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High-temperatures reduce yield of wheat and with global warming episodes of heat waves (only few days of high maximum temperatures) during grain filling will become more frequent. It has been recently reported that the magnitude of the yield penalties imposed by high temperatures under field conditions may interact with nitrogen (N) availability both in barley and maize. We determined, under field conditions, the penalties imposed by post-anthesis high-temperatures waves (increased maximum –but not minimum– temperatures during part of the grain filling period) on wheat yield under contrasting soil N supply during two consecutive years. The high temperature treatment was imposed for 10 d starting 10 d after anthesis by placing over the crops transparent polyethylene film (125 μm) mounted on wood structures of 1.5 m height above the ground. This high-temperature and the unheated controls were imposed on 5 modern and well adapted cultivars under contrasting N availabilities (376, 268 and 68 KgN ha−1). Averaged across N conditions, high-temperature treatments reduced yield by c. 1.5 Mg ha−1 (a loss of c. 17%) even though the treatment was rather mild in terms of different average temperature during grain filling. The magnitude of the loss was consistently shaped by the N condition in which the treatment was imposed: yield penalty produced by high-temperature increased from less than 1 to 2.6 Mg ha−1 (which represents losses from 10 to 25%) in parallel with the increased N supply. The penalties were related to both yield components (grain number and average grain weight) which also were more severely penalised under high than under low N supply. As episodes of high-temperature waves will become more frequent in the future the tools used to establish the needs of N fertilisation should be revised as the rates maximising yield (or gross margin) might induce higher sensitivities to these episodes. Also simulation models used to upscale physiological responses to regional or even global domains might need to be revised to include the effect of heat waves (which would be larger per °C increase than what is estimated from experiments increasing temperature during the whole day and over longer periods) as well as the interaction with N supply. Authors thank Semillas Batlle S.A. for their support in the setting up and maintenance of the field plots. Funding was provided by project AGL2012-35300 of the Ministry of Economy and Competitiveness of Spain.

Future increases in grain number may be achieved through improving fruiting efficiency (FE; grains set per unit spike dry weight at anthesis). In recent experiments it was found a negative relationship between the average weight of the grains and FE. The objective of this paper was to determine whether this negative relationship was constitutive (i.e. the increased FE caused all grains to be smaller) or resulted from the increased proportion of grains of smaller potential size. Four experiments, involving 8 different environmental conditions, were carried out during two consecutive growing seasons (2008–2009 and 2009–2010) in which two durum wheat cultivars contrasting in FE and average grain weight were compared. In these conditions we determined FE and carried out a comprehensive study analysing in detail the weights of each individual grain along each of the spikelets. Averaging all experimental conditions, there was a negative relationship between average grain weight (GW) and fruiting efficiency (FE). Donduro with low FE produced in average heavier grains than Vitron. However, when considering individual grains there were, in general, no differences in GW. Therefore, the negative relationship between average grain weight and FE would not be constitutive, and would mostly represent the increase in the proportion of distal grains within the spikelets or of grains from apical spikelets as a consequence of an increased FE, reducing the average size of the grain but mostly unaffecting the size of particular grains. This provides further and stronger support to the idea of using FE as a criterion to further raise yield potential in wheat breeding programmes.

A major aim in breeding programs is to improve nitrogen use efficiency (NUE). The critical level of specific leaf nitrogen (SLNc) maximising growth and yield is a relevant trait influencing NUE. The relationship between growth or yield and SLN is hyperbolic indicating that levels of SLN higher than the critical would tend to decrease NUE. It has been recently proposed that maize breeding may profit of this relationship by phenotyping SLN and selecting for genotypes with SLN = SLNc (SLN SLNc would bring about high yields but at the expense of low NUE); being the SLNc = 1.5 gN m −2 . For this proposal to be realistic, genotypic variation in SLNc should be negligible. We aimed to determine the degree of genetic variation in SLNc in a range of modern maize hybrids. For this purpose, we carried out four field experiments with 11 contrasting maize hybrids grown under fertilized (200 kgN ha −1 ) or unfertilized conditions in each of the four experiments. At silking, leaf area and N concentration of leaves were determined and at maturity, yield and biomass were measured. Analysing the whole dataset together ( n = 88) we found a very large range of all variables measured and calculated: yield varied between c. 6 and c. 18 Mg ha −1 and SLN from c. 0.7 to c. slightly more than 2.5 gN m −2 . Within that context we found a significant bi-linear regression between yield and SLN ( p −2 . The variation was also substantial calculating SLNc with an alternative methodology and if leaf N content instead of SLN were used as independent variable. Genotypic differences in SLNc were positively related to N uptake but unrelated to other traits for which hybrids varied, including yield potential. Additionally, genotypes with low SLNc show a tendency for a better NUtE. We concluded that it does not seem appropriate to phenotype for a particular value of SLNc as any particular threshold might bring about selected lines with either a yield potential lower than possible and/or with a relatively lower than possible NUE.

Waterlogging, if occurring within the stem elongation period (SE), is particularly critical for yield determination. We quantified for the first time the effect of waterlogging duration during SE on yield and studied whether the effects were only direct on resource capture or whether there were feed-forward effects as well. We grew wheat (cv. Soissons) outdoors in long tubes (1.25 m deep) forming a normal canopy and imposed different treatments in SE to finish simultaneously around anthesis (0, 4, 8, 12, 16, 20 and 24 days) plus two complementary treatments (8 and 16 days) starting 10 days after the onset of SE. Yield was reduced linearly with the duration of waterlogging c. 2 % dwaterlogging−1. Treatments mainly affected pre-anthesis spike growth reducing the number of fertile florets and grains, not affecting fruiting efficiency. The magnitude of grain number loss was inversely proportional to the hierarchy of the spikes and spikelets. Grain weight was more marginally reduced, likely through the effects on the size of the ovaries of the developing florets. This reveals a direct effect of waterlogging on the capture of resources with no major feed-forward effects. Losses were in agreement with those from other studies for particular durations of waterlogging.

Carolight® is a transgenic maize variety that accumulates extraordinary levels of carotenoids, including those with vitamin A activity. The development of Carolight® maize involved the technical implementation of a novel combinatorial transformation method, followed by rigorous testing for transgene expression and the accumulation of different carotenoid molecules. Carolight® was envisaged as a way to improve the nutritional health of human populations that cannot access a diverse diet, but this ultimate humanitarian application can only be achieved after extensive testing for safety, agronomic performance and nutritional sufficiency. In this article, we chart the history of Carolight® maize focusing on its development, extensive field testing for agronomic performance and resistance to pests and pathogens, and feeding trials to analyze its impact on farm animals (and their meat/dairy products) as well as animal models of human diseases. We also describe more advanced versions of Carolight® endowed with pest-resistance traits, and other carotenoid-enhanced maize varieties originating from the same series of initial transformation experiments. Finally we discuss the further steps required before Carolight® can fulfil its humanitarian objectives, including the intellectual property and regulatory constraints that lie in its path. European Research Council Advanced Grant (BIOFORCE) and Proof of Concept Grant (Multinutrient Maize) to PC; Spanish Ministry of Economy and Competitiveness (AGL2014-53970-C2-1-R, AGL2015-65846-R, BIO2014-54426-P and BIO2014-54441-P); RecerCaixa project PC084082; Catalan Autonomous Community 2014 SGR 1296 Agricultural Biotechnology Research Group and Agrotecnio Research Center. JDG thanks the UdL for a Ph.D. fellowship.

Barley is one of the most popular crops in dryland agricultural systems of Mediterranean areas, where it is assumed that barley, or traditional wheat cultivars, performs better than modern wheat under low-yielding conditions. It was tested whether variations in net leaf photosynthetic rate (PN) during grain filling provide any basis for the potential better performance of barley and traditional wheat compared to modern wheats in Mediterranean areas. Two groups of field experiments were conducted in Agramunt (NE Spain) during 2005/06 (06) and 2006/07 (07) growing seasons combining low and high nitrogen (N) availabilities under rain-fed and irrigated conditions. Cultivars used in the first group of experiments were a traditional (Anza) and a modern (Soissons) wheat, whilst in a second group of experiments, a wheat (Soissons) and a barley (Sunrise) modern cultivars were used. Both wheat cultivars showed a similar PN during grain filling but higher than that of the modern barley cultivar. Differences between species in PN were maximized under high-yielding conditions. There were no differences between cultivars in instantaneous water-use efficiency. The barley cultivar showed a higher specific leaf area, but lower N content per unit of leaf area, than wheat. Photosynthetic nitrogen-use efficiency was similar between the traditional and the modern cultivar but lower than barley. Decreases in PN after anthesis were not exactly observable in SPAD measurements. In conclusion, we found no consistent differences between cultivars in terms of post-anthesis photosynthetic activity to support the assumption of better performance under Mediterranean farm conditions of traditional wheat or barley against modern wheat. Fil: Abeledo, Leonor Gabriela. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Savin, Roxana. Universidad de Lleida; España. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Slafer, Gustavo Ariel. Institució Catalana de Recerca i Estudis Avancats; España. Universidad de Lleida; España. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

It is frequently assumed that durum wheat is more tolerant to stress than bread wheat. Unfortunately few research papers compare the performance of both species side-by-side under a wide range of environments in field conditions. We aimed to compare durum and bread wheat performance in a field study under contrasting treatments of water and nitrogen during three experimental seasons. In addition we compiled a comprehensive database with data from field experiments in which both species were grown in the same field conditions. A cross-over interaction of yield from bread vs. durum wheat was found, but oppositely to the hypothesis, bread outyielded durum wheat in the low-yielding conditions while durum wheat tended to have higher potential yield. We then divided the database in decades in which the cultivars were released and found that in the 1960s bread wheat outyielded durum wheat in almost any comparison whilst in the 2000s durum wheat outyielded bread wheat in most comparisons. Grain weight was constitutively higher in durum than in bread wheat, likely associated with a lower fruiting efficiency in the former; but in both types of wheat grain number per m2 was the component responsible for yield sensitivity to environmental changes. Differences in yield were also related to differences in water and nitrogen use efficiencies: under low-yielding conditions bread wheat was consistently more efficient than durum wheat and under high-yielding conditions durum wheat was more efficient.

Wheat yield is frequently analysed in terms of yield components (spikes per m2, grains per spike, grain size), and correlations between components are commonly reported, but partially understood. Compensations between components are one of the main barriers to improve yield using this approach. Understanding better the nature of these relationships is therefore important. We compiled a large database (n = 846) of wheat yield (ranging from 1.3 to 14.8 Mg ha−1) under field conditions to further investigate the relationships between yield components from the viewpoint of phenotypic plasticity. We found two main hierarchies between plasticities. Hierarchy 1, grains per m2 ≫ grain size, has been widely described before and is supported empirically and theoretically; here this hierarchy lends confidence in our analytical method. Hierarchy 2, spikes per m2 > grains per spike, is demonstrated for the first time. These hierarchies are interpreted in terms of coarse and fine regulation of grain yield (Hierarchy 1), and grains per m2 (Hierarchy 2). This means small changes in yield or grains per m2 can be accounted for by any of their components, but large changes in yield can only be accommodated by grains per m2, and large changes in grains per m2 are primarily associated with heads per m2. Further, we showed that the rankings of responses of yield components depend on the nature of the driver, i.e. genotype or environment. Both hierarchies are much stronger when the driver is environmental factors (e.g. water supply). When the driver is genotype, and this means we are not strictly dealing with plasticity but trait responsiveness to genotype, the rankings are weaker. Strong, negative relationships between components were found for small changes in yield or in grains per m2 for both environmental and genetic factors, implying strong trade-offs. For large changes, trade-offs were generally less relevant but much stronger for components of yield than for components of grains per m2. For large changes in grains per m2 associated with environmental factors, the negative relationship between grains per spike and of spikes per m2 was weak but when they were associated with genetic factors, the negative relationship was strong. In conclusion, our study reinforces the hierarchy of plasticities between components of grain yield, reveals a hierarchy between the components of grains per m2, and demonstrates that the strength of the trade-off between components of either yield or grains per m2 depends upon the magnitude of yield changes and, for large changes, the source of variation. A practical corollary is that breeding and agronomy could potentially achieve modest to intermediate yield increase involving any components, which would exhibit some trade-offs. Agronomic interventions are more likely to lead to large yield improvement, mainly through increase in grains per m2 with negligible trade-offs in grain size.

The frequency and intensity of extreme high temperature events are expected to increase with climate change. Higher temperatures near anthesis have a large negative effect on maize (Zea mays, L.) grain yield. While crop growth models are commonly used to assess climate change impacts on maize and other crops, it is only recently that they have accounted for such heat stress effects, despite limited field data availability for model evaluation. There is also increasing awareness but limited testing of the importance of canopy temperature as compared to air temperature for heat stress impact simulations. In this study, four independent irrigated field trials with controlled heating imposed using polyethylene shelters were used to develop and evaluate a heat stress response function in the crop modeling framework SIMPLACE, in which the Lintul5 crop model was combined with a canopy temperature model. A dataset from Argentina with the temperate hybrid Nidera AX 842 MG (RM 119) was used to develop a yield reduction function based on accumulated hourly stress thermal time above a critical temperature of 34 °C. A second dataset from Spain with a FAO 700 cultivar was used to evaluate the model with daily weather inputs in two sets of simulations. The first was used to calibrate SIMPLACE for conditions with no heat stress, and the second was used to evaluate SIMPLACE under conditions of heat stress using the reduction factor obtained with the Argentine dataset. Both sets of simulations were conducted twice; with the heat stress function alternatively driven with air and simulated canopy temperature. Grain yield simulated under heat stress conditions improved when canopy temperature was used instead of air temperature (RMSE equal to 175 and 309 g m−2, respectively). For the irrigated and high radiative conditions, raising the critical threshold temperature for heat stress to 39 °C improved yield simulation using air temperature (RMSE: 221 g m−2) without the need to simulate canopy temperature (RMSE: 175 g m−2). However, this approach of adjusting thresholds is only likely to work in environments where climatic variables and the level of soil water deficit are constant, such as irrigated conditions and are not appropriate for rainfed production conditions. Fil: Gabaldón Leal, C.. Centro Alameda del Obispo; España Fil: Webber, H.. Universitat Bonn; Alemania Fil: Otegui, Maria Elena. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Producción Vegetal; Argentina Fil: Slafer, Gustavo Ariel. Universidad de Lleida; España. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Institució Catalana de Recerca i Estudis Avancats; España Fil: Ordóñez, R. A.. Universidad de Lleida; España Fil: Gaiser, T.. Universitat Bonn; Alemania Fil: Lorite, I. J.. Centro Alameda del Obispo; España Fil: Ruiz Ramos, M.. Universidad Politécnica de Madrid; España Fil: Ewert, F.. Universitat Bonn; Alemania

The number of seeds per unit land area, the major yield component in soybean (Glycine max (L.) Merrill) is largely determined after the beginning of flowering, particularly from R3 to R6. Environmental factors increasing crop growth rate (e.g. radiation) or extending the duration of the reproductive phases (e.g. photoperiod) increase the number of seeds. We aimed to compare the mechanisms by which photoperiod and radiation affect the definition of final seed number during the critical period of R3–R6. Two field experiments were conducted with indeterminate soybeans at intermediate maturity group. All plots in each experiment were grown under natural conditions until the beginning-pod stage (R3); and from then onwards different treatments were imposed. Treatments consisted of the factorial combination of two levels of radiation (natural or shading) and two photoperiod regimes (natural or extended). Extended photoperiod increased the duration of reproductive phases, the number of nodes and the number of pods produced on the nodes that flowered during or after the applications of the treatments. Shading had negligible effects on development and node number, but reduced crop growth rate and also reduced the number of pods produced on most nodes of the plants. The number of seeds was positively related to the crop growth rate during R3–R6, but photoperiod increased the number of seeds produced per unit of crop growth rate, due to the lengthening of the phase. The number of seeds was therefore even better related to accumulated growth during R3–R6, irrespective of the factor that increased the accumulated biomass (higher daily radiation or longer duration of the phase) suggesting that long photoperiods increased the number of pods and seeds established per unit land area, mainly through increasing the total resource availability during a phase that is critical for the determination of seed number in soybean. However, photoperiod regulation involved additional changes in the development, evidenced by changes in the pod distribution pattern within the canopy.

Highlight Outcomes of floret initiation, mortality/survival, grain set/abortion, and fruiting efficiency have been quantified in 30 cultivars and connected to the processes determining the fate of floret primordia using ovary size., Spike fertility traits are critical attributes for grain yield in wheat (Triticum aestivum L.). Here, we examine the genotypic variation in three important traits: maximum number of floret primordia, number of fertile florets, and number of grains. We determine their relationship in determining spike fertility in 30 genotypes grown under two contrasting conditions: field and greenhouse. The maximum number of floret primordia per spikelet (MFS), fertile florets per spikelet (FFS), and number of grains per spikelet (GS) not only exhibited large genotypic variation in both growth conditions and across all spikelet positions studied, but also displayed moderate levels of heritability. FFS was closely associated with floret survival and only weakly related to MFS. We also found that the post-anthesis process of grain set/abortion was important in determining genotypic variation in GS; an increase in GS was mainly associated with improved grain survival. Ovary size at anthesis was associated with both floret survival (pre-anthesis) and grain survival (post-anthesis), and was thus believed to ‘connect’ the two traits. In this work, proximal florets (i.e. the first three florets from the base of a spikelet: F1, F2, and F3) produced fertile florets and set grains in most cases. The ovary size of more distal florets (F4 and beyond) seemed to act as a decisive factor for grain setting and effectively reflected pre-anthesis floret development. In both growth conditions, GS positively correlated with ovary size of florets in the distal position (F4), suggesting that assimilates allocated to distal florets may play a critical role in regulating grain set.

Highlights • Time to terminal spikelet and from then to anthesis were largely independent. • The length of the stem elongation phase was slightly but positively related to grains per m2. • Fruiting efficiency was critical for determining grain number, but it was also negatively related to grain weight. • The length of the stem elongation phase seems to have imposed an upper threshold for fruiting efficiency., Developmental patterns strongly influence spike fertility and grain number, which are primarily determined during the stem elongation period (i.e. time between terminal spikelet phase and anthesis). It has been proposed that the length of the stem elongation phase may, to an extent, affect grain number; thus it would be beneficial to identify genetic variation for the duration of this phase in elite germplasm. Variation in these developmental patterns was studied using 27 elite wheat lines in four experiments across three growing seasons. The results showed that the length of the stem elongation phase was (i) only slightly related to the period from seedling emergence to terminal spikelet, and (ii) more relevant than it for determining time to anthesis. Thus, phenological phases were largely independent and any particular time to anthesis may be reached with different combinations of component phases. Yield components were largely explained by fruiting efficiency of the elite lines used: the relationships were strongly positive and strongly negative with grain number and with grain weight, respectively. Although fruiting efficiency showed a positive trend with the duration of stem elongation that was not significant, a boundary function (which was highly significant) suggests that the length of this phase may impose an upper threshold for fruiting efficiency and grain number, and that maximum values of fruiting efficiency may require a relatively long stem elongation phase.

Highlights • The Rht8 introgression was associated with robust height reduction across different nitrogen and water treatments. • The Rht8 NIL had increased root-lodging resistance at agronomically-relevant nitrogen levels. • Decreased spike length associated with Rht8 resulted in a semi-compact spike. • Yield penalty associated with Rht8 was driven by reduced grain number and spike number. • The yield penalty was overcome at low nitrogen and in irrigated conditions., Reduced height 8 (Rht8) is the main alternative to the GA-insensitive Rht alleles in hot and dry environments where it reduces plant height without yield penalty. The potential of Rht8 in northern-European wheat breeding remains unclear, since the close linkage with the photoperiod-insensitive allele Ppd-D1a is unfavourable in the relatively cool summers. In the present study, two near-isogenic lines (NILs) contrasting for the Rht8/tall allele from Mara in a UK-adapted and photoperiod-sensitive wheat variety were evaluated in trials with varying nitrogen fertiliser (N) treatments and water regimes across sites in the UK and Spain. The Rht8 introgression was associated with a robust height reduction of 11% regardless of N treatment and water regime and the Rht8 NIL was more resistant to root-lodging at agronomically-relevant N levels than the tall NIL. In the UK with reduced solar radiation over the growing season than the site in Spain, the Rht8 NIL showed a 10% yield penalty at standard agronomic N levels due to concomitant reduction in grain number and spike number whereas grain weight and harvest index were not significantly different to the tall NIL. The yield penalty associated with the Rht8 introgression was overcome at low N and in irrigated conditions in the UK, and in the high-temperature site in Spain. Decreased spike length and constant spikelet number in the Rht8 NIL resulted in spike compaction of 15%, independent of N and water regime. The genetic interval of Rht8 overlaps with the compactum gene on 2DS, raising the possibility of the same causative gene. Further genetic dissection of these loci is required.

High-carotenoid corn (Carolight®) has been developed as a vehicle to deliver pro-vitamin A in the diet and thus address vitamin A deficiency in at-risk populations in developing countries. Like any other novel crop, the performance of Carolight® must be tested in different environments to ensure that optimal yields and productivity are maintained, particularly in this case to ensure that the engineered metabolic pathway does not attract a yield penalty. Here we compared the performance of Carolight® with its near isogenic white corn inbred parental line under greenhouse and field conditions, and monitored the stability of the introduced trait. We found that Carolight® was indistinguishable from its near isogenic line in terms of agronomic performance, particularly grain yield and its main components. We also established experimentally that the functionality of the introduced trait was indistinguishable when plants were grown in a controlled environment or in the field. Such thorough characterization under different agronomic conditions is rarely performed even for first-generation traits such as herbicide tolerance and pest resistance, and certainly not for complex second-generation traits such as the metabolic remodeling in the Carolight® variety. Our results therefore indicate that Carolight® can now be incorporated into breeding lines to generate hybrids with locally adapted varieties for further product development and assessment. This work was supported by Agrotecnio (Fundació Centre de Recerca en Agrotecnologia, VitaMaize 01 project) and Fundació la Caixa (Grant P13005).

Yield differences among wheat cultivars and its responsiveness to resource availability are usually related to grain number per m 2 , and further increases in grain number are required, but now beyond differences in time to anthesis and plant height (that are mostly optimised in traditional growing regions). The objective of this paper was to determine and quantify differences in yield physiology between different modern well adapted durum wheats grown in contrasting conditions (in addition we also tested if a higher amount of resources due to removal of competition could affect yield through the same determinants to nitrogen (N) availability). Four experiments were carried out during two growing seasons (2008–09 and 2009–2010); all in all under eight different growing conditions (Gc1–Gc8). In the first season four different modern cultivars were used and in the second season we selected the two highest-yielding cultivars, which differed in their responses to N in terms of spike fertility. Yield was closely related to biomass and N uptake due to both growing conditions and genotypic effects in all experiments. The existence of variation among modern cultivars in these yield determinants is relevant as further increases in yield must be achieved beyond further increases in partitioning. Yield differences among cultivars were based on their differences in grains per m 2 or average grain weight depending on which cultivars were compared. Overall grain number was related to spike dry weight at anthesis, and no evidences were found for a direct involvement of N in grain number determination, beyond the general effect of N availability on spike dry matter. However, this overall effect was mainly driven by growing conditions whilst differences between genotypes seemed associated with either spike dry weight at anthesis or fruiting efficiency, which varied significantly between cultivars. Interestingly, grain weight was consistently higher in the cultivars with lower fruiting efficiency than in cultivars maximising the number of grains set per unit of spike dry weight at anthesis suggesting a constitutive component for the commonly reported negative relationship between grain weight and grain number. In conclusion, the main differences in yield between modern, well adapted wheats were related to their biomass and N uptake and to the sink-strength during post-anthesis, being this strength increased either by having more grains or grains of potentially greater size, depending on the specific cultivar and as a consequence of a trade-off between fruiting efficiency and grain size.

Wheat provides 20% of calories and protein consumed by humans. Recent genetic gains are

In order to identify genotypes of durum wheat expressing improved yield and determining whether selection for individual plant efficiency in producing grains would improve plant and crop yield, we firstly compared the performance of segregating mutants and control cultivars and then selected divergent lines for number of grains per unit stem length, representing extreme source-sink balances further characterising the offspring lines. Research included three field experiments with individual segregating plants within the semi-arid region of the Ebro Valley during the 2006/07, 07/08 and 08/09 growing seasons; a fourth experiment with segregating plants conducted under controlled conditions at Rothamsted in 2008/09 and finally a conventional field plot experiment with the most promising lines derived from the selection. In the initial characterization of the selected mutants, there was a clear response to the selection made in M2, and differences in plant yield were due to differences in grains per plant and biomass. There was a clear response to selection for sink-strength in improving the number of grains exhibited by the offspring lines through the generations (M2–M5) and the overall differences between the two divergent groups were consistently clear throughout the whole process. Response to selection was similarly expressed in field and in controlled conditions, implying high broad sense heritability of grains per plant (when there were no consistent differences in height and then it reflects grains per unit stem length). The best selections outyielded plants of the controls, without reducing the protein concentration of the grains. It seems clear that increasing the efficiency of conversion of growth during stem elongation into grains may be a relevant trait to further raise yield and that the trait used in the present study as a proxy of such efficiency (the number of grains per unit stem length) seemed appropriate as a selection criteria in early generations as it expressed similarly in isolated plants and in crop stands.

Yield components are relatively easy to measure and their interpretation is intuitive. However, strong environmental influences, genetic and physiological controls, and evolutionary constraints collectively lead to lack of independence among yield components that restrict their value in breeding and agronomic applications. Here, we first sketch a framework of plant responses to environmental factors to highlight the modulation of yield components by resources and their interplay with non-resource factors including developmental cues (e.g. maternal effects), extreme events (e.g. frost), predicting factors (e.g. photoperiod) and synchronising and integrating information (e.g. spectral composition of light). We suggest that, to the extent that non-resource cues allow plants to predict future availability of resources, simple resource-based models may be sufficient to capture the macroscopic responses of yield components to the environment. Next, we expand the original concept of hierarchy of plasticities between grain size (a relatively stable trait) and grain number (a plastic trait) to test the hypothesis of a broader hierarchy in the plasticities of yield components. Using published data for wheat, rice, barley and triticale, we verified that heritabilities capture the established hierarchy between plasticity of grain size and number. Median heritabilities of 0.31 for tiller number, 0.58 for inflorescence number, 0.59 for grains per inflorescence, and 0.79 for grain size supported the hierarchy of plasticities: tiller number > inflorescence number ≈ grains per inflorescence > seed size. The heritability of grain yield was consistently higher than the heritability for tillering, consistently lower than the heritability for grain size, and suggestively close to the heritability of inflorescence number and grains per inflorescence, the components of grain number per unit ground area. We conclude that understanding the environmental regulation of yield components in cereals would benefit from a dual focus on yield-related traits per se and their plasticity.

SUMMARYRainfed wheat is frequently exposed to periods of water stress that generate low and variable grain yields. Field experiments (with studies in Tunisia and Morocco) carried out in the context of a European research project of co-operation with Mediterranean partner countries (WatNitMED) showed that nitrogen (N) fertilization may be a tool to increase productivity of rainfed wheat in Mediterranean environments. However, most farmers in Northern Africa do not fertilize their rainfed cereals. In the present study, we aimed to analyse whether the generally accepted positive yield response to N fertilization in rainfed Mediterranean conditions corresponds to actual advantages achieved in the fields of working farmers, attempting a further up-scaling of knowledge from field experiments to real fields. We attempted to apply research results to Tunisian working farmers’ fields by conducting a farm pilot experiment. The pilot experiment was conducted in two different regions (a low-yielding region and a relatively high-yielding region) of cereal production in Tunisia, where wheat production represents typical rainfed Mediterranean agro-ecosystems in North Africa. First, we compared the yield response to N fertilization against unfertilized conditions (a common situation for many of the farmers in North Africa), and secondly we compared what the farmers suggested as an optimal N fertilization practice in their fields against the WatNitMED's recommendation which was based on an N-fertilization scheme derived from field experiments from the European research project in Mediterranean conditions. The WatNitMED fertilization scheme suggested higher rates of fertilization than those considered optimal by farmers (on average 40 kg N ha−1 higher). Unfertilized grain yield across both locations ranged from about 1 to 3.5 Mg ha−1 (typical of farmers’ yields in the region), and fertilizing increased grain yields in most situations. Within the two alternative fertilization treatments, WatNitMED fertilization produced higher yields than the fertilization rate considered optimal by farmers. This trend was observed at the low-yielding location as well as at the high-yielding location. These responses demonstrated that fertilization in working farmers’ field conditions may be a reliable means of improving dryland wheat grain and straw yields. They also showed that rates of fertilization regarded as optimal by real farmers were below the optimum for these regions.

Stem lodging, a permanent displacement of cereal stems which may reduce wheat yields significantly, affects wheat crops in both developed and developing countries, mainly under high-yielding conditions. Although breeding has decreased these losses by reducing the likelihood of the plant lodging through reduced height (mainly by the introgression of dwarfing genes), lodging continues to affect wheat yields. We aimed to quantify how wheat breeding has modified the sensitivity of yield to lodging, identifying physiological causes for yield reductions. Two field experiments were carried out in Mediterranean Spain during the 2006/07 and 2007/08 growing seasons. The first season two genotypes (Aragon 03 and ID-2151) and two lodging treatments (control and lodged near anthesis) were analysed. The second season four genotypes (Aragon 03, Estrella, Anza and ID-2151) and three lodging treatments (control, lodged from either jointing to maturity or anthesis to maturity) were imposed. In addition, in the 2007/08 experiment the source–sink ratios of five representative spikes of each plot were modified through hand trimming all spikelets from one side of each spike soon after anthesis. Yield losses due to early lodging were reduced by wheat breeding: yield penalties in the oldest and newest genotypes were 61% and 43% (mean values of both lodging treatments), respectively while it was 57% in intermediate cultivars (mean value of both lodging treatments and cultivars). Lodging decreased both the number of grains per m 2 and the average grain weight (AGW). The decrease of the number of grains per m 2 was associated with reductions in the crop growth, while the AGW loss seemed related to both a reduction of the availability of assimilates to fill grains and a direct effect on grain size potential. Lodged plants exhibited stronger source-limitation during grain filling than those un-lodged, while the response of the grain weight to sink-strength reductions in lodged plants was very similar to that in the un-trimmed controls, indicating that grain filling in un-lodged and in strongly lodged canopies was similarly balanced in terms of source–sink ratios.

Under Mediterranean environments, farmers usually prefer to sow barley rather than wheat as it is generally believed that barley yields more under stressful conditions. As terminal stresses such as high temperature and water are common constraints in Mediterranean regions, higher grain weight stability may confer a clear advantage in order to maintain higher yields. The objective of the present study was to compare the stability in terms of grain weight and its components for barley, bread wheat, and durum wheat, exploring a wide range of nitrogen and water availabilities in experiments conducted in a Mediterranean region. Grain weight ranged from 23.8 to 47.7 mg grain−1, being higher for durum wheat than barley and bread wheat. Durum wheat presented higher variability both in maximum grain filling rate and duration of grain filling period than bread wheat or barley. The three species responded similarly in terms of grain nitrogen content to changes in the environmental conditions explored. It is concluded that in terms of grain weight barley is as stable as bread wheat. However, durum wheat presented a lower stability than barley and bread wheat.

Further increasing yield potential remains one of the main objectives of wheat breeding, even in stressful environments. In general, past genetic gains were associated with increases in harvest index, and future gains should be related to greater biomass. Identifying genetic sources for such improvement may be relevant. Researchers of TRITIMED identified DH lines of durum wheat apparently possessing not only high yield potential but also good yield stability. We aimed to determine physiological attributes responsible for yield and stability among a set of genotypes derived from two parents (Cham 1 and Lahn) and four of the most promising lines of the DH population (2401, 2408, 2410, 2517). Seven field trials were carried out within the Mediterranean agricultural region of the Ebro Valley, under a wide range of conditions (ca 2–10 mg ha−1). In four of these experiments, sub-plots were included with source-sink manipulations imposed after anthesis. Cham 1, a cultivar known for high yields in semi-arid conditions, showed the highest yield potential. Although it showed less yield stability than Lahn, even under the lowest yielding conditions its yield was not significantly lower than that of Lahn. RILs 2408, 2410, 2004 and 2517 slightly outyielded Lahn in high-yielding conditions, but under poorer environments they tended to yield less. Interestingly, yield differences were closely related to their biomass rather than harvest index. Thus yield differences relating to the number of grains per m2 were due to differences in spike dry matter at anthesis, reflecting in part genotypic differences in crop growth from jointing to anthesis. In general grain weight did not respond to spike trimming after anthesis, although in two experiments the grain weight of Cham 1 did so. Thus, even the highest-yielding cultivar possessed grains that overall seemed more limited by its constitutive capacity to grow than by the availability of resources to reach this capacity (though occasionally they may be co-limited). Overall, the most interesting feature was the empirical evidence that improvement of biomass within elite material is a worthwhile objective.

36 Pag., 3 Tabl., 2 Fig. The definitive version is available at: http://www.sciencedirect.com/science/journal/03784290, Extending the phase of stem elongation (SE) has been proposed as a tool to further improve yield potential in small-grain cereals. The genetic control of pre-heading phases may also contribute to a better understanding of phenological traits conferring adaptability. Given that an optimized total time to heading is one of the most important traits in a breeding program, a prerequisite for lengthening SE would be that this and the previous phase (leaf and spikelet initiation, LS) should be under different genetic control. We studied the genetic control of these two pre-heading sub-phases (from sowing to the onset of stem elongation, LS, and from then to heading, SE) in terms of Quantitative Trait Loci (QTL) in a barley double-haploid population derived from the cross Henni × Meltan, both two-rowed spring North European barley cultivars. DH lines (118) and their parents were studied in four field trials in North-Eastern Spain. Genetic control of a number of traits related to leaf appearance and tillering dynamics, which could be important for an early crop canopy structure, were also studied. LS and SE are, at least partially, under a different genetic control in the Henni × Meltan population, mainly due to a QTL on chromosome 2HS. The QTLs responsible for a different control of LS and SE did not seem to correspond with any major gene reported in the literature. Moreover shortening LS, so as to lengthen SE without modifying heading date, would not necessarily imply a negative drawback on traits that could be important for early vigour, such as phyllochron and the onset of tillering., GB held a pre-doctoral FPU scholarship from the Spanish Ministry of Science and Innovation. This study was partially funded by the European Union – INCO - MED program (ICA3-CT2002-10026) Mapping Adaptation of Barley to Drought Environments (MABDE) and by the Spanish Ministry of Science and Innovation competitive grants AGL2006-07814, AGL2007-63625 and AGL2008-05541. The Centre UdL-IRTA forms part of the Centre CONSOLIDER on Agrigenomics.

The stem elongation phase seems critical in yield potential determination in barley ( Hordeum vulgare L.). Extending its duration, without modifying total time to anthesis, has been proposed as a promising breeding tool. A prerequisite for its use is that the duration of phases before and after jointing (that including leaf and spikelet initiation, LS, and that of stem elongation, SE) should be under different genetic control. In addition, little is known about the implications of changes in the duration of LS and SE upon other developmental traits which could affect other aspects of yield generation, such as phyllochron and tillering. Thus, the objectives of the present work were to study the genetic variability in LS and SE, in traits related to leaf appearance and tillering, as well as their relationships, in a double-haploid (DH) population derived from the cross Henni × Meltan. DH lines and both parents were studied in four field trials. Despite the similarity in development between parents, there was significant genetic variability in duration of both LS and SE ( i.e . considerable transgressive segregation was observed), with no major genetic correlations found between them. Although some significant genetic correlations were found between duration of phases and leaf appearance and tillering traits, it has been shown that modifying the duration of LS does not necessarily imply concomitant changes in traits that could be important for an early expansion of the crop canopy (i.e. phyllochron, onset and rate of tillering).

Past breeding achievements in grain yield were mainly related to increases in harvest index (HI) without major changes in biomass production. As modern cultivars have already high HI, future breeding to improve grain yield will necessarily focus on increased biomass. Improved biomass would depend on our capacity to improve the amount of photosynthetically active radiation intercepted by the crop (IPAR%) or the efficiency with which the canopy converts that radiation into new biomass (radiation use efficiency, RUE). Four field experiments with a set of wheat cultivars selected, bred and introduced in the Mediterranean area of Spain and that represent important steps in wheat breeding in Spain were conducted in order to identify whether and how wheat breeding in this area affected the amount of IPAR% and RUE both before and after anthesis. Although there was genotypic variability, cultivars did not show any consistent trend with the year of release of the cultivars for their biomass, pre and post-anthesis IPAR%, Crop growth rate (CGR) or RUE but, the post-anthesis CGR and RUE of the two oldest genotypes were lower than that of the other cultivars. As the oldest genotypes have lower number of grains per m2 than their modern counterparts, it is suggested that post-anthesis RUE in these cultivars was reduced by lack of sinks and therefore further increases in grains per unit area in modern cultivars could permit to improve biomass via increases in post-anthesis RUE.

Bread wheat has been frequently characterised as sink-limited during grain filling but the degree of sink-limitation could vary with the contribution of breeding in increasing the number of grains per unit land area. This hypothetical change in the level of sink-limitation due to breeding has been insufficiently documented. Two source–sink manipulation experiments under field conditions with three released cultivars and an advanced breeding line representing important steps in wheat breeding in the Mediterranean area of Spain were conducted in order to quantify whether genetic improvement of grain yield in Mediterranean wheat modified the source–sink balance during grain filling, and how it affected grain weight and post-anthesis photosynthetically active radiation intercepted by the crop (IPAR) and radiation use efficiency (RUE). Average grain weight of control and trimmed spikes during grain filling was not significantly affected by halving the number of growing grains in the two oldest cultivars, but it was significantly increased in the most modern line, and had an intermediate response in the intermediate cultivar. In those cases in which a certain degree of source-limitation during grain growth occurred the magnitude of the response reflected a co-rather than a source-limitation. Considering grains from different positions within the spikes the smaller (distal) grains responded more markedly than the larger (proximal) grains. No differences in post-anthesis IPAR were found between the trimmed and control sub-plots for any of the genotypes. However, trimming the spikes reduced post-anthesis RUE, a fact corroborated by a simultaneous reduction in leaf net photosynthetic rate at noon. It seems that bread wheat breeding has tended to reduce the strength of the sink-limitation during post-anthesis even under Mediterranean conditions, and consequently the most modern line presented a sort of co-limitation.

The need to accelerate breeding for increased yield potential and better adaptation to drought and other abiotic stresses is an issue of increasing urgency. As the population continues to grow rapidly, the pressure on resources (mainly untouched land and water) is also increasing, and potential climate change poses further challenges. We discuss ways to improve the efficiency of crop breeding through a better physiological understanding by both conventional and molecular methods. Thus the review highlights the physiological basis of crop yield and its response to stresses, with special emphasis on drought. This is not just because physiology forms the basis of proper phenotyping, one of the pillars of breeding, but because a full understanding of physiology is also needed, for example, to design the traits targeted by molecular breeding approaches such as marker-assisted selection (MAS) or plant transformation or the way these traits are evaluated. Most of the information in this review deals with cereals...

To publish papers that have impact is indispensable for good scientists. It is frequently accepted that the impact factor (IF) of a journal reflects the likelihood of a paper to have impact. Many scientists may then attempt publishing their papers in journals with the highest possible IF. This is relevant for crop scientists as in many cases our hypotheses may be relevant to agronomy/agriculture but the product of our work may be published in the more basic plant science journals, which in general have higher IF than agronomic journals. To test whether agronomic journals may be better vehicles than plant science journals for crop physiological work, I did an analysis of my own publications (only “standard” papers, disregarding reviews) relating their annual citation rates against the IF of the journal in which they were published. The relationship was virtually inexistent, and my most frequently quoted papers were published in agronomic rather than in plant sciences journals. Conversely, restricting the analysis to the papers published within agronomic journals there was a relationship between the record of citations of the papers and the IF of the journals, particularly if the analysis is restricted to the most quoted papers in each journal. I then analyzed the cases of three other well-recognized crop scientists, to check whether the findings with my results were exceptional, and in the three cases results were remarkably similar. Therefore, it seems that the journal IF might be a valuable criterion for choosing the best journal in which to publish our best contributions only when comparing within agronomic journals, but not within combinations of agronomy and plant science journals. This should be also taken into account in evaluation processes when comparing scientists working in related but not identical fields.

The critical period for grain yield determination has not been determined for triticale. We aimed to identify it, determining the relative importance of both the major yield components and the dry matter acquisition by the spikes at anthesis. A field experiment was carried out with two triticales, differing in tillering capacity, subjected to shading treatments at five different timings from early tillering to maturity. Results showed that reductions in grain yield were more significant when shading was imposed during 3 weeks before and 1 week after anthesis. Reductions in grain yield by shading treatments were associated with lower number of grains per m2 more than with changes in the average grain weight. Reductions in grains per m2 were due to reductions in the number of fertile florets per spike, affecting grains per spike. The assimilate acquisition by the spikes during the critical period was a key determinant of floret survival. Grain number per m2 was related with photothermal quotient during 30 days before anthesis and spike dry weight at anthesis, though the goodness of the prediction compared with wheat, was lowered by poorer grain setting percentage.

Three field experiments comparing bread wheats representing different eras of genetic improvement in the Mediterranean area of Spain (one landrace, seven cultivars released since 1950 and two advanced breeding lines) were carried out at the province of Lleida (Catalonia, north-eastern Spain). Experiments were conducted during the 2004/05, 2005/06 and 2006/07 growing seasons at Gimenells and during 2005/06 at Foradada in order to quantify gains in yield, and in its physiological determinants, during much of the last century. At Gimenells, the first two seasons were conducted under relatively high-yielding backgrounds (Gimenells, irrigated) and in the last season under moderately stressed conditions (Gimenells, rainfed), while at Foradada the experiment was conducted under a severely stressed low-yielding environment. For almost all the traits analyzed in this paper, there were only significant differences when cultivars were grown under relatively high-yielding environments. In this conditions, grain yield increased with the year of release of the cultivars from 1940 to the 1970s, with no clear further improvements thereafter. On the other hand, total biomass did not show any association with the year of release of the cultivars. Results showed that, even when breeding was performed under Mediterranean conditions, harvest index was the main attribute responsible for yield improvements. Stem height was linearly and negatively related with harvest index, implying a marked height reduction until the 1970s, with no clear further reductions thereafter. In general yield was lineally and positively associated with number of grains per m2, while average grain weight did not exhibit any clear trend with the year of release of the cultivars. The increase in number of grains was more associated with that in grains per spike than with differences in spikes per m2. Finally, the increase in number of grains per m2 was associated with both number of grains per unit of spike dry weight at anthesis, or “fruiting efficiency”, and spike dry weight at anthesis.

A better understanding of responsiveness of time to anthesis to water stress in triticale and wheat might help to explain their differences in performance under stress and to identify which attributes or components of time to anthesis are most affected. Three experiments were carried out during the 2004 and 2005 growing seasons to (i) evaluate genotypic variability in phenology responsiveness to drought in triticale and to (ii) explore the variation in the duration of pre-anthesis phases occurring before and after the onset of stem elongation as well as their responsiveness to water stress. Important variation was found among triticale cultivars on time to anthesis, allowing classification of cultivars into long, intermediate and short cycle. Differences in the duration of the stem elongation phase (i.e. from terminal spikelet initiation (TS) to anthesis (ANT)) were as high as 200 °Cd for cultivars with similar time to flowering. Although water stress reduced the time to anthesis (in average by ca. 125 °Cd), cultivars showed a differential responsiveness to drought in phases occurring before or after TS. Some cultivars that were highly sensitive to drought in the emergence (Eme)–TS phase were insensitive in the phase TS–ANT and vice-versa. Water shortage tended to reduce the grain filling period and was most evident when a Mediterranean environment treatment was simulated.

Spike growth during the stem elongation phase is critical for the establishment of the number of fertile florets (FF). A longer period of spike growth would lead to an increased number of FF and grains in wheat. The aim of this study was: (i) to analyze in three different commercial cultivars the impact of a photoperiod extension (NP + 10) during the stem elongation phase on the number of FF and (ii) to determine whether the photoperiod extension effect might be reversed by increasing the availability of assimilates by a direct modification of the source/sink ratio at booting. The number of FF per spike was reduced by extended photoperiod in the experiment sown in an optimum date, though no differences were observed when sown much later, probably due to the poor environmental conditions of a spring sowing. The detrimental effect of lengthening the photoperiod on the number of FF per spike was reversed by trimming the spike at booting in two of the three cultivars analyzed. This reversion, together with the effect of photoperiod extension on FF associated with similar effects on spike growth, may be considered as a confirmation that, at least in part, the detrimental effects of photoperiod extension on FF would be mediated by changes in assimilate supply to the developing florets. No differences were observed between photoperiod treatments on the onset of rapid spike growth; however, extended photoperiod reduced the duration of spike growth phase without differences in the maximum rate of spike growth in two of the three cultivars. Although a positive association was found between the number of FF and spike dry weight at anthesis, differences among cultivars were observed in this relationship, suggesting different carbohydrates partitioning (i.e., FF per unit of spike weight) among them.

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).

Despite that the idea of better yield adaptation to low-yielding conditions of barley than wheat is widespread, there have been few efforts in directly comparing their performance in Mediterranean conditions. We compared wheat and barley regional yields in 41 counties of Catalonia for the period 1992-2004. No differences were clear, particularly at low-yielding conditions, with a trend for a better wheat performance in relatively high-yielding environments. We then conducted field experiments during two consecutive seasons, sowing wheat and barley with six levels of nitrogen fertilisation under rainfed conditions (2003-04, experiment I) and two levels of nitrogen fertilisation and two water regimes (rainfed and irrigated) in 2004-05 (experiment II). In experiment I, wheat outyielded barley in treatments that received no N fertiliser (4.58 and 3.60 Mg ha -1 , respectively) indicating that the higher yield potential of wheat was associated with better performance in a condition of relatively low yield. In experiment II, wheat and barley yields were found not to be significantly different across all treatments (2.86 and 2.62 Mg ha -1 respectively) or in the lowest yielding treatments (1.40 and 1.07 Mg ha -1 , respectively). Therefore, it seems that it may not be universally accepted that under Mediterranean conditions barley would unequivocally behave better than wheat.

† Background and Aims Long photoperiods from flowering to maturity have been found to delay reproductive development in soybean (Glycine max) and to increase the number of seeds per unit land area. This study was aimed to evaluate whether sensitivity to photoperiod after flowering (a) is quantitatively related to the length of exposure to long days and (b) persists throughout the whole pod-setting period. It was also evaluated whether seed number was related to changes in the duration of post-flowering phenophases. † Methods Two field experiments were conducted with an indeterminate cultivar of soybean of maturity group V. In expt 1, photoperiods 2 h longer than natural daylength were applied during different numbers of days from the beginning pod stage (R3) onwards, while in expt 2 these photoperiod extensions were imposed during 9 consecutive days starting at different times between R3 and R6 (full seed) stages. † Key Results There was a quantitative response of development to the number of cycles with a long photoperiod. The exposure to long photoperiods from R3 to R5 (beginning of seed growth) increased the duration of R3‐R6 regardless of the timing of exposure. The stages of development comprised in the R3‐R6 phase were delayed by current as well as by previous exposure to long days. A positive relationship was found between seed number and the duration of R3‐R6, irrespective of the timing and length of exposure to the long photoperiod. † Conclusions Sensitivity to photoperiod remained high during the reproductive period and was highly and positively coupled with the processes of generation of yield.

An early prediction of crop biomass at maturity and yield is important in different circumstances. The use of spectral reflectance indices, such as the Normalized Difference Vegetation Index (NDVI), has been proposed as a fast, nondestructive way of estimating crop growth capacity. In this study, we examined whether NDVI assessment relatively early in the crop cycle may be useful for predicting final biomass and yield in wheat. To that end, NDVI was measured and biomass quantified regularly from tillering to maturity for six different wheat genotypes grown under a contrasting range of N and water availabilities. In addition, final biomass and yield were measured at maturity. In line with expectations from the literature, we found that NDVI at milk-grain stage was well correlated to final yield and biomass. However, it was also observed that NDVI at the onset of stem elongation was also reasonably correlated to both attributes. Because crop growth in wheat from the end of tillering to anthesis is related to the determination of grain number and yield, we propose the use of NDVI at the onset of stem elongation as a complementary criterion for establishing the required late crop management (N fertilisation, irrigation) practices.

The stem elongation phase in wheat [Triticum aestivum (L.)] is considered critical for yield determination. A longer duration of this phase could hypothetically increase grain set and therefore yield. Genetic variation in the relative duration of the stem elongation phase having been reported, the aim was to pinpoint whether this variability was associated with sensitivity to photoperiod, vernalizing temperatures or to differences in intrinsic earliness. Pairs of cultivars identified as having different duration of the stem elongation phase (from the appearance of the first visible node to anthesis) were grown under natural (short) or extended photoperiod, with or without vernalization. Variability in the duration of this phase, in the cultivars analysed, was related to different sensitivity to photoperiod, while differences in the previous phases were related to sensitivity to both photoperiod (though different to the sensitivity of the following phase) and vernalization.

The stem elongation phase in wheat (Triticum aestivum, L.) and barley (Hordeum vulgare) is important for yield determination as it is the phase when stems and spikes grow actively. A longer duration of this phase could hypothetically increase assimilate availability, fertile florets at anthesis and final grain number. Argentine commercial wheat and barley cultivars were studied to analyse the range of genetic variability existing in the duration of the stem elongation phase, in particular, considering cultivars with similar time to anthesis. It was found that cultivars differing in time to anthesis, not only differed in the length of their early, mostly vegetative phases but also in the stem elongation phase (range 301-535 °C day for wheat and 252-404 °C day for barley), and that the partitioning of a similar time to anthesis into phases was substantially different between cultivars. Various studies with other cultivars were re-analysed, showing that the stem elongation phase did present genetic variability as well. As a preliminary step to identifying the genetic causes behind this variability, an approximation to the possible photoperiod and/or vernalization sensitivities of this large group of Argentine cultivars was presented, by comparing behaviour in two contrasting sowing dates. This has proved useful to breeders since there have been no other previous studies including this large number of commercial cultivars.

Field experiments with soybean demonstrated that the extension of photoperiod after flowering increases both the duration of the post-flowering phase and the production of seeds. These results suggest that cultivars with increased duration of the post-flowering phase could be selected to improve soybean yields. The aims of this paper were to: (a) evaluate the ability of the CROPGRO-soybean model to reproduce the experimental relationships between seed number and duration of the critical phase between first and last pod, and (b) assess the putative benefits and trade-offs of variable durations of the critical phase in a south–north transect in the Pampas of Argentina. We varied the genetic coefficients accounting for photothermal requirements and photoperiod sensitivity of soybean A5409-RG (maturity group V), reducing pre-flowering phase while maintaining time to maturity. The model produced sound estimates of crop phenology and reproduced the positive relationship between seed production and the duration of the critical period between first and last pod found in field studies. Linking the model with long-term climate records for six locations between 31 and 37°S, indicated that substantial yield gains could result from increasing the relative duration of post-flowering phases. A hypothetical cultivar with flowering time typical of cultivars of maturity group III and total cycle typical of cultivars of group V, outyielded the traditional cultivar of group V in most cases. For well-watered crops, extension of the critical period had a positive effect in yield in all seasons and locations, whereas for rainfed crops, the extension of the critical period increased yield in 95% of the simulated scenarios. The magnitude of the effect was strongly asymmetric: yield gains were up to 1 Mg ha −1 whereas losses were below 0.2 Mg ha −1 . The modelled results in this paper indicate that shortening pre-flowering period without changing the duration of the whole cycle should increase yields in a broad range of latitudes and environmental conditions.

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%.

The understanding of crop phenology is critical for both improvement of yield potential and adaptation to stress. Matching ‘critical’ phases (when the most important yield components are determined) and best environmental conditions is crucial to maximize yield. The processes regulating crop development are complex and are strongly influenced by genetic and environmental factors. In this chapter, we describe the main developmental stages, delimiting major phenological phases of wheat and soybean, and the relationships between crop phenology, adaptation and yield determination. Analysis of environmental control of development is restricted to the main drivers: temperature, including temperature per se and vernalization (for wheat), and photoperiod. The effects of major genes are outlined: Vrn, Ppd and Eps in wheat and Dt (growth habit) and genes of the series E and J in soybean. Finally, we integrate the environmental and genetic effects on phenology into the determination of crop adaptation and yield potential.

Further improvements in wheat yields are critical, for which increases in grain number would be required. In the recent past, higher grain number was achieved through increased growth of the juvenile spikes before anthesis, due to the reduction in stem growth. As current cultivars have already an optimum height, alternatives must be identifi ed for further increasing grain number. One of them is increasing fruiting effi ciency (grains set per unit of spike dry weight at anthesis). Fruiting effi ciency is the fi nal outcome of the fate of fl oret development and differences in this trait within modern cultivars would be related to higher survival of fl oret primordia. Then there are two alternative physiological pathways to improve fruiting effi ciency by allowing a normal development of most vulnerable fl oret primordia: an increased allocation of assimilates for the developing fl orets before anthesis, or reduced demand of the fl orets for maintaining their normal development. Both alternatives may be possible, and it might be critical to recognize which of them is the actual cause of differences in fruiting effi ciency. When considering this trait in breeding we must be aware of potential trade- offs and therefore it must be avoided that increases in fruiting effi ciency be constitutively related to decreases in either spike dry weight at anthesis or grain weight. In this review we described fruiting effi ciency and its physiological bases, analyzing genetic variation and considering potential drawbacks that must be taken into account to avoid increases in fruiting effi ciency being compensated by other traits Fil: Gustavo A. Slafer. AGROTECNIO; España. Universidad de Lleida. Departamento de Producción Vegetal y Ciencia Forestal; España. Institució Catalana de Recerca i Estudis Avançats; España Fil: Elia, Mónica. Universidad de Lleida. Departamento de Producción Vegetal y Ciencia Forestal; España. AGROTECNIO; España Fil: Savin, Roxana. Universidad de Lleida. Departamento de Producción Vegetal y Ciencia Forestal; España. AGROTECNIO; España 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; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal; Argentina Fil: Terrile, Ignacio Ismael. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Norte. Estación Experimental Agropecuaria Pergamino; Argentina Fil: Ferrante, Ariel. The University of Queensland. Queensland Alliance for Agriculture and Food Innovation; Australia 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; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal; Argentina Fil: González, Fernanda Gabriela. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Norte. Estación Experimental Agropecuaria Pergamino; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

In Mediterranean environments with scarce and variable rainfall and unfertile soils, rain-fed cereals are exposed to different severity of water stress, which often combines with heat stress and nitrogen deficit. In this chapter, we revise three elements that are commonly accepted for cereal production in Mediterranean type-environments. First, the notion that annual crops in these environments are exposed to ‘terminal drought’. Using physiological and environmental analysis, we showed that this label overemphasizes grain filling, and neglects the most critical pre-flowering period; this has implications for both crop management and breeding. Second, the notion that barley performs better than wheat at the lowest end of the rainfall range. We emphasize the lack of solid scientific evidence supporting this view, and briefly consider the implications for patterns of land allocation. Third, the notion that nitrogen fertilization may reduce yield in low rainfall sites and seasons. We argue that, again in this case, the scientific evidence does not fully support this viewpoint, and discuss the opportunities to improve yield and water-use efficiency by better management of nitrogen fertilization.

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

This study explored whether the average grain weight of wheat tends to be reduced when grain number is increased due to either competition or, to a consistent increase in the relative proportion of grains of smaller weight potential. Three field experiments considering environmental, genetic and environmental × genetic effects on yield and its main components were analysed during the 2003/2004 growing season in two different locations within the Mediterranean area of Catalonia, Spain. The relationship between grain weight and number of grains per unit land area was analysed for both the average of all grains (AGW) and for grains in specific positions of the main-shoot spikes: proximal (CPg) and distal (CDg) grains of central spikelets, and proximal grains of the near apical (APg) and near basal (BPg) spikelets. The proportional contribution of grains per spike for the different grain positions and the relative contribution of spikes per m 2 made by the main shoot or tillers were also examined. In the three experiments, AGW was reduced when grain number was increased due to genetic and/or environmental factors. However, the slopes of the straight-lines that represented the negative relationship between grain number and grain weight were lower (less negative) and less significant for CPg ( b = −0.20, P > 0.20), CDg ( b = 0.06, P > 0.20) and BPg ( b = −0.21, P > 0.20) than for AGW ( b = −0.40, P

Lesquerella fendleri and Lesquerella mendocina are two species with potential for domestication as crops for semiarid regions. Understanding the environmental influences on development is a critical step for the introduction of a wild species into cultivation. Under controlled conditions these species responded differently to temperature: L. fendleri phenological approach toward flowering responded linearly to temperature, whereas initiation of flowering in L. mendocina was relatively insensitive to temperature. L. fendleri exhibited a quantitative response to supra-optimal temperatures (with rate of development reduced with further increases in temperature) whereas L. mendocina showed a qualitative response, no flower development at supra-optimal temperatures. In this work undertaken in the field we studied phenological development in L. fendleri and L. mendocina as a function of planting date, quantified the time required to reach particular phenological stages under the various thermal environments, and compared these results with those previously obtained with controlled conditions. We also studied the influence of photoperiod on plant phenology in field situations and through experiments done under controlled conditions. Development rate for both species varied with sowing date with plant cycles shorter in spring sown plants, even if measured in thermal time. L. mendocina plants sown in late spring displayed a biennial cycle. These results are consistent with those obtained under controlled conditions. However, cycle shortening in thermal time with delays in sowing date suggested that factors other than temperature also influenced phenology of these two species. Further studies under controlled conditions showed that phenological development of L. fendleri plants was also altered by photoperiod, with plants displaying a typical long-day response. At the highest temperatures used in these studies L. mendocina plants did not respond to photoperiod. The possibility that incident radiation is involved in L. mendocina response to sowing date is discussed.

Spring cultivars of barley (Hordeum vulgare L.), oat (Avena sativa L.), and wheat (Triticum aestivum L.) are the most important crops in Finnish agricultural systems. The increasing need to reduce pollution from N fertilizer is concomitantly strengthening the importance of improving the understanding of nitrogen use efficiency (NUE) of these crops. The aim of this work was to study the differences in NUE, defined as the crop's ability to produce yield with one available N unit, among spring cereal cultivars, and to determine the achievements of plant breeding in NUE under northern European growing conditions. Field experiments were conducted in Finland during 2003 and 2004. Samples from matured plants of 17 to 18 cultivars of each of the three cereal species released between 1909 and 2002 were studied. There were no clear differences in NUE among modern spring cultivars. However, there were cultivar differences within species and significant NUE improvements on wheat and particularly for oat across time. There was no clear trend of NUE and year of release of cultivars in two-row spring barley, probably because breeding for malting barley involves consistent selection for low-protein cultivars. The study revealed that most breeding effects on NUE were associated with changes in nitrogen uptake efficiency (UPE).

A detailed and accurate phenotyping of mapping populations is an important “bottleneck” for the understanding of the phenotype–genotype relationships. Grain number per unit area (GN), the main wheat yield component, can be analyzed through physiological components as spike dry weight at flowering, determined by crop growth rate and biomass partitioning to spike during stem elongation phase, and fruiting efficiency. The phenotypic variability of these physiological traits responsible for variation in GN and the relationships among them was analyzed in an elite wheat doubled-haploid (DH) population grown in two different environments. Positive transgressive segregation (i.e. DH lines that exceed parental phenotypic values) was observed for all GN determining traits, suggesting that increases in GN could be achieved through their improvement. However, focusing on top DH lines, which represent a feasible genetic improvement, fruiting efficiency was the most relevant physiological trait for consistently improving GN, and thereby grain yield, in both environments. 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: Serrago, Roman Augusto. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cerealicultura; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: González, Fernanda Gabriela. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Norte. Estación Experimental Agropecuaria Pergamino; Argentina Fil: Slafer, Gustavo Ariel. Institució Catalana de Recerca i Estudis Avancats; España. 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: Reynolds, Matthew P.. Centro Internacional de Mejoramiento de Maíz y Trigo; México 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