Source-sink manipulation effects on postanthesis photosynthesis and grain setting on spike in winter wheat

Source-sink manipulation could regulate the net photosynthetic rate (PN) of winter wheat after anthesis, however, the direction and magnitude of the regulation varied with time after anthesis. The PN was significantly increased by source reduction at the initial time of grain filling, but sink reduction had little influence on the PN, which suggested that the sink (spike) limitation did not occur at this time. Source-sink relation markedly affected PN during rapid grain filling. The PN was increased by source reduction and decreased by sink reduction significantly, which indicated that PN was closely associated with the change of source or sink size. The effect of source-sink manipulation on PN had some relationship with the occurrence of plant senescence at the time of late grain filling. Source reduction accelerated the senescence and dropped the PN, meanwhile, sink reduction delayed the senescence and promoted the PN. A direct relation between the effect of source-sink manipulation on PN and stomatal limitation was not found. Removing one quarter of leaves (RQ) had little influence on spike development after anthesis. In this case there was enough compensation in source production through photosynthesis. Removing one half of leaves (RH) made grain mass per spike and mass of grains lowered, especially the grain mass in the top and base positions of spike declined markedly. The source supply was grain-limiting. Removing one quarter of spikelets (RS) was beneficial to grain-setting in the remaining spikelets, leading to the increase of grain mass. Thus promoting the source supply of photosynthates after anthesis is of major importance for grain to set and to develop.     

Nitrogen Translocation in Wheat Plants Under Soil Water Deficit

Accumulation and translocation of nitrogen (N) in the vegetative organs and grains of winter wheat (Triticum aestivum L.) are important processes in determining yield and quality. The present study was conducted to compare the effects of water deficit and cultivars (cv. Lumai 21 and Jinan 17) on N translocation from vegetative organs to grains in a mobile rain-shelter using ¹⁵N-labeled ammonium sulfate fertilizer. The N translocation amounts (defined as the difference between the N amount at anthesis and the N amount at maturity for a vegetative organ) in leaves were greatest for the two cultivars, followed by glumes, stems, and sheaths, respectively. The N translocation ratio (defined as the ratio of the translocation amount to N amount at anthesis) in total above-ground parts were greater for Lumai 21 (0.65 g g⁻¹ DW) than for Jinan 17 (0.60 g g⁻¹ DW), and Lumai 21 plants had a higher N translocation ratio for the N derived from fertilizers. The N contribution (defined as the ratio of the translocation amount to grain N amount) of total vegetative parts aboveground to grain N ranged from 0.50 to 0.77 g g⁻¹ DW, and that of the leaf was the greatest. The results showed that water deficit remarkably increased the N translocation ratio derived from soil and the contributions of N in various vegetative organs to grain N. It is suggested that water deficit would weaken the availability of fertilizer N but enhance the remobilization of prestored N to the grains.     

Postanthesis allocation of photosynthates and grain growth in wheat cultivars as affected by source/sink change

Two wheat cultivars, Hesheng 2 with large grain yield potential, and Shannong 505 with small grain yield potential, were used for investigating the responses of postanthesis photosynthesis, dry matter accumulation and allocation, and grain growth to source/sink changes. At the initial grain filling stage, Hesheng 2 was sensitive to source reduction leading to an increase of net photosynthetic rate (P_N) by 10 %; however, little effect of sink reduction was observed. In Shannong 505, P_N was obviously decreased by sink reduction, and changed a little after source reduction. At the rapid grain filling stage, Hesheng 2 was sensitive to both source and sink reduction resulting in the increase or decrease of P_N, respectively. However, the response of P_N in Shannong 505 to source/sink changes was similar to that in previous stage. The dry matter (DM) accumulation after anthesis was affected by source/sink changes. In Hesheng 2, the decrease in DM was higher than that in Shannong 505 after the same source or sink reduction. Source reduction caused a decrease in the allocation of DM to the sheath and stem, and promoted the reserve photosynthates to be reallocated to grain. The effect of sink reduction was contrary. The grain mass of Hesheng 2 was more easily regulated by source/sink changes than that of Shannong 505. The effect source/sink changes on grain mass was in order upper > basal > middle spikelets on spike. As for a spikelet, the effect was found mainly in the grain mass at the positions 3 and 4 from base of the spikelet. This revised version was published online in July 2006 with corrections to the Cover Date.     

Root growth and water uptake in winter wheat under deficit irrigation

Root growth is critical for crops to use soil water under water-limited conditions. A field study was conducted to investigate the effect of available soil water on root and shoot growth, and root water uptake in winter wheat (Triticum aestivum L.) under deficit irrigation in a semi-arid environment. Treatments consisted of rainfed, deficit irrigation at different developmental stages, and adequate irrigation. The rainfed plots had the lowest shoot dry weight because available soil water decreased rapidly from booting to late grain filling. For the deficit-irrigation treatments, crops that received irrigation at jointing and booting had higher shoot dry weight than those that received irrigation at anthesis and middle grain filling. Rapid root growth occurred in both rainfed and irrigated crops from floral initiation to anthesis, and maximum rooting depth occurred by booting. Root length density and dry weight decreased after anthesis. From floral initiation to booting, root length density and growth rate were higher in rainfed than in irrigated crops. However, root length density and growth rate were lower in rainfed than in irrigated crops from booting to anthesis. As a result, the difference in root length density between rainfed and irrigated treatments was small during grain filling. The root growth and water use below 1.4 m were limited by a caliche (45% CaCO₃) layer at about 1.4 m profile. The mean water uptake rate decreased as available soil water decreased. During grain filling, root water uptake was higher from the irrigated crops than from the rainfed. Irrigation from jointing to anthesis increased seasonal evapotranspiration, grain yield, harvest index and water-use efficiency based on yield (WUE), but did not affect water-use efficiency based on aboveground biomass. There was no significant difference in WUE among irrigation treatments except one-irrigation at middle grain filling. Due to a relatively deep root system in rainfed crops, the higher grain yield and WUE in irrigated crops compared to rainfed crops was not a result of rooting depth or root length density, but increased harvest index, and higher water uptake rate during grain filling.     

根茎半灌木羊柴对光合同化物的克隆整合

羊柴为根茎半灌木,主要分布于我国北方半干旱区的沙地。该种的营养繁殖是由根茎的水平延伸使顶端分生组织与腋生分生组织序列化不断产生而进行的。本项研究采用^14C标记和去叶实验,探讨了母株、子株所组成的分株对内的光合同化物的整合。在24h的传输中,相当可观量的14C光合同化物自母株传输给子株、子株的根系和根茎,且它们的汇活度均超过了10%。在^14C-光合化物向基向传输（由子株向母株）中,传输率较小,且汇活度不足1%,但根茎在这一传输中的汇活度却超过2%。去叶影响着母株与子株之间的光合同化物整合。保持完整的母株增大向遭受去叶的子株传输光合产物;反之亦然。母相提并论和子株都向根茎传输一定量的同化物,表明根茎自分株获得光合同化物的支持。羊柴的相连分株间通过根茎而发生克隆整合,可能使其分株和基株在不利的沙地生境中都获得净收益。     

Pathway and sink activity for photosynthate translocation in <Emphasis Type="Italic">Pisolithus</Emphasis> extraradical mycelium of ectomycorrhizal <Emphasis Type="Italic">Pinus thunbergii</Emphasis> seedlings

The purpose of this study was to identify the pathway and sink activity of photosynthate translocation in the extraradical mycelium (ERM) of a Pisolithus isolate. We labelled ectomycorrhizal (ECM) Pinus thunbergii seedlings with ¹⁴CO₂ and followed ¹⁴C distribution within the ERM by autoradiography. ¹⁴C photosynthate translocation in the ERM resulted in ¹⁴C distribution in rhizomorphs throughout the ERM, with ¹⁴C accumulation at the front. When most radial mycelial connections between ECM root tips and the ERM front were cut, the whole allocation of ¹⁴C photosynthates to the ERM was reduced. However, the overall pattern of ¹⁴C distribution in the ERM was maintained even in regions immediately above and below the cut, with no local ¹⁴C depletion or accumulation. We inferred from this result that every portion in the ERM has a significant sink activity and a definite sink capacity for photosynthates and that photosynthates detour the cut and reach throughout the ERM by translocation in every direction. Next, we prepared paired ECM seedlings, ERMs of which had been connected with each other by hyphal fusion, alongside, labelled the left seedling with ¹⁴CO₂, and shaded none, one or both of them. ¹⁴C photosynthates were acropetally and basipetally translocated from the left ERM to ECM root tips of the right seedling through rhizomorphs in the left and right ERMs, respectively. With the left seedling illuminated, ¹⁴C translocation from the left to the right ERM increased by shading the right seedling. This result suggests that reduced photosynthate transfer from the host to its ERM increased sink activity of the ERM.     

Yield and water use of wheat (Triticum aestivum) in a Mediterranean environment: Cultivar differences and sowing density effects

Yield of eight wheat cultivars was evaluated under rainfed and irrigated conditions in a Mediterranean environment. Variation in grain yield resulted from variation in both aboveground biomass production and in harvest index. Under rainfed compared to irrigated conditions, grain yield, biomass and days to heading were decreased, whereas harvest index was increased. Grain yield of the different cultivars under rainfed conditions correlated with that under irrigated conditions in one of the two years. Among cultivars, harvest index under rainfed and irrigated conditions were correlated in both years.Water was used more efficiently for biomass production, and equally efficiently for grain production, under irrigated compared to rainfed conditions. Under rainfed conditions, crop water use efficiency was higher for cultivars developed for rainfed environments than for those developed for high-rainfall or irrigated environments. Cultivars with low-rainfall target environments had the lowest evapotranspiration under rainfed conditions. Under rainfed conditions, differences between the cultivar groups in crop water use efficiency corresponded with trends in water use efficiency of individual plants and with the ratio of photosynthesis to transpiration, measured on plants grown in a growth room.Early in the season, water was used more efficiently for biomass production at high sowing densities than at low sowing densities. Through faster biomass production and ground cover a smaller proportion of the evapotranspired water was lost in soil evaporation and a larger proportion was transpired. However, the net effect was a greater water use in the early phases of growth and consequently a lower water availability later in the season, leading to similar yields regardless of sowing density.     

Sink to source transition in developing leaf blades of tall fescue

This study aims to characterize the translocation of photosynthates within and from developing tall fescue ( Festuca arundinacea ) leaves at the time of transition from sink to source. The developing leaf contains a source, the exposed tip, and a sink, the growing basal portion. When the exposed tip of the developing blade is labelled with ¹⁴CO₂, it exports photosynthates exclusively to sinks within the developing blade until the blade reaches 80% of its final length, when photosynthates begin to be exported from the blade and pass through the collar to reach the growing sheath and the next expanding leaf. Concurrently, the previous mature leaves reduce their level of photosynthate export to the developing blade; export stops as soon as the sheath of the developing leaf elongates beyond 10 mm. Export from the mature leaves to the growing sheath and to the next expanding leaf blade increases rapidly. Thus, in a developing tall fescue leaf blade photosynthate importation and exportation are exclusive events: the expanding blade imports photosynthate from mature leaves until it reaches 80% of its final length, then exportation begins and importation ceases.     

冬小麦籽粒淀粉合成相关酶活性的日变化

蔗糖向淀粉的转化是决定小麦籽粒产量的重要因素.田间条件下研究了两个小麦(Triticum aestivum L.)品种"鲁麦22"和"鲁麦14"籽粒淀粉合成相关酶:蔗糖合酶(sucrose synthase,SS)、腺苷二磷酸葡萄糖焦磷酸化酶(ADP-glucose pyrophosphorylase,ADPGPPase)、可溶性淀粉合酶(soluble starch synthase,SSS)、束缚态淀粉合酶(starch granule-bound synthase,GBSS)的活性以及籽粒ATP含量的日变化.结果表明,上述酶活性呈现明显的昼夜变化特征,酶活性一般在白天较低,而在夜间呈现较高活性,而籽粒ATP含量趋势相反.相关分析表明,白天较低的酶活性可能与气温超过其适宜温度有关.对籽粒淀粉合成相关酶活性日变化的可能因子进行了讨论.     

冬小麦籽粒淀粉合成相关酶活性的日变化

蔗糖向淀粉的转化是决定小麦籽粒产量的重要因素。田间条件下研究了两个小麦(TriticumaestivumL.)品种“鲁麦22”和“鲁麦14”籽粒淀粉合成相关酶:蔗糖合酶(sucrosesynthase,SS)、腺苷二磷酸葡萄糖焦磷酸化酶(ADP-glucosepyrophosphorylase,ADPGPPase)、可溶性淀粉合酶(solublestarchsynthase,SSS)、束缚态淀粉合酶(starchgranule-boundsynthase,GBSS)的活性以及籽粒ATP含量的日变化。结果表明,上述酶活性呈现明显的昼夜变化特征,酶活性一般在白天较低,而在夜间呈现较高活性,而籽粒ATP含量趋势相反。相关分析表明,白天较低的酶活性可能与气温超过其适宜温度有关。对籽粒淀粉合成相关酶活性日变化的可能因子进行了讨论。     

Clonal integration and its ecological significance in Hedysarum laeve,a rhizomatous shrub in Mu Us Sandland

Hedysarum laeve, a rhizomatous clonal half-shrub, commonly dominates in inland dunes in semiarid areas of northern China. This species propagates vegetatively by the extension of horizontal rhizomes resulting in programmed reiteration of apical and/or axillary meristems. In this study, (14)C labeling and experimental defoliation were employed to test the photosynthate translocation within the interconnected parent-daughter ramet pairs. A proportion of (14)C-photosynthates was transported from the parent ramet into the daughter ramet, the roots of the daughter ramet, and the rhizome; these three components showed more than 70% sink activity after 24-h translocation. On the other hand, the basipetal translocation (from daughter ramet into parent ramet) was relatively small with sink activity of less than 5%, but sink activity of the rhizome exceeded 10%. Defoliation had an influence on the photosynthate translocation between parent and daughter ramets. The intact parent ramets significantly increased their (14)C-photosynthate translocation into defoliated daughter ramets when compared to intact daughter ramets. The daughter ramets transported significantly more (14)C-photosynthates to the defoliated parent ramets than to the intact parent ramets. A portion of (14)C-photosynthates was transported into the rhizome from both parent and daughter ramets, indicating that the rhizome is supported by both ramets for photosynthates. The clonal integration between ramets of the species through rhizome connection may confer benefit both to the ramets and the genet in adverse environments.     

Use of positron-emitting tracer imaging system for measuring the effect of salinity on temporal and spatial distribution of C tracer and coupling between source and sink organs

Salinity stress affects photosynthate partitioning between sources and sinks of plants, but how it affects these systems is less well understood. Because sources and sinks are closely tied, any adverse effect under suboptimal conditions on one of these is often misinterpreted for an effect on the other. Carbon partitioning is indispensable for stress resistance and good plant growth. In the present study, carbon partitioning in tomato plants (Lycopersicon esculentum L. cv. Momotarou) in a saline (NaCl) environment was studied by feeding radioactive ¹¹C and stable ¹³C isotopes. Pulse-chases were conducted to measure the spatial and temporal distribution of ¹³C. ¹³C was measured by a standard conventional technique, but ¹¹C distribution was monitored using a positron-emitting tracer imaging system (PETIS). Salt stress resulted in reduced carbon translocation toward roots. The majority of the photosynthate accumulated in the leaf. We also observed that the reduction in translocation of carbon occurred well before the salt stress symptoms of reduced photosynthesis and reduced plant growth in salt-exposed plants. The effect on sink activity was also shown by a decrease in stem diameter. In addition, PETIS analysis of ¹¹C translocation indicated that carbon translocation to roots was inhibited under salt conditions without a direct effect on leaf Na accumulation or osmotic stress. These results suggest that NaCl has direct effects on plants, inhibiting carbon partitioning within a few hours of salt exposure without inhibition of source activity.     

施钾时期对冬小麦旗叶光合特性和籽粒淀粉积累的影响

在相同施钾量的基础上。采用一次性基施,1／2基施、1／2于拔节期追施。研究施钾时期对小麦旗叶光合特性和籽粒淀粉积累的影响．结果表明。分期施钾比一次性施钾提高了小麦开花后旗叶的光合速率、旗叶中磷酸蔗糖合成酶(SPS)和籽粒中腺苷二磷酸葡萄糖焦磷酸化酶(ADPGPPase)的活性,提高了籽粒中蔗糖的供应强度和淀粉积累速率。增加了籽粒产量．研究还表明。两个施钾处理均提高了小麦叶片中蔗糖的合成能力和其在籽粒中转化为淀粉的能力,施钾提高产量的主要原因是施钾较好地协调了光合物质合成、运输与转化,即较好地协调了淀粉合成的源库关系．     

Source-sink relations in maize mutants with starch-deficient endosperms

Partitioning and translocation of photosynthates were compared between a nonmutant genotype (Oh 43) of corn (Zea mays L.) and two starch-deficient endosperm mutants, shruken-2 (sh2) and brittle-1 (bt1), with similar genetic backgrounds. Steady-state levels of ¹⁴CO₂ were supplied to source leaf blades for 2-hour periods, followed by separation and identification of ¹⁴C-assimilates in the leaf, kernel, and along the translocation path. An average of 14.1% of the total ¹⁴C assimilated was translocated to normal kernels, versus 0.9% in sh2 kernels and 2.6% in btl kernels. Over 98% of the kernel ¹⁴C was in free sugars, and further analysis of nonmutant kernels showed 46% of this label in glucose and fructose. Source leaves of mutant plants exported significantly less total photosynthate (24.0% and 36.3% in sh2 and bt1 compared to 48.0% in the normal plants) and accumulated greater portions of label in the insoluble (starch) fraction. Mutant plants also showed lower percentages of photosynthate in the leaf blade and sheath below the exposed blade area. The starch-deficient endosperm mutants influence the partitioning and translocation of photosynthates and provide a valuable tool for the study of source-sink relations.     

不同供水条件对小麦强、弱势籽粒中淀粉粒度分布的影响

以3个淀粉含量不同的冬小麦品种山农12、鲁麦21和济南17为材料,设灌溉和旱作2种栽培处理,对不同水分条件下小麦强、弱势籽粒中淀粉粒的体积、数目和表面积的分布特征进行了研究.结果表明,小麦强、弱势籽粒均含有A(＞9.8 μm)、B(2.0～9.8 μm)、C(＜2.0 μm)3种类型的淀粉粒,但不同类型淀粉粒的分布状况存在明显差异.在强势籽粒中,淀粉粒的体积和表面积分布均表现为三峰分布,而弱势籽粒中淀粉粒的体积和表面积分布则表现为双峰分布.与弱势粒相比较,强势粒中C型淀粉粒(＜2.0 μm)的体积百分比为7.25%～9.31%,表面积百分比为34.88%～41.51%,而弱势粒的体积和表面积百分比分别为5.33%～6.40%和26.31%～33.54%.强、弱势籽粒中＜0.6 μm和0.6～2.0 μm范围内的淀粉粒数目存在明显差异,强势粒为1.86%～6.13%和83.77%～87.77%,而弱势粒为25.72%～37.42%和52.77%～58.48%.与灌溉栽培相比较,旱作栽培条件下籽粒中B、C型淀粉粒体积和表面积百分比显著增加,而A型淀粉粒体积和表面积显著减少;弱势粒中＜0.6 μm的淀粉粒数目显著增加,强势籽粒中淀粉粒的数目无显著变化.与弱势粒相比较,强势粒中的蛋白质含量较高,C型淀粉粒的体积和表面积所占比例较大,而强势粒中的淀粉含量较低,且A、B型淀粉粒比例也较小.与灌溉栽培相比较,旱作栽培条件下强、弱势籽粒中B、C型淀粉粒体积和表面积百分比增加,蛋白质含量也显著增加,淀粉含量降低.表明水分亏缺能提高籽粒中B、C型淀粉粒体积和表面积百分比及蛋白质含量.     

Planting density effects on assimilation and partitioning of photosynthates during grain filling in the late-sown wheat

Leaf blades of the late-sown winter wheat produced the major portion, i.e., more than 60 %, of the total ¹⁴C-photosynthates at grain filling, but ear (rachis and glumes) only about 15 %, sheaths about 11 %, and stem internodes about 11 %. The change of plant density in this experiment had little influence on the ¹⁴CO2-photoassimilation of the ear (rachis and glumes), flag leaf lamina, sheaths and stem internodes, but markedly affected photosynthesis of the second, the third and lower leaves. The photosynthetic rate [expressed as specific radioactivity, s-¹ kg-¹(d.m.)] and the amount of ¹⁴CO₂ photosynthates decreased significantly in the second, the third and other lower leaves at a high plant density. Upon grain-filling of the late-sown wheat, the grain was the major importer of photosynthates. Yet partitioning to the stem internodes depended on the plant density. Stem was the importer of photosynthates at a low plant density, but the exporter at a high plant density. In plants at a low plant density a fairly large proportion of photosynthates was distributed into the roots. The middle and lower above-ground parts of the late-sown wheat at a high plant density decreased or lost their function early. As a result, the plant senesced earlier. However, the grain setting, filling and yielding were restricted. An appropriately low plant density was suitable for prolonging the function of the middle and lower organs, delaying the senescence of plant, increasing the source supply for grain filling, and improving the grain yield. This revised version was published online in August 2006 with corrections to the Cover Date.     

高等植物光合同化物的运输与分配

高等植物光合同化物的运输受维管束发育状况影响较大,有时会限制产量。而同化物在各库器官间的分配主要决定于库本身的特性,它常用库强度和优先权来描述。库强度是库容量和库活力的乘积,库容量用细胞数目来度量,而库活力常用相对生长速度来度量。近年来人们也用酶少戌一来度量库活力或库强度。而库的优先权描述的是各库器官需求同化物的优先次序,种子被认为是优等权最高的库。同化物的运输分配不仅决定于植物本身源、流、库的特     

Clonal integration and its ecological significance in Hedysarum laeve, a rhizomatous shrub in Mu Us Sandland

Hedysarum laeve, a rhizomatous clonal half-shrub, commonly dominates in inland dunes in semiarid areas of northern China. This species propagates vegetatively by the extension of horizontal rhizomes resulting in programmed reiteration of apical and/or axillary meristems. In this study, ¹⁴C labeling and experimental defoliation were employed to test the photosynthate translocation within the interconnected parent–daughter ramet pairs. A proportion of ¹⁴C-photosynthates was transported from the parent ramet into the daughter ramet, the roots of the daughter ramet, and the rhizome; these three components showed more than 70% sink activity after 24-h translocation. On the other hand, the basipetal translocation (from daughter ramet into parent ramet) was relatively small with sink activity of less than 5%, but sink activity of the rhizome exceeded 10%. Defoliation had an influence on the photosynthate translocation between parent and daughter ramets. The intact parent ramets significantly increased their ¹⁴C-photosynthate translocation into defoliated daughter ramets when compared to intact daughter ramets. The daughter ramets transported significantly more ¹⁴C-photosynthates to the defoliated parent ramets than to the intact parent ramets. A portion of ¹⁴C-photosynthates was transported into the rhizome from both parent and daughter ramets, indicating that the rhizome is supported by both ramets for photosynthates. The clonal integration between ramets of the species through rhizome connection may confer benefit both to the ramets and the genet in adverse environments. Received: April 12, 2001 / Accepted: November 26, 2001     

Sink-limitation to yield and biomass: a summary of some investigations in spring wheat

Yield potential can be expressed as a product of light interception, radiation use efficiency (RUE), and the partitioning of biomass to grain yield, or harvest index (HI). Traits related to early or late light interception have not been shown to be associated with genetic improvement of spring wheat yield in favourable environments. It is, however, well established that yield improvement is largely a result of increased HI, although the most recent studies comparing genetic progress in HI over time in spring wheat indicate that it has not made any additional progress since the mid 1980s. These observations suggest that future genetic progress in yield will most likely be achieved by focusing on constraints to RUE. Considering the possibility that RUE may be influenced indirectly by sink limitation, it is apparent that biomass may be increased by increasing grain number, for example. Experiments with high yielding spring wheat lines containing the alien translocation 7DL.7Ag showed increased grains m‐2 (15%), yield (12%), and biomass (9%) compared with controls. The translocation was also associated with a larger investment in spike mass at anthesis (15%), more grains/spike (10%), and increased flag‐leaf photosynthetic rate during grain‐filling (20%). The data suggest that increased biomass in 7DL.7Ag lines was due to significantly increased RUE post‐anthesis, as a result of a larger kernel number (sink) that increased the demand for photosynthesis during grain‐filling. The hypothesis that increased photosynthesis and RUE may respond directly to a larger number of grains/spike was tested experimentally by imposing a light treatment during boot stage. The treatment was associated with a small increase (5%) in the proportion of biomass invested in spike mass at anthesis, reflected by on average three extra grains/spike at maturity. The treatment was associated with 25% more yield and 22% more biomass than controls, while carbon assimilation rate measured on flag‐leaves during grainfilling was 10% higher than controls. The results suggest that RUE can be increased indirectly by increasing sink strength and that the current yield limiting process in spring wheat is the determination of kernel number. Experimental data are presented on how spike fertility may be increased through breeding, for example by introgression of the multi‐ovary trait to increase grain number per spikelet. In addition, results of analysis of the physiological bases of genotype × year interaction in high yield environments are presented in the context of how such information can provide a focus for genetic studies of sink limitation.     

Physiological and yield responses of recombinant chromosome substitution lines of barley to terminal drought in a Mediterranean‐type environment

Physiological traits and productivity of the recombinant chromosome substitution lines (RCSLs) of barley, developed through the cross of Hordeum vulgare ssp. vulgare cv. Harrington and the wild ancestor Hordeum vulgare ssp. spontaneum, were measured in plants growing in microplots (with and without irrigation) and in field conditions in two Mediterranean‐type environments, Cauquenes (rainfed) and Santa Rosa (irrigated). The objectives were to assess the degree of phenotypic variability in response to terminal drought stress and to test whether the introgression of the wild ancestor into cv. Harrington can increase the terminal drought tolerance of RCSLs of barley. Days from emergence to anthesis and from anthesis to maturity of the 80 RCSLs were reduced in only 2–4 days under water stress, in microplots. Specific leaf area (SLA) and stomatal conductance (gs) of 80 RCSLs and cv. Harrington decreased greatly under water stress in plants growing in microplots and field conditions (in 2004/05 growing season). No G × E interaction was detected except for SLA in the microplot experiment. The principal component analysis provided a clear distinction between RCSLs. Along the first principal component, it was possible to identify 24 RCSLs which represent the whole range of grain yield (GY), gs and SLA observed in the 80 RCSLs. The selected 24 RCSLs were evaluated in field conditions at Cauquenes and Santa Rosa, during two growing seasons (2007/08 and 2008/09). The gs and carbon isotope discrimination in grains (Δ¹³C) were significantly (P < 0.001) lower in the rainfed condition (Cauquenes), but the water‐soluble carbohydrates (WSC) in stems at anthesis and maturity was significantly (P < 0.001) higher than in well‐irrigated condition (Santa Rosa). Grain yield was reduced by 63% under drought conditions. Differences between RCSLs in gs, WSC and GY were significant (P < 0.001) in 2007/08. The stress tolerance index (STI) was highly (P < 0.01) correlated with GY in all environments (rainfed and irrigated conditions and the two growing seasons). The relationship between STI and Δ¹³C under rainfed condition allowed identifying drought tolerant and susceptible RCSLs; the former were high yielding lines under rainfed and irrigated conditions (and higher STI values), but with similar GY to cv. Harrington, but presented higher grain Δ¹³C values than cv. Harrington. The drought susceptible lines presented lower GY, STI and Δ¹³C values than cv. Harrington. These results suggest that H. spontaneum has contributed alleles that increase terminal drought tolerance to some of the RCSLs.