatments, the 5-day irrigation produced greater number and heavier pods and beans compared with the 10-day irrigation. For the shade-irrigation combinations the range of values were: weights of pods (78000 to 6000 kg/plant), beans (4.8 to 3.2 t/ha) and water productivities: Irrigation WUE: 0.45 to 0.33 mm/kg/ha) and ET WUE: 0.11 to 0.09 mm/kg/ha). The shade-irrigation strategy enhanced cacao leaf area index, water use and bean yields and ameliorated climate stress.

Phenotypic variability for early drought stress resistance in tetraploid wheat accessions correlates with terminal drought performance

AbstractDurum wheat (Triticum durum Desf.) is a fundamental staple food for the countries of the Mediterranean basin. Climate change is predicted to cause a trend of increasing drought severity in this region in the near future, necessitating the improvement of durum wheat's resilience to drought stress. Using polyethylene glycol to simulate water scarcity, early vigour parameters in germinating seeds are quickly, easily and affordably assessed. Many screenings, however, only consider the seedling stage; consequently, genotypes identified as promising for cultivation in drought scenarios, may not show such features if drought appears in later phenological phases, as happens in Mediterranean climatic areas, generally prone to terminal drought. The correlation between drought stress resistance during the seedling stage (early vigour) and later stages in the life cycle is elusive due to the lack of scientific efforts. Here we used polyethylene glycol screening to classify fifty‐five tetraploid wheat accessions into three clusters (susceptible, medium resistant and highly resistant to drought), based on morpho‐physiological traits. These accessions included durum wheat cultivars and landraces, as well as ancestors like durum emmer wheat and wild emmer wheat. The results of the screenings were combined with subsequent pot experiments using nine randomly selected accessions, imposing terminal drought, and evaluating their performance. Principal component analysis was performed on data for net photosynthesis, stomatal conductance, transpiration and grain yield. Notably, the genotypes that performed best in the pot experiments were also those that performed well in the screening. Highly resistant candidates had in fact higher physiological and performance parameters than susceptible candidates. In summary, polyethylene glycol screening of germinating seeds resulted to be suitable to predictively evaluate drought resistance in tetraploid wheat accessions under terminal drought conditions, typical of Mediterranean climate zones. The reported data, thus evidence of how this inexpensive and simple method might be efficiently applied for large‐scale phenotyping.

Nutrient uptake and nutrient use efficiency of Valencia peanut genotypes with different levels of drought tolerance under terminal drought

Selection of suitable peanut genotypes with resistance to drought is an important strategy to combat problems of drought. This study aimed to investigate nutrient uptake and nutrient use efficiencies of Valencia peanut genotypes in response to terminal drought. A pot experiment was conducted in a factorial randomized complete block design with 4 replications. Factor A consisted of two soil water regimes (field capacity and 1/3 available water), and ten Valencia peanut genotypes were assigned as factor B. Macronutrient uptakes and nutrient use efficiencies (NUE) were examined; drought reduced nutrient uptakes, NUE for biomass and NUE for pod yield. Unique behaviors of some tested Valencia peanut genotypes on given traits were found. Genotype PI536121 had the highest K, Ca and Mg uptakes, while two genotypes ICG10890 and ICG10092 showed the highest NUE for biomass and pod yield. Genotype ICG14127 performed well regarding K, Ca and Mg uptakes and NUE for pod yield. Total nutrient uptakes of N, P, K, Ca and Mg were significantly positively correlated with biomass and pod yield (r = 0.48**–0.76**), whereas the number of seeds per pod and 100-seed weight were positively correlated with total nutrient uptakes of N, K, Ca and Mg (r = 0.23*–0.47**). Three tested genotypes ICG10092, ICG10890 and ICG14127 are promising genetic sources for further improvements of Valencia peanuts for drought tolerance.

Selection of superior bread wheat genotypes based on grain yield, protein, iron and zinc contents under normal irrigation and terminal drought stress conditions

The selection of high-yielding genotypes with high micronutrient and protein contents can play a major role in reducing protein-energy and micronutrient malnutrition. In this study, 20 bread wheat genotypes were examined under normal irrigation and end-season water deficit stress conditions. The grain yield (GY), thousand-kernel weight (TKW), protein (PR), iron (Fe), and zinc (Zn) contents were determined. The data were analyzed using the genotype by yield*trait (GYT) biplot method, and the superiority index was calculated from the integration of all yield-trait combinations. According to the results, the polygon view of GYT biplot under normal irrigation conditions showed that G20 was the best genotype in combining GY with TKW and PR contents. The G19 was the best genotype in combining GY with Fe and Zn contents. Under end-season water deficit stress, G20 was the best genotype in combining GY with TKW and Fe content. In addition, the G6 was the best genotype in combining GY with PR and Zn. The average tester coordinate (ATC) view of GYT biplot showed that there is not any genotype that was higher than the average yield-trait combination. However, G20 and G19 were relatively superior to other genotypes in this study. According to the superiority index, G20 and G19 genotypes were superior. Based on our results, G20, G19, and G6 genotypes were the best genotypes in combining GY with all or some evaluated traits, in two conditions. Therefore, they can be considered in genetic biofortification programs or variety introduction.

High-throughput phenotyping for terminal drought stress in chickpea (Cicer arietinum L.)

Most chickpea cultivation occurs in rainfed environments, where unpredictable rainfall leads to drought stress, consequently reducing growth and productivity. Fast and robust image-based screening methods would greatly facilitate drought tolerance research. In this study, an experiment was conducted in a climate-controlled environment, using radio frequency-enabled ID (RFID) tagged plant carriers on Lemnatec's high-throughput phenotyping platform. The agro-physiological characteristics of six chickpea genotypes under drought stress conditions imposed at the early podding stage were explored. Using non-destructive techniques, including Red, Green, and, Blue (RGB), Near-Infrared (NIR), Infrared (IR), and chlorophyll fluorescence (Fv/Fm) imaging, data was captured at various stages of drought stress, quantified as the fraction of transpirable soil water, using LemnaGrid software. Traits such as plant phenology, yield, yield components, and physiological parameters (e.g., leaf temperature and photosynthetic characteristics) for both drought-stressed and well-watered plants were recorded manually. Seed yields ranged from 9.9 to 18.1 g plant−1 under WW, and 2.6–13.7 g plant−1 under DS. DS decreased yield the most in ICC 1882 and RSG 888 (73.7%) and the least in ICC 4958 (24.3%) relative to WW. Our findings revealed significant genotype × water treatment interactions for all manually recorded traits. Moreover, strong positive correlations were observed between manually recorded and image-based traits, i.e., between aboveground dry weight and projected area, aboveground dry weight and convex hull area, plant height and caliper length, photosynthetic rate, and chlorophyll fluorescence, stomatal conductance and NIR reflectance, IR thermometer temperature and IR imaging temperature. Notably, the strong positive correlations between NIR reflectance and stomatal conductance, and between chlorophyll fluorescence and photosynthesis, underscore the immense potential of harnessing image-based screening methods in breeding programs to enhance drought tolerance.

Yield improvement with antitranspirant application in droughted wheat associated with both reduced transpiration and reduced abscisic acid

AbstractIn Mediterranean-type climates, terminal drought induces grain yield losses in wheat. Antitranspirants can reduce the impacts of terminal drought and improve yield, but the mechanisms involved are not fully understood. Among other impacts, drought elevates endogenous abscisic acid (ABA) concentration. Here, the effectiveness of a film antitranspirant (di-1-p-menthene) was studied in relation to plant water status and spike ABA. The objective was to determine whether drought amelioration with di-1-p-menthene was solely mediated through a reduction in ABA by comparing its effects to that of fluridone (an ABA inhibitor). The treatments were assessed in a randomized complete block design in two field experiments in spring and summer of 2020, with six and eight replicate blocks, respectively, at Harper Adams University, UK, to compare their effects on spike ABA, gas exchange and agronomic traits under progressive drought conditions. Di-1-p-menthene was applied at 1 l/ha; and fluridone at 10, 20 and 50 μM concentrations, at flag leaf emergence, growth stage 37 (GS37). Drought increased spike ABA and downregulated photosynthesis. Di-1-p-menthene and fluridone at some concentrations, reduced spike ABA and photosynthesis. Di-1-p-menthene suppressed transpiration and spike ABA, each by 21% but increased grain yield by 27%. In contrast, although fluridone (at 10 and 50 μM) also reduced spike ABA (by 16%), overall, it did not alter transpiration or grain yield. The results suggest that yield improvement with di-1-p-methene is mediated through mechanisms that involve conservation of plant water linked to reduced transpiration, with inhibition of spike ABA playing a secondary role.

Phenological Variation in Chickpea (Cicer arietinum L.) Varieties through Foliar Application of Cytokinin Analogs and Nutrients under Water Deficit Stress

Chickpea (Cicer arietinum L.), a rainfed crop predominantly grown in temperate and subtropical climates, faces significant challenges in production due to terminal drought stress impacting various phenological stages. This study addresses the challenges posed by terminal drought stress on the phenological stage of chickpea varieties viz., JG 36 and JG 14. The experiment was conducted during the Rabi seasons of 2021-2022 and 2022-2023 at the Experimental Research Farm, Seed Technology Research Unit, JNKVV, Jabalpur (M.P), using a split-split plot design with three replications. This research also investigates the impact of foliar applications of cytokinin analogs viz., Thiourea, Thidiazuron, and Benzyladenine and nutrients viz., ZnSO4 and KCl on chickpea under water deficit stress conditions. The results revealed significant differences in days to pod formation, seed formation, physiological maturity, and harvest maturity among the irrigation levels, varieties, and foliar spray of plant growth regulators and nutrients. Under different irrigation levels, D1 (Irrigation at 30 DAS and flower initiation) exhibited delayed phenological stages of the crop, while D2 (Drought stress at flowering up to physiological maturity) showed an early onset of all the phenological stages. Under water deficit conditions, JG 14 exhibited accelerated maturity beyond its typical early maturation in comparison to well-watered conditions, highlighting the impact of environmental stress on varietal responses. With respect to the application of plant growth regulators and nutrients, treatment T12 (TDZ @ 10 ppm + 1% KCl) significantly delayed pod and seed formation, as well as physiological and harvest maturity as compared to untreated control (T1). Foliar application of TDZ @ 10 ppm + 1% KCl (T12) enhanced seed filling duration by 2.59 days compared to the untreated control. Further investigations are needed to identify the impact of Thidiazuron and KCl in enhancing seed yield and seed weight of chickpea under optimal and sub-optimal soil water conditions, to provide recommendations for chickpea growers.

Effect of Terminal Drought and Biochar Plus N and P on Growth and Fruit Yield of Watermelon (Citrullus vulgaris Schard)

Effect of Terminal Drought and Biochar Plus N and P on Growth and Fruit Yield of Watermelon (Citrullus vulgaris Schard)

Comprehensive Proteomic Analysis of Common Bean (Phaseolus vulgaris L.) Seeds Reveal Shared and Unique Proteins Involved in Terminal Drought Stress Response in Tolerant and Sensitive Genotypes.

This study identified proteomic changes in the seeds of two tolerant (SB-DT3 and SB-DT2) and two sensitive (Merlot and Stampede) common bean genotypes in response to terminal drought stress. Differentially expressed proteins (DEPs) were abundant in the susceptible genotype compared to the tolerant line. DEPs associated with starch biosynthesis, protein-chromophore linkage, and photosynthesis were identified in both genotypes, while a few DEPs and enriched biological pathways exhibited genotype-specific differences. The tolerant genotypes uniquely showed DEPs related to sugar metabolism and plant signaling, while the sensitive genotypes displayed more DEPs involved in plant-pathogen interaction, proteasome function, and carbohydrate metabolism. DEPs linked with chaperone and signal transduction were significantly altered between both genotypes. In summary, our proteomic analysis revealed both conserved and genotype-specific DEPs that could be used as targets in selective breeding and developing drought-tolerant common bean genotypes.

Genomic Selection as an Approach to Select for Reduced Aflatoxin Contamination in Peanut Under Terminal Drought Stress

Pre-harvest aflatoxin contamination (PAC) occurs when the peanut is exposed to severe drought and heat stress prior to harvest. Development of genotypes that are either resistant or limiting to Aspergillus infection and/or that can curtail aflatoxin production is a key objective in peanut breeding. Using SNP markers and phenotype data on aflatoxin resistance collected in previous years, we utilized genomic selection (GS) to study PAC resistance in peanut. The technique was validated in the Florida-07 x GP-NC WS 16 recombinant inbred population by assessing high heritability traits. GS was then deployed to study PAC resistance in the Tifrunner x C76-16 and Florida-07 x C76-16 populations. The resultant models yielded prediction accuracy values of 0.24 and 0.23 which while low, were comparable to the heritability values of 0.31 and 0.1 for each population, respectively. Using genomic estimated breeding values (GEBVs), entries were selected for two drought shelter studies. Manual scoring and multispectral imaging were used to acquire end season drought stress data. Low correlation values (-0.15 for shelter A and 0.32 for shelter B) were observed between the GEBVs and actual end season aflatoxin content. Correlations between visual drought ratings and PAC were also low (0.23 and 0.16 for shelter A and B respectively). While strong inverse correlations were observed between GNDVI and visual drought ratings (-0.74 and -0.73 for shelters A and B respectively), GNDVI did not confer a clear advantage for selection of PAC resistance. Ideally, the use of genome-spanning markers in GS may enable selection for a difficult to phenotype trait like PAC resistance. Although this study did not show clear advantages of the method over conventional selection, it is an important step for implementation of GS and the use of GEBVs for trait selection in peanut.

Physiological, agro-morphological, and germination responses of a worldwide chickpea (Cicer arietinum) collection subjected to drought stress by applying polyethylene glycol (PEG) on germinating seeds and by exposure plants to water restriction at the vegetative stage

Given that agriculture uses considerable quantities of water to meet food requirements, the scarcity of rainfall and the drying up of water tables could compromise agricultural production. Faced with the urgency of a world undergoing demographic change and a current agro-climatic trend marked by low rainfall at the vegetative stage, the sustainability of chickpea production requires new varieties with resilience and adaptation to climatic change. The aim of this study is the selection genotypes that are tolerant to early drought stress and able to avoid terminal drought. To this end, a collection of 159 genotypes was evaluated, using an augmented-RCBD (Randomized Complete Block Designs), in two experiments (drought stress by water restriction and stress imposition by Polyethylene glycol (PEG) application) simulating the effect of drought. Our results show significant genetic variability and a fairly significant genotype effect in both trials. We noted an interesting positive correlation between germination percentage in the presence of PEG and pod and seed production under water stress at the vegetative stage, and these same traits showed strong heritability. 16 genotypes had a germination percentage ≥50% in the 20% PEG treatment. In addition, 18 Desi and 4 Kabuli genotypes performed well in both trials, with good germination percentage, pod and seed production, good canopy coverage, better normalized difference vegetation index, and low to medium wilting. It would therefore make sense to exploit these genotypes in hybridization programs for the creation of pure drought-tolerant lines, and also to evaluate them in different arid and semi-arid regions over several years.

Genome wide association study of Ethiopian barley for terminal drought stress tolerance under field and climate chamber conditions

In order to detect markers for drought stress tolerance, field experiments in Ethiopia were conducted for three years at two naturally drought-prone locations and two optimum moisture locations using 239 Ethiopian barley landraces and 21 barley breeding lines. Furthermore, a climate chamber experiment applying drought stress at different water regimes (70% soil water capacity (WC) for control and 20% WC for drought stress conditions) after flowering was conducted for selected 196 accessions. Results revealed reduced grain biomass by 47% and 80% under field and climate chamber conditions, respectively, as well as significantly (p < 0.05) reduced days to maturity and plant height, in both experimental designs. Based on 10,644 SNP markers, GWAS was conducted to identify marker trait associations (MTA) for drought stress tolerance. For days to maturity, relative chlorophyll content, plant height, number of seeds per spike, thousand kernel weight, and harvest index under field and climate chamber drought stress treatments, 58 significant MTAs were identified. In total, 41.4% of the MTAs were located on chromosome 2H, of which one is very close to the Ppd-H1 flowering locus. These findings underpin the importance of this genome region for drought tolerance. Another MTA on chromosome 1H was detected for days to maturity under field drought stress treatment in the vicinity of the known flowering time ELF3 gene. Additionally, 13 and 3 Ethiopian landraces that tolerate severe and moderate drought stress in climate chamber and field experiments were identified, respectively, using drought indices. The results highlight the tolerance of Ethiopian landraces to different levels of drought stress as well as their potential to be considered in future barley improvement programs.

Resurrected seeds from herbarium specimens reveal rapid evolution of drought resistance in a selfing annual.

Increased aridity and drought associated with climate change are exerting unprecedented selection pressures on plant populations. Whether populations can rapidly adapt, and which life history traits might confer increased fitness under drought, remain outstanding questions. We utilized a resurrection ecology approach, leveraging dormant seeds from herbarium collections to assess whether populations of Plantago patagonica from the semi-arid Colorado Plateau have rapidly evolved in response to approximately ten years of intense drought in the region. We quantified multiple traits associated with drought escape and drought resistance and assessed the survival of ancestors and descendants under simulated drought. Descendant populations displayed a significant shift in resource allocation, in which they invested less in reproductive tissues and relatively more in both above- and below-ground vegetative tissues. Plants with greater leaf biomass survived longer under terminal drought; moreover, even after accounting for the effect of increased leaf biomass, descendant seedlings survived drought longer than their ancestors. Our results document rapid adaptive evolution in response to climate change in a selfing annual and suggest that shifts in tissue allocation strategies may underlie adaptive responses to drought in arid or semi-arid environments. This work also illustrates a novel approach, documenting that under specific circumstances, seeds from herbarium specimens may provide an untapped source of dormant propagules for future resurrection experiments.