Green leaf area decline of wheat flag leaves: the influence of fungicides and relationships with mean grain weight and grain yield

A modified Gompertz model was derived to describe the fractional decline in green area of wheat flag leaves in field experiments where green leaf area at time t=100exp[‐exp(‐k(t‐m))]. Curves fitted over time to visual assessments of green leaf area (% of total leaf area) throughout flag leaf life accounted for more than 98% of variation in 45 of 48 wheat cultivar × fungicide treatment (+/?) comparisons. This data set spanned 17 yr and therefore included cultivars of contrasting parentage and age. In the absence of fungicide, green leaf area decline was associated with drought or infection with a number of foliar pathogens including Septoria tritici (sexual stage Mycospherella graminicola), Erysiphe graminis and Puccinia striiformis. Fungicides applied to the flag leaf included propiconazole, propiconazole plus tridemorph, flusilazole or azoxystrobin. Fungicide effects on m (i.e. time to 37% green area) were closely related to fungicide effects (% of untreated) on mean grain weight (variation accounted for (VAF) = 80%) and grain yield (VAF = 85%).     

Contribution of the wheat (Triticum aestivum L.) flag leaf to grain yield in response to plant growth regulators

In West-Europe, intensive cereal management uses plant growth regulators (PGRs) especially for wheat. A green-house experiment compared the effects of two PGRs on flag leaf characteristics and yield of winter wheat. Chlormequat chloride + choline chloride (CCC) and chlormequat chloride + choline chloride + imazaquin (CCC+I) were applied to winter wheat at growth stage 5 (Feekes Large scale). CCC and CCC+I significantly increased flag leaf surface area at anthesis. Both treatments also enhanced chlorophyll content of the main stem flag leaf. The grain filling period was extended with PGR application by 2 days. CCC and CCC+I significantly increased net CO₂ assimilation rates during the flag leaf life. No effects of PGR spraying were observed on the pattern of ¹⁴C labelled assimilate distribution. Increased grain yield was due to the increase in average grain weight. The results indicate that PGR treatments increased flag leaf contribution to grain filling. The addition of imazaquin (I) to chlormequat (CCC) improved the effects of CCC.     

Effect of Indol-3-yl Acetic Acid on Photosynthetic Characteristics of Wheat Flag Leaf During Grain Filling

Area and fresh and dry masses of flag leaf show two phases of development during grain filling in Triticum aestivum. The initial large increase in leaf size is mainly due to water intake. Contents of chlorophylls and carotenoids, reducing sugars, and sucrose, Hill reaction rate, and photosynthetic activity increased during leaf growth, but a noticeable decline in these parameters followed throughout leaf senescence. The maximum accumulation of polysaccharides and proteins occurred at the beginning of grain set, but a continuous decline in their absolute values was manifested during grain filling. Grain priming with indol-3-yl acetic acid (IAA) at 25 mg kg^-1 stimulated the flag leaf growth, namely its fresh and dry masses and its area. Furthermore, the stimulatory effect was mainly due to the increase in the pigment formation that in turn increased the photosynthetic activity of flag leaf during grain filling. On the other hand, the highest dose of IAA (50 mg kg^-1) attenuated the growth and physiological activity of flag leaf through its inhibitory action on leaf fresh and dry masses, leaf area, pigments, saccharides and protein formation, as well as its effect on ¹⁴CO₂ assimilation.     

播种量和施氮量对垄沟覆膜栽培冬小麦花后生理性状的影响

为协调冬小麦个体与群体间的关系,充分发挥旱作条件下垄沟栽培优势,以冬小麦品种小偃22为材料,采用二元二次正交旋转组合设计,通过田间试验研究了垄下集中施肥、垄上覆膜、膜际种植模式下播种量和施氮量对冬小麦花后生理性状的影响.结果表明： 花后叶面积指数、旗叶叶绿素含量和净光合速率均随施氮量的增加而增加.灌浆前中期叶面积指数随播种量的增加呈先增后稳的趋势;灌浆后期叶面积指数随播种量的增加而降低.随播种量的增加,旗叶的叶绿素含量和净光合速率降低,单株产量呈先减少后增加的趋势.适宜的播种量可以协调个体与群体间的矛盾,而适量增施氮肥有利于花后小麦生理性状的改善和产量的提高.在供试条件下,小偃22在播种量112.5 kg·hm-2与施氮量180～222 kg N·hm-2配置时,个体与群体的关系比较协调,花后叶面积指数较高,群体结构适宜,而且旗叶叶绿素含量、净光合速率和单茎产量较高,能获得高产.     

播种量和施氮量对垄沟覆膜栽培冬小麦花后生理性状的影响

为协调冬小麦个体与群体间的关系,充分发挥旱作条件下垄沟栽培优势,以冬小麦品种小偃22为材料,采用二元二次正交旋转组合设计,通过田间试验研究了垄下集中施肥、垄上覆膜、膜际种植模式下播种量和施氮量对冬小麦花后生理性状的影响.结果表明:花后叶面积指数、旗叶叶绿素含量和净光合速率均随施氮量的增加而增加.灌浆前中期叶面积指数随播种量的增加呈先增后稳的趋势;灌浆后期叶面积指数随播种量的增加而降低.随播种量的增加,旗叶的叶绿素含量和净光合速率降低,单株产量呈先减少后增加的趋势.适宜的播种量可以协调个体与群体间的矛盾,而适量增施氮肥有利于花后小麦生理性状的改善和产量的提高.在供试条件下,小偃22在播种量112.5 kg hm-2与施氮量180 ～222 kg N·hm-2配置时,个体与群体的关系比较协调,花后叶面积指数较高,群体结构适宜,而且旗叶叶绿素含量、净光合速率和单茎产量较高,能获得高产.     

潘庆民1,于振文2,王月福2

采用盆栽和水泥池栽研究了追氮时期对小麦光合作用、14C同化物运转分配和硝酸还原酶(NR)活性的影响.结果表明,拔节(雌雄蕊原基形成)期较起身(二棱)期追施氮肥,显著提高了小麦开花后的旗叶叶绿素含量和单叶光合速率;灌浆期旗叶14C同化物向籽粒转移比例显著提高,而在营养器官的滞留比例显著降低;旗叶和根系中硝酸还原酶(NR)活性亦显著提高.小麦穗粒数、粒重和产量增加,蛋白质含量提高.     

Effect of Nitrogen Fertilizer on Photosynthesis and Ribulose 1,5-Diphosphate Carboxylase Activity in Spring Wheat in the Field

Wheat was grown in the field with different levels of nitrogenousfertilizer, and the rate of photosynthesis and the activityof ribulose 1,5-diphosphate carboxylase in the flag leaves determined.Additional nitrogen increased the dry-weight and leaf area ofthe plants, but did not increase grain yield; the rate of photosynthesisof the flag leaves was unchanged but the activity of ribulose1,5-diphosphate carboxylase increased. The significance of theseobservations to the loss of potential yield of wheat and therelationship between, photosynthesis and carboxylase activityis considered.     

Photosynthetic characteristics and enzymatic antioxidant capacity of flag leaf and the grain yield in two cultivars of Triticum aestivum (L.) exposed to warmer growth conditions

Using late sowing practice, the reproductive growth (anthesis and kernel filling) phase of two wheat cultivars, HD 1553 and HD 2307 was exposed to warmer growth conditions, and the effect on grain yield was examined. The grain weight declined in late-sown plants of both cultivars, but the number of grains per spike decreased drastically in HD 1553 plants. In this cultivar exposure to warmer temperature during reproductive phase led to 67% fewer grains per spike. Examination of photosynthetic and enzymatic antioxidant capacity in flag leaves of late-sown plants revealed a marked reduction in chlorophyll and carotenoid pigmentation in addition to a decline in the activity of H2O2 metabolising enzymes in HD 1553 cultivar. The photo-oxidative pigment loss due to warmer growth conditions in late-shown HD 1553 plants could lead to a reduction in flag leaf photosynthesis and contribute to poor grain yield.     

灌溉和种植方式对冬小麦生育后期旗叶光合特性及产量的影响

于2009—2011年通过田间试验,以高产中筋冬小麦品种济麦22为材料,设等行距平作、宽窄行平作、沟播3种种植方式,每种种植方式下设不灌水(W₀)、灌拔节水(W₁)、灌拔节水+开花水(W₂)、灌拔节水+开花水+灌浆水(W₃)4种灌溉处理(每次灌水量为60 mm),研究不同灌溉和种植方式对冬小麦生育后期旗叶光合特性和产量的影响.结果表明: 随冬小麦灌水量的增加,3种种植方式下小麦花后旗叶叶面积和光合速率均增加,光系统Ⅱ最大光化学效率和实际光化学效率也增加;与W₀处理相比,各灌水处理提高了小麦籽粒产量,但水分利用效率(WUE)降低.同一灌溉条件下,与其他两种种植方式相比,沟播方式小麦花后旗叶光合速率、光系统Ⅱ最大光能转化效率和实际光化学效率均较高,且W₂处理籽粒产量显著高于其他处理.统筹考虑冬小麦的籽粒产量和WUE,沟播结合灌拔节水+开花水是华北平原冬麦区较适宜的节水种植方式.     

Effects of awns on the photosynthesis and yield of wheat, Triticum aestivum

Two pairs of awned and awnless near-isogenic lines of winter wheat were used in a field study in which canopy enclosure apparatus and carbon-14 dosing were employed to assess the contribution of the awns to photosynthesis and grain yield. Awns contributed an average of 12-2% to canopy gross photosynthesis but did not increase the net photosynthesis of the complete canopy. The presence of awns decreased photosynthesis in the remaining ear structures and in the flag and penultimate leaf laminae. Seven days after dosing during the phase of rapid grain filling, 80% of the carbon recovered was located in the grains. The awns intercepted 9% of the incident visible radiation when fully green, and senesced at similar rates as the ears and flag leaves. In a second experiment the effect of awns on grain yield and its components was investigated in crosses segregating for height and presence of awns. Awns did not increase grain yields in either experiment. It appears that for British conditions in the absence of severe drought there is little advantage to be gained at present by breeding awned varieties of wheat.     

Photosynthesis of Ears and Flag Leaves of Wheat and Barley

Immediately after anthesis ears of spring wheat absorbed lessthan 0.5 mg CO₂, per hour in daylight and later evolved CO₂,in the light and in the dark. The rate of apparent photosynthesisof the combined flag-leaf lamina and sheath and peduncle (collectivelycalled flag leaf) of two spring wheat varieties, Atle and JufyI, was 3–4 mg per hour; the rates of the flag leaf andthe ear of two spring barleys, Plumage Archer and Proctor, wereeach about 1 mg per hour. The gas exchange of ears and flag leaves between ear emergenceand maturity accounted for most of the final grain dry weight.The CO₂, fixed by the wheat ear was equivalent to between 17and 30 per cent of the grain weight, but more than this waslost by respiration, so assimilation in the flag leaf was equivalentto 110–20 per cent of the final grain weight. In barley,photosynthesis in the flag leaf and the net CO₂ uptake by theear each provided about half of the carbohydrate in the grain. Barley ears photosynthesized more than wheat ears because oftheir greater surface, and flag leaves of wheat photosynthesizedmore than those of barley because they had more surface anda slightly greater rate of photosynthesis per dm².     

三种栽培模式下不同基因型冬小麦旗叶衰老代谢比较

为了探索冬小麦在不同栽培模式下功能叶片衰老代谢的生理机制,以cp02(213)、cp99(1)和陕农512为材料,比较研究了常规栽培、覆草栽培、地膜覆盖3种栽培模式下小麦旗叶衰老代谢特性.结果表明,覆草栽培叶面积、旗叶功能期、叶绿素含量、叶片保护酶活性(SOD、POD、CAT)显著高于常规栽培,膜脂过氧化程度较低,叶片衰老速度缓慢,代谢强度旺盛,有利于籽粒灌浆和光合产物的积累.灌浆前期,地膜覆盖叶面积、旗叶功能期、叶绿素含量、叶片保护性酶活性(SOD、POD、CAT)显著高于常规栽培,膜脂过氧化程度低于常规栽培;灌浆后期,叶绿素含量急剧下降,叶片衰老速度加快,膜脂过氧化程度加剧.参试品种(系)中陕农512叶片衰老速度缓慢,保绿性好.     

The nature of the effects of the aphids Sitobion avenae and Metopolophium dirhodum on the growth of wheat

Field-caged, post-anthesis populations of the aphids Sitobion avenae and Metopolophium dirhodum reduced grain weight of wheat by 14 and 7% respectively and induced changes in the senescence of the flag leaf. Spikelet number and grain number were unaffected as they are normally determined by pre-anthesis factors. Percentage grain protein was significantly reduced by both aphid species. The pattern of grain weight reduction within the ear was consistent with known limitations on the distribution of flag leaf assimilates among the grains. The relative effects of the two aphid species apparently resulted from the degree of nutrient drain imposed at particular feeding sites and the reduction in the leaf area duration of the flag leaf.     

Effect of Nitrogen Fertilizer on Photosynthesis of Several Varieties of Winter Wheat

The rates of gross photosynthesis of the flag leaf and the nextleaf below (second leaf) in crops of winter wheat were estimatedfrom the ¹⁴C uptake of the leaves after exposure to short pulsesof ¹⁴CO₂. The photosynthetic rates of both leaves during thegrain-filling period decreased with increase in nitrogen fertilizerbecause the intensity of photosynthetically active radiationwas less at the surface of the leaves in the dense crops withadditional nitrogen. In addition, the rate of photosynthesisat saturating light intensity was slightly decreased by nitrogen.The effects of nitrogen, in decreasing the rate of photosynthesisper unit area of leaf and in increasing the leaf-area indexof the top two leaves, were such that the photosynthetic productivityper unit area of land of the flag leaf was increased by nitrogenbut the productivity of the second leaf was unaffected. Applying180 kg N ha^–1 increased the productivity of the top twoleaves by a factor of 2.3 but increased grain yield by only1.8. The photosynthetic productivity of the second leaf duringthe grain-filling period was about half that of the flag leaf. There was no difference in photosynthetic rate per unit areaof leaves of Cappelle-Desprez and Maris Huntsman which couldaccount for the larger yield of the latter cultivar. There wasa slight indication that the leaves of the semi-dwarf cultivarsMaris Fundin and Hobbit photosynthesized faster than those ofMaris Huntsman. Triticum aestivum L., winter wheat, photosynthesis, nitrogen fertilizer     

Genotypic variation in source and sink traits affects the response of photosynthesis and growth to elevated atmospheric CO2

This study aimed to understand the response of photosynthesis and growth to e-CO₂ conditions (800 vs. 400 μmol mol⁻¹) of rice genotypes differing in source–sink relationships. A proxy trait called local C source–sink ratio was defined as the ratio of flag leaf area to the number of spikelets on the corresponding panicle, and five genotypes differing in this ratio were grown in a controlled greenhouse. Differential CO₂ resources were applied either during the 2 weeks following heading (EXP1) or during the whole growth cycle (EXP2). Under e-CO₂, low source–sink ratio cultivars (LSS) had greater gains in photosynthesis, and they accumulated less nonstructural carbohydrate in the flag leaf than high source–sink ratio cultivars (HSS). In EXP2, grain yield and biomass gain was also greater in LSS probably caused by their strong sink. Photosynthetic capacity response to e-CO₂ was negatively correlated across genotypes with local C source–sink ratio, a trait highly conserved across environments. HSS were sink-limited under e-CO₂, probably associated with low triose phosphate utilization (TPU) capacity. We suggest that the local C source–sink ratio is a potential target for selecting more CO₂-responsive cultivars, pending validation for a broader genotypic spectrum and for field conditions.     

Dynamics of light and nitrogen distribution during grain filling within wheat canopy

In monocarpic species, during the reproductive stage the growing grains represent a strong sink for nitrogen (N) and trigger N remobilization from the vegetative organs, which decreases canopy photosynthesis and accelerates leaf senescence. The spatiotemporal distribution of N in a reproductive canopy has not been described in detail. Here, we investigated the role of the local light environment on the spatiotemporal distribution of leaf lamina N mass per unit leaf area (SLN) during grain filling of field-grown wheat (Triticum aestivum). In addition, in order to provide some insight into the coordination of N depletion between the different vegetative organs, N dynamics were studied for individual leaf laminae, leaf sheaths, internodes, and chaff of the top fertile culms. At the canopy scale, SLN distribution paralleled the light gradient below the flag leaf collar until almost the end of grain filling. On the contrary, the significant light gradient along the flag leaf lamina was not associated with a SLN gradient. Within the top fertile culms, the time course of total (alive + necrotic tissues) N concentration of the different laminae and sheaths displayed a similar pattern. Another common pattern was observed for internodes and chaff. During the period of no root N uptake, N depletion of individual laminae and sheaths followed a first-order kinetics independent of leaf age, genotype, or N nutrition. The results presented here show that during grain filling, N dynamics are integrated at the culm scale and strongly depend on the local light conditions determined by the canopy structure.     

花后干旱或渍水下氮素供应对小麦光合和籽粒淀粉积累的影响

防雨池栽条件下,设置渍水、干旱和对照3个土壤水分处理,每水分处理下再设置两个施氮水平,研究了花后渍水和干旱逆境下氮素水平对两个蛋白质含量不同的小麦品种光合特性和籽粒淀粉积累的影响.结果表明,与对照相比,花后渍水和干旱处理显著降低小麦旗叶净光合速率和SPAD值,干物质积累量下降.干旱处理下,增施氮肥提高旗叶光合速率和SPAD值,渍水处理下则相反.水分逆境明显降低籽粒可溶性总糖含量,且渍水处理下增施氮肥降低小麦叶片和籽粒可溶性总糖含量,干旱状态下规律相反.渍水处理下增施氮肥降低淀粉积累速率.水分逆境明显降低小麦粒重、产量和淀粉产量,且干旱处理下增施氮肥有利于籽粒重、产量和淀粉产量的提高,而渍水下增施氮肥使粒重和产量进一步降低.试验结果表明,花后渍水和干旱逆境下施用氮肥对小麦旗叶光合速率和籽粒淀粉积累有明显的调节效应.     

Leaf photosynthetic rate and mesophyll cell anatomy changes during ontogenesis in backcrossed <Emphasis Type="Italic">indica</Emphasis> × <Emphasis Type="Italic">japonica</Emphasis> rice inbred lines

The high-yielding indica rice variety, ‘Takanari’, has the high rate of leaf photosynthesis compared with the commercial japonica varieties. Among backcrossed inbred lines from a cross between ‘Takanari’ and a japonica variety, ‘Koshihikari’, two lines, BTK-a and BTK-b, showed approximately 20% higher photosynthetic rate than that of ‘Takanari’ for a flag leaf at full heading. This is a highest recorded rate of rice leaf photosynthesis. Here, the timing and cause of the increased leaf photosynthesis in the BTK lines were investigated by examining the photosynthesis and related parameters, as well as mesophyll cell anatomy during ontogenesis. Their photosynthetic rate was greater than that of ‘Takanari’ in the 13th leaf, as well as the flag leaf, but there were no differences in the 7th and 10th leaves. There were no consistent differences in the stomatal conductance, or the leaf nitrogen and Rubisco contents in the 13th and flag leaves. The total surface area of mesophyll cells per leaf area (TA_mes) in the 13th and flag leaves increased significantly in the BTK lines due to the increased number and developed lobes of mesophyll cells compared with in ‘Takanari’. The mesophyll conductance (g _m) became greater in the BTK lines compared with ‘Takanari’ in the flag leaves but not in the 10th leaves. A close correlation was observed between TA_mes and g _m. We concluded that the increased mesophyll conductance through the development of mesophyll cells during the reproductive period is a probable cause of the greater photosynthetic rate in the BTK lines.     

Genotype and fungicide effects on late-season root growth of winter wheat

The aim of this work was to investigate differences among genotypes in post-anthesis root growth and distribution of modern UK winter wheat cultivars, and the effects of fungicide applications. Post-anthesis root growth of up to six cultivars of winter wheat (Triticum aestivum L.), given either one or three applications of fungicide, was studied in field experiments during two seasons. Total root mass remained unchanged between GS63 (anthesis) and GS85, but root length increased significantly from 14.7 to 31.4 km m⁻² in one season. Overall, there was no evidence for a decline in either root mass or length during grain filling. Root mass as a proportion of total plant mass was about 0.05 at GS85. There were significant differences among cultivars in root length and mass especially below 30 cm. Malacca had the smallest root length and Savannah the largest, and Shamrock had a significantly larger root system below 40 cm in both seasons. Fungicide applied at ear emergence had no significant effect on root mass in either season but increased root length (P<0.01) in the more disease-prone season. By maintaining a green canopy for longer, fungicide applied at flag leaf emergence may have resulted in delayed senescence of the root system and contributed to the post-anthesis maintenance of root mass and length. Section Editor: R. W. Bell     

Nighttime Warming Will Increase Winter Wheat Yield Through Improving Plant Development and Grain Growth in North China

A better understanding of the actual impacts of nighttime warming on winter wheat growth will assist in breeding new varieties and agronomic innovation for food security under future climates. A 3-year experiment was conducted over an entire growth period of winter wheat using a passive warming facility in North China. An increase of 1.1 °C in mean nighttime temperature promoted wheat development, causing a 6-day reduction of the preanthesis period but a 5-day extension of the postanthesis period. This warming significantly stimulated the rate of leaf respiration at nighttime, resulting in higher carbohydrate depletion compared to that of the unwarmed control. However, stimulation of nighttime respiration and carbohydrate depletion could be compensated for by warming-led promotion of daytime photosynthesis and carbohydrate assimilation. Meanwhile, the flag leaf area per plant and the total green leaves area were significantly higher in the warmed plots than in the unwarmed plots. Besides extending the duration of grain filling, nighttime warming significantly promoted the filling rates of the superior and inferior grains, resulting in a significant increase in the 1,000-grain weight by 6.3 %. Consequently, this moderate increase in nighttime air temperature significantly increased wheat aboveground biomass and grain yield by 12.3 and 12.0 % (p < 0.05), respectively. A moderate warming at nighttime can improve the sink-source balance of winter wheat for higher yield. Our results suggest that climatic warming may benefit winter wheat production through improvement of plant development and grain growth in North China.