Grain weight responses to post-anthesis spikelet-trimming in an old and a modern wheat under Mediterranean conditions

Average grain weight is a major yield component contributing to its variation, especially in Mediterranean regions where grain weight is frequently exposed to terminal stresses affecting grain growth. Most of the literature agrees that wheat grain growth is hardly limited by the source. However, no source–sink ratios studies seem to have been conducted in the Mediterranean region to determine to what degree wheat grain growth is actually limited by the source in these particular regions. We conducted two field experiments in Catalonia (north-eastern Spain), where an old cultivar (Anza) and a more recently released one (Soissons) were sown in a range of different nitrogen and water availabilities and sowing dates. This was to analyse the degree of source limitation for grain growth. Sink size was modified by removing half of the spikelets c. 10 days after anthesis, virtually doubling the availability of assimilates per grain effectively growing.Trimming the spikes did not produce significant changes in grain growth rate or duration of grain filling. Consequently, grain weight did not respond noticeably to the reduction in sink demand and any eventual response has been far from representing a strong competition among grains during grain filling.     

Evaluation of Grain Filling Rate and Duration in Bread and Durum Wheat, under Heat Stress after Anthesis

Bread and durum wheat genotypes were submitted to heat stress during the grain filling period, and relationships between grain weight and accumulated time from anthesis until maturity, using days after anthesis and growing degree days, were described by cubic polynomials. Maximum grain weight and the duration and rate of grain filling were estimated from the fitted curves. It was found that bread and durum wheat exposure to high temperatures significantly decreased grain weight and hastens physiological maturity (shortening the grain filling period). High temperatures significantly affected the rate (on a growing degree day basis) and duration (on Julian day units) of grain filling. The grain filling rate, on a thermal time basis, was positively associated with the final grain weight and the estimated maximum grain weight. The duration of grain filling does not appear to be a limiting factor for genotype grain weight stability, being mainly fixed by temperature. Grain weight of the controlled plants was positively correlated with the final and maximum grain weight of heat stressed plants. It was concluded that a high grain filling rate and a high potential grain weight are major traits that can be useful to improve heat tolerance of Triticum under Mediterranean environments.     

高油玉米源、库生理特性研究 Ⅰ.高油玉米产量受叶源的限制

以大田放任生长的种植密度在开花期减源和半量不饱和授粉的疏库处理，比较研究了高油玉米的源、库特性。结果表明，在1.5株/m2密度下，与普通玉米相比，高油玉米单株籽粒产量显著低于普通玉米，产量构成中穗粒数差异不显著，千粒重较低（达显著水平）；两类型玉米的单株库容量相当，但高油玉米籽粒灌浆速率低，籽粒充实度低，     

Green Area Duration during the Grain Filling Period of an Argentine Wheat Cultivar as Influenced by Sowing Date, Temperature and Sink Strength

The effects of sowing date, air temperature during the grain filling period, sink-strength, and then-interactions on the wheat green area (leaves, leaf sheaths and peduncles) duration from anthesis to total senescence were determined under field conditions at Buenos Aires (Argentina). The individual grain weight was determined as an average of either all grains or basal grains of the spikelets 7 and 8 through the treatments.
The delayed sowing date reduced the period of leaf senescence when it was regarded as calendar time between anthesis to maturity, but it did not affect that period regarded as thermal time. Similarly, the increased temperature has also increased the rate of senescence. On the other hand, the sink strength did not affect the green area duration; since neither the rate nor the period of senescence was altered.
Similarly, both sowing date and mean temperature decreased the individual grain weight, but the sink strength did not affected the weight of the basal grains, which could be interpreted as the effects of the other two factors were independent to the availability of assimilates per grain.
The effect of increased grain filling temperature on reducing grain weight did not operate via reducing the availability of assimilates although it also reduced the total grain area duration. We observed that the increased temperature decreased the individual grain weight of the basal grains at any source sink ratio.     

Contribution of Different Organs to Grain Filling in Durum Wheat under Mediterranean Conditions I. Contribution of Post‐Anthesis Photosynthesis and Remobilization

Under Mediterranean conditions, drought affects cereals production principally through a limitation of grain filling. In this study, the respective role of post‐anthesis photosynthesis and carbon remobilization and the contribution of flag leaf, stem, chaff and awns to grain filling were evaluated under Mediterranean conditions in durum wheat (Triticum turgidum var. durum) cultivars. For the purpose, we examined the effects of shading and excision of different parts of the plant and compared carbon isotope discrimination (Δ) in dry matter of flag leaf, stem, chaff, awns and grain at maturity and in sap of stem, flag leaf, chaff and awns, this last measurement providing information on photosynthesis during a short period preceding sampling. Source–sink manipulations and isotopic imprints of different organs on final isotope composition of the grain confirmed the high contribution of both carbons assimilated by ears and remobilized from stems to grain filling, and the relatively low contribution of leaves to grain filling. Grain Δ was highly and significantly associated with grain yield across treatments, suggesting the utilization of this trait as an indicator of source–sink manipulations effects on grain yield. Chaff and awns Δ were better correlated with grain Δ than stem and leaf Δ, indicating that chaff were more involved in grain filling than other organs. Moreover, in chaff, sap Δ was highly significantly correlated with dry matter Δ. These results suggest the use of Δ for a rapid and non‐destructive estimation of the variation in the contribution of different organs to grain filling.     

穗分化期外施24-表油菜素内酯(EBR)促进水稻源、库及籽粒灌浆的生理机制

水稻产量高低与其籽粒灌浆能力的强弱密切相关, 而籽粒灌浆能力的强弱受源和库的影响。已有研究表明, 油菜素甾醇类化合物(brassinosteroids, BRs)对水稻生长发育和产量具有正向调节作用。为进一步阐明BRs调控水稻源强、库容和库活性的生理机制及其相互关系, 本研究在大田条件下, 以粳稻日本晴为试验材料, 在穗分化期喷施24-表油菜素内酯(24-epibrassinolid, EBR), 分析其相关影响。首先, 两种不同浓度的EBR处理通过促进光合产物的合成及其在灌浆过程中的转运提高了水稻的源强。其次, 两种浓度EBR处理均增大了水稻的库容, 但两种处理的影响方式存在差异, 低浓度处理(T1) 显著提高水稻籽粒的千粒重, 对穗粒数的影响较小; 高浓度处理(T2)则显著增加单位面积的穗数和穗粒数, 对千粒重的影响较小。再次, 两处理同时提高了水稻强、弱势粒的蔗糖裂解酶活性, 尤其对弱势粒酸性转化酶(acid invertase, AI)活性的影响较大, 有助于光合产物向弱势粒分配, 进而促进弱势粒淀粉合成和籽粒灌浆, 提高其充实度和结实率。最后, 两处理均显著增加了水稻的产量, T1和T2分别平均增加5.6%和15.2%, T2比T1平均增产9.1%。因此, 与低浓度EBR处理下的千粒重增大相比, 高浓度处理下穗粒数的增加对产量影响更大。综上所述, 穗分化期进行EBR处理能够增大水稻的源强、库容和库活性, 进而促进光合物质的积累和分配, 有利于籽粒灌浆; 在光合物质供应充足和库活性显著提高的基础上, 库容的增大有助于产量的明显提高。     

Effect of N and CO2 supply on source size per grain at anthesis and its relationship with grain growth in wheat

Rising atmospheric CO₂ concentration ([eCO₂]) increases the yield of wheat mainly by increasing grain number, but effects on single grain weight are variable. It is discussed whether single grain growth is limited by the sink or the source size under a non-stress environment. This study explores the effect of e[CO₂] combined with varying N supply on the source and sink size during grain filling. Source size was defined as the amount of stem reserves per grain (SRG) and the proportion of incident radiation intercepted by the green canopy per grain (f_IRG) at anthesis. Data from a 2-year free-air CO₂ enrichment experiment with wheat with three N levels (on average 38 [Nd], 190 [Nad] and 320 kg N ha⁻¹ [Nex]) and two CO₂ levels (393 and 600 ppm) on SRG, f_IRG and grain filling rate (GFR) and duration (GFD) were evaluated. SRG ranged from 2.5 to 12.9 mg and f_IRG from 4.0 × 0.001% to 6.8 x 0.001%. Rising N supply or e[CO₂] decreased SRG and f_IRG via their increases in grain number. Accordingly, there was a negative linear relationship between grain number and SRG (r² ≥ 0.84) or f_IRG (r² ≥ 0.97). Increasing N supply decreased GFR, but increased GFD, and GFR was increased by e[CO₂] under Nad and Nex. For GFR and final grain weight, there was a strong positive (r² ≥ 0.85), and for GFD, a strong negative linear relationship (r² ≥ 0.76) with f_IRG under Nad and Nex. Under these N levels, f_IRG supplied the largest share (>86%) for grain growth and thus single grain growth was possibly source limited under Nad and Nex. Under high grain number such as under Nex and e[CO₂], there might be a risk for low final grain weight due to the low SRG that is insufficient for buffering assimilate shortage under unfavourable environmental conditions in early grain filling.     

冬小麦产量形成模拟模型研究

根据小麦生理生态学理论，建立了冬小麦产量形成及最终产量模拟模型（WYSM），作为小麦生长模型的子模型。模型较为全面地考虑了孕穗期水分、低温霜冻、高温及生长后期干热风对冬小麦粒数的影响，将灌浆期分成3个阶段，引入3个品种参数，考虑每个阶段最大灌浆速率，并利用温度、水分、籽粒体内N/C比等因子进行修正，考虑源库限制，最后采用产量构成因素方法建立小麦最终产量模型。利用北京地区和河南地区不同年份和不同品种的试验资料对模型进行了验证。结果表明，WYSM模型对小麦产量构成因子及最终产量的模拟效果很好，模拟值与实测值吻合度高，粒数、粒重、产量及灌浆过程模拟的相对均方差（NRMSE）为4.2%～10.9%，相对误差（RE）绝对值的平均值为2.9%～6.7%，决定系数R2为0.88～0.99，说明模型不仅具有较强的机理性而且具有较高的预测性和适用性。     

小麦开花后源库关系分析

小麦开花后的源库关系分析结果表明，库容量的大小影响开花后光合产物的生产和分配，较大的库容可以促进叶片光合潜力的发挥和光合产物向穗部的运转。开花后绿叶面积的大小和光合强度的高低影响籽粒的灌浆速率，粒重受花后干物质积累量的制约。说明小麦开花后库对源有反馈调节作用，而源又影响库的充实，源库关系在动态变化中相互协调取得平衡。栽培措施应使源库关系在高水平上取得动态平衡，才能获得高产，粒叶比既反映了库容的相对     

Late‐season photosynthetic rate and senescence were associated with grain yield in winter wheat of diverse origins

There is a lack of studies that have investigated grain yield, its components and photosynthesis in late stages of wheat growth, giving us insufficient understanding of how these factors interact to contribute to yield during this period. As a result, three field experiments were carried out examining 20 winter wheat genotypes of diverse origins under irrigated, terminal drought and dryland conditions in the southern Idaho. Our objective was to evaluate the interaction between post‐anthesis physiological traits, especially leaf‐level photosynthetic capacity, senescence and yield components on grain yield in different moisture regimes. Genotype differences were found in leaf‐level photosynthesis and senescence, canopy temperature depression, grain yield and yield components in each water regime. Grain yield was closely associated with traits related to grain numbers. In all three moisture regimes, positive correlations were observed between grain yield and photosynthesis that were dependent on the timing or physiological growth stage of the photosynthetic measurement: highly significant correlations were found in the mid‐ and late grain filling stages, but no correlations at anthesis. Consistent with these findings, flag leaf senescence at the late grain filling stage was negatively correlated with grain yield and photosynthetic rate (under terminal drought and dryland conditions). These findings provided evidence that grain yield was sink‐limited until the final stages of growth, at which time sustained photosynthesis and delayed senescence were critical in filling grain. Because the trends were consistent in moisture sufficient and deficient conditions, the results suggest that late‐season photosynthesis and delayed leaf senescence are driven by the size of the reproductive carbon sink, which was largely governed by factors affecting grain numbers.     

基于控制授粉技术的玉米弱势粒发育与库特征的关系

明确弱势粒败育和灌浆受限与其库容量或库活性关系,对于探讨弱势粒调控途径、实现密植群体产量挖潜具有重要意义。本研究以典型玉米杂交种郑单958和先玉335为材料,在控制授粉条件下(不完全授粉IcP、完全授粉CP),比较成功发育弱势粒(IcP处理)和发育不良弱势粒(CP处理)的库容量和库活性及籽粒灌浆参数的差异。结果表明,不同控制授粉处理下,玉米弱势粒胚乳细胞增殖过程和最大胚乳细胞数无显著差异;IcP处理弱势粒可溶性酸性蔗糖转化酶(SAI)活性显著高于CP处理,平均差异和最大差异分别达12.6%和21.8%,且实测百粒重、籽粒终极生长量、最大灌浆速率和平均灌浆速率皆表现为IcP处理高于CP处理。可见,玉米果穗顶部弱势粒败育或灌浆停滞不受其库容量的限制,籽粒形成期的库活性是弱势粒败育或灌浆受限的核心限制因子。     

冬小麦子粒充实度及灌浆模式的研究

通过对小麦子粒灌浆及发育的研究分析,提出了子粒充实度的概念及计算公式,并据此对河南省小麦子粒灌浆模式进行了研究,结果表明,品种间的子粒充实度存在着显著差异,它可以较好地反映子粒生长潜力的发挥程度。河南省的高产小麦品种可以划分为四种灌浆模式：①高灌浆速度与短灌浆持续期相结合类型;②长灌浆持续期与早开花相结合类型;③长灌浆持续期与晚开花相结合类型;④低灌浆速度与长灌浆持续期相结合类型。其中,①②模式类型比较适合河南省的生态条件,子粒充实度较高。子粒充实度与子粒灌浆持续期、子粒灌浆完成期、开花期、起始生长势等密切相关     

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

Heat 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.     

Grain yield of wheat (Triticum aestivum L.) under long‐term heat stress is sink‐limited with stronger inhibition of kernel setting than grain filling

The aim of the study was to investigate source‐sink relations of wheat under continuous heat stress and to identify bottle necks of yield formation. A pot experiment was conducted in two climatic chambers exposing wheat plants (Triticum aestivum L. cv. Thasos) either to day/night temperatures of 20/20°C (control conditions) or of 30/25°C (heat stress) during the whole vegetation period in the absence of plant water deficit. Plants were harvested at four phenological stages: three‐node stage (DC 33), start of flowering (DC 61), grain filling (DC 75) and maturity (DC 94). Heat stress shortened the development phases of the plants and caused a significant decrease in total above‐ground biomass between 19% and 41%. At grain filling and at maturity, the reductions in total shoot biomass mainly resulted from grain yield depressions by 77% and 58%, respectively. The ear number per plant was significantly higher under heat stress in comparison with the control, at maturity it was more than doubled. On the contrary, under heat stress, the kernel number per ear was strongly decreased by 83% and 75% during grain filling and at maturity, respectively. The decrease in individual kernel weight was 23% at maturity. Thus, the heat‐stressed plants were able to strongly increase the number of ear‐bearing tillers which were able to set only a small number of kernels, yet these kernels showed good grain filling. The harvest index (HI) of heat‐stressed plants was significantly reduced by 36% (control: HI = 50.1% ± 0.4, heat: HI = 32.2% ± 0.9***). The plants in the stress treatment adapted to the adverse conditions by less biomass production which presumably allowed a higher transpiration without an increase in total water consumption. Nevertheless, under heat stress, the water use efficiency (WUE_grain) was strongly decreased by 62% as a result of a small grain yield. In ears and grains, the sucrose, glucose and fructose concentrations were not significantly different between control and heat stress at start of flowering and during grain filling. Thus, the supply of assimilates was not restricted (no source limitation). Sink capacity was reduced by heat stress, as lesser and smaller kernels were produced than in the control. Concerning sink activity, the sink‐limiting step during kernel set is probably the active transport of hexoses across the plasma membrane into the developing kernels, which could also affect grain filling. This needs to be investigated in more detail in further studies.     

Efficiency of grain production of winter wheat as affected by N fertilisation under particular consideration of single culm sink size

Grain yield and yield components of winter wheat were recorded during 2-year field trials in Southern Bavaria, Germany. The impact of single ear sink size on the efficiency of grain production was studied in plants differing in single ear weight. While total grain yield showed only slight differences between N fertiliser treatments, significant variations were detected in harvest index and N harvest index. For single culms, a decrease in ear weight was related to decreasing values of harvest index and N harvest index. This correlation could not be altered by means of N fertilisation. The most efficient grain production, i.e. high value of harvest index and N harvest index, was regularly recorded in plant stands developing large single ear weights. The study confirms that with increasing sink size, the efficiency of grain production in winter wheat is improved. A N fertilisation strategy, favouring the formation of a large sink size, is described. In this respect, lower N rates in early spring and emphasis on N fertilisation during stem elongation proved to be decisive. This strategy favoured the generative growth at the expense of vegetative growth without excessively decreasing the corresponding source size.     

Effects of an Early Application of Sulphur or Etephon as Foliar Spray on the Growth and Yield of Spring Barley in a Mediterranean Environment

Leaf area development, biomass production and yield of four spring barley varieties grown in a Mediterranean environment (southern Spain) in response to an early application of foliar sulphur or etephon have been studied. Both sulphur and etephon produced similar results compared to the control. Thus, whereas the maximum leaf area index on untreated plots was reached at the beginning of shooting, the growth of foliar area in the treated ones was extended until anthesis and its decline during maturity was similarly retarded. This led to a significant improvement in the biomass at anthesis (which was closely correlated with grain yield) as well as in the leaf area duration during grain filling. These effects were principally due to variations in the number of leaves per plant, caused by a higher tiller production in the treated plants and not by an increase in the number of leaves per tiller or by leaf size.
An application of sulphur or etephon at tillering increases grain yield by raising both the number of ears per plant and per plot, without modifying the number of grains per ear or 1000-grain weight. The similarity between the effects of sulphur and etephon may be due to the fact that sulphur absorbed by the leaves results in an increase in methyonine, the biological precursor or ethylene. The positive correlation between biomass at anthesis and number of ears over grain yield suggests that sink capacity and source activity are closely related and both simultaneously limited by the environment.     

川东南高温伏旱区杂交中稻品种库源结构对稻米整精米率与垩白粒率的影响

以25个杂交中稻组合为材料,研究了品种齐穗期库源结构对稻米整精米率与垩白粒率的影响。结果表明：整精米率与源库比呈极显著负相关,垩白粒率与源库比呈显著或极显著正相关。其原因在于,随着杂交组合每穗着粒数的增加,单位颖花的源占有量减少,稻穗籽粒灌浆速率降低,灌浆历期延长,籽粒容重增大,整精米率提高;当籽粒灌浆     

Modification of the Sink/Source Relationships in Bread Wheat and its Influence on Grain Yield and Grain Protein Content*

Artificial manipulation of sink and source was carried out in several bread wheat varieties in order to study the variations in the pattern of storage products accumulation in the grain. In a first experiment, partial ablation of the laminae did not cause any significant variation in the yield components, while total elimination of the laminae resulted in a decreased fertility of the spikelets and in a lower kernel weight. The protein content of grain turned out to be a function of the amount of vegetative organs left in the different treatments, and ranged from 11.1 % in leafless plants to 16.5% in the control. The halving of the spikes led to a 14% increase in the size of the kernels, while the protein content per spike showed a 20 % drop in comparison to the control. Reduction of sink affected nitrogen accumulation to a lesser extent than carbohydrates storage in the grain. Reduction of sink induced remarkable increases in the protein fractions: gliadins +59%, glutelins +44%, insoluble residue +30%, non-proteic nitrogen +28%, albumins and globulins + 16%. The increase of GPC or of specific solubility classes did not influence significantly the quality of the flour evaluated by the Zeleny and Pelshenke indices. The presented data suggest some caution in adopting kernel size and GPC as main selection criteria in early generations. It seems more convenient to select for a prolonged grain filling period and for a higher biomass without increasing plant height.     

源库调节对小麦不同品种籽粒微量元素及蛋白质含量的影响

为了解小麦籽粒微量营养元素含量的调控机制及其与籽粒重和蛋白质含量的关系, 以9个冬小麦品种为材料, 通过开花后减源(去叶、穗遮光)、减库(去50%小穗)处理, 分析了成熟籽粒中Fe、Zn、Mn、Cu等微量元素含量与籽粒重、蛋白质含量变化及其相互关系, 并探讨了籽粒微营养素积累的源库调控作用。结果表明, 籽粒中Fe、Zn、Mn、Cu、蛋白质含量和籽粒重均在品种间和源库处理间存在显著差异。去叶源不仅使籽粒重和籽粒蛋白质含量显著降低, 而且使籽粒Fe、Zn、Mn和Cu含量明显降低; 穗遮光使籽粒重显著降低, 蛋白质含量略有提高, 籽粒微量元素含量的变化因品种和元素类型而异, 总体趋势为Fe、Zn和Cu含量增加, Mn含量降低; 去小穗减少库, 使各品种剩余籽粒粒重略有增加, 而蛋白质含量提高, 籽粒Fe、Zn、Mn和Cu含量均较大幅度提高。籽粒Fe、Zn、Mn和Cu含量主要受各元素供源的限制, 不同元素受供源影响程度不同, 且与品种基因型有关。籽粒中4种微量元素含量之间及其与粒重和蛋白质含量之间具有一定的正相关性, 说明籽粒微量元素含量与籽粒重和蛋白质含量存在同步提高的可 能性。     

油菜素内酯对春玉米灌浆期叶片光合功能与产量的调控效应

以玉米品种"郑单958"为材料,在大田条件下,采用植物生长调节物质油菜素内酯(brassinolide,BR)对苞叶和穗位叶喷施处理,研究了BR对玉米穗位叶功能、籽粒灌浆及产量的调控作用。结果表明,灌浆期随生育进程,玉米穗位叶叶绿素含量、光合速率、磷酸烯醇式丙酮酸羧化酶(PEPCase)、1,5-二磷酸核酮糖羧化酶(Ru BPCase)以及蔗糖磷酸合酶和蔗糖合酶的活性均显著下降。同时,籽粒蔗糖含量显著降低,但淀粉含量和粒重均显著增加。与对照相比,BR处理显著增加玉米穗位叶叶绿素含量,提高光合速率,增强PEPCase、Ru BPCase、蔗糖磷酸合酶和蔗糖合酶的活性。BR处理显著增加籽粒蔗糖和淀粉积累,提高玉米籽粒干物质积累。在产量构成上,BR显著缩短秃尖长度,增加穗粒数和千粒重,显著提高产量。本研究说明,灌浆期喷施BR可提高玉米叶源的活性,延长叶片光合功能持续期,促进籽粒灌浆和物质积累,从而实现增产。