Water Soluble Carbohydrates Remobilization Research Articles

Retrospective study in U.S. commercial sorghum breeding: II. Physiological changes associated to yield gain

AbstractUnderstanding physiological changes in response to long‐term selection for yield can inform breeding decisions and hasten genetic gain. The objective of this study was to characterize changes over time in yield‐relevant physiological traits for hybrids with different years of release for grain sorghum (Sorghum bicolor L. Moench). Field trials were conducted during the 2018 and 2019 seasons in 8 site‐years across the states of Kansas and Texas including 20 commercially available grain sorghum hybrids released by Pioneer between 1963 and 2017. Detailed yield‐related physiological traits were determined in 2 site‐years including grain yield and its components, grain filling, plant biomass, panicle length, and water‐soluble carbohydrates (WSC) during the reproductive period. Consistent with estimates using historical yield data, sorghum yield improvement was 27 kg ha−1 yr−1. For the 2 site‐years with detailed yield‐related physiological traits, no changes in final grain weight, grain‐filling duration, and rate over time were documented. In contrast, grain number increased at a rate of 100 grains m−2 yr−1. Modern hybrids had larger panicle size and showed greater accumulation of WSC during vegetative period (as measured at the start of flowering) and greater remobilization of WSC during the reproductive period (after flowering) to grain, thus, maintaining grain size on the increased grain number per unit area and harvest index. These findings suggest that WSC dynamics play a critical role on past genetic yield gain in sorghum and its potential for future improvements should be considered.

The role of different stem segments in the deposition of water-soluble carbohydrates in winter wheat varieties under drought conditions

Aim. Evaluation of the role of different internodes and leaf sheaths of winter wheat stem in storage and remobilization of reserve water-soluble carbohydrates (WSC) under natural water deficit in order to develop effective criteria for selection of high-yielding genotypes. Methods. The specific content and total amount of WSC at the onset and the end of grain filling and the quantity of WSC remobilized in different parts of the stem were determined. Results. It was found that the main part of reserve WSC in plants of modern winter wheat varieties was accumulated and mobilized in the 2nd, 3rd and 4-5th (counting from above) internodes, the contribution of peduncle and leaf sheaths was much smaller. The highest WSC depositing capacity of all stem segments were found in the high-yielding variety Kyivska 17 and the lowest one in the less productive variety Poradnytsia. Conclusions. The values of accumulation and remobilization of WSC in the 2nd and 3rd from the top internodes can characterize the storage capacity of the stem and be used to assess the relationships with grain productivity in the breeding winter wheat in arid conditions.

Genome-Wide Association of Stem Carbohydrate Accumulation and Remobilization during Grain Growth in Bread Wheat (Triticum aestivum L.) in Mediterranean Environments.

Water deficit represents an important challenge for wheat production in many regions of the world. Accumulation and remobilization of water-soluble carbohydrates (WSCs) in stems are part of the physiological responses regulated by plants to cope with water stress and, in turn, determine grain yield (GY). The genetic mechanisms underlying the variation in WSC are only partially understood. In this study, we aimed to identify Single Nucleotide Polymorphism (SNP) markers that account for variation in a suite of WSC and GY, evaluated in 225 cultivars and advanced lines of spring wheat. These genotypes were established in two sites in the Mediterranean region of Central Chile, under water-limited and full irrigation conditions, and assessed in two growing seasons, namely anthesis and maturity growth periods. A genome-wide association study (GWAS) was performed by using 3243 SNP markers. Genetic variance accounted for 5 to 52% of phenotypic variation of the assessed traits. A rapid linkage disequilibrium decay was observed across chromosomes (r2 ≤ 0.2 at 2.52 kbp). Marker-trait association tests identified 96 SNPs related to stem weight (SW), WSCs, and GY, among other traits, at the different sites, growing seasons, and growth periods. The percentage of SNPs that were part of the gene-coding regions was 34%. Most of these genes are involved in the defensive response to drought and biotic stress. A complimentary analysis detected significant effects of different haplotypes on WSC and SW, in anthesis and maturity. Our results evidence both genetic and environmental influence on WSC dynamics in spring wheat. At the same time, they provide a series of markers suitable for supporting assisted selection approaches and functional characterization of genes.

Integrating nitrogen and water‐soluble carbohydrates dynamics in maize: A comparison of hybrids from different decades

AbstractDuring a century of maize (Zea mays L.) breeding, yield genetic gain was largely determined by increased reproductive resilience under stress and establishment of sink size (number of grains per unit area). Considering grains as competing sinks for C and N assimilates, understanding changes in the C and N economy can provide insights to define selection criteria towards a sustained yield improvement. A cognitive framework to define such criteria may consist in connecting the water‐soluble carbohydrates (WSC) and N dynamics in stem and leaves with the reproductive sink strength during post‐flowering. The objectives of this study were to advance such framework by (a) quantifying grain N demand and remobilization capacity in two hybrids as affected by N availability, and (b) formalizing how the interplay between N and WSC remobilization influence grain growth. Single cross hybrids 3394 and P1197 (released in 1991 and 2014) were evaluated to represent keystone phases of germplasm development (conventional and molecular breeding eras). P1197 outyielded 3394 consistently under high N supply, and its better N utilization efficiency was reflected through a lower grain N concentration. Under high N, the ability to maintain a greater leaf area during late grain‐filling for P1197 resulted in a reduced leaf N remobilization. Although yield was not limited by C supply, 3394 exposed greater remobilization of WSC during late grain‐filling. This study contributes to advance the development of a relevant C to N framework to further analyze drivers of genetic yield gain and assist in selection strategies in maize.

Dynamic responses of accumulation and remobilization of water soluble carbohydrates in wheat stem to drought stress

Remobilization of stem water soluble carbohydrates (WSC) can supply crucial carbon resources for grain filling against drought stress. Here, spatiotemporal variations in post-anthesis WSC levels and compensatory effects for grain weight from different internodes of the main stem were investigated, when exposed two wheat genotypes with contrasting drought tolerance to drought-stressed and well-watered conditions. Analysis of variance revealed that stem WSC levels were predominantly affected by days after anthesis, water stress and their interactions. Compared with well-watered conditions, the peak time of WSC levels was curtailed by 7–14 days in drought-stressed plants. Drought stress highly promoted WSC levels (ca. 20–30%) in upper internodes during the early period of grain filling, but significantly reduced WSC levels (ca. 40–90%) in all internodes during the late period. The drought-tolerant genotype LJ196 was more superior in WSC partitioning than the drought-prone genotype XD18, due to its stronger capacity for stem WSC remobilization, especially for pre-anthesis reserves under drought stress. This was associated with a better grain filling and compensation to the loss of grain weight. The WSC levels induced by drought stress formed a high-to-low concentration gradient from the lower to the upper internodes. Presumably, it might favorably drive WSC flux from stem to developing kernels, indicative of higher WSC remobilization efficiency generally in lower internodes than in upper ones. These findings provide the well-understanding of the spatiotemporal pattern of post-anthesis WSC accumulation and remobilization along stem internodes and their roles in the wheat grain-filling process under drought stress.

Genetic dissection of stem WSC accumulation and remobilization in wheat (Triticum aestivum L.) under terminal drought stress

BackgroundThe accumulation and remobilization of stem water soluble carbohydrates (WSC) are determinant physiological traits highly influencing yield potential in wheat against drought stress. However, knowledge gains of the genetic control are still limited. A hexaploid wheat population of 120 recombinant inbred lines were developed to identify quantitative trait loci (QTLs) and to dissect the genetic basis underlying eight traits related to stem WSC under drought stress (DS) and well-watered (WW) conditions across three environments.ResultsAnalysis of variance (ANOVA) revealed larger environmental and genotypic effects on stem WSC-related traits, indicating moderate heritabilities of 0.51–0.72. A total of 95 additive and 88 pairs of epistatic QTLs were identified with significant additive and epistatic effects, as well as QTL× water environmental interaction (QEI) effects. Most of additive QTLs and additive QEIs associated with drought-stressed environments functioned genetic effects promoting pre-anthesis WSC levels and stem WSC remobilization to developing grains. Compared to other genetic components, both genetic effects were performed exclusive contributions to phenotypic variations in stem WSC-related traits. Nineteen QTL clusters were identified on chromosomes 1B, 2A, 2B, 2D, 3B, 4B, 5A, 6A, 6B and 7A, suggestive of the genetic linkage or pleiotropy. Thirteen additive QTLs were detectable repeatedly across two of the three water environments, indicating features of stable expressions. Some loci were consistent with those reported early and were further discussed.ConclusionStem WSC-related traits were inherited predominantly by additive and QEI effects with a moderate heritability. QTL cluster regions were suggestive of tight linkage or pleiotropy in the inheritance of these traits. Some stable and common loci, as well as closely linked molecular markers, had great potential in marker-assisted selection to improve stem WSC-related traits in wheat, especially under drought-stressed environments.

Abscisic acid associated with key enzymes and genes involving in dynamic flux of water soluble carbohydrates in wheat peduncle under terminal drought stress

Remobilization of stem water soluble carbohydrates (WSC) can supply crucial carbon resources for grain filling under drought stress, while the regulatory metabolism associated with abscisic acid (ABA) is still limited. Two cultivars, LJ196 (drought-tolerant) and XD18 (drought-prone), were pot-grown under well-watered (WW) and drought-stressed (DS) conditions. Concentrations of WSC components and ABA, and fructan metabolizing enzymes and genes were investigated in peduncle after anthesis. When compared with those under the WW, LJ196 remained higher grain yield and grain-filling rate than XD18 under the DS. During the early period of grain filling (0–14 DAA), DS increased concentrations of total WSC and its components, but thereafter substantially reduced them. The gene expression levels and enzymatic activities of fructan 1-exohydrolases (1-FEH) and fructan 6-exohydrolases (6-FEH) showed similar trends, whereas those of fructan: fructan 1-fructosyltransferase (1-FFT), and sucrose: fructan 6-fructosyltransferase (6-SFT) were depressed and declined over the period of examination. LJ196 still showed higher levels of ABA and fructan metabolizing. The ABA concentration under the DS was positively and significantly correlated with total WSC and fructan concentration, and expression levels of these enzymes and genes as well, with more prominently with those of 6-FEH. Presumably, ABA could enhance fructan hydrolysis by strongly up-regulating the gene expression and enzymatic activity of 6-FEH to accelerate WSC remobilization. However, stem WSC induced by DS could be not fully remobilized to grains, due to its weaker correlation with grain-filling rate and finally indicating lower grain yield. The findings would provide useful information for wheat production under water-deficit environments.

Variabilidad en carbohidratos solubles del tallo y su contribución al rendimiento de grano en trigo

En trigo la capacidad para almacenar carbohidratos solubles (CHS) en el tallo y remobilizarlos hacia el grano, constituye una característica deseable a incorporar en el germoplasma dirigido a regiones donde ocurre con frecuencia sequía terminal. El objetivo del trabajo fue evaluar la variabilidad en la acumulación y remobilización de los carbohidratos solubles en agua (CHS) y su contribución al rendimiento de grano cuando la fuente postantesis es alterada por defoliación y estrés hídrico. Los experimentos se llevaron a cabo en el ciclo verano-otoño 2013 (temporal, exp. 1) e invierno-primavera 2013-2014 (riego, exp. 2) en Toluca, México, a una densidad de 350 semillas m-2, en el exp. 1 la defoliación se realizó 7 días después de antesis y en el exp. 2 no se regó después de antesis. En el exp. 1 se estudiaron 60 líneas élite de trigo y dos tratamientos de reducción de fuente (defoliado y sin defoliar, llamados ambientes en adelante), bajo un diseño de parcelas divididas con 2 repeticiones. El exp. 2 consistió en 20 genotipos seleccionados del exp. 1 y sometidos a dos regímenes hídricos (riego y sequía postfloración) en un diseño de bloques completos al azar con 3 repeticiones en donde cada régimen hídrico se consideró un ambiente. Se observó gran variabilidad para rendimiento de grano (RG) y las características fisiológicas asociadas. El RG fue reducido en promedio 14% por efecto de la defoliación y sequía pos-antesis. La mayor contribución de CHS estuvo en línea con una mayor eficiencia de remobilización. Existen genotipos promisorios para usarse en programas de mejoramiento genético con miras a incorporar características fisiológicas para incrementar el rendimiento potencial bajo condiciones de estreses bióticos o abióticos en pos-antesis.

Variation of Water-Soluble Carbohydrates and Grain Yield in Iranian Cold Barley Promising Lines Under Well-Watered and Water Stress Conditions

ABSTRACT In order to evaluate promising lines in terms of grain yield and water-soluble carbohydrates remobiliza-tion, an experiment with fifteen promising lines and two checks was carried out under full irrigation and terminal water stress conditions at Miyandoab Agricultural Research and Natural Resources Station. Mobilized dry matter content and remobilization percentage from shoot to grain under water deficit (177mg)(11.2%) were greater than those under well watering condition. The lowest (110 mg) and the highest (260mg) mobilized dry matter to grain were obtained for C-79-18 and C-83-15lines, respectively. Water deficit reduced grain yield of barley genotypes by 200-1600 kg/ha, and mean grain yield reduction was 800 kg/ha. Line 14 with 5.880and 5.300t/ha grain yield in favorable and water stress conditions was superior to the other lines. Under water deficit condition, line 14 had greater grain yieldby20% and 38% than the Bahman and Makouee cultivars, respectively. The results showed that greater grain yield in tolerant lines under water deficit was due to remobilization of unstructured carbohydrates from shoot to grain. Thus, it seems that selection of lines with higher translocated dry matter and contribution of pre-anthesis assimilate in grain filling under water stress, the suitable way for achieving genotypes with high grain yield under water stress condition.

A wheat 1-FEH w3 variant underlies enzyme activity for stem WSC remobilization to grain under drought.

In wheat stems, the levels of fructan-dominated water-soluble carbohydrates (WSC) do not always correlate well with grain yield. Field drought experiments were carried out to further explain this lack of correlation. Wheat (Triticum aestivum) varieties, Westonia, Kauz and c. 20 genetically diverse double haploid (DH) lines derived from them were investigated. Substantial genotypic differences in fructan remobilization were found and the 1-FEH w3 gene was shown to be the major contributor in the stem fructan remobilization process based on enzyme activity and gene expression results. A single nucleotide polymorphism (SNP) was detected in an auxin response element in the 1-FEH w3 promoter region, therefore we speculated that the mutated Westonia allele might affect gene expression and enzyme activity levels. A cleaved amplified polymorphic (CAP) marker was generated from the SNP. The harvested results showed that the mutated Westonia 1-FEH w3 allele was associated with a higher thousand grain weight (TGW) under drought conditions in 2011 and 2012. These results indicated that higher gene expression of 1-FEH w3 and 1-FEH w3 mediated enzyme activities that favoured stem WSC remobilization to the grains. The CAP marker residing in the 1-FEH w3 promoter region may facilitate wheat breeding by selecting lines with high stem fructan remobilization capacity under terminal drought.

Traits in Spring Wheat Cultivars Associated with Yield Loss Caused by a Heat Stress Episode after Anthesis

AbstractHeat stress resulting from climate change and more frequent weather extremes is expected to negatively affect wheat yield. We evaluated the response of different spring wheat cultivars to a post‐anthesis high temperature episode and studied the relationship between different traits associated with heat tolerance. Fifteen spring wheat (Triticum aestivum L.) cultivars were grown in pots under semifield conditions, and heat stress (35/26 °C) and control treatments (20/12 °C) were applied in growth chambers for 5 days starting 14 days after flowering. The heat stress treatment reduced final yield in all cultivars. Significant variation was observed among cultivars in the reduction in average grain weight and grain dry matter yield under heat stress (up to 36 % and 45 %, respectively). The duration of the grain‐filling period was reduced by 3–12 days by the heat treatment. The reduction in the grain‐filling period was negatively correlated with grain nitrogen yield (r = −0.60). A positive correlation (r = 0.73) was found between the treatment effect on green leaf area (GLA) and the reduction in yield resulting from heat stress. The amount of stem water‐soluble carbohydrates (WSC) was not related to treatment effects on grain yield or grain weight. However, the treatment effect on stem WSC remobilization was negatively correlated with reduction in grain‐filling duration due to heat stress (r = −0.74) and positively with treatment effect on grain N yield (r = 0.52). The results suggest that the effect of the heat treatment on GLA was the trait most associated with yield reduction in all cultivars. These findings suggest the importance of ‘stay green’‐associated traits in plant breeding as well as the need for better modelling of GLA in crop models, especially with respect to brief heat episodes during grain filling. There is in particular a need to model how heat and other stresses, including interacting effects of heat and drought, affect duration of GLA after flowering and how this affects source–sink relations during grain filling.

REMOBILIZATION OF WATER SOLUBLE CARBOHYDRATES IN NON-LEAF ORGANS AND CONTRIBUTION TO GRAIN YIELD IN WINTER WHEAT UNDER REDUCED IRRIGATION

The remobilization of water soluble carbohydrates (WSC) has an important role for grain yield. This study investigated the accumulation and remobilization of WSC in non-leaf organs (chaff, upper stem, and lower stem) and their contribution to grain yield, under different irrigation levels (rainfed, reduced irrigation, and full irrigation) and seeding rate treatments (450, 600 and 750 plants m -2 ) using two winter wheat cultivars, Shijiazhuang 8 (SJZ-8) and Lumai 21 (LM-21), in two field experiments. Results showed that decreasing irrigation and increasing seeding rates increased WSC accumulation and remobilization, remobilization efficiency, and contribution to grain yield in non-leaf organs. When the organs are ranked from highest to lowest in terms of the WSC accumulation amount, remobilization amount, remobilization efficiency, and contribution to grain yield, they are: the lower stem, the upper stem, and then the chaff. And between cultivars, these amounts were higher in SJZ-8 than in LM-21. The total contribution, pre-anthesis contribution, and post-anthesis contribution of WSC remobilization from all non-leaf organs to grain yield ranged from 11.7 to 21.5%, 4.8 to 9.4%, and 6.9 to 12.1%, respectively. This increase in WSC accumulation, remobilization, and contribution to grain yield in non-leaf organs is an important reason high grain yields can be maintained in water-saving and optimal high density management systems.

Increasing the harvest index of wheat in the high rainfall zones of southern Australia

The harvest index (HI) of wheat in the high rainfall zones (HRZ) of Australia is low compared with values in similar rainfall environments in Europe. From 2005 to 2007, we examined dry matter (DM) partitioning, yield formation, post-anthesis dry matter accumulation, and remobilization of water soluble carbohydrates (WSC) of a number of wheat genotypes (5 spring wheat and 1 winter wheat) to determine the factors influencing the HI in the HRZ of south-western Australia. Grain yield was strongly correlated with grain number (GN) in all three years and with the sum of post-anthesis DM accumulation and WSC in stems at anthesis when the amount of assimilates available to fill grains was less than 600gm−2. However, when the amount of assimilates exceeded 600gm−2, grain yield reached a plateau and did not increase with the increased availability of assimilates because of sink limitations. Genotypes with more GN tended to extract more WSC to fill grains than ones with fewer GN in 2005 and 2007. GN increased with increased spike DM at anthesis, the number of grainsg−1 of spike DM, and the duration of spike growth, but was not correlated to the fraction of DM partitioned to the spike at anthesis for individual genotypes and across the 3 years. Compared to winter wheat in the UK, Australian spring and winter wheat had a lower number of grainsg−1 spike DM and g−1 chaff DM. HI was positively related to WSC at anthesis and post-anthesis DM accumulation in the drought year of 2006, but not in average (2007) and above-average rainfall (2005) years. HI was negatively related to the proportion of stem DM to above-ground dry matter (AGDM), but positively related to the proportion of spike DM to AGDM. Dry matter partitioning indicated that the proportion of stem DM to AGDM and chaff DM to AGDM was 20% and 50% higher than that of winter wheat grown in the UK, respectively. This was related to a lack of remobilization of WSC and a net increase between spike DM at anthesis and chaff DM at maturity. Therefore, we suggest that increasing the number of grainsm−2 by breeding for more grainsg−1 spike DM, reducing dry matter partitioning into stem and chaff, and remobilizing WSC can lead to an improved HI. We conclude that the yield of wheat can be increased without increasing AGDM and the potential HI can reach 0.50 in the HRZ of south-western Australia if the number of grainsm−2 can be increased.

Identification of Quantitative Trait loci and Environmental Interactions for Accumulation and Remobilization of Water-Soluble Carbohydrates in Wheat (Triticum aestivum L.) Stems

Genetic analyses of nine traits associated with stem water-soluble carbohydrate (SWSC) accumulation and remobilization at grain-filling period under drought stress (DS) and well-watered (WW) conditions were undertaken using doubled haploid lines (DHLs) derived from two Chinese common wheat cultivars. Some significantly and very significantly positive correlation was observed among nine traits associated with SWSC. Higher phenotypic values for most traits were detected under DS. Broad sense heritabilities (h(B)(2)) of the traits showed wide fluctuations between two water treatments. A total of 48 additive and 62 pairs of epistatic QTL for nine traits were identified as distributing on all 21 chromosomes. A majority of QTL involved significant additive and epistatic effects with interactions of QTL and environments (QEIs). Two additive and two pairs of epistatic loci involved only QEIs without corresponding significant additive or epistatic effects. The contributions of the additive QEIs were two- to fourfolds higher than those of their corresponding additive QTL. Most of the additive QEIs for traits associated with SWSC interacted with DS. In addition, some QTL for the grain-filling efficiencies and thousand-grain weight were colocated in the same or adjacent chromosome intervals with QTL for accumulation and remobilization efficiency of SWSC before 14 days after flowering.

Absence of Fructan Degradation During Fructan Accumulation in Wheat Stems

Summary Turnover of fructan accumulated in the penultimate internode of wheat (Triticum aestivum L.) was studied after anthesis. Two genotypes differing in the rate of accumulation and remobilization of water-soluble carbohydrates in the stem were used in the study; plants were grown in growth chambers at ambient CO2. After anthesis the set of plants was divided into two groups and each group was maintained at 1000 or 300 µL CO2 L-1 in order to alter the supply of photosynthates to the stem. Between 7–15 days after anthesis plants were labelled with 14CO2 during a whole photoperiod. Plants were harvested before labelling and at one to two-day intervals up to 6 days after 14C application in the 300 µL CO2 L-1 treatment and up to 12 days in the 1000 µL CO2 L-1 treatment, respectively. Water-soluble carbohydrates (WSC) were extracted and the concentrations and 14C content of their components determined. The WSC concentration increased at a linear rate during the observation period and was exclusively due to accumulation of fructan. The rate of fructan synthesis differed between genotypes and was higher at 1000 than at 300µL CO2 L-1. 14C-activity determined in the penultimate internodes was highest one day after labelling and mainly present in sucrose and already in fructan as well. The amount of label then decreased to about two-thirds of its initial value. A strong incorporation of 14C in fructan occurred only during the first two days after labelling. For the following 10 or 5 days, 14C-activity in fructan remained constant in the penultimate internodes of both genotypes growing at 1000 or at 300 µL CO2 L-1, respectively, whereas 14C-activity in the remaining WSC components was low or decreased drastically. The results indicate that no degradation of recently synthesized fructan occurred during the phase of net fructan accumulation in wheat stems which means that there was no continuous turnover of the fructan pool in both genotypes at either 1000 or 300 µL CO2 L-1. Differences in fructan accumulation observed between genotypes or CO2 concentrations were therefore due exclusively to differences in fructan synthesis. The lack of turnover of the fructan pool during WSC accumulation in wheat internodes contrasts with findings for gramineous leaves where fructan seems to be turning over rapidly, indicating that fructan metabolism in wheat stems is regulated differently and that this carbohydrate fraction in wheat stems is a longterm storage pool.