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Background and Aims The pericarp weight comprises Methods Two spring wheat cultivars contrasting in kernel weight (Bacanora and Kambara) were sown in field conditions during seasons 2012–13 and 2014–15. Both genotypes were grown under contrasting plant density (control, 370 plants m–2; and low plant density, 44 plants m–2) and night temperatures, i.e. at ambient and increased (>6 °C) temperature for short periods before and after anthesis. From anthesis onward, grains were harvested every 3 or 4 d. Grain samples were measured and the pericarp was removed with a scalpel. Whole grain and pericarp fresh and dry weight were weighed with a precision balance. At harvest, 20 grains from ten spikes were weighed and grain dimensions were measured. Key Results Fresh weight, dry matter and water content of pericarp dynamics showed a maximum between 110 and 235 °Cd. Maximum dry matter of the pericarp ranged between 4.3 and 5.7 mg, while water content achieved values of up to 12.5 mg. Maximum values and their timings were affected by the genotype, environmental condition and grain position. Final grain weight was closely associated with maximum dry matter and water content of the pericarp. Conclusions Maximum pericarp weight is a determinant of grain weight and size in wheat, which is earlier than other traits considered as key determinants of grain weight during grain filling. Better growing conditions increased maximum pericarp weight, while higher temperature negatively affected this trait.

Background Grain weight (GW) is a key component of sunflower yield and quality, but may be limited by maternal tissues. Cell growth is influenced by expansin proteins that loosen the plant cell wall. This study aimed to identify spatio-temporal expression of EXPN genes in sunflower reproductive organ tissues (ovary, pericarp, and embryo) and evaluate correlations between reproductive organ growth and expansin genes expression. Evaluations involved eight different developmental stages, two genotypes, two source-sink treatments and two experiments. The genotypes evaluated are contrasting in GW (Alybro and confection variety RHA280) under two source-sink treatments (control and shaded) to study the interactions between grain growth and expansin genes expression. Results Ovaries and grains were sampled at pre- and post-anthesis, respectively. Final GW differed between genotypes and shading treatments. Shading treatment decreased final GW by 16.4 and 19.5% in RHA280 and Alybro, respectively. Relative expression of eight expansin genes were evaluated in grain tissues. EXPN4 was the most abundant expansin in the ovary tissue, while EXPN10 and EXPN7 act predominantly in ovary and pericarp tissues, and EXPN1 and EXPN15 in the embryo tissues. Conclusions Specific expansin genes were expressed in ovary, pericarp and embryo in a tissue-specific manner. Differential expression among grain tissues was consistent between genotypes, source-sink treatments and experiments. The correlation analysis suggests that EXPN genes could be specifically involved in grain tissue extension, and their expression could be linked to grain size in sunflower. Electronic supplementary material The online version of this article (10.1186/s12870-018-1535-7) contains supplementary material, which is available to authorized users.

Summary Wheat is the most widely grown crop globally, providing 20% of all human calories and protein. Achieving step changes in genetic yield potential is crucial to ensure food security, but efforts are thwarted by an apparent trade‐off between grain size and number. Expansins are proteins that play important roles in plant growth by enhancing stress relaxation in the cell wall, which constrains cell expansion.Here, we describe how targeted overexpression of an α‐expansin in early developing wheat seeds leads to a significant increase in grain size without a negative effect on grain number, resulting in a yield boost under field conditions.The best‐performing transgenic line yielded 12.3% higher average grain weight than the control, and this translated to an increase in grain yield of 11.3% in field experiments using an agronomically appropriate plant density.This targeted transgenic approach provides an opportunity to overcome a common bottleneck to yield improvement across many crops., See also the Commentary on this article by Cosgrove, 230: 403‐405.

Lentil is a cool season grain legume produced primarily in the Mediterranean and temperate regions of the world where water and heat stress in critical developmental windows constrain yield. The effect of stress on yield depends on the timing, intensity and duration of stress; here we focus on timing relative to phenological development. To determine the critical period for grain yield and grain protein, we compared unshaded controls and crops exposed to sequential 10–14 d shading periods using two locally adapted varieties at Roseworthy, south-eastern Australia, and Valdivia, southern Chile. Yield of unstressed controls varied from 1 t ha−1 at Roseworthy to 7 t ha-1 at Valdivia, and grain protein from 22.0 % at Valdivia to 27.6 % at Roseworthy. Irrespective of growing conditions, the most sensitive period was at 50–126 °Cd after flowering, around pod emergence. Grain number and biomass accounted for most of the variation in yield. Grain protein concentration varied according to a bi-linear model, with minor reduction (

Grain weight (GW) is an important component of grain yield and quality of sunflower and the improvement of this trait has been proposed as an aim for breeding of this crop. There is strong evidence suggesting the pre-flowering period as key to determining GW in different crops; however, the key traits and mechanisms controlling GW during this phase are still largely unknown in sunflower. This study conducted a detailed survey of how the pre-flowering period determines grain growth dynamics by assessing the early developmental process during the growth of reproductive organs and the sensitivity of GW, grain number (GN) and grain oil concentration to different source–sink manipulations immediately before flowering. Two experiments were carried out under field conditions in two growing seasons. In Exp. 1 two sunflower oilseed hybrids contrasting in GW (Alybro and SG) were sown at the Experimental Station of the Universidad Austral de Chile in Valdivia (39°47′S, 73°14′W), Chile. In Exp. 2, the same hybrids plus a confectionery genotype (RHA) were evaluated in the Experimental Station where two source–sink treatments were performed: a control (without manipulation) and a shading treatment starting 16 days previous to anthesis, i.e. during the R2-R5 period. Crop development, average and individual GW, GN and oil concentration of grains were assessed at harvest. Also, flower and grain traits and their dynamics were measured from early reproductive stage (ovary at R3) to harvest in different grain positions from the capitulum (e.g., fresh and dry weight and dimensions of grains, pericarp and embryo and grain oil concentration). GW was significantly affected by genotype and shading treatments imposed at pre-anthesis, but no statistical effect of the lower source–sink ratio was found on GN. Contrary to GW, grain oil of oilseed genotypes was highly conservative under the source–sink reduction in our study. Positive associations were found between final GW and: ovary weight at R3, at anthesis (R5), ovary growth rate, grain dimensions and water content. Final GW also showed a linear association with ovary growth rate. This study is the first to evaluate the ovary weight from the early development stage and the ovary growth rate during the pre-anthesis period in sunflower and the effect of source reduction at pre-anthesis on grain oil concentration, supporting the importance of the maternal tissues on the setting of potential and actual GW in sunflower.

Annual crops accommodate environmental variation through grain number, whereas grain weight is more stable. Grain number is determined in a species-specific window which has been established for many crops, but not for oat. Field trials were established at two sites in southern Australia and in one site in southern Chile where successive, single 14-d shading periods were applied from crop establishment to maturity to identify the developmental window when the crop is most responsive to stress. Three oat varieties were compared in Australia (Mitika, Williams and Wintaroo) and two in Chile (Mitika and Yallara). Unshaded controls yielded from 327 g m −2 in Australia to 747 g m −2 in Chile. The overall pattern of yield response to time of stress was similar to that of wheat; it spanned the period from stem elongation (GS31) to about 10 days after anthesis. In line with theory, most of the yield response was mediated through response in grain number; further, the two environments in Australia where reduction in grain number in response to stress shortly before anthesis was larger, individual grain weight increased with shading. Grains per panicle was more responsive to stress than panicles per m 2 , in contrast to other cereals. The critical period is often assumed to be species-specific. However, our limited comparison of varieties suggests that there might also be varietal differences in oat. Interaction between time of shade and variety was significant for harvest index in all locations. Hence, we propose genotype-dependent response to time of stress is worth exploring.

Breeding heavier seeds while maintaining seed number has been proposed as an effective strategy to improve oil crop production. Recent studies assessing rapeseed source-sink (S-Sratio) reduction after flowering suggest a window in the early seed-filling period that can compensate, either partially or totally, for a decrease in the number of seeds. However, little evidence has been reported in relation to the key window for seed plasticity in rapeseed. Furthermore, such studies have only assessed spring rapeseed genotypes and there is a lack of information on winter rapeseed. This study aims to elucidate the occurrence of a narrow window when seed plasticity is greatest, which is hypothesized to occur during the early stages of seed filling after the beginning of flowering in both winter and spring rapeseed genotypes. To asses this hypothesis, two winter and two spring rapeseed hybrids were evaluated under three S-Sratio treatments in two experiments performed in field conditions in Valdivia, Chile. The winter hybrids Trust and Mercedes were assessed under different nitrogen levels, and the spring hybrids Lumen and Solar were assessed using two sowing dates. S-Sratio treatments in both rapeseed genotypes consisted of a control without S-Sratio manipulation, a reduced S-Sratio from the beginning of flowering [BBCH 61] to 15 days after flowering (DAF) and a reduced S-Sratio from 15 to 30 DAF. The S-Sratio was reduced by shading the crop with black nets to intercept 75 % of the incoming solar radiation. Shading treatments decreased seed yield relative to the control between 13 and 42 % for the winter genotypes and from 23 to 44 % for the spring genotypes. The negative effect of shading on seed number under both S-S reduction timings explains the seed yield reduction. Interestingly, different windows of time for seed weight plasticity were found in response to the lower S-Sratio for winter and spring genotypes (i.e., 15–30 and 0–15 DAF, respectively). In the winter-type genotypes, seed weight increased between 28 and 33 % under the 15–30 DAF shading treatment, while seed weight in spring-type genotypes increased from 15 to 39 % during the 0–15 DAF treatment. Seed weight change was almost negligible outside of the sensitivity window as this trait increased only 2% at 0–15 DAF in winter-type genotypes and 7% at 15–30 DAF in spring-type genotypes, across treatments. In parallel, the S-S reduction decreased seed number by 23.6 and 40 %, at the 0–15 and 15–30 DAF treatment, respectively. The study showed statistical differences for seed oil and protein concentration across treatments, but both quality traits remained highly stable to the S-S reduction and showed similar behavior in winter and spring rapeseed types. Seed oil concentration changed little while seed protein concentration was more sensitive to seed weight response. The findings of the present study suggest that seeds per silique and seed weight are determined by the plant assimilate S-Sratio; therefore, seed number and seed weight determinations overlap as has been demonstrated in other crops like wheat, barley, sorghum and sunflower.

The cellular expansion of maternal tissues has been suggested as strongly associated to grain volume determination in wheat and is therefore a key process to understand potential grain weight determination. The dynamics of grain growth in seed size-contrasting diploid, tetraploid and hexaploid genotypes of wheat were evaluated to explore the relationships between the final grain weight and: a) grain volume, b) water content, c) epidermal pericarp cell size and d) the rate of cell area (area per cell) increase. The assessment of cell expansion was reinforced by the study of the expression of the XTH5 gene in pericarp tissues, as this gene codifies a cell wall-remodeling agent. Differences in grain weight across ploidies and experiments (greenhouse and field evaluations) were attributable to the grain-filling rate (ANOVA p

Quinoa high nutritive value increases interest worldwide, especially as a crop that could potentially feature in different cropping systems, however, climate change, particularly rising temperatures, challenges this and other crop species. Currently, only limited knowledge exists regarding the grain yield and other key traits response to higher temperatures of this crop, especially to increased night temperatures. In this context, the main objective of this study was to evaluate the effect of increased night temperature on quinoa yield, grain number, individual grain weight and processes involved in crop growth under the environmental conditions (control treatment) and night thermal increase at two phases: flowering (T1) and grain filling (T2) in southern Chile. A commercial genotype, Regalona, and a quinoa accession (Cod. BO5, N°191, grain bank from Semillas Baer, hereby referred to as Accession) were used, due to their adaptability to Southern Chilean conditions and contrasting grain yield potential, grain weight and size of plants. Temperature was increased ≈4°C above the ambient from 8 pm until 9 am the next morning. Control treatments reached a high grain yield (600 and 397 g m-2, i.e., Regalona and Accession). Temperature increase reduced grain yield by 31% under T1 treatment and 12% when under T2 in Regalona and 23 and 26% in Accession, respectively. Aboveground biomass was negatively affected by the thermal treatments and a positive linear association was found between grain yield and aboveground biomass across treatments. By contrast, the harvest index was unaffected either by genotype, or by thermal treatments. Grain number was significantly affected between treatments and this key trait was linearly associated with grain yield. On the other hand, grain weight showed a narrow range of variation across treatments. Additionally, leaf area index was not affected, but significant differences were found in SPAD values at the end of T1 treatment, compared to control. Little change was found in the harvest index, individual grain weight, grain protein content or water soluble carbohydrates in response to the increased night temperature in this crop.

Understanding the response of the number of seeds and seed weight to the availability of assimilates is crucial for designing breeding strategies aimed to increase seed and oil yield in oilseed rape. This study aims to answer the questions: i) do seed number and seed weight in oilseed rape differ in their plasticity in response to the availability of assimilates at flowering? and ii) how sensitive are oil and protein concentrations to the availability of assimilates during flowering? A spring oilseed rape hybrid was sown in two field experiments and the treatments were combinations of i) two plant densities and ii) shading or no shading between the beginning and end of flowering. Seed yield was not affected by plant density or by shading. Lower plant density was compensated by an increase in seed number per plant, without effects on single-seed weight. However, the negative effect of shading during flowering on seed number per area was fully compensated by an increase in single-seed weight by 47–61%. The plasticity of single-seed weight observed in the present study of oilseed rape has never been reported for annual seed crops. Shading at flowering increased both the seed filling rate and the duration of the seed filling period at all positions in the canopy. We also observed that the reduction of the source-sink ratio at flowering increasing seed weight does not necessarily modify oil or protein concentrations. Thus, single-seed weight could be targeted to increase seed yield in oilseed rape without compromising oil content.

Faba bean is a cool-season, indeterminate grain legume grown in Mediterranean and temperate environments where yield loss associated with abiotic and biotic stress is common. Yield responses depend on the timing of stress relative to the species-specific vulnerable stages in the crop lifecycle. To determine the critical period for yield determination in faba bean, we used sequential 14-d shading periods in locally-adapted varieties grown in five environments with yield of unshaded controls from 2.3 to 6.8 t ha−1. Yield of shaded treatments diverged from the controls around 450 °Cd before flowering, reached the largest difference around 100 °Cd after flowering, and converged with controls towards 700–800 °Cd after flowering; the most critical stage aligned with pod emergence. Seed number accounted for most of the variation in yield response to shading. Shading increased seed size when stress severely reduced seed number. Pod number accounted for most of the variation in seed number for shading before flowering, and both pod number and seeds per pod contributed to the reduction in seed number in crops shaded after flowering. The defined critical period is a useful reference for breeding and agronomic solutions to improve yield under stress.

There is a noticeable gap in knowledge about the key phases for grain yield determination in temperate legume crop species such as lupin and pea. For this reason, the aim of the present study was to comparatively assess the critical period for grain yield and grain number determination of narrow-leafed lupin ( Lupinus angustifolius L.) and pea ( Pisum sativum L.). Two field experiments were conducted during the 2007–08 (Exp. 1) and 2009–10 (Exp. 2) growing seasons at the experimental station of the Universidad Austral de Chile. Treatments were the combination of (i) two crops (narrow-leafed lupin and pea) and (ii) seven shading treatments (control without shading and six shading treatments imposed for 15 days throughout the crop cycle). Lupin showed a longer ( P P P

Purple wheat grains are a promising source of anthocyanins and have been proposed as raw material for baking. However, little information is available about the effect of physiological and management variables on grain anthocyanins. This research aimed to (i) characterize the anthocyanin dynamic of grains set at different positions within the spikelet, (ii) evaluate the effect of different source–sink ratios on anthocyanins, and (iii) assess the response of anthocyanins to magnesium fertilization and harvest timing. Four source–sink ratios (pre- and post-anthesis spike halving, spike-shading and control) and two agronomic practices (Mg fertilization and early harvesting) were evaluated in field trials. Grain position affected grain weight and anthocyanin content, decreasing at distal positions. Both variables showed positive response to higher source–sink ratio. Pre-anthesis halving increased anthocyanin content by 54 and 37% (Exps. 1 and 2), while post-anthesis halving increased this trait by 31 and 29%. Source reduction decreased anthocyanin content by 26% and 51%. Changes in anthocyanin content associated with source–sink treatments and with grain positions were the result of different maximum anthocyanin content reached by physiological maturity. Magnesium fertilization and early harvesting increased anthocyanin content and concentration by 65 and 39%, respectively, seeming promising to increase anthocyanins in purple wheat.

Among the yield components, grain weight is considered a conservative trait whose determination is still beyond our complete understanding. Crop physiology uses a whole approach to study this complex trait, which can provide helpful information to plant breeders and molecular biologists. This study emphasizes the understanding of pre- and post-anthesis determinants of final grain weight. A field experiment was carried out in two growing seasons evaluating two wheat cultivars contrasting in grain weight potential. Carpel weight at pollination, grain dimensions, grain water, dry matter and volume dynamics were assessed. Among grain dimensions, grain length was the trait, which explained final grain weight (r2 = 0.78; P

Several studies have been conducted to evaluate the response of crops, especially temperate cereals, to different source–sink ratios during grain filling. However, there is much less information about temperate legumes and even less work comparing the two. The objective of this study was to evaluate the response of both grain yield and grain nitrogen concentration of wheat ( Triticum aestivum L.), narrow-leafed lupin ( Lupinus angustifolius L.) and pea ( Pisum sativum L.) to similar source reduction during grain filling. Two field experiments were conducted in a high yielding environment of Southern Chile. In experiment 1 wheat and narrow-leafed lupin were grown for two consecutive years. Experiment 2 evaluated wheat and pea on two sowing dates. In both experiments a reduction in the source–sink ratio was imposed by using black nets that intercepted 90% of the incident solar radiation from the commencement of the linear dry matter accumulation to physiological maturity. Grain yield was differentially ( p p vs. temperate legumes.

Ozone layer depletion increases the level of ultraviolet radiation reaching the earth's surface affecting both natural and agricultural ecosystems, especially in the Southern Hemisphere. Considering the harmful effects UV-B radiation has on plant growth the future productivity of wheat crops in Southern Chile could be challenged by both (i) the forthcoming level of UV-B increase and (ii) the sensitivity of this crop to higher UV-B radiation. In this study the effect of increased UV-B radiation at different phenophases on a spring wheat cultivar (Pandora) was investigated in two experiments at plant and crop levels under out-door conditions. The experiments consisted of controls, increased UV-B radiation at specific phenophases (from 3 leaf stage to booting 3L-Bo, and from booting to maturity Bo-PM), and increased UV-B radiation for the majority of the crop cycle (from 3 leaf stage to maturity). UV-B radiation was increased by Q panel UV-313 lamps set in plastic framed structures. Control plants were grown either without frames or below the same framed structures as those which received increased UV-B treatments. Phenology, above-ground biomass, grain yield, components, grain protein concentration, leaf area index (LAI), Fv / Fm and pigments were measured at booting and/or at harvest. Above-ground biomass and yield decreased by 11–19 and 12–20%, respectively, when UV-B radiation was increased at the 3L-Bo phase, while no effect was observed when irradiation was applied later in the crop cycle (Bo-PM). No additional UV-B effects to those observed at booting were detected in plants irradiated during the majority of the entire crop cycle (3L-PM). Biomass variation was strongly associated ( r = 0.99; P Fv / Fm , chlorophyll, carotenoid concentration and carotenoid:chlorophyll ratio were found at crop level (experiment 2) under higher UV-B in the 3L-Bo and 3L-PM treatments. The flavonoid concentration responded differently in the two experiments, probably due to the optimum responses these pigments had to expose UV-B doses.

Nitrogen (N) uptake at heading and at maturity was evaluated under four N treatments (20, 50, 110 and 160 kgN ha−1 at sowing) in four malting barley cultivars released to the market from 1944 to 1998 in Argentina. Grain N concentration was slightly lower in the newest cultivar than in the oldest one. Grain N yield showed cultivar × N interaction: modern cultivars tended to increase their grain N yield in response to N fertilization more than old cultivars. Grain N yield was correlated to grain yield as well as to total above-ground biomass. Nitrogen fertilization affected total N in above-ground biomass at maturity, but no differences among cultivars were found. Nitrogen harvest index of the most modern cultivar (0.76) was higher than that of the oldest cultivar (0.67). Modern cultivars tended to have a higher N content in ears at heading than old cultivars, and the magnitude of the differences increased with N availability. Physiological nitrogen efficiency for grain yield was significantly higher in the newest than in the oldest cultivar (57 and 43 g grain g N − 1 , respectively).

SUMMARYThe increase of ultraviolet (UV-B) radiation could be a challenge for wheat production systems in Southern Chile, as in other areas. Previous reports have shown that increased UV-B radiation decreases wheat yield by affecting both grain number and grain weight. However, contrasting results have also been published showing no effect on wheat biomass and grain yield. In addition, little is known about the effect of higher UV-B radiation at particular periods of the crop cycle on grain quality traits. The objective of the present study was to evaluate grain yield, yield components and grain quality in response to increased UV-B radiation during key periods of yield component determination. Two experiments were carried out under field conditions in the Universidad Austral de Chile (latitude 39°62′S). Two spring wheat cultivars were exposed to two periods of supplemented UV-B radiation (280–320 nm): (i) between booting and anthesis,c. 20 days, and (ii) from 10 days after anthesis until physiological maturity,c. 40 days. Ultraviolet radiation was increased to levels of 3·8 and 4·9 kJ/m2/day in experimental years 1 and 2, respectively, by using UV-B lamps. At harvest, plants were sampled to quantify aboveground biomass, grain yield, grain number and average grain weight. In addition, protein and gluten concentration of grains were measured. Grain yield was not affected (P>0·05) by the UV-B increase at pre- or at post-anthesis treatments. Similar results were found for each yield component. In addition, grain protein and gluten concentration showed similar values in the increased UV-B and control treatments. Therefore, if increases in UV-B radiation take place during the latter stages of the crop cycle as is expected, the present results do not support the speculation that increases of UV-B radiation in Southern Chile will compromise wheat production systems.

In temperate cereals are commonly accepted that determination of grain number (GN) and grain weight (GW) scarcely overlap during the crop cycle. However, the assumption that GW is determined exclusively after anthesis needs to be critically reviewed in the light of reports published over the few years where temperature treatments imposed before anthesis decreased GW of bread wheat. Although these evidences suggest that both GW and GN could be affected by environmental conditions before anthesis little is known about the effect of pre-anthesis temperature on these two main yield components in wheat, barley and triticale at field conditions. In addition, the effect of temperature on GW and GN at different stages prior to anthesis has been scarcely evaluated. The objectives of the current study were: (i) to evaluate the overall response, and specific differences, of GN and GW to pre-anthesis temperature, and (ii) to study the effect of different timings of high temperature at pre-anthesis on GN and GW in wheat, barley and triticale. Three fully irrigated field experiments were carried out in three successive seasons. At each season, a wheat, barley and triticale high yielding cultivar was evaluated at three temperature regimes: control, and two timings of heating before anthesis. During the first and second seasons, the timings of heating were booting-anthesis and heading-anthesis. In the thirst season, the timings were beginning of stem elongation-booting and booting-anthesis. Plots were arranged in a split-plot design with three replicates, where the main plot was assigned to thermal regime and the sub-plots to crop species. To apply heat, transparent chambers equipped with thermostatically controlled electric heaters were used. The thermal regime was controlled by sensors connected to a temperature regulator and recorded using data loggers. Temperature within the chambers was stable across developmental stages, crops, and seasons; it averaged 5.5 °C higher than air temperature. Thermal treatments consistently reduced grain yield (p < 0.05), the magnitude of the effect ranged between 5 and 52%. The highest effect was found when temperature increased during stem elongation (yield decrease: 46%), lowest when treatments were imposed during heading-anthesis (15%) and intermediate for treatments imposed during booting-anthesis (27%). Most effects of thermal treatments on yield were due to parallel effects on GN. However, thermal treatments significantly (p < 0.05) decreased GW during the three seasons. The most effecting treatment on GW was when the crops were heated during the B-A period, i.e. GW decreased up to 23%.

For many years yield improvement reported in wheat was associated with increased dry matter partitioning to grain, but more recently increases in above-ground biomass have indicated a different mechanism for achieving yield potential. The most likely way of increasing crop biomass is by improving radiation use efficiency (RUE); however there is evidence that sink strength is still a critical yield limiting factor in wheat, suggesting that improving the balance between source and sink (source/sink (SS)) is currently the most promising approach for increasing yield, biomass, and RUE. Experiments were designed to establish a more definitive link of SS traits with yield, biomass and RUE in high-yield environments using progeny deriving from parents contrasting in some of those traits. The SS traits formed three main groups relating to (i) phenological pattern of the crop, (ii) assimilation capacity up until shortly after anthesis, and (iii) partitioning of assimilates to reproductive structures shortly after anthesis. The largest genetic gains in performance traits were associated with the second group; however, traits from the other groups were also identified as being genetically linked to improvement in performance parameters. Because many of these traits are interrelated, principal component analysis (PCA) multiple regression and path analysis were used to expose these relationships more clearly. The trait most consistently associated with performance traits was biomass at anthesis (BMA). The PCA indicated a fairly close association among traits within this group (i.e. assimilation-related traits) while those from the other two groups of SS traits (i.e. phenological and partitioning) appeared to have secondary but independent effects. These conclusions were partially born out by stepwise multiple regression for individual crosses where BMA was often complemented by traits from the two other groups. Taken together, the data suggest that the assimilation traits biomass in vegetative stage (BMV) and BMA have partially independent genetic effects in this germplasm and were complementary to achieving improved performance. The identification of a number of SS traits associated with yield and biomass, which both PCA and multiple regression suggest as being at least partially independent of one another, support the idea that additive gene action could be achieved by adopting a physiological trait based breeding approach where traits from different groups are combined in a single background. A second breeding intervention based on these results would be in selecting progeny for BMA and BMV using spectral reflectance approaches since those traits that lend themselves to large-scale screening. Path analysis confirmed the importance of the spike primordial stage in the genotype by environment interaction for these traits.

Grain weight (GW) and number per unit area of land (GN) are the primary components of grain yield in wheat. In segregating populations both yield components often show a negative correlation among themselves. Here we use a recombinant doubled haploid population of 105 individuals developed from the CIMMYT varieties Weebill and Bacanora to understand the relative contribution of these components to grain yield and their interaction with each other. Weebill was chosen for its high GW and Bacanora for high GN. The population was phenotyped in Mexico, Argentina, Chile and the UK. Two loci influencing grain yield were indicated on 1B and 7B after QTL analysis. Weebill contributed the increasing alleles. The 1B effect, which is probably caused by to the 1BL.1RS rye introgression in Bacanora, was a result of increased GN, whereas, the 7B QTL controls GW. We concluded that increased in GW from Weebill 7B allele is not accompanied by a significant reduction in grain number. The extent of the GW and GN trade-off is reduced. This makes this locus an attractive target for marker assisted selection to develop high yielding bold grain varieties like Weebill. AMMI analysis was used to show that the 7B Weebill allele appears to contribute to yield stability Fil: Griffiths, Simon. John Innes Institute; Reino Unido Fil: Wingen, Luzie. John Innes Institute; Reino Unido Fil: Pietragalla, Julian. Centro Internacional de Mejoramiento de Maíz y Trigo; México Fil: García, Guillermo Ariel. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cerealicultura; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Hasan, Ahmed. Universidad Austral de Chile. Plant Production and Plant Protection Institute; Chile Fil: Miralles, Daniel Julio. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cerealicultura; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Calderini, Daniel F.. Universidad Austral de Chile. Plant Production and Plant Protection Institute; Chile Fil: Bipinchandra Ankleshwaria, Jignaben . John Innes Institute; Reino Unido Fil: Leverington Waite, Michelle . John Innes Institute; Reino Unido Fil: Simmonds, James. John Innes Institute; Reino Unido Fil: Snape, John. John Innes Institute; Reino Unido Fil: Reynolds. Matthew P.. Centro Internacional de Mejoramiento de Maíz y Trigo; México

Two field experiments were carried out to evaluate the effect of the genetic improvement of barley on leaf and tiller appearance. Four malting barley cultivars were used to represent the main genotypes released from 1944 to 1998 in Argentina. One experiment was carried out with 110 kg N ha −1 of nitrogen availability at sowing, while in the other experiment cultivars were grown with 20, 50, 110 or 160 kg available N ha −1 . There was no difference in final leaf number among cultivars, which ranged from 9.5 to 11.2 leaves per main stem. Differences in phyllochron between old and modern cultivars were only observed for the early leaves and under treatments of low nitrogen availability (20 and 50 kg N ha −1 ). Cultivars began tillering at a similar time. Nitrogen treatments modified the range of maximum tiller number per plant from three (N 20 ) to seven (N 160 ) across cultivars. In addition, higher nitrogen availability delayed the time to maximum tiller number. Differences in the number of tillers per plant were explained by the rate of tiller appearance. High levels of tillering were accompanied by high levels of intercepted radiation and associated with modern cultivars growing under high levels of nitrogen. Accumulated intercepted radiation during the jointing–heading period had a trend to increase with years from release, at a mean rate of 1.17 MJ m −2 per year.

Barley breeding programs have empirically selected for improving grain yield and quality. The objective of this study was to quantify genetic gains in yield in 2-rowed malting barley cultivars released from 1944to 1998 in Argentina, identifying the major physiological traits responsible for them. For this purpose, a field experiment was conducted in absence of biotic and abiotic stressful factors and with lodging being prevented mechanically. Until the 1970's,potential yield was maintained nearly constant at 5.25 mg ha-1 and since then it increased at a rate of 41 kg ha-1 year-1. That bi-linear trend was closely related to the trend of averaged yields obtained by farmers. The contribution made by breeding yield potential to the total yield gains achieved by farmers was estimated in c. One third. Neither time to heading nor time to maturity were systematically modified by breeding. However, the partitioning of the developmental time was modified: time to achieve both maximum number of floret primordia and length of the jointing –heading period were increased with the year of release of the cultivars. The main component associated with yield was the number of grains per m2, due to variations in number of spikes per m2.Total and vegetative biomass at maturity increased with the year of release of the cultivars, at a rate of 45 and 19 kg ha-1 year-1, while both harvest index and stem height remained virtually unmodified. Differences in biomass at heading among cultivars were related to the improvement on the abilities to capture more radiation.

Element concentration in wheat grains is an important objective of plant breeding programs. For this purpose, synthetic hexaploid lines (Triticum durum ×Aegilops tauschii) have been identified as potential sources of high element concentration in grains. However, it is not known if these lines reach higher element concentrations in grains as the consequence of a dilution effect due to lower grain yield. In addition, most of the studies carried out with these lines did not evaluate above-ground element uptake. The objective of this study was to improve understanding of grain element concentrations as a function of grain yield, element uptake and biomass and element partitioning to grains in synthetic and conventional cultivars of wheat. One experiment with two standard sowing dates was carried out under field conditions. Biomass, grain yield, and macronutrient(Ca, Mg, K, P and S) and micronutrient (Cu,Fe, Mn and Zn) concentrations in grains and vegetative tissues were measured in two cultivars and one synthetic (chosen from ten lines). The synthetic showed higher element concentration in grains, e.g. between 25 and 30% for Fe, Mn and Zn across sowing dates, than cultivars while grain yield was similar or lower, depending on the sowing date. On the contrary, the synthetic showed lower concentration of Cain grains. This line showed also higher uptake of Fe, Mn, K and P than cultivars. The superior grain element concentration of the synthetic line was not only due to a dilution effect but also to a higher uptake efficiency. Therefore, synthetics would bea valuable source of germplasm for increasing element grain concentration, at least in this case for Fe, Mn, K and P.

Traditionally, barley in Argentina has been cultivated in low-yielding environments. A study was conducted to test whether breeding for improved performance under these conditions would have also improved the responsiveness to nitrogen availability. Four cultivars of two-rowed malting barley (released in 1944, 1960,1982 and 1998) were grown under 4 rates of nitrogen fertilizer at sowing (20, 50, 110and 160 kgN ha-1). All cultivars increased their yield with the increase in soil nitrogen. But yield of modern cultivars responded more strongly than yield of old ones. For modern cultivars, increase in grain yield was of 12 ± 0.6 kgha-1 for each 10 kg ha-1 of increase in the mean yield (environmental index). Absolute values of genetic gain were related to nitrogen availability: 1.59, 2.58, 4.52 and 4.29 g m-2 year-1 for the N20, N50, N110 and N160 treatments, respectively. Grain yield was associated with grain number m-2, which was dependent on spikes m-2 and grains spike-1. Total biomass at maturity also explained the changes in yield. It is concluded that selection under stress conditions was, in this case, beneficial to identify cultivars with high yields under a wide range of nitrogen availabilities.

Although individual grain weight is an important source of variation forgrain yield, there is still poor understanding of the causes determining finalgrain weight. Almost all studies conducted for understanding thedeterminants of grain weight have been focused on the post-anthesis period.However, there is important evidence that pre-anthesis conditions couldalso modify final grain weight. Three experiments including different sowingdates, genotypes and temperature regimes between booting and anthesis,were carried out in Argentina and Mexico to analyse the effect oftemperature and associated traits during the pre- and post-anthesis periodson grain weight under field conditions. In these experiments final grainweight could not be explained by average or maximum temperature duringthe post-anthesis period. However, average temperature between bootingand anthesis was closely related to the observed grain weight differences,probably as a consequence of the effects of this factor on carpel growth.Differences in grain weight between genotypes and grain position weresuccessfully explained by differences in carpel weight at anthesis. Theseresults suggest that our knowledge to determine grain weight could improveif the immediately pre-anthesis period conditions were taken into account.

The understanding of ecophysiological basis of wheat (Triticum aestivum L.) grain yield potential provides a useful framework to complement conventional breeding aimed at achieving genetic gains. This study analyzed the ecophysiological performance of an elite wheat mapping population (105 double-haploid lines derived from two modern cultivars, Bacanora and Weebil, with similar phenology but different and stable combinations of grain number per area unit (GN) and grain weight (GW) resulting in high grain yield) grown in four contrasting high-yielding environments, to determine the most successful strategies to increase grain yield potential. Main effect of environment on grain yield was significant (p < 0.0001) but the genotypic component was larger than genotype × environment interaction (30%). A robust and positive relationship between grain yield and biomass production was observed across all environments (r2 > 0.82, p < 0.0001), and relatively high harvest indexes were expressed (0.39–0.51). While GN was clearly the dominant numerical component in terms of association with grain yield (r2 > 0.51, p < 0.0001), a wide range in both components (i.e., GN and GW) was observed across all environments. This population represents a valuable resource for prebreeding studies, as the transgressive segregation in physiological and numerical yield components in combination with favorable expression of all agronomic traits could allow a fine phenotyping and mapping to identify key traits and quantitative trait loci linked with grain yield. Fil: García, Guillermo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Hasan, Ahmed K.. Universidad Austral; Chile Fil: Puhl, Laura E.. Universidad de Buenos Aires. Facultad de Agronomia; Argentina Fil: Reynolds, Matthew P.. Centro Internacional de Mejoramiento de Maíz y Trigo; México Fil: Calderini, Daniel F.. Universidad Austral; Chile Fil: Miralles, Daniel Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina

The effect of plant breeding on yield and their physiological determinants has been widely studied in wheat. However, it is poorly understood how, and to what extent, yield stability has been modified. To attempt a direct analysis of changes in absolute and relative yield stability, data of yield of cultivars released in different eras in different environments were obtained from records from our lab and from the literature. Depending on the availability of data, effects of plant breeding on yield stability of cultivars released in Argentina, Australia, Italy and the United Kingdom were evaluated using a quantitative approach. In this paper it was assumed that the slope of yield vs. environmental index estimates the instability of the cultivars. In addition, a more qualitative approach for Mexico, and the former USSR complemented this analysis. There was a clear decrease in yield stability assessed in absolute terms as a consequence of wheat breeding. In Argentina, Australia, Italy and the UK this decrease was related to the magnitude of yield increases. However, the decrease in yield stability in Argentina and Australia was less than for Italy and the UK, particularly so during the last 30 years. Modern cultivars released in Argentina and Australia showed a trend to maintain yield stability as a percentage of their yield similar to that of their predecessors, while the two European countries analysed tended to a slight decrease in yield stability even in relative terms. The complementary, less quantitative evaluation of Mexico and the former USSR appeared to confirm the quantitative trends described for the other countries, i.e. a general decrease in yield stability (assessed in absolute terms) with genetic gains in yield potential.

A field experiment was conducted under non-limiting water and nutritional conditions with three near-isogenic lines of spring wheat (dwarf, DD; semi-dwarf, SD and standard height, SH) to study the impact of the GA-insensitive alleles Rhtl and Rht2, at the cellular level, on the growth of different vegetative organs and of the pericarp of grains. Cell length and width of blades of different leaves (3, 7 and flag leaf), the flagleaf sheath and the penultimate internode as well as the pericarp of basal grains from central spikelets of the spike were evaluated. With the exception of the flag leaf, dwarfing genes produced a significant reduction in cell length in all the different vegetative organs analysed. There was no effect on the number of cells nor their width. Therefore, in vegetative organs, the effects of these alleles appeared to be exclusively due to a reduction in cell length. It would appear that dwarfing genes act on cell elongation without affecting cell division. The Rht alleles did not modify cell length nor width in the pericarp. Grain weight was different between the lines and these differences were associated with grain volume at the beginning of linear grain growth. Thus, they reduced the size of individual grains by reducing the total number of cells in the pericarp. It appears that Rht alleles reduced the final sizes of vegetative organs (such as internodes and leaves) and of tissues (pericarp) associated with reproductive structures (grains), but the modes of action in these different organs were different.

Field experiments were conducted during 1991 and 1992 to identify the effect of wheat breeding on crop biomass production and its physiological determinants, i.e. radiation interception and radiation-use efficiency. To address this objective, biomass accumulation and its physiological attributes of seven cultivars (including a commercial hybrid) released between 1920 and 1990 were compared in fertilised and irrigated plots. Weeds, pests, diseases and lodging were controlled or prevented. Crop radiation interception was calculated from measurements of incident and transmitted radiation at different times after sowing. Above-ground dry matter was determined at particular stages of development of the cultivars. Radiation-use efficiencies and crop growth rates were calculated for each cultivar for pre-anthesis (in both years) and post-anthesis (in 1992) periods. Biomass at anthesis tended to be less in most recently released cultivars than in older materials. Accumulated intercepted radiation at similar developmental stages also differed between cultivars. These differences, as well as the trend of biomass at anthesis, were caused by differences in the length of developmental phases between cultivars rather than by changes in the architecture of the canopies. The most recently released cultivars had shorter seedling emergence-anthesis periods than older cultivars. Moreover, all cultivars had similar canopy light extinction coefficients ( k ), pre-anthesis radiation-use efficiencies, and crop growth rates. After anthesis, the two oldest cultivars accumulated the least biomass and their radiation-use efficiencies and crop growth rates were smaller than those of modern cultivars. Remarkably, modern cultivars maintained during post-anthesis almost the same levels of crop growth rates and radiation use efficiencies reached during the pre-anthesis period.

Although it has been generally recognized that the difference in yield potential amongst wheat cultivars released in different eras is related to differences in their reproductive sink strength, there have been few investigations about changes in source–sink ratios as a consequence of wheat breeding. In the present study, two field experiments, in which plots were fertilized and irrigated and lodging and diseases were prevented, were carried out with seven cultivars (including a commercial hybrid) representing different periods of plant breeding in Argentina from 1920 to 1990. The cultivars were defoliated during post-anthesis to analyse the response of grain weight at particular positions within the spike (which have intrinsic differences in potential size).Individual grain weight was virtually unaffected by defoliation in the old cultivars, but modern cultivars exhibited a significant reduction in individual grain weight for several positions within the spike, although this reduction was small (c. 15%) and many grains were unaffected. In addition, no relationship was found between individual grain weight in the controls and its reduction due to defoliation.We concluded that if the source–sink ratio is further reduced, the grain yield of modern wheats will be simultaneously limited by the source and the sink. Future breeding should therefore attempt to improve simultaneously both sink and source strengths.

Two experiments were carried out with three isogenic lines (standard height, semi-dwarf and double dwarf) of wheat under field conditions without water and nutritional stresses, with the objective of assessing the effects of Rht1 and Rht2 leaf alleles on leaf appearance and leaf blade area development. Possession of dwarfing genes did not affect phenological development, final number of leaves nor the rate of leaf appearance on the mainstem. The relationship between number of appeared leaves and thermal time could be described by a bi-linear model with an inflection point at the sixth-leaf stages independently of any particular ontogenic stage. Rht alleles caused significant reduction in the growth of leaves and stems, but did not affect internode diameter. Rht alleles were also associated with decreased individual leaf blade area, mainly through reductions in leaf blade length caused by reduced rates rather than durations of extension. The data presented confirm that Rht alleles affect internode growth more than leaf blade expansion; two hypotheses are discussed.

Several studies have analysed the effects of wheat breeding on dry matter accumulation and partitioning, but little has been done to understand the effects on nutrient economies. The objective of this study was to identify the changes produced by wheat breeding in the economy of nitrogen and phosphorus under field conditions. Two experiments were carried out with seven genotypes (including a commercial hybrid) representing different eras of plant breeding. Wheat breeding has increased grain nitrogen and phosphorus yield but total absorbed nutrients have not shown any trend during this century. The main attribute closely related to the increase in grain nitrogen and phosphorus yields was their harvest indices. The higher nutrient partitioning in the newer cultivars was associated with lower grain nitrogen and phosphorus concentrations in their grains. Therefore, there was a negative effect of genetic improvement in grain nitrogen and phosphorus concentrations. The main cause for the decreased concentration of these nutrients in the grains of the modern cultivars appeared to be a dilution by an even more increased dry matter partitioning. It is suggested that future breeding should be aimed to select for higher nitrogen uptake as a way to increase the level of this nutrient in grain.

Two field experiments were carried out with seven wheat cultivars (three of them, including a commercial hybrid, released during the last 10 years) representing different eras of plant breeding, to evaluate genetic improvement over the last century in grain yield, height, biomass, harvest index and grain yield components. Plots were fertilized and irrigated, and lodging and diseases were prevented. Main culm height was negatively correlated with the year of release of the cultivars, probably as a consequence of selection for increased lodging resistance. There was no significant association between total above-ground biomass and year of release of the cultivars. On the other hand, grain yield increased as newer cultivars were released. Results indicate that during recent years harvest index has been kept as the main attribute responsible for increases in grain yield. In general, number of grains/m2 was associated with increases in grain yield during the century. However, the newest cultivars showed an increased grain weight. In both growing seasons, cultivars released before 1980 showed a trend towards reduced grain weight, but cultivars released after 1987 had a similar number of grains per m2 with a higher grain weight than their predecessors. This was probably because the most modern cultivars have a longer grain-filling duration with a similar length of growth cycle.

The importance of yield improvement at farm conditions is highly dependent on the interaction between genotype and environment. The aim of the present work was to assess the attainable yield of a traditional and a modern malting barley cultivar growing under a wide range of soil nitrogen (N) availabilities and different water scenarios (low, intermediate and high rainfall conditions during the fallow period and throughout the crop cycle) considering a 25-year climate dataset for two sites (a shallow and a deep soil) in the Pampas, Argentina. For that purpose, a barley model was first calibrated and validated and then used to expand field research information to a range of conditions that are not only much wider but also more realistic than experiments on experimental farms. Yield of the modern cultivar was at least equal to (under the lowest yielding conditions) or significantly higher (under most growing conditions) than that of the traditional cultivar. Averaged across all the scenarios, yield was ~20% higher in the modern than in the traditional cultivar. The average attainable yield represented 42% of the yield potential in the shallow and 79% in the deep soil profiles. Yield advantage of the high yielding cultivar was based on using N more efficiently, which not only determined higher attainable yields but also reduced the requirements of soil N to achieve a particular yield level. Farmers would face little risk in adopting higher yielding cultivars in both high and low yielding environments and even in the latter ones N fertilisation could be beneficial in most years. Fil: Abeledo, Leonor Gabriela. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cerealicultura; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario; Argentina Fil: Calderini, Daniel F.. Universidad Austral de Chile; Chile Fil: Slafer, Gustavo A.. Universitat de Leida; España

A substantial increase in grain yield potential is required, along with better use of water and fertilizer, to ensure food security and environmental protection in future decades. For improvements in photosynthetic capacity to result in additional wheat yield, extra assimilates must be partitioned to developing spikes and grains and/or potential grain weight increased to accommodate the extra assimilates. At the same time, improvement in dry matter partitioning to spikes should ensure that it does not increase stem or root lodging. It is therefore crucial that improvements in structural and reproductive aspects of growth accompany increases in photosynthesis to enhance the net agronomic benefits of genetic modifications. In this article, six complementary approaches are proposed, namely: (i) optimizing developmental pattern to maximize spike fertility and grain number, (ii) optimizing spike growth to maximize grain number and dry matter harvest index, (iii) improving spike fertility through desensitizing floret abortion to environmental cues, (iv) improving potential grain size and grain filling, and (v) improving lodging resistance. Since many of the traits tackled in these approaches interact strongly, an integrative modelling approach is also proposed, to (vi) identify any trade-offs between key traits, hence to define target ideotypes in quantitative terms. The potential for genetic dissection of key traits via quantitative trait loci analysis is discussed for the efficient deployment of existing variation in breeding programmes. These proposals should maximize returns in food production from investments in increased crop biomass by increasing spike fertility, grain number per unit area and harvest index whilst optimizing the trade-offs with potential grain weight and lodging resistance.

Grain weight is one of the most important components of cereal yield and quality. A clearer understanding of the physiological and molecular determinants of this complex trait would provide an insight into the potential benefits for plant breeding. In the present study, the dynamics of dry matter accumulation, water uptake, and grain size in parallel with the expression of expansins during grain growth in wheat were analysed. The stabilized water content of grains showed a strong association with final grain weight (r(2)=0.88, P

The physiological and genetic basis of yield improvement in wheat is only partially understood. Nonetheless, a significant increase in yield and biomass has been observed in several backgrounds when alien chromatin associated with Lr19 was introgressed from Agropyron elongtatum Theoretically, higher yield and biomass may be achieved through (i) greater interception of incident radiation, (ii) increased radiation use efficiency, (iii) a more optimal source-sink balance permitting higher sink demand and/or a higher partitioning of assimilates to yield. The objectives of the current study were to evaluate the performance of near isogenic lines differing in Lr19 to observe the physiological basis of superior performance Lr19 was associated with increases in yield (average 13%), final biomass (10%) and grain number (15%) in all backgrounds studied. Differences were not associated with improved light interception based on measurements of biomass shortly after canopy closure, nor with improved radiation use efficiency (RUE) prior to grain filling based on biomass accumulation rate and direct measurement of flag-leaf photosynthetic rate prior to anthesis. Lr19 was associated with an increased partitioning of biomass to spike growth at anthesis (13%), a higher grain number per spike, and higher RUE and flag-leaf photosynthetic rate during grain filling. The mechanism causing increased partitioning of assimilates to spikes relative to the rest of the plant in Lr19 isolines was apparently not related to phenology or assimilation capacity.

Soil constraints affect potential grain yield of wheat. Among these constraints acidic soils are especially important due to their combined effect on aluminum (Al) toxicity and phosphorus (P) fixation. The objective of the present study was to evaluate the response of final leaf number (FLN), phyllochron and tillering dynamic of wheat in response to different Al and P concentrations in the soil under field conditions. Two field experiments were conducted in an Andisol in Valdivia (39°47′S, 73°14′W), Chile, during the 2006–07 (Expt 1) and 2007–08 (Expt 2) growing seasons. Treatments in Expt 1 consisted of a factorial arrangement of: (i) two spring wheat cultivars with different sensitivities to Al toxicity (the sensitive cultivar: Domo.INIA and the tolerant cultivar: Dalcahue.INIA) and (ii) five exchangeable soil Al levels (from 0 to 2.7 cmolc kg–1). In Expt 2 treatments consisted of a control, two levels of Al toxicity and two P treatments with three replicates in both experiments. Leaf appearance was measured from seedling emergence to anthesis; their dynamics were recorded according to the scale developed by Haun. FLN and tiller appearance were recorded in the same plants at the same time. Exchangeable Al affected FLN in Expt 1 showing a linear association in both cultivars (r = 0.99). In Expt 2 FLN was unaffected by both Al and P levels because there was a lower soil Al concentration in this experiment. Leaf appearance rate (LAR) was adjusted to bilinear equations, differentiating among early and later leaves. In Expt 1 soil Al concentration affected phyllochron of early leaves, increasing this trait by 14 and 33 degree-days in the Al-sensitive and Al-tolerant cultivars, respectively. Similarly, phyllocron of later leaves was also increased but at a higher extent in the same cultivars (62 and 38 degree-days). Both Al toxicity and P shortage decreased the maximum (MNT) and final number of tillers (FNT). Leaf area index at anthesis was positively associated with FLN (r = 0.77) and MNT (r = 0.95 and 0.99 in the Al-sensitive and Al-tolerant cultivars, respectively), with no regard to Al or P constraints.

Source limitation during grain filling is important for both management and breeding strategies of grain crops. There is little information on the sensitivity of grain weight of temperate cereals to variations in source–sink ratios, and no studies are available on the comparative behaviour of temperate cereals growing together in the same experiment. The objective of the current study was to evaluate, under field conditions, the response of grain weight to different source–sink ratios during grain filling in high-yielding cultivars of bread wheat, durum wheat, and triticale at 2 contrasting locations. Two experiments were carried out at C. Obregon and El Batan in Mexico. In each location, 6 genotypes (2 bread wheat, 2 durum wheat, 2 triticale) were evaluated. A week after anthesis, 2 source–sink (control and halved spikes) treatments were imposed. Location and genotype significantly (P < 0.01) affected grain yield and components. Significant grain weight increases (P < 0.05) were found only in 2 cases in El Batan. The highest response of 17% was found in triticale, with less than 10% in most of the other genotypes. The effect of genotype and location is discussed.

Little is known about nutrient distribution within the spike of bread wheat (Triticum aestivum L.). This knowledge is important for determining breeding strategies aimed at increasing grain yield without affecting nutritional quality. The objective of this study was to gain a better understanding of how grain position affects nutrient concentration, dry matter distribution, and water dynamics of grains. An experiment using two sowing dates was performed under field conditions. Dry weight and concentrations of macronutrients (Ca, Mg, K, P, and S) and micronutrients (Cu, Fe, Mn, and Zn) in grains from the basal (BS), central (CS), and apical spikelets (AS) of two cultivars and one synthetic hexaploid line were determined. Grain water dynamics and nutrient and dry matter concentrations were also measured throughout the grain-filling period for the second sowing date. Genotypes showed different distributions of dry matter in different grain positions. Grain macronutrient and micronutrient concentrations in all genotypes decreased at grain positions more distal from the rachis. This reduction was as great as 30% (Ca) but varied by nutrient (e.g., Zn = -18%; S = -10%; K = +1%). Grain water content did not differ between grains. The observed differences in grain weight and nutrient concentration between grain positions could have important implications for wheat breeding. They suggest that it might be more effective to select for higher grain yield by increasing individual grain weight rather than grain number, a strategy that, in addition, would be less likely to affect the balance of nutrient concentrations within the spike.

Grain weight is a trait which has hardly been exploited for raising genetic yield potential of wheat. A clearer understanding of physiological determinants of grain weight potential would be useful in establishing the potential value of this trait in future breeding programs. The objective of this study was to improve understanding of how intra-spikelet competition for assimilates pre- and post-anthesis affect grain weight potential, and to evaluate possible mechanisms determining final grain weight in wheat. Two experiments were carried out under field con-ditions. Proximal or distal grains from the two central spikelets of spikes of three synthetic hexaploid lines were detached at heading or 7 d after anthesis. Synthetic wheats were used since they represent a potential source of genetic variability for grain weight potential. Carpel size at anthesis and grain weight during the grain filling period were measured. The de-graining treatment at heading significantly increased grain weight, especially in distal posi-tions. On the contrary, the de-graining treatment carried out after anthesis caused no increase in final grain weight. The largest response to pre-anthesis de-graining occurred in grain positions with the lowest grain mass. In addition, the effect of de-graining prior to anthesis was associated hyperbolically with weight of carpels at anthesis within each grain position. Therefore, carpel weight at anthesis could be partially associated with the regulation of grain weight potential.

Individual grain weight is an important source of variation for grain yield in wheat. The aim of this study was to investigate the effect of short periods of high temperature immediately pre-anthesis, or during post-anthesis, on grain weight under field conditions. Thus, two wheat cultivars of different grain weight potential were sown on four different sowing dates to provide different temperature conditions during the pre- and post-anthesis periods. In addition, for two sowings, acrylic boxes were installed to increase spike temperature either immediately before anthesis, or during the lineal phase of the grain-filling period. Final grain weight was significantly affected by sowing date, genotype and grain position on the spike. Grain weight showed a clear relationship with the average temperature of the grain filling period, but this relationship was either linear or curvilinear, depending on the cultivar. Both high temperature treatments, i.e. at pre- or post-anthesis, significantly diminished final grain weight, and their effect was similar with the exception of heavier grains, which were unresponsive to the high temperature treatment at pre-anthesis. Finally, a better understanding of final grain weight was reached when temperatures from the pre-anthesis period were included in the analysis of grain weight response to temperature.

Grain quality is a complex character primarily determined by processes at the crop level. This chapter reviews the effects of environment, genotype, and their interactions, on grain oil and protein concentration and composition. The focus is on sunflower as an oilseed model and bread wheat as a cereal model. Sunflower oil composition is analyzed in terms of concentration and composition of fatty acids, tocopherols and phytosterols while, in bread wheat, grain prolamin composition is considered. Process-based crop models accounting for grain yield in both species, and for concentration and composition of oil (sunflower) and protein (wheat) are described. A combination of modeling and experiments allowed analysis of the relationships between quality traits and yield. Finally, we use physiologically-based relationships of yield and oil attributes (sunflower) and yield and protein attributes (wheat) to design management and breeding strategies for grain quality improvement.