Post-anthesis Drought Research Articles

Morphological, Physiological, and Photosynthetic Differences of Tartary Buckwheat Induced by Post-Anthesis Drought.

Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn) is a crop of significant interest due to its nutritional value and resilience to drought conditions. However, drought, particularly following flowering, is a major factor contributing to yield reduction. This research employed two distinct Tartary buckwheat genotypes to investigate the effects of post-anthesis drought on growth and physicochemical characteristics. The study aimed to elucidate the response of Tartary buckwheat to drought stress. The findings indicated that post-anthesis drought adversely impacted the growth, morphology, and biomass accumulation of Tartary buckwheat. Drought stress enhanced the maximum photosynthetic capacity (Fv/Fm) and light protection ability (NPQ) of the 'Xiqiao-2' genotype. In response to drought stress, 'Dingku-1' and 'Xiqiao-2' maintained osmotic balance by accumulating soluble sugars and proline, respectively. Notably, 'Xiqiao-2' exhibited elevated levels of flavonoids and polyphenols in its leaves, which helped mitigate oxidative damage caused by drought. Furthermore, rewatering after a brief drought period significantly improved plant height, stem diameter, and biomass accumulation in 'Dingku-1'. Overall, 'Xiqiao-2' demonstrated greater long-term tolerance to post-anthesis drought, while 'Dingku-1' was less adversely affected by short-term post-anthesis drought.

Split application of phosphorus fertilizer increased wheat grain weight under post-anthesis drought stress by delaying programmed cell death of endosperm

Drought is one of the important factors affecting wheat yield. However, the effect of split application of phosphorus fertilizer on the programmed cell death (PCD) of wheat endosperm cells under different post-anthesis water treatments is still unclear. In this study, three phosphorus fertilization methods (P1, all phosphorus fertilizer was applied at the spring green-up stage; P2, 50 % and 50 % of phosphorus fertilizer were applied at the spring green-up stage and jointing stage, respectively; P3, 40 %, 30 %, and 30 % of phosphorus fertilizer were applied at the spring green-up, jointing, and grain filling stages, respectively) were designed. Besides, two post-anthesis water treatments were designed: WT, full irrigation treatment; DT, drought stress treatment. Then, the effects of P1, P2, and P3 treatments on the endosperm cell development, nuclear number, nuclease activity, DNA fragmentation, DNA content, grain weight, and phosphorus content of winter wheat variety “Xindong 23” under WT and DT conditions were determined at different stages after anthesis. The results showed that under WT and DT conditions, the degree of nuclear deformation and nuclear membrane depression in P3 treatment was milder than that in P1 and P2 treatments. The ACPase amount in P3 treatment was more than that in P1 and P2 treatments. The number of endosperm nuclei in P3 treatment was higher than that in P1 and P2 treatments. Under DT condition, the endosperm DNA content of wheat grains collected 14–35 days post anthesis (DPA) in P3 treatment increased, and the peak time of genomic DNA fragmentation in P3 treatment was later, compared with those in P1 treatment. Under DT condition, the grain weight and grouting rate in P3 treatment were higher than those of P1 treatment at 7–28 DPA, and the 1000-grain weight of P3 was the highest under both WT and DT conditions, reaching 47.03 and 40.57 g, respectively. Under WT and DT conditions, compared with P1 treatment, the protein content change rate (3.16 % and 5.59 %, respectively) and the total phosphorus content change rate (34.36 % and 35.08 %, respectively) of wheat grains in P3 treatment were the highest. In summary, under the DT condition, split application of phosphorus fertilizer (P3, spring green-up stage stage: jointing stage: filling stage = 4: 3: 3) could increase the phosphorus uptake and utilization of wheat plants and grains, suppress the DNA fragmentation of endosperm cells, and delay the deformation and disintegration of nuclei, which ultimately delayed the PCD in endosperm and realized high grain weight and protein content.

Multigenerational Drought Reveals a Stable Wheat Seed Fungal Community

Wheat ( Triticum spp.) is a staple food crop, providing a fifth of the world's protein and caloric needs. Our research examines the impact of multigeneration postflowering drought stress on the wheat seed endophytic fungal community. Understanding how wheat seed fungal communities respond to drought stress over several generations can improve our knowledge of legacy drought stress. In this article, we aim to identify seed-associated fungi that play critical roles within the wheat seed under drought stress conditions. We examined the endophytic seed fungal communities of three winter wheat cultivars, Catawba, Shirley, and USG 3640. Moderate drought was imposed on a subset of plants immediately after flowering, with plants relieved from drought stress after 1 week. Seeds harvested from generation 1 were planted for a second generation of drought experiments. When examining the postflowering drought impact on wheat physiology, drought-exposed plants consistently exhibited lower daily transpiration rates, chlorophyll-a values, and seed yield compared with control plants, indicating that drought implementation was successful. Internal transcribed spacer 1 metabarcoding revealed that wheat seed fungal community species richness decreased during postanthesis drought stress across both generations. We also observed that generation accounted for variation in fungal species richness and community structure, independent of drought treatment. The most abundant taxa recovered across all cultivars, treatments, and generations included Cladosporium, Penicillium, Alternaria, and Epicoccum. These results support our hypothesis that postanthesis drought shapes the wheat seed fungal community.

EVALUATION FOR IMPACT OF CLIMATE CHANGE ON WHEAT (TRITICUM AESTIVUM L.) GRAIN QUALITY AND YIELD TRAITS

Climate change is increasing stress on agricultural production, notably in developing nations where crop yields are critically impacted. Swift changes in climate conditions directly diminish wheat yields and adversely influence key grain constituents such as starch, fibre, protein, amino acids, and essential nutrients. The studies were conducted for six years, from 2017-18 to 2022-23, to understand the impact of changing climate on wheat grain composition and quality. The results indicated that November is the best month for sowing wheat. The post-anthesis drought or less water availability helps the plants accumulate more protein and gluten contents, and starch contents decrease. The quality of the grain, however, is more significantly influenced by the variety of wheat, the type of environmental stress, and the duration and severity of exposure. Faisalabad 08 had the highest protein and gluten contents, while Galaxy 13 had the highest starch contents in D2. Galaxy 13 indicated the highest value of test weight and 1000-grain weight in November.

Multi-omics analysis of response mechanism of programmed cell death in wheat endosperm to post-anthesis drought stress

Post-anthesis drought stress (PADS) greatly influences wheat grain development and programmed cell death (PCD) in endosperm. However, the response mechanism of PCD in wheat endosperm to abiotic stress is still unclear at present. In this study, the physiological parameters and transcriptome and proteome of winter wheat varieties Xindong No. 18 (XD18, drought-sensitive variety) and Xindong No. 22 (XD22, drought-tolerant variety) under PADS were analyzed. The results showed that under PADS, the endosperm cell viability of XD18 and XD22 decreased, the number of nuclei with DNA break increased by 21% and 9%, respectively, the chromatin condensed, and the nuclear envelope rupture and cytoplasm leakage occurred, compared with those in the control group. Besides, the nuclei count of XD18 and XD22 decreased by 6.07% and 7.5%, respectively, and the DNA hydrolase activity (24.7% and 28.9%), H2O2 content (54.3% and 38.7%), and MDA content (44.1% and 33.8%) all increased. A total of 21,677 differentially expressed genes (DEGs) and 3388 differentially expressed proteins (DEPs) were detected. Among them, 48 PCD-related proteins were identified. The ubiquitin protein (TraesCS1A01G397400.1) exhibited a high expression level in XD22. The integrated transcriptomic and proteomic analysis showed that the expression of genes related to DNA repair and membrane functions were up-regulated, which confirmed the results of physiological analysis. Particularly, the glutathione-ascorbic acid cycle pathway and the mitogen-activated protein kinase (MAPK) signaling cascade pathway mediated by Ca2+, abscisic acid (ABA), ethylene (ETH), and flg22 were significantly enriched. Therefore, the two were key pathways involved in the regulation of wheat endosperm PCD under PADS. This study will deepen our understanding of the PCD in wheat endosperm in response to PADS, and is of great significance for screening candidate genes related to wheat stress resistance.

Amino acid metabolism response to post-anthesis drought stress during critical periods of elite wheat (Triticum aestivum L.) endosperm development

Drought is an important environmental factor leading to wheat yield loss in arid areas. The accumulation of amino acids during the filling stage is closely related to wheat drought resistance and yield, but the mechanism is still unclear. In this study, winter wheat plants (cultivars Xindong 18 (XD18) and Xindong 22 (XD22)) were subjected to post-anthesis drought treatment (DT) and sufficient water treatment (WT), and the measurement of free amino acid and carbohydrates content and the proteomic and transcriptomic analysis of wheat grains were conducted 7 and 14 days after anthesis (DAA). Finally, the improvement effect of application of exogenous glutamate (Glu) on the drought resistance of wheat was validated by hydroponic and field experiments. The results showed that sucrose and soluble sugar contents of XD22 grains were higher than those of XD18 grains under DT. The grain weight and filling rate of both wheat cultivars increased in the early stage of DT but reduced in the late stage. The content of most free amino acids in grains reduced under DT, but the Glu content increased. Regression analysis of grain weight and free amino acid content found that Glu was involved in the responses of wheat to DT and WT. The transcriptomic analysis results showed that XD18-DT7/WT7 and XD22-DT7/WT7 had 161 and 350 differentially expressed genes (DEGs) related to amino acid metabolism, respectively, and XD18-DT14/WT14 and XD22-DT14/WT14 had 380 and 326 DEGs related to amino acid metabolism, respectively. Proteomic analysis results showed that XD18-DT7/WT7 and XD22-DT7/WT7 had 163 and 117 differentially expressed proteins (DEPs） related to amino acid metabolism, respectively, and XD18-DT14/WT14 and XD22-DT14/WT14 had 29 and 109 DEPs related to amino acid metabolism, respectively. Besides, the expression level of most DEPs involved in Glu metabolism (> 95 %) was significantly up-regulated at the early stage of DT. It should be noted that the application of different concentrations of exogenous Glu at seedling stage, heading stage, and flowering stage significantly reduced wheat root/shoot ratio and relative conductivity (RC) under DT, and increased the SPAD value, grain weight, and filling rate. The free amino acids and carbohydrates in wheat grains changed significantly under DT, and a large number of DEPs involved in the Glu metabolism pathway were up-regulated to cope with drought stress. Finally, exogenous Glu application can improve the drought resistance of drought-stressed wheat at seedling and filling stages and increase grain weight.

Evaluation of Diverse Sorghum for Leaf Dhurrin Content and Post-Anthesis (Stay-Green) Drought Tolerance

Post-flowering drought tolerance (stay-green) in grain sorghum (Sorghum bicolor (L.) Moench) is an important agronomic trait in many arid and semiarid environments throughout the world. Stay-green has been associated with increased grain yields, as well as resistance to lodging and charcoal rot disease. Nonetheless, the relative effects of genotype, environment, and genotype × environment interactions are not well understood for this trait; similarly, the relationship between various leaf sugars and stay-green has not been sufficiently evaluated in diverse germplasm. Thus, the goals of this study were to determine the genotype, environment, and genotype by environment (GxE) effects for leaf dhurrin, sugars, and stay-green in ten diverse grain sorghum breeding lines, to evaluate the Pearson’s correlation coefficients (r) between these traits, and to determine entry-mean repeatability (R) for each of these traits. Of the compositional traits studied, we determined that leaf dhurrin had the highest correlation with the stay-green phenotypes (r = −0.62). We found that stay-green sorghum lines contained approximately 2–3 times as much dhurrin as non-stay-green lines, with B1778 containing the highest concentration of dhurrin (84.8 µg/cm2) and Tx7000 containing the least (20.9 µg/cm2). The differences between the environments for several of the traits were high, and all the traits examined had high repeatability (R = 0.89–0.92). These data demonstrate a relationship between leaf dhurrin and the stay-green phenotypes in sorghum, and further study will allow researchers to determine the causal effect that dhurrin has on post-flowering drought tolerance in sorghum.

Integrating stay-green and PIN-FORMED genes: PIN-FORMED genes as potential targets for designing climate-resilient cereal ideotypes.

Plant architecture modification (e.g. short-stature crops) is one of the key outcomes of modern crop breeding for high-yielding crop varieties. In cereals, delayed senescence, or stay-green, is an important trait that enables post-anthesis drought stress adaptation. Stay-green crops can prolong photosynthetic capacity during grain-filling period under post-anthesis drought stress, which is essential to ensure grain yield is not impacted under drought stress conditions. Although various stay-green quantitative trait loci have been identified in cereals, the underlying molecular mechanisms regulating stay-green remain elusive. Recent advances in various gene-editing technologies have provided avenues to fast-track crop improvement, such as the breeding of climate-resilient crops in the face of climate change. We present in this viewpoint the focus on using sorghum as the model cereal crop, to study PIN-FORMED (PIN) auxin efflux carriers as means to modulate plant architecture, and the potential to employ it as an adaptive strategy to address the environmental challenges posed by climate uncertainties.

Contribution of Agro-Physiological and Morpho-Anatomical Traits to Grain Yield of Wheat Genotypes under Post-Anthesis Stress Induced by Defoliation

Post-anthesis drought affects wheat production worldwide, primarily through the limitation of grain filling. The enhanced remobilization of stem reserves induced by drought can provide considerable carbon sources for grain filling. The aim of this study, which was part of an ongoing wheat-breeding program targeting drought tolerance, was to assess the ability of 20 contrasting common wheat genotypes (2 cultivars, 8 F6:7 families (FAM), and 10 parent genotypes (PAR) used to make the families) to remobilize stem dry matter under water-stressed conditions simulated via defoliation 10 days after anthesis, and to estimate the contribution of stem dry matter remobilization to grain weight. In two-year field trials, the genotypes were scored for agro-physiological and peduncle morpho-anatomical traits. Stem reserve contribution to grain weight per spike was significantly enhanced in defoliated plants but did not differ amongst the groups of genotypes. F6:7 families had higher grain-filling rate and 1000-grain weight but without improvement in grain weight per spike under defoliation compared with parental groups. The total area of chlorenchyma, phloem-area-related traits, and stem reserve contribution to grain weight were positively associated with grain weight per spike under defoliation, whilst in both treatments, the grain-filling rate was determined by stem height. These results imply that the grain-filling rate is a trait desirable for drought tolerance that can be improved during the breeding process.

Nitrogen enhances the effect of pre-drought priming against post-anthesis drought stress by regulating starch and protein formation in wheat.

Drought stress is one of the most serious environmental stress factor constraining crop production across the globe. Among cereals, wheat grains are very sensitive to drought as a small degree of stress can affect the enzymatic system. This study aimed to investigate whether nitrogen and pre-anthesis drought priming could enhance the action of major regulatory enzymes involved in starch accumulation and protein synthesis in bread wheat (Triticum aestivum L.). For this purpose, cultivars YM-158 (medium gluten) and YM-22 (low gluten) were grown in rain-controlled conditions under two nitrogen levels, that is, N180 (N1) and N300 (N2). Drought priming was applied at the jointing stage and drought stress was applied 7 days after anthesis. Drought stress reduced starch content but enhanced protein content in grains. N2 and primed plants kept higher contents of nonstructural carbohydrates, fructans, and sucrose; with higher activity of sucrose-phosphate synthase in flag leaves. Furthermore, N2 and priming treatments showed higher sink ability to develop grains by showing higher sucrose-to-starch conversion activities of adenosine diphosphate-glucose pyrophosphorylase, uridine diphosphate glucose pyrophosphorylase, sucrose-synthase, soluble-starch synthase, starch branching enzyme, and granule-bound starch synthase as compared to N1 and non-primed treatments. The application of N2 and primed treatment showed a greater ability to maintain grain filling in both cultivars as compared to N1 and non-primed crops. Our study suggested that high nitrogen has the potential to enhance the effect of pre-drought priming to change source-sink relationships and grain yield of wheat under drought stress during the filling process.

Response of African Sorghum Genotypes for Drought Tolerance under Variable Environments

Sorghum (Sorghum bicolor (L.) Moench) is the main food staple for millions of people in Sub-Saharan Africa (SSA) and Asia. Sorghum is relatively drought tolerant and cultivated in arid and semi-arid regions under rain-fed production. However, severe drought stress often leads to crop loss and declined productivity. The development and deployment of high-yielding and drought-adapted genotypes is a cost-effective strategy for sustainable sorghum production globally. The objective of this study was to determine drought tolerance and genotype-by-environment interaction (GEI) effects on grain yields of a population of African sorghum genotypes to identify high-yielding and drought-adapted genotypes for direct production and also for use in breeding programs. Two hundred and twenty-five sorghum genotypes were evaluated under non-stressed (NS), pre-anthesis drought stress (PreADS), and post-anthesis drought stress (PoADS) conditions under field and greenhouse environments using a 15 × 15 alpha lattice design in two replicates. The three water regimes and two environments resulted in six testing environments. Data were collected on grain yield and drought tolerance parameters, and additive main effect and multiplicative interaction (AMMI) analysis were computed. The mean grain yield under NS, PreADS, and PoADS were 3.70, 1.76, and 2.58 t/ha, in that order. The best genotypes adapted to non-stressed environments were G09, and G109, whereas G114 and G56 were suitable for non-stressed and stressed conditions. G72 and G75 displayed the best performance in PreADS conditions only, whereas genotypes G210 and G12 were identified as high performers under PoADS only. The AMMI analysis revealed that genotype (G), environment (E), and GEI were significant (p < 0.05), which accounted for 38.7, 44.6, and 16.6% of the total explained variation in grain yield. AMMI 4 was the best-fitting model for grain yield. Based on AMMI 4 and the Best Linear Unbiased Estimates (BLUPs) calculations, genotypes G119 and G127 with a grain yield of 5.6 t/ha and 6.3 t/ha were selected as being suitable for non-stressed conditions. Genotypes G8 and G71 with BLUPs of 2.5 t/ha and 2.6 t/ha were best-suited for pre-anthesis drought stress conditions, whereas genotypes G115 and G120 with BLUPs of 4.2 t/ha and 4.3 t/ha are recommended for post-anthesis drought-prone environments, respectively. The identified sorghum genotypes are recommended for production in dry agro-ecologies of sub-Saharan Africa characterized by pre-and-post anthesis drought stress. In addition, the identified genotypes are valuable genetic resources to develop novel drought-tolerance material.

Starch and Sugar Metabolism Response to Post-Anthesis Drought Stress During Critical Periods of Elite Wheat (Triticum aestivum L.) Endosperm Development

Starch and Sugar Metabolism Response to Post-Anthesis Drought Stress During Critical Periods of Elite Wheat (Triticum aestivum L.) Endosperm Development

Abscisic acid and its role in the modulation of plant growth, development, and yield stability.

Abscisic acid (ABA) is known to confer stress tolerance; however, at elevated levels it impairs plant growth under prolonged stress. Paradoxically, at its basal level, ABA plays many vital roles in promoting plant growth and development, including modulation of tillering, flowering, and seed development, as well as seed maturation. In this review, we provide insight into novel discoveries of ABA fluxes, ABA signaling responses, and their impact on yield stability. We discuss ABA homeostasis implicated under pre- and postanthesis drought and its impact on productive tillers, grain number determination, and seed development to address yield stability in cereal crops while considering the new knowledge that emerged from the model plant systems.

Effects of Post-Anthesis Drought and Irrigation on Grain Yield, Canopy Temperature and 13C Discrimination in Common Wheat, Spelt, and Einkorn

Fluctuations in precipitation and higher evapotranspiration due to rising temperatures are reflected in reduced wheat yields, even in areas with a low historical incidence of drought. In this study, the effects of drought (S) and irrigation (IR) on spelt, einkorn wheat, and two common wheat cultivars were assessed in a field experiment in the years 2018–2021. Water availability was differentiated from the flowering stage using a mobile cover and drip irrigation. Grain yield, canopy temperature, and discrimination of 13C in grain (Δ 13C) were monitored. Drought reduced the average grain yield of common wheat to 5.24 t.ha−1, which was 67.00% of the rain-fed control (C) yield, and 62.09% of the irrigated wheat yield. For spelt and einkorn wheat, the average grain yield from stressed plants was 2.02 t.ha−1; this was 79.97% of the C-variant yield, and 70.82% of the IR-variant yield. Higher stand temperatures were an excellent indicator of water deficit in the stressed crops. The relationship between temperature and final grain yield in the monitored variants was always negative. In all years, discrimination of 13C in grain corresponded to water availability; in its effect on yields, the correlation was always positive. Between 2018 and 2020, spelt and einkorn exhibited lower Δ 13C in comparison with common wheat in all variants, suggesting a greater impact of differentiated water supply. The results of the experiment conclusively demonstrated systematic effects of drought after flowering upon yields and other studied characteristics.

Improving the effects of drought priming against post-anthesis drought stress in wheat (Triticum aestivum L.) using nitrogen.

Water and nitrogen (N) deficiencies are the major limitations to crop production, particularly when they occur simultaneously. By supporting metabolism, even when tissue water capacity is lower, nitrogen and priming may reduce drought pressure on plants. Therefore, the current study investigates the impact of nitrogen and priming on wheat to minimize post-anthesis drought stress. Plant morphology, physiology, and biochemical changes were observed before, during, and after stress at the post-anthesis stage. The plants were exposed to three water levels, i.e., well watering (WW), water deficit (WD), and priming at jointing and water deficit (PJWD) at the post-anthesis stage, and two different nitrogen levels, i.e., N180 (N1) and N300 (N2). Nitrogen was applied in three splits, namely, sowing, jointing, and booting stages. The results showed that the photosynthesis of plants with N1 was significantly reduced under drought stress. Moreover, drought stress affected chlorophyll (Chl) fluorescence and water-related parameters (osmotic potential, leaf water potential, and relative water content), grain filling duration (GFD), and grain yield. In contrast, PJWD couple with high nitrogen treatment (N300 kg ha–1) induced the antioxidant activity of peroxidase (37.5%), superoxide dismutase (29.64%), and catalase (65.66%) in flag leaves, whereas the levels of hydrogen peroxide (H2O2) and superoxide anion radical (O2–) declined by 58.56 and 66.64%, respectively. However, during the drought period, the primed plants under high nitrogen treatment (N300 kg ha–1) maintained higher Chl content, leaf water potential, and lowered lipid peroxidation (61%) (related to higher activities of ascorbate peroxidase and superoxide dismutase). Plants under high nitrogen treatment (N300 kg ha–1) showed deferred senescence, improved GFD, and grain yield. Consequently, the research showed that high nitrogen dose (N300 kg ha–1) played a synergistic role in enhancing the drought tolerance effects of priming under post-anthesis drought stress in wheat.

Osmotic Adjustment in Wheat (Triticum aestivum L.) During Pre- and Post-anthesis Drought.

Pre-anthesis drought is expected to greatly increase yield losses in wheat (Triticum aestivum L.), one of the most important crops worldwide. Most studies investigate the effects of pre-anthesis drought only at maturity. The physiology of the plant before anthesis and how it is affected during drought is less studied. Our study focused on physiological patterns in wheat plants during pre- and post-anthesis drought. To this end, we measured leaf xylem water potential, osmotic potential and water content in different plant parts at a high temporal frequency: every 3 days, three times a day. The experiment started just before booting until 2 weeks after flowering. Drought stress was induced by withholding irrigation with rewatering upon turgor loss, which occurred once before and once after anthesis. The goal was to investigate the patterns of osmotic adjustment, when it is used for protection against drought, and if the strategy changes during the phenological development of the plant. Our data gave no indication of daily osmotic adjustment, but did show a delicate control of the osmotic potential during drought in both leaves and stem. Under high drought stress, osmotic potential decreased to avoid further water loss. Before anthesis, rewatering restored leaf water potential and osmotic potential quickly. After anthesis, rewatering restored water potential in the flag leaves, but the osmotic potential in the stem and flag leaf remained low longer. Osmotic adjustment was thus maintained longer after anthesis, showing that the plants invest more energy in the osmotic adjustment after anthesis than before anthesis. We hypothesize that this is because the plants consider the developing ear after anthesis a more important carbohydrate sink than the stem, which is a carbohydrate sink before anthesis, to be used later as a reserve. Low osmotic potential in the stem allowed turgor maintenance, while the low osmotic potential in the flag leaf led to an increase in leaf turgor beyond the level of the control plants. This allowed leaf functioning under drought and assured that water was redirected to the flag leaf and not used to refill the stem storage.

Drought Tolerance and Application of Marker-Assisted Selection in Sorghum

Simple SummarySorghum is a climate-resilient crop grown in limited rainfall areas globally. However, climate change has increased temperature and shortened rainfall durations, which has constrained crop yield. We reviewed mechanisms of drought tolerance and application of marker-assisted selection in sorghum. Marker-assisted selection uses DNA molecular markers to map quantitative trait loci (QTL) associated with stay-green. Stg1, Stg2, Stg3, Stg4, Stg3A, and Stg3B QTLs associated with stay-green and high yield, have been mapped in sorghum. These QTLs are used for introgression into the senescent sorghum varieties through marker-assisted backcrossing.Sorghum is an important staple food crop in drought prone areas of Sub-Saharan Africa, which is characterized by erratic rainfall with poor distribution. Sorghum is a drought-tolerant crop by nature with reasonable yield compared to other cereal crops, but such abiotic stress adversely affects the productivity. Some sorghum varieties maintain green functional leaves under post-anthesis drought stress referred to as stay-green, which makes it an important crop for food and nutritional security. Notwithstanding, it is difficult to maintain consistency of tolerance over time due to climate change, which is caused by human activities. Drought in sorghum is addressed by several approaches, for instance, breeding drought-tolerant sorghum using conventional and molecular technologies. The challenge with conventional methods is that they depend on phenotyping stay-green, which is complex in sorghum, as it is constituted by multiple genes and environmental effects. Marker assisted selection, which involves the use of DNA molecular markers to map QTL associated with stay-green, has been useful to supplement stay-green improvement in sorghum. It involves QTL mapping associated with the stay-green trait for introgression into the senescent sorghum varieties through marker-assisted backcrossing by comparing with phenotypic field data. Therefore, this review discusses mechanisms of drought tolerance in sorghum focusing on physiological, morphological, and biochemical traits. In addition, the review discusses the application of marker-assisted selection techniques, including marker-assisted backcrossing, QTL mapping, and QTL pyramiding for addressing post-flowering drought in sorghum.

Trait association studies in soybean genotypes under post anthesis drought stress

The present study was carried out during kharif 2018 considering 30 soybean genotypes under both stress and normal condition. Analysis of variance, correlation and path coefficient analysis were studied. The analysis of variance under both stress and normal condition revealed that the mean sum of squares due to genotypes were highly significant for all traits under study. Correlation analysis revealed that seed yield per plant showed highly significant correlation with harvest index followed by number of seeds per plant, number of pods per plant, biological yield per plant, number of seeds per pod and number of pod clusters per plant under stress condition whereas under normal condition, seed yield per plant showed highest significant positive correlation with harvest index followed by biological yield per plant, number of seeds per plant, number of pod clusters per plant, number of pods per plant and 100 seed weight. Path coefficient analysis of different yield traits under stress condition revealed that harvest index, biological yield, number of seeds per plant, days to 50% flowering recorded positive direct effect on seed yield per plant. These traits have also shown positive indirect effect via each other which indicated that simultaneous improvement of these traits and ultimately the yield can be achieved. Whereas, path coefficient analysis of different yield traits under normal condition revealed that harvest index have shown high positive direct effect on seed yield per plant number of pod clusters per plant, days to flower initiation, biological yield per plant, number of seeds per plant, number of secondary branches per plant and 100seed weight showed positive direct effect on seed yield perplant. Days to flower initiation, number of pods clusters per plant, number of seeds per plant, biological yield and harvest index have also shown indirect effect via each other.

Drought priming improved water status, photosynthesis and water productivity of cowpea during post-anthesis drought stress

Drought occurring at the reproductive stage is the most critical phase affecting cowpea production. It remains unclear whether drought priming at the early growth stage can be employed to alleviate drought stress during the post-anthesis drought period and improve water productivity (WP) in cowpea. Therefore, the physiological responses and WP as affected by drought priming were investigated. Two cowpea varieties (tolerant (V1) and sensitive (V2) to drought stress) were submitted to drought priming followed by water recovery and then subjected to subsequent drought stresses (80%, 60% and 40% of soil water holding capacity (SWHC)). The results showed that cowpea pre-exposed to drought priming acquired a stress imprint that alleviated the subsequent drought stress which occurred during the later growth stage as exemplified by the improvement of water status, photosynthesis, water productivity of biomass (WPb) and yield (WPy) as well as the modulation of plant hormones. Under the drought stress during the post-anthesis period, primed plants maintained lower [ABA]leaf and higher [IAA]leaf than plants without priming due to better plant water status for drought-primed plants. The results revealed that drought priming could modulate against [ABA]leaf increase under drought, as elevated [ABA]leaf was the main reason for stomatal limitation, thereby decreasing photosynthesis and leading to great yield loss. Primed plants consumed 32% and 24% less water for V1 and V2, respectively, which significantly increased WP while decreased intrinsic water use efficiency (WUEi) of drought-primed plants. It is suggested that drought priming during the early growth period can be used as a promising strategy to save water use for irrigation while improving WP of crops in the regions where water is scarce.

Assessment of Morpho-Physiological, Yield and Yield Attributing Traits Related to Post Anthesis Drought in Wheat Genotypes Under Rainfed Condition in Rampur, Chitwan

A set of twenty wheat (Triticum aestivum L.) genotypes was evaluated to assess morpho-physiological, yield and yield attributing traits related to post-anthesis drought in wheat genotypes under rainfed condition in a Randomized completely block design with three replications at research farm of Faculty of Agriculture, Rampur, Chitwan, during winter season of 2016/2017. The result revealed highly significant genotypic effects for number of tillers per m2 area, plant height, spike length, number of grains per spike, weight of grains per spike, 1000 kernels weight, days to booting, days to heading, days to anthesis, days to flag leaf senescence, days to maturity, SPAD meter reading, peduncle length, grain filling duration and reproductive growth period. Significant genotypic effects were found for grain yield, biological yield and harvest index and an array of variation was found among the genotypes for each trait. But non-significant genotypic effect was found for canopy temperature depression. WK2373 gave highest grain yield kg/ha (3035 kg/ha) and biomass yield kg/ha (8080 kg/ha).
 This study presented WK2373, WK2379, WK2380, WK2386, WK2388, WK2383, WK 2378 and WK1481 the best genotypes governing different valuable traits. These potential genotypes for valuable traits found in different clusters. Crossing genotypes belonging to different clusters could maximize the opportunities for transgressive segregation as there is a higher probability that unrelated genotypes would contribute unique desirable alleles at different loci. Therefore, this study can help breeders to increase genetic diversity by selecting materials of divergent parentage for crosses, thereby reducing vulnerability to diseases and climate changes. 
 Int. J. Appl. Sci. Biotechnol. Vol 8(3): 323-335