Post‐flowering night respiration and altered sink activity account for high night temperature‐induced grain yield and quality loss in rice (Oryza sativa L.)

High night temperature (HNT) is a major constraint to sustaining global rice production under future climate. Physiological and biochemical mechanisms were elucidated for HNT‐induced grain yield and quality loss in rice. Contrasting rice cultivars (N22, tolerant; Gharib, susceptible; IR64, high yielding with superior grain quality) were tested under control (23°C) and HNT (29°C) using unique field‐based tents from panicle initiation till physiological maturity. HNT affected 1000 grain weight, grain yield, grain chalk and amylose content in Gharib and IR64. HNT increased night respiration (Rn) accounted for higher carbon losses during post‐flowering phase. Gharib and IR64 recorded 16 and 9% yield reduction with a 63 and 35% increase in average post‐flowering Rn under HNT, respectively. HNT altered sugar accumulation in the rachis and spikelets across the cultivars with Gharib and IR64 recording higher sugar accumulation in the rachis. HNT reduced panicle starch content in Gharib (22%) and IR64 (11%) at physiological maturity, but not in the tolerant N22. At the enzymatic level, HNT reduced sink strength with lower cell wall invertase and sucrose synthase activity in Gharib and IR64, which affected starch accumulation in the developing grain, thereby reducing grain weight and quality. Interestingly, N22 recorded lower Rn‐mediated carbon losses and minimum impact on sink strength under HNT. Mechanistic responses identified will facilitate crop models to precisely estimate HNT‐induced damage under future warming scenarios.     

Selection of drought tolerant and sensitive genotypes from wheat DH population

Drought has significant effect on wheat production by decreasing grain yield. Phenotyping the populations is a useful tool for understanding the interactions between phenotype and genotype. 135 doubled haploid (DH) genotypes and their parental varieties Plainsman (Pl) and Cappelle Desprez (CD) were phenotyped in glasshouse under well-watered (WW) and drought-stress (DS) conditions. The response of plant height, heading time, aboveground biomass, grain yield, root dry mass harvest index (HI) under both conditions, and stress tolerance index (STI) and water consumption in WW conditions was studied. We found 20% decrease in the plant growth, 66% decrease in the aboveground biomass, and 77% decrease in the grain yield. Under WW conditions, high water consumption was not related to high yields, STI, and HI. The tolerant and the sensitive genotypes were selected. In the WW and water consumption treatment, the sensitive genotype group had better grain yield performance, but under DS, the tolerant group had higher grain yield. The average yield loss was 59% in the tolerant group compared to the WW treatment, and the sensitive yield loss was 68%. Correlation was found between the grain yield and root dry mass in the tolerant group. There was significant difference between the tolerant and sensitive groups on water consumption, as the sensitive genotypes had higher water need. We found strong positive correlation between the water consumption and the grain yield in the tolerant group. This study showed that the tolerant genotypes had improved water regulating efficiency.     

Enhanced N-metabolites,ABA and IAA-conjugate in anthers instigate heat sensitivity in spring wheat

Unraveling the metabolic and phytohormonal changes in anthers exposed to heat stress would help identify mechanisms regulating heat stress tolerance during the sensitive reproductive stage. Two spring wheat genotypes contrasting for heat tolerance were exposed to heat stress during heading in controlled environment chambers. Anthers were collected from main and primary spikes for metabolic and phytohormonal profiling. A significant reduction in seed set (38%), grain number (54%) and grain weight (52%) per plant was recorded in the sensitive (KSG1177) but not in the tolerant (KSG1214) genotype under heat stress compared to control. Anther metabolite accumulation did not vary quantitatively between main and primary spikes. Hierarchical clustering of the genotypes and treatments using metabolites and phytohormones revealed a distinct cluster for KSG1177 under heat stress from that of control and KSG1214. A significant increase in N-based amino acids, ABA, IAA-conjugate and a decrease in polyamines and organic acids were observed in wheat anthers exposed to heat stress. Unlike KSG1214, a significantly higher accumulation of amino acids, ABA and IAA-conjugate in anthers of the sensitive KSG1177 was recorded under heat stress. These findings provide the rationale and direction towards developing molecular markers for enhancing heat stress tolerance in wheat.     

Reduction in seed set upon exposure to high night temperature during flowering in maize

High temperature reduces crop production; however, little is known about the effects of high night temperature (HNT) on the development of male and female reproductive organs, pollination, kernel formation and grain yield in maize (Zea mays L.). Therefore, a temperature-controlled experiment was carried out using heat-sensitive maize hybrid and including three temperature treatments of 32/22°C (day/night; control), 32/26°C and 32/30°C during 14 consecutive days encompassing the flowering stage. When exposed to 30°C night temperature, grain yield and kernel number reduced by 23.8 and 25.1%, respectively, compared with the control. The decrease in grain yield was mainly because of the lower kernel number rather than change in kernel weight under HNT exposure around flowering. No significant differences in grain yield and kernel number were found between 22 and 26°C night temperatures. HNT had no significant effects on the onset of flowering time and anthesis-silking interval but significantly reduced time period of pollen shedding duration and pollen viability, and increased leaf night respiration. Different from high daytime temperature, HNT had no lasting effects on daytime leaf photosynthesis, biomass production and assimilate transportation. From the perspective of source–flow–sink relationship, the unchanged source and flow capacities during daytime are supposed to alleviate the adverse effects on sink strength caused by HNT compared with daytime heat stress. These new findings commendably filled the knowledge gaps concerning heat stress in maize.     

Carbon dioxide responsiveness mitigates rice yield loss under high night temperature

Increasing night-time temperatures are a major threat to sustaining global rice (Oryza sativa L.) production. A simultaneous increase in [CO₂] will lead to an inevitable interaction between elevated [CO₂] (e[CO₂]) and high night temperature (HNT) under current and future climates. Here, we conducted field experiments to identify [CO₂] responsiveness from a diverse indica panel comprising 194 genotypes under different planting geometries in 2016. Twenty-three different genotypes were tested under different planting geometries and e[CO₂] using a free-air [CO₂] enrichment facility in 2017. The most promising genotypes and positive and negative controls were tested under HNT and e[CO₂] + HNT in 2018. [CO₂] responsiveness, measured as a composite response index on different yield components, grain yield, and photosynthesis, revealed a strong relationship (R² = 0.71) between low planting density and e[CO₂]. The most promising genotypes revealed significantly lower (P < 0.001) impact of HNT in high [CO₂] responsive (HCR) genotypes compared to the least [CO₂] responsive genotype. [CO₂] responsiveness was the major driver determining grain yield and related components in HCR genotypes with a negligible yield loss under HNT. A systematic investigation highlighted that active selection and breeding for [CO₂] responsiveness can lead to maintained carbon balance and compensate for HNT-induced yield losses in rice and potentially other C₃ crops under current and future warmer climates.

Active selection for carbon dioxide responsiveness in rice and other C₃ crops can mitigate yield loss induced by high night temperature.     

Heat susceptibility of grain filling in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) linked with rapid chlorophyll loss during a 3-day heat treatment

Brief heat events (1–3 days, >30 °C) commonly reduce wheat (Triticum aestivum L.) grain size and consequently yield. To identify mechanisms of tolerance to such short heat events, 36 wheat genotypes were treated under day/night temperatures of 37 °C/27 °C for 3-days in a growth chamber, at 10 days after anthesis, and a range of developmental, chlorophyll and yield-related traits monitored. The degree of flag leaf chlorophyll loss during the treatment was the variable that showed the highest correlation to grain weight loss (r = 0.63; p < 0.001), identifying chlorophyll stability during this brief period as a potential determinant or indicator of grain weight stability under heat. Variables summarizing the combined during- and post-heat chlorophyll losses showed similar or lower correlations with heat tolerance of grain filling, despite the fact that genotypes varied in their ability to resume normal chlorophyll loss rates after the heat treatment. Additionally, heat tolerance of grain size showed no correlation with grain filling duration or traits relating to utilization of stem carbon reserves under heat stress. Measurement of chlorophyll loss over a forecasted heat wave was thereby identified as a potential basis for developing tools to help breeders select heat tolerant genotypes.     

Wheat leaf lipids during heat stress: I. High day and night temperatures result in major lipid alterations

Understanding how wheat (Triticum aestivum L.) plants under high temperature (HT) regulate lipid composition is critical to developing climate‐resilient varieties. We measured 165 glycerolipids and sterol derivatives under optimum and high day and night temperatures in wheat leaves using electrospray ionization‐tandem mass spectrometry. Levels of polar lipid fatty acyl chain unsaturation were lower in both heat‐tolerant genotype Ventnor and susceptible genotype Karl 92 under HT, compared with optimum temperature. The lower unsaturation was predominantly because of lower levels of 18:3 acyl chains and higher levels of 18:1 and 16:0 acyl chains. Levels of 18:3‐containing triacylglycerols increased threefold/more under HT, consistent with their possible role in sequestering fatty acids during membrane lipid remodelling. Phospholipids containing odd‐numbered or oxidized acyl chains accumulated in leaves under HT. Sterol glycosides (SG) and 16:0‐acylated sterol glycosides (ASG) were higher under HT than optimum temperatures. Ventnor had lower amounts of phospholipids with oxidized acyl chains under HT and higher amounts of SG and 16:0‐ASG than Karl 92. Taken together, the data demonstrate that wheat leaf lipid composition is altered by HT, in which some lipids are particularly responsive to HT, and that two wheat genotypes, chosen for their differing physiological responses to HT, differ in lipid profile under HT.     

Comparative analyses of albumin/globulin grain proteome fraction in differentially salt‐tolerant Tunisian barley landraces reveals genotype‐specific and defined abundant proteins

• Salinity is one of the major abiotic stresses threatening crop production and yield worldwide. Breeding programmes are therefore needed to improve yield under cultivation in soil. Traits from locally adopted landraces provide a resource to assist breeding of novel elite genotypes. Here, we examine differentially expressed proteins by performing comparative proteomic profiling of the albumin/globulin grain fraction of Tunisian barley genotype landraces with contrasting salinity tolerance.
• Tunisian barley Boulifa (B, tolerant) and Testour (T, sensitive) mature grains were assessed in 2‐DE profiles. Differentially expressed spots, with an abundance enhanced 1.5‐fold in the grain, were subjected to MALDI TOF/TOF MS for identification.
• Distinctiveness between tolerant and sensitive genotypes was proved in the albumin/globulin fraction using PCA; 64 spots showed significant differential abundance. Increased accumulation of 40 spots was confirmed in Boulifa with, interestingly, four genotype‐specific spots. Two of these four spots were sHSP. Proteins with highest abundance were serpin Z7, 16.9 KDa Class I HSP and phosphogluconolactonase 2. Proteins such as expansin, kiwellin, kinesin and succinyl‐CoA ligase were identified for the first time in barley grain. Moreover, ß‐amylase, LEA family and others were identified as abundant in Boulifa. On the other hand, proteins more accumulated in Testour are implicated mainly in ROS scavenging and protease inhibition.
• Our results clearly indicate proteomic contrast between the two selected genotypes. With identification of specific HSP, high abundant stress‐protective and other defined proteins, we provide biochemical traits that will support breeding programmes to address the threat of salinity in agricultural production.

     

Wheat leaf lipids during heat stress: II. Lipids experiencing coordinated metabolism are detected by analysis of lipid co‐occurrence

Identifying lipids that experience coordinated metabolism during heat stress would provide information regarding lipid dynamics under stress conditions and assist in developing heat‐tolerant wheat varieties. We hypothesized that co‐occurring lipids, which are up‐regulated or down‐regulated together through time during heat stress, represent groups that can be explained by coordinated metabolism. Wheat plants (Triticum aestivum L.) were subjected to 12 days of high day and/or night temperature stress, followed by a 4‐day recovery period. Leaves were sampled at four time points, and 165 lipids were measured by electrospray ionization‐tandem mass spectrometry. Correlation analysis of lipid levels in 160 leaf samples from each of two wheat genotypes revealed 13 groups of lipids. Lipids within each group co‐occurred through the high day and night temperature stress treatments. The lipid groups can be broadly classified as groups containing extraplastidic phospholipids, plastidic glycerolipids, oxidized glycerolipids, triacylglycerols, acylated sterol glycosides and sterol glycosides. Current knowledge of lipid metabolism suggests that the lipids in each group co‐occur because they are regulated by the same enzyme(s). The results suggest that increases in activities of desaturating, oxidizing, glycosylating and acylating enzymes lead to simultaneous changes in levels of multiple lipid species during high day and night temperature stress in wheat.     

Grain growth and endosperm cell size under high night temperatures in rice (Oryza sativa L.)

BACKGROUND AND AIMS: High night temperatures are more harmful to grain weight in rice than high day temperatures. Grain growth rate and growth duration were investigated to determine which was the cause of the decrease in final grain weight under high night temperatures. Endosperm cell number and cell sizes were also examined to determine which might cause the decrease in final grain weight. METHODS: Rice plants were grown outdoors in plastic pots and moved at heading time to three temperature-controlled glasshouses under high night temperature (HNT; 22/34 degrees C), high day temperature (HDT; 34/22 degrees C) and control conditions (CONT; 22/22 degrees C). Grains were sampled periodically, and the time-course of grain growth was divided into rate and duration by logistic regression analysis. Endosperm cell numbers and cell sizes were analysed by digitalized hand-tracing images of endosperm cross-sections. KEY RESULTS: The duration of grain growth was reduced by high temperature both day and night. However, the rate of grain growth was lower in HNT than in HDT. The number of cells in endosperm cross-sections in HNT was similar to that in HDT, and higher than that in CONT. The average cell area was smaller in HNT than in either CONT or HDT. The differences in average cell areas between HNT and HDT were greater at distances 60-80 % from the central point of endosperm towards the endosperm surface. CONCLUSIONS: The results show that HNT compared with HDT reduced the final grain weight by a reduction in grain growth rate in the early or middle stages of grain filling, and also reduced cell size midway between the central point and the surface of endosperm.     

Stripe Rust Partial Resistance Increases Spring Bread Wheat Yield in South‐eastern Anatolia,Turkey

Stripe rust caused by Puccinia striiformis f.sp. tritici is the most serious disease of wheat globally including south‐eastern Anatolia of Turkey, where wheat originated. In this study, 12 spring wheat genotypes were artificially inoculated and preserved in two locations, Diyarbak?r and Ad?yaman, during the 2011–2012 season to investigate loss in yield and yield components. Genotypes were evaluated at the adult plant stage using two partial resistance parameters: final disease severity and area under the disease progress curve (AUDPC). AUDPC ranged from 14.8 to 860 in Diyarbak?r, and 74 to 760 in Ad?yaman. Yield loss ranged from 0.6 to 68.5% in Diyarbak?r and 9.8 to 56.8% in Ad?yaman. Genotypes G1, G5, G7 and G8 were found to lose less yield, while higher yield loss was observed in G3, G4 (Nurkent), G5 and G9 (Karacada?‐98). The highest loss in thousand kernel weight was observed in a susceptible cultivar Karacada?‐98 in Diyarbak?r followed by 43.4 and 24.4% in Ad?yaman. Test weight loss reached 8.89% in Diyarbak?r and 20.8% in Ad?yaman. Yield loss and AUDPC had a positive significant relationship. Based on the values of AUDPC, final disease severity and yield loss, three major clusters were formed for 12 wheat genotypes. Partially resistant genotypes were found to lose less grain yield and seemed to be stronger against severe stripe rust pressure.     

Growth response to subsurface soil acidity of wheat genotypes differing in aluminium tolerance

Subsurface soil acidity coupled with high levels of toxic Al is a major limiting factor in wheat production in many areas of the world. This study examined the effect of subsurface soil acidity on the growth and yield of two near-isogenic wheat genotypes differing in Al tolerance at a single genetic locus in reconstructed soil columns. In one experiment, plants were grown in columns with limed topsoil and limed or acidic subsurface soils, and received water only to the subsurface soil at a late part of the growth period. While shoot dry weight, ear number and grain yield of Al-tolerant genotype (ET8) were not affected by subsurface soil acidity, liming subsurface soil increased shoot weight and grain yield of Al-sensitive genotype (ES8) by 60% and ear number by 32%. Similarly, root length density of ET8 was the same in the limed and acidic subsurface soils, while the root length density of ES8 in the acidic subsurface soil was only half of that in the limed subsurface soil. In another experiment, plants were grown with limed topsoil and acidic subsurface soil under two watering regimes. Both genotypes supplied with water throughout the soil column produced almost twice the dry weight of those receiving water only in the subsurface soil. The tolerant genotype ET8 had shoot biomass and grain yield one-third higher than ES8 when supplied with water throughout the whole column, and had yield 11% higher when receiving water in the subsurface soil only. The tolerant genotype ET8 produced more than five times the root length in the acidic subsurface soil compared to ES8. Irrespective of watering regime, the amount of water added to maintain field capacity of the soil was up to 2-fold higher under ET8 than under ES8. The results suggest that the genotypic variation in growth and yield of wheat grown with subsurface soil acidity results from the difference in root proliferation in the subsurface soil and hence in utilizing nutrient and water reserves in the subsurface soil layer.     

Rice yield formation under high day and night temperatures—A prerequisite to ensure future food security

Increasing temperatures resulting from climate change dramatically impact rice crop production in Asia. Depending on the specific stage of rice development, heat stress reduces tiller/panicle number, decreases grain number per plant and lower grain weight, thus negatively impacting yield formation. Hence improving rice crop tolerance to heat stress in terms of sustaining yield stability under high day temperature (HDT), high night temperature (HNT), or combined high day and night temperature (HDNT) will bolster future food security. In this review article, we highlight the phenological alterations caused by heat and the underlying molecular-physiological and genetic mechanisms operating under different types of heat conditions (HDT, HNT, and HDNT) to understand heat tolerance. Based on our synthesis of HDT, HNT, and HDNT effects on rice yield components, we outline future breeding strategies to contribute to sustained food security under climate change.     

Root Respiration,Photosynthesis and Grain Yield of Two Spring Wheat in Response to Soil Drying

The effects of soil water regime and wheat cultivar, differing in drought tolerance with respect to root respiration and grain yield, were investigated in a greenhouse experiment. Two spring wheat (Triticum aestivum) cultivars, a drought sensitive (Longchun 8139-2) and drought tolerant (Dingxi 24) were grown in PVC tubes (120 cm in length and 10 cm in diameter) under an automatic rain-shelter. Plants were subjected to three soil moisture regimes: (1) well-watered control (85% field water capacity, FWC); (2) moderate drought stress (50% FWC) and (3) severe drought stress (30% FWC). The aim was to study the influence of root respiration on grain yield under soil drying conditions. In the experiment, severe drought stress significantly (p < 0.05) reduced shoot and root biomass, photosynthesis and root respiration rate for both cultivars, but the extent of the decreases was greater for Dingxi 24 compared to that for Longchun 8139-2. Compared with Dingxi 24, 0.04 and 0.07 mg glucose m⁻² s⁻¹ of additional energy, equivalent to 0.78 and 1.43 J m⁻² s⁻¹, was used for water absorption by Longchun 8139-2 under moderate and severe drought stress, respectively. Although the grain yield of both cultivars decreased with declining soil moisture, loss was greater in Longchun 8139-2 than in Dingxi 24, especially under severe drought stress. The drought tolerance cultivar (Dingxi 24), had a higher biomass and metabolic activity under severe drought stress compared to the sensitive cultivar (Longchun 8139-2), which resulted in further limitation of grain yield. Results show that root respiration, carbohydrates allocation (root:shoot ratio) and grain yield were closely related to soil water status and wheat cultivar. Reductions in root respiration and root biomass under severe soil drying can improve drought tolerant wheat growth and physiological activity during soil drying and improve grain yield, and hence should be advantageous over a drought sensitive cultivar in arid regions.     

Response of wheat restricted‐tillering and vigorous growth traits to variables of climate change

The response of wheat to the variables of climate change includes elevated CO₂, high temperature, and drought which vary according to the levels of each variable and genotype. Independently, elevated CO₂, high temperature, and terminal drought affect wheat biomass and grain yield, but the interactive effects of these three variables are not well known. The aim of this study was to determine the effects of elevated CO₂ when combined with high temperature and terminal drought on the high‐yielding traits of restricted‐tillering and vigorous growth. It was hypothesized that elevated CO₂ alone, rather than combined with high temperature, ameliorates the effects of terminal drought on wheat biomass and grain yield. It was also hypothesized that wheat genotypes with more sink capacity (e.g. high‐tillering capacity and leaf area) have more grain yield under combined elevated CO₂, high temperature, and terminal drought. Two pairs of sister lines with contrasting tillering and vigorous growth were grown in poly‐tunnels in a four‐factor completely randomized split‐plot design with elevated CO₂ (700 µL L^?1), high day time temperature (3 °C above ambient), and drought (induced from anthesis) in all combinations to test whether elevated CO₂ ameliorates the effects of high temperature and terminal drought on biomass accumulation and grain yield. For biomass and grain yield, only main effects for climate change variables were significant. Elevated CO₂ significantly increased grain yield by 24–35% in all four lines and terminal drought significantly reduced grain yield by 16–17% in all four lines, while high temperature (3 °C above the ambient) had no significant effect. A trade‐off between yield components limited grain yield in lines with greater sink capacity (free‐tillering lines). This response suggests that any positive response to predicted changes in climate will not overcome the limitations imposed by the trade‐off in yield components.     

Genetic dissection of pre‐anthesis sub‐phase durations during the reproductive spike development of wheat

Flowering time is an important factor affecting grain yield in wheat. In this study, we divided reproductive spike development into eight sub‐phases. These sub‐phases have the potential to be delicately manipulated to increase grain yield. We measured 36 traits with regard to sub‐phase durations, determined three grain yield‐related traits in eight field environments and mapped 15 696 single nucleotide polymorphism (SNP, based on 90k Infinium chip and 35k Affymetrix chip) markers in 210 wheat genotypes. Phenotypic and genetic associations between grain yield traits and sub‐phase durations showed significant consistency (Mantel test; r = 0.5377, P < 0.001). The shared quantitative trait loci (QTLs) revealed by the genome‐wide association study suggested a close association between grain yield and sub‐phase duration, which may be attributed to effects on spikelet initiation/spikelet number (double ridge to terminal spikelet stage, DR‐TS) and assimilate accumulation (green anther to anthesis stage, GA‐AN). Moreover, we observed that the photoperiod‐sensitivity allele at the Ppd‐D1 locus on chromosome 2D markedly extended all sub‐phase durations, which may contribute to its positive effects on grain yield traits. The dwarfing allele at the Rht‐D1 (chromosome 4D) locus altered the sub‐phase duration and displayed positive effects on grain yield traits. Data for 30 selected genotypes (from among the original 210 genotypes) in the field displayed a close association with that from the greenhouse. Most importantly, this study demonstrated specific connections to grain yield in narrower time windows (i.e. the eight sub‐phases), rather than the entire stem elongation phase as a whole.     

High night temperatures during grain number determination reduce wheat and barley grain yield: a field study

Warm nights are a widespread predicted feature of climate change. This study investigated the impact of high night temperatures during the critical period for grain yield determination in wheat and barley crops under field conditions, assessing the effects on development, growth and partitioning crop‐level processes driving grain number per unit area (GN). Experiments combined: (i) two contrasting radiation and temperature environments: late sowing in 2011 and early sowing in 2013, (ii) two well‐adapted crops with similar phenology: bread wheat and two‐row malting barley and (iii) two temperature regimes: ambient and high night temperatures. The night temperature increase (ca. 3.9 °C in both crops and growing seasons) was achieved using purpose‐built heating chambers placed on the crop at 19:000 hours and removed at 7:00 hours every day from the third detectable stem node to 10 days post‐flowering. Across growing seasons and crops, the average minimum temperature during the critical period ranged from 11.2 to 17.2 °C. Wheat and barley grain yield were similarly reduced under warm nights (ca. 7% °C^?1), due to GN reductions (ca. 6% °C^?1) linked to a lower number of spikes per m². An accelerated development under high night temperatures led to a shorter critical period duration, reducing solar radiation capture with negative consequences for biomass production, GN and therefore, grain yield. The information generated could be used as a starting point to design management and/or breeding strategies to improve crop adaptation facing climate change.