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Context Although waterlogging is known to decrease grain yield in wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.), its effect on plant N traits is still unknow. Aims This study evaluated biomass N dynamics and partitioning to grains, in wheat and barley plants subjected to waterlogging. Methods Under contrasting environmental conditions, two pot experiments exposing wheat and barley plants to waterlogging events for 15–20 days at five different developmental stages, from emergence to maturity were performed. Grain N concentration, grain N content, biomass N concentration, N utilisation efficiency (NUE) and N remobilisation were recorded. Key results Both species responded similarly to waterlogging for most N traits. Reductions in grain N content differed according to the moment waterlogging occurred. The greatest reductions (46–77% compared to the control) being for waterlogging from the beginning of stem elongation to anthesis, which also showed the highest reductions in N remobilisation, N uptake at maturity, and N partitioning to the grains, but only a slight decrease in NUE. Grain N concentration raised drastically (up to 45 mg N g DW−1) with minimal grain yields. N concentration of aboveground biomass decreased during waterlogging, recovering control values at maturity. N content at maturity was related to the total biomass. Conclusions Waterlogging differentially reduced N uptake and remobilisation to grains of wheat and barley depending on the developmental stage when water excess occurred. Implications The impact of waterlogging on N economy of wheat and barley appears indirect and predominantly related to carrying effects of the stress on carbon economy due to growth reductions.

Fil: Cantoro, Renata. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas Fisicoquimicas y Naturales. Instituto de Investigacion en Micologia y Micotoxicologia. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Investigacion en Micologia y Micotoxicologia; Argentina

Most of the required increases in food production over the next decades are expected to be achieved through increases in crop yield. As wheat is essential for food security it is worrying that its yield gains over the last two decades were small. To achieve further yield increases it is critical to continue increasing number of grains per unit area (GN m(-2)), the trait best related to yield. In this context, it is relevant to identify the main determinants of GN m(-2) in response to genetic and environmental factors as well as the trade-offs between them. In the present study we compiled a large database across the literature to analyse the relative importance of components when affected by genetic or environmental factors, producing small or large changes in GN m(-2) and its components, either numerical (the number of spikes per m(2), SN m(-2); and the number of grains per spike, GN spike(-1)) or physiological (spike dry weight at anthesis, SDWa; and fruiting efficiency, FE) determinants. The database included 367 papers published in: (i) Field Crop Research (FCR), (ii) European Journal of Agronomy (EJA), (iii) Crop Science (CS) and (iv) Crop and Pasture Science (CPS, formerly Australian Journal of Agricultural Research) between 1990 and 2020. The complete dataset was split into classes, depending on the source of experimental variation, environment or genotype and was normalised to remove the differences between experiments and determine the environmental and genotypic effects within each experiment. Normalised data showed that the responsiveness of GN m(-2)was similarly explained by changes in both SN m(-2) and GN spike(-1), but in terms of physiological components SDWa was more relevant than FE for explaining the variations in GN m(-2). Considering the numerical components of GN m(-2) genotypic and environmental factors modified more GN spike(-1) than in SN m(-2). On the other hand, physiological components were differently modified by genotype and environment: for genotypic effects FE was more critical than SDWa and the other way around for environmental factors. A tradeoff between numerical and physiological components was observed although was greater between physiological than between numerical components. Research of the authors on wheat yield physiology has been funded along years by many different grants from different funding bodies; most recently mainly from (i) the International Wheat Yield Partnership (IWYP25FP) , (ii) , the Spanish State Agency for Research (latest project was RTI2018-096213-B-100) , and (iii) Argentine Fund for Scientific and Technological Research (latest project PICT RAICES 2019-04333) .

Late foliar diseases that appear during the grain filling period reduce radiation interception/absorption decreasing assimilation supply, inducing reductions in grain weight and yield. We hypothesize that crops with higher source-sink ratio (established immediately after anthesis) could have more capacity to avoid reductions in terms of yield, at same level of foliar disease. Thus, it is speculated that the yield reduction caused by late foliar diseases is a complex interaction between current photosynthesis availability per grain and the remobilization capacity according to the sink size determined demand. The objective of the present study was to analyze physiological attributes associated with yield reduction caused by late foliar diseases in wheat when source-sink ratio is modified. Experiments were carried out during two consecutive years (2009 and 2010) applying a combination of (i) two disease levels (i.e. healthy and diseased plots), (ii) two different levels of incident radiation applied immediately previous to anthesis, to reduce grain number exclusively (i.e. non-shaded and shaded plots) and (iii) source-sink manipulations during grain filling (i.e. control and trimmed spikes). Shading during pre-anthesis significantly reduced grain number and then, the source-sink ratio was modified between non-shaded and shaded plots, being two fold higher in non-shaded than in shaded plots. In both years and shading treatments, diseases appeared after anthesis, the diseased plots showing higher values of non-green leaf area than healthy plots, in both shaded and non-shaded treatments. Late foliar diseases significantly reduced grain yield in both, 2009 and 2010 mainly due to reductions in grain weight. There was significant interaction in the crop performance to foliar diseases between shading treatments and growing seasons. While the reduction caused by late foliar diseases was similar between shading treatments during 2009, in 2010 significant differences were observed, being reductions lower in shaded than in non-shaded plots. The source-sink manipulation treatment confirmed these responses, as there were no significant differences in grain weight of trimmed spikes between healthy and diseased crops, confirming that the grain weight reduction due to late foliar diseases is driven by the source sink balance.

Promising yield-determining responses to artificial photoperiod manipulation during post-flowering phases have been identified in soybean [Glycine max (L.) Merrill]. These responses enhance resource capture as a result of changes in phase duration, and resource use efficiency as a result of changes in node production and pod development, alleviating intra-node pod interference. This work aims to evaluate the relevance of these responses under natural conditions and discriminate direct from indirect photoperiodic effects, that is, effects caused by changes in the capture of resources. Two field experiments were conducted with a combination of sowing dates, with similar pre- and different post-flowering photoperiod, indeterminate genotypes including near isogenic lines and commercial varieties with different photoperiod sensitivity, and shadings with different incident radiation during post-flowering. Longer post-flowering photoperiod and higher plant photoperiod sensitivity delayed crop development, particularly in lines with alleles E2, E3 or Clark background. This delay resulted in extra radiation capture and node production, which were positively related to yield. Direct photoperiodic effects on nodes per m2 were evidenced in response to changes in post-flowering photoperiod and plant photoperiod sensitivity. The distribution of available resources such as radiation in more nodes per m2 increased use efficiency. Longer post-flowering photoperiod and higher plant photoperiod sensitivity enhanced pod establishment on usually dominated positions such as lateral racemes, affecting pods per m2. Finding these relevant yield-determining effects under natural conditions suggests that processes related to post-flowering photoperiodic responses are a plausible way to enhance resource capture and use efficiency and yield in soybean production systems. In cropping systems in which the whole growing season is used to maximize yield, these post-flowering photoperiodic responses could be adopted at the expense of the pre-flowering phase duration.

Efforts to anticipate how climate change and variability will affect future crop production can benefit from understanding the impacts of current and historic changes. This study aimed to quantify and compare the impact of increased night temperature on potential yield and phenology of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) crops modelled using APSIM with historical climate series (1961–2014) in sites representative of the Argentinean Pampas. For each site, the sowing date was adjusted to avoid frost and heat events at flowering, based on historical probability. The critical period was the more sensitive crop phase (shortened by 0.6 d decade−1) for the observed asymmetric warming; regional minimum temperature trend of ca. 0.14 and 0.16 °C decade−1 in wheat and barley, respectively. Wheat and barley yields declined across the region between ca. 2% and 9% per °C increase in the minimum temperature during the critical period, linked to lower cumulative radiation capture as a result of a shorter crop phase and lower incident radiation due to displacement towards winter. Regional variability in the simulated yield response to the observed night warming was mainly explained by differences the response of incident solar radiation during the critical period to the minimum temperature increase. 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: 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 Fil: Serrago, Roman Augusto. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Alzueta, Ignacio. 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: Huth, Neil. CSIRO Agriculture and Food; Australia Fil: Dreccer, Maria Fernanda. CSIRO Agriculture and Food; Australia

Malt extract is the most relevant parameter describing malting quality in barley. The observed differences in malt extract from crops grown in different environments are complex to explain, and their interpretation might represent an opportunity to improve malting quality for barley crops grown under field conditions. Although the effect of some grain attributes on malt extract are overall known (e.g. protein content and grain size) other are less understood and are complex to replicate across experiments, with few evidence of how they are controlled by the environment during grain filling (e.g. hordeins and pasting properties). Four commercial malting barley cultivars were sown on eleven sowing dates across four years to explore a wide range of thermal conditions during grain filling. Contrasting nitrogen availabilities were included to promote variability in the protein content. Grain plumpness, protein content, pasting temperature, and the amount of d - and γ-hordeins showed a significant effect on malt extract. Protein content showed a negative effect on malt extract only when it was above a threshold value of ca. 10 %, although that threshold varied between cultivars. Pasting temperature presented a significant interaction with protein content. d -hordein showed a negative effect on malt extract only when the protein content was below the threshold, explaining some of the contradictory results reported in the literature. Evidence of a negative effect of γ-hordeins on malt extract was found as well. The period between pollination and physiological maturity was arbitrarily divided into thermal-time intervals, and correlation analyses were performed between mean temperature during each period and the grain attributes affecting malt extract. For all the cultivars, only two attributes were found to be modulated by the thermal environment explored by the crop during grain filling: pasting temperature was positively correlated to the mean temperature explored by the crop during the middle of grain filling, whereas grain plumpness was negatively correlated with the mean temperature during the second half of grain filling. Quantitative models reported in the present study in addition to offering an explanation of how malting quality is shaped in the field, constitute a useful tool for agro-climatic zoning for the suitability of high-quality malting barley production.

Sunlight is a crucial environmental factor for photosynthesis. Plant density affects both quality and quantity at light penetration into the canopy. The effects of plant density on the expression of photomorphogenic traits in cultivated spring rapeseed (Brassica napus L.), and their consequences on seed production per unit area are unknown. The aims of this work were to: i) analyze the magnitude of shade avoidance responses to plant densities in five spring rapeseed genotypes, ii) describe the dynamics of floral branching in response to genotype and plant density, and iii) study yield and its components and seed quality in field-cultivated plants with contrasting plant densities (15 and 240 pl m−2). Rosette diameter was the main attribute of vegetative plasticity modified by plant density, without significant changes in petiole length. Plant density changed the relationship between intercepted solar radiation (ISR) and red/far red ratio (R/FR) during crop development, but at flowering all densities reached ISR = 95% and R/FR ratio

tThe use of physiological traits for indirect selection may help to increase wheat yield potential. Fruitingefficiency (FE, grain number per unit of spike dry weight at anthesis −SDWa-) may be an alternativeto increase grain number per unit area (GN), but the possible cross-over genotype (G) × environment(E) interaction and trade-off with SDWa and grain weight (GW) may limit its usefulness. The presentpaper aimed to determine (i) the degree of G × E interaction of FE at plot, main stem and tiller levels,(ii) the relationship between GN and FE, and (iii) the possible trade-off between FE and (a) SDWa, and(b) GW. Three FE contrasting genotypes (B11 and B19 ? high FE, and B2002 ? low FE) were grown underdifferent Nitrogen (N) availability at sowing [(i) low ? Ni: ca. 50 kg N ha−1; (ii) middle −130 kg N ha−1and (iii) high −200 kg N ha−1). Two other treatments were applied within the 200N: (iv) late sowing, i.e.delaying sowing 30 days in relation to optimum date (200N + LS) and (v) shading the canopy during stemelongation (200N + SH). The FE showed G × E interaction (year × genotype and genotype × treatment) butit only explained 13.4% of its variation. The environment (year) had similar impact than the genotype,explaining both ca. 38% of FE variation (19% each). The FE of tiller spikes was higher than that of mainstem spikes, but the difference among cultivars was maintained. Thus, canopies of the same genotypewith different proportion of main stem and tiller spikes may present different FE value at plot level.Nevertheless, a high correlation (r = 0.82, p < 0.0001) and a close 1:1 relationship was observed between FEat plot level and FE in main stems, for all treatments and cultivars, suggesting that sampling the main stemspikes represents the FE at plot level in dense canopies. A G × E cross-over interaction was observed whenthe sowing was delayed one month (200N + LS) from the optimum date because B19 reached anthesislater than B2002, exploring higher heat stress index (◦Ch > 27◦C) around anthesis, which reduced FE.The correlation of GN with FE was high and significant (r = 0.74, p < 0.00001) for all treatments and fora wide range of SDWa values (from 90 to 188 g m−2). The B19, selected as a high FE genotype, showedhigher GN than B2002 (selected as a low FE genotype) under all treatments, while B11 (also of high FE)showed similar or higher GN than B2002, depending on treatment. Thus, despite the G × E interaction, thegenotypes with higher FE had more GN under a wide range of environments. Nevertheless, the SDWa andGW were negatively correlated with FE (for SDWa r = −0.73 p < 0.005, without considering 200N + SH; andfor GW r = −0.48 p < 0.01 for all treatments or r = −0.75 p < 0.08 for genotypes only). Then, special attentionshould be given to SDWa and GW when selecting for higher FE in a breeding program. Fil: Terrile, Ignacio Ismael. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Norte. Estación Experimental Agropecuaria Pergamino; Argentina 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; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cerealicultura; Argentina Fil: González, Fernanda Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia del Noroeste de la Provincia de Buenos Aires. Universidad Nacional del Noroeste de la Provincia de Buenos Aires. Centro de Investigaciones y Transferencia del Noroeste de la Provincia de Buenos Aires; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Norte. Estación Experimental Agropecuaria Pergamino; Argentina

Tan spot [Pyrenophora tritici-repentis (Died.) Drechs., anamorph Drechslera tritici-repentis) (Died.) Shoem.] and leaf rust (Puccinia triticina Eriks) are major diseases worldwide and some of the main biotic causes of yield and quality reduction in wheat (Triticum aestivum L.). Although wheat crop losses due to foliar diseases have already been studied based on an ecophysiological approach, none of these studies analyzed the independent effects of foliar pathogens with different nutritional habits. The aim of the present study was to determine the independent effects of (i) Py. tritici-repentis (necrothroph) and (ii) Puccinia triticina (biotroph) on the physiological components of biomass production: accumulated intercepted by green tissue photosynthetic active radiation (IGPAR), radiation use efficiency calculated by intercepted radiation (RUEint) as well as by intercepted by green tissue (RUEgt) in a wide range of Argentine commercial bread wheat cultivars growing in two field environments. Field experiments were carried out during two consecutive years combining a large range of wheat bread commercial cultivars and two levels of inoculation to promote infection of Tan spot and Leaf rust diseases, including a control without inoculation. Treatments were arranged in an experimental split-split plot design with three replications, where the main plots were both diseases, subplots corresponded to inoculation treatments 1- without inoculation (WI), 2- low concentration of inoculum of each disease (LC), 3- high concentration of inoculum of each disease (HC) and ten Argentine bread wheat commercial cultivars were the sub-subplots. Area under disease progress (AUDPC), area under percentage of non-green leaf area (AU %NGLA), crop growth rate (CGR) and healthy area duration (HAD) were calculated. Green leaf area index (GLAI), aboveground biomass (AGB), IGPAR and RUE were measured at three different crop stages (GS39, GS61 and GS82). Increases of inoculum concentration decreased AGB between 8 and 20% mainly explained by reductions in HAD and decreases on IGPAR by 14–18% with higher reductions when the crop was inoculated with Py. tritici-repentis than with P. triticina. Although both diseases reduced the physiological components of accumulated biomass related to radiation interception (IGPAR), RUEint (−23%), RUEgt (−11%) and CGR (−29%) were more reduced, respect to WI, when plants were inoculated with P. triticina compared to Pyrenophora tritici-repentis. The differential responses in RUE could be associated with the nutritional habit of P. triticina that reduces leaf nitrogen concentration, enhance assimilates consume by leaf respiration, reducing radiation use efficiency. Fil: Schierenbeck, Matías. Universidad Nacional de La Plata. Facultad de Ciencias Agrarias y Forestales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Fleitas, María Constanza. Universidad Nacional de La Plata. Facultad de Ciencias Agrarias y Forestales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina 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 Fil: Simon, Maria Rosa. Universidad Nacional de La Plata. Facultad de Ciencias Agrarias y Forestales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Identification of secondary traits in mapping populations is usually hindered by the strong effect of anthesis time. Thus, considering the variability in time to anthesis in combination with an accurate phenotyping of mapping populations and available molecular tools is a possible way for recognising secondary traits to improve yield potential. The aim of this work was to identify secondary traits to perform indirect selection for grain yield (GY) in a bread wheat mapping population consisting of 124 doubled haploid lines, derived from the cross between two soft red winter wheat genotypes with contrasting photoperiod response. Genomic regions linked to different traits were analysed under two environments. The population showed a strong effect of time to anthesis over GY, as expected. A large variability in GY was observed but only two QTLs were detected on chromosome 5A for this trait, which co-localized with QTLs of time to anthesis. GY variation was partially associated with above-ground dry matter at maturity (AGDM) and to a lesser extent with harvest index (HI). Detected QTLs for grains per m2 (GN), grain weight, AGDM and HI explained between 25 and 61% of the GY additive genetic variance. GN, defined as the product between spike dry weight at anthesis (SDW) and fruiting efficiency (FE), was the main numerical component that explained most of the variation in GY. Five QTLs were detected for SDW, which did not co-localize with QTLs of time to anthesis and captured ca. 50% of the additive genetic variance, while there was a weak relationship between NG and FE. When genotypes were filtered by similar anthesis time and plant height, SDW was identified as a promising secondary trait to be targeted for indirect selection of GY.

Determining the optimum time for rapeseed harvest is challenging due to non-uniform seed maturity resulting from asynchronous flowering and pod dehiscence from sequential racemes. Identifying physiological maturity (PM) by visual methods is subjective and results can be affected by environmental conditions. PM can be determined using a quantitative model based on seed water concentration (SWC) as previously demonstrated for several other crops, although not yet developed for rapeseed crop. The objective of this work was to study the relationship between the dynamics of seed dry weight and water concentration in seven spring rapeseed cultivars grown at two contrasting densities (15 and 60 pl m−2) in three experiments at one location in Buenos Aires (Argentina). We evaluated the timing of PM on the basis of SWC in seeds located in the main raceme, second and fourth floral branches. The evolution of seed fresh and dry weight was followed bi-weekly from the beginning of flowering to harvest maturity. In Exp. 1, the grain-filling duration ranged from 39 to 57 days (700–1100 °C d) and the growth of seeds from floral branches finished 3–8 days later than those from the main raceme. Seed dry weight at PM ranged from 2.4 to 2.7 and from 3.0 to 3.2 mg for Lynx and Monty cultivars, respectively, without significant effects of floral position or plant density. Bi-linear functions were used to fit the relationship between relative seed dry weight (RSDW) and SWC relationships (R2 from 0.85 to 0.95). Across cultivars and floral positions, PM was attained when seeds exhibited 46.3 ± 0.7% SWC (R2 = 0.90, P < 0.001, n = 441). This model was validated against independent data from Exps. 2 and 3, successfully simulating the dynamics of relative seed dry weight based on fruit WC (r = 0.88; P < 0.001, n = 275). At PM, the water content (WC) of whole pod was about 70% and the pod shattering began after this point, when the WC of the pod dropped drastically. We conclude that under non-stressful conditions, PM in rapeseed occurs at 46% SWC. Swathing can be conducted from SWC < 46%, instead of the currently recommended 35%, advancing the harvest and leaving the land available for sowing the next crop, which would represent an advantage for double cropping in intensified agricultural systems. Fil: Menendez, Yesica Cristina. 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: Botto, Javier Francisco. 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: Gomez, Nora V.. Universidad de Buenos Aires. Facultad de Agronomía; Argentina 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 Fil: Rondanini, Deborah Paola. Universidad Nacional de Lomas de Zamora. Facultad de Ciencias Agrarias. Instituto de Investigación en Producción Agropecuaria Ambiente y Salud. - Comisión de Investigaciones Científicas de la Provincia de Buenos Aires. Instituto de Investigación en Producción Agropecuaria Ambiente y Salud; Argentina

In wheat, warmer nights during the critical period reduce grain yield due to a diminished grain number per unit area, associated with lower spike number. Previous studies have evaluated the impact of increased night temperatures, but only under potential growing conditions. The aims of this study were to: (i) evaluate the impact of warmer nights during the critical period (i.e. from third detectable node to 10 days after anthesis) on grain yield and its numerical components, under contrasting nitrogen (N) and water levels and (ii) determine whether plant density could be useful as a management strategy to reduce yield losses caused by warmer nights. Two sets of experiments were conducted in Buenos Aires, the first in 2015 and 2016. In both years trials were carried out combining (i) two levels of nitrogen availability (60 and 200 kg N ha−1), (ii) two levels of water availability (rainfed and irrigated) and (iii) two conditions of night temperature (increased night temperature from third visible node to 10 days after anthesis and unheated crops during the whole crop cycle). The second experiment was performed in 2017 and combined: (i) three plant densities (ca. 100, ca. 150 and 300 plants m−2) and (ii) two-night temperature regimes (increased night temperature from third visible node to 10 days after anthesis and unheated crops during the whole crop cycle). Night temperatures were increased by heating systems, during the critical period average night temperatures ranged from 10.7 °C to 15.1 °C. Yield losses occurred when plants were exposed to warmer nights at high nitrogen levels (ca. 7% - i.e. 550 g m−2 - loss per °C of increase) but no effects were apparent under lower nitrogen availability. Warmer nights increased tiller mortality only under high nitrogen availability. No conclusions could be reached concerning water supply management or the convenience of this strategy to reduce the impact of warmer nights due to the lack of response of grain yield or grain number to modifications in water availability. Grain yield was significantly reduced by increases in night temperature only under higher nitrogen supply mostly due to a reduction in grain number per unit area, associated with reductions in spike dry weight; however, crops under high nitrogen levels yielded significantly more than those grown under low nitrogen, even when exposed to warmer nights. For all three densities, warmer nights reduced grain yield similarly (on average ca. 15 %).

Precise phenology modelling of grain filling is essential to understand how the environment explored by barley crops in the field affects malting quality. Grain-filling duration is controlled by temperature; hence thermal time models are widely used for describing grain development. Although a precise base temperature is essential for the accuracy of thermal time models, estimations of this parameter for barley grain filling are scarce in the literature; moreover, the methods employed for its determination seldom establish clearly whether grain filling is being treated as a development or as a growth phenomenon. Even worse, the base temperature during grain filling is usually arbitrarily set to zero. In this work we tested five different methods to estimate the thermal time requirement for completing grain filling in four commercial barley cultivars and the base temperature above which temperature must be accumulated for its calculation, using field-collected data. The crops were sown in a wide range of different dates during three consecutive years and grown under two contrasting nitrogen availabilities. All the estimation methods performed relatively well. Developmental base temperature was close to 8 °C for all cultivars, although genotypic differences were noted. Optimum temperatures for grain filling are reported for three of the four cultivars; however, including this parameter in the models only slightly improved the predictions in one out of three cultivars. The effect of nitrogen availability was negligible and inconsistent across cultivars and environments thus indicating that the models developed can be applied in a wide range of nutritional situations. A broad application model, with a base temperature of 8.4 °C and a thermal time requirement for completing grain filling of 352 °Cd, is reported for barley grain development. All the models were validated against independent data. These models can be used by researchers aiming to unscramble the effects of environment explored by the mother plant on grain malting quality. Further applications include predicting the timing of physiological maturity, and with it, harvest time.

Wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) crops are exposed to warm nights during their growing seasons and this trend is unlikely to change. The aim of this work was to evaluate the effect of higher post-anthesis night temperatures on field-grown crop yield, focusing on final grain weight determination. Experiments combined: (i) two well-adapted crops with similar phenology: bread wheat and two-row malting barley, under (ii) two temperature regimes: ambient and high night temperatures from 10 days after anthesis to physiological maturity during (iii) two contrasting growing seasons in terms of radiation and temperature: late sowing in 2011 and early sowing in 2013. The night temperature increase (ca. 4.1 °C) was achieved using purpose-built heating chambers placed on the crop at 7 pm and removed at 7 am every day during the heating period. Across growing seasons and crops, the average minimum temperature during that period ranged from 14.3 °C to 21.9 °C. Thousand grain weight was reduced by ca. 3% per °C of night temperature increase, similarly for wheat and barley, causing a grain yield reduction of ca. 4% per °C. An accelerated development under high night temperatures led to a shorter effective grain filling period, reducing the final grain weight. The lack of consistent impact on source availability between crops and seasons, measured as senescence and stem water soluble carbohydrates, as well as a similar impact in magnitude and direction on individual grain weight for different grain positions along wheat or barley spikes, suggest that the negative effects of warm nights on grain weight were directly related to processes within the grain itself. 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: Serrago, Roman Augusto. 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: Dreccer, M. Fernanda. The University Of Queensland; 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. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina

The aim of this study was to analyse (i) the crop attributes that determine flowering time (i.e. final leaf number, FLN; and phyllochron, Phy), (ii) the dynamics of tiller appearance and (iii) the synchrony between leaf and tiller appearance in wheat and barley plants exposed to waterlogging. Two experiments were carried out in pots, in which wheat and barley cultivars were exposed to five waterlogging treatments, during different periods throughout the crop cycle, from emergence to maturity. The appearance of leaves and tillers on the main stem was measured twice a week in labelled plants. Waterlogging from emergence to flag leaf appearance significantly delayed time to flowering. The delay was greater when waterlogging occurred at the beginning of tillering, lengthening the period from emergence to flowering 24 % (13–15 days) in barley and 10–15 % (6–10 days) in wheat, as compared to control. Phy was the main attribute explaining the delay in flowering, as FLN was not altered. Waterlogging during the early stages of development reduced tiller appearance rate (TAR) in both species, but this effect was partially counterbalanced by a lengthening of the tillering phase, so the effect on final tiller number at maturity was limited. In conclusion, the exposure of wheat and barley to waterlogging during early stages of development delayed time to flowering and reduce TAR in both species. Waterlogging during more advanced crop stages produced slight effects on tillering dynamics, which would indicate that waterlogging affected structure generation more than mortality.

Water shortage, caused by large variations in the amount, frequency and timing of rainfall during the crop cycle, is one of the major abiotic stresses limiting crop production. In this context, environmental variability represents a significant challenge for farmers as optimal management practices vary from season to season. The aim of this study was to optimize wheat (Triticum aestivum L.) management practices considering rainfall variability in the West sandy Pampas of Argentina. This region is characterized by a high annual rainfall variability with predominant summer rainfall and probable deficits during winter and early spring in analogy with many other regions around the world. Two commercial cultivars, commonly used by farmers, with different time to flowering (LF: late flowering; EF: early flowering), under three initial soil water conditions (well-watered, moderately-watered and dry conditions) at three sowing dates were simulated with CERES-WHEAT for a series of 39 years. Wheat yield was higher for the LF than the EF cultivar under average (LF = 5437 vs. EF=5112 kg ha−1) and no-water restriction years (LF = 7915 vs. EF=6956 kg ha−1), while the opposite was observed in dry years (EF = 4128 vs. LF=3255 kg ha−1). Reductions in grain yield were associated with reductions in grain number, mainly explained by a lower partitioning to reproductive organs, principally limited by water shortage. The LF cultivar used more water than the EF cultivar before anthesis depleting soil water reserves (p

The aim of this study was to identify the critical period for yield determination in buckwheat by applying successive shading periods (of 14-days duration) throughout the crop cycle, from nine days after emergence to crop maturity. Experiments were carried out under field conditions during the 2017 and 2018 growing seasons. The critical period was defined as the interval when crop yield was significantly reduced by the shading treatments. This period extended from 74 °C days after the first open flowers to the first brown fruits stage (i.e. 390 °C days duration). Aerial biomass and its partitioning to the achenes (i.e. harvest index) were also reduced by shading. Achene number was reduced in a similar way to that of yield, and crop yield was highly associated with this yield component, while the shading treatments did not affect achene weight. The main cause of achene number reduction was the lower number of achenes per raceme, as the number of racemes was not affected. It is possible to speculate that radiation restriction imposed during the critical period could have increased floret mortality and thereby the number of achenes per raceme. However, further studies are required to determine the causes of reductions in the number of achenes per raceme during the critical period.

Grain yield variations in bread wheat and two-row barley are better explained by changes in grain number (GN) than mean grain weight. However, the strategies for building GN are different in both species because in two-row barley the variations in GN are more frequently related to the number of spikes m−2, due to its higher tillering capacity than wheat, whereas in bread wheat both grain number spike−1 and the number of spikes m−2 contribute to the establishment of GN. The higher tillering capacity and leaf area index at the beginning of the crop cycle in two-row barley allows a higher radiation accumulation than in bread wheat. We hypothesize that the higher early vigor of two-row barley, associated with its greater leaf area exposure relative to wheat, represents an initial advantage that is capitalized at the end of the cycle as higher biomass accumulation driven by a larger GN and consequently higher grain yield. The main objective of this work was to compare different physiological traits of bread wheat and two-row barley growing together under different temperature and radiation conditions. We evaluated two genotypes of each species, with similar phenology, growing under four different environments without water or nutritional deficiencies. Numerical yield components, biomass, radiation interception and harvest index were measured. Despite no differences being observed between genotypes of bread wheat and two-row barley in terms of total grain yield and total grain number when exposed to different environments, each species had a different strategy for establishing the final yield. Although two-row barley showed initial advantages in radiation interception, bread wheat genotypes accumulated more intercepted photosynthetic active radiation (iPAR) and used it in a more efficient way than two-row barley, thus allowing a higher biomass accumulation. Both species showed a reduction in grain weight due to increases in mean night and high temperatures. Grain weight reductions were higher in bread wheat than in two-row barley, and were directly associated with shortening of the duration of grain filling without consequences for the grain-filling rate. This suggested a direct effect of temperature on grain development rather than a growth limitation due to a lack of source. Fil: Alvarez Prado, Santiago. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cerealicultura; Argentina Fil: Gallardo, Jose M.. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cerealicultura; Argentina Fil: Kruk, Betina Claudia. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cerealicultura; Argentina 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. Universidad de Buenos Aires. Facultad de Agronomía; Argentina

Predicting phenology, in particular heading time, is crucial to avoid and/or minimize risk of damage offrost, drought and high temperatures during grain filling. Although some of the major genes controllingdevelopment, associated with photoperiod and vernalization responses, were identified, the associationbetween the molecular characterization of those genes and photoperiod sensitivity, vernalizationresponses and earliness per se has been poorly studied. The present study was conducted to determinethe effects of photoperiod and vernalization genes (and their allelic combination characterized by molecularapproach) on heading time and its correlation with the phenological parameters determined by fieldexperiments in a wide range of Argentine bread wheat commercial cultivars. Additionally, the associationbetween photoperiod and vernalization responses with earliness per se was analyzed. Molecularcharacterization showed that most of the commercial Argentine wheat cultivars available in the marketcorrespond to spring growth habit with dominant insensitive photoperiod alleles (SI) followed by springhabit sensitive to photoperiod (SS), while winter insensitive (WI) habit represented a minority group. Allgenotypes included in the present study (even those classified as SI and WI) were photoperiod sensitivewhen that trait was quantified from a physiological analysis as the slope of the relationship betweenduration of a particular phase and mean photoperiod sensed during the period between emergence andheading. SI showed lower photoperiod sensitivity than SS and WI, without clear differences betweenboth later groups. In all cases, photoperiod sensitivity was the main attribute that determined the differencesin time to heading even when vernalization requirements were not completely fulfilled in the WI.The genotypes with different photoperiod and vernalization allele combinations showed a wide range ofduration of earliness per se. However, differences in earliness per se did not show any particular associationwith the groups classified by molecular markers for photoperiod and vernalization. The informationincluded in the present study can be used to build a gene-based model for predicting phenology. However,the variations in photoperiod and/or vernalization sensitivity within the same allelic combinationcould still determine mismatching in the prediction of the models based on Ppd-1 and Vrn-1 genes. Fil: Gomez, Dionisio Tomas. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Córdoba. Estación Experimental Agropecuario Marcos Juarez; Argentina Fil: Vanzetti, Leonardo Sebastián. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Córdoba. Estación Experimental Agropecuario Marcos Juarez; Argentina Fil: Helguera, Marcelo. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Córdoba. Estación Experimental Agropecuario Marcos Juarez; Argentina Fil: Lombardo, Lucio Andrés. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Córdoba. Estación Experimental Agropecuario Marcos Juarez; Argentina Fil: Fraschina, Jimena. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Córdoba. Estación Experimental Agropecuario Marcos Juarez; Argentina 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. Cátedra de Cerealicultura; Argentina

Increases in crop yields are important to ensure food supply for humanity. Global yield trends have been analyzed considering public national average data, mainly for cereals but not for rapeseed. As rapeseed and wheat compete for land in crop rotation, it is also important to know how the rapeseed-to-wheat yield ratio is modified in different environments so as to make rapeseed an attractive alternative for farmers around the world. The present study analyzed historical records of rapeseed from FAO determining yield stability trends over the last 40yr, as well as rapeseed competitiveness compared to wheat. Twelve countries representing a wide range of environments and farming systems were taken into account. Regressions were fitted to the rapeseed yield/time relationships and residuals of these regressions were used to evaluate trends in yield stability. Results showed a global rapeseed yield gain of 27kgha -1yr -1 along the past 40yr, although fluctuating among decades. In relative terms to 1970, world rapeseed yield increased 3.4%yr -1. Yield gain in different countries varied from 15 to 40kgha -1yr -1, exhibiting linear, bi- or tri-linear yield trends. Opposite yield trends were observed for Chile and the UK, with sustained yield gain for the former and leveling off for the latter since the mid 1980s. This does not seem to be related to the supply of environmental resources (both countries yielding >3000kgha -1). A high variability was detected in national yields (0-750kgha -1 or 0-60% of yield) and yield stability did not increase over the last 40yr in any country. Rapeseed and wheat yields, expressed in relative terms to their values for 1970, increased in a similar proportion over the last four decades. Global rapeseed-to-wheat ratio ranged 40-60% over the last 40yr, but rapeseed yields can increase up to 80-100% with respect to wheat in poor environments for wheat (4000kgha -1). It was concluded that rapeseed yields have increased steadily in the last 40yr in most studied countries, the yield gain was not accompanied by greater yield stability, and rapeseed competitiveness compared to wheat is at least 40-50% in environments with good supply of resources. © 2011 Elsevier B.V. Fil: Rondanini, Deborah Paola. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cerealicultura; Argentina Fil: Gomez, Nora Valentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cultivos Industriales; Argentina Fil: Agostini, María Belén. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cultivos Industriales; Argentina 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; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cerealicultura; Argentina

In wheat, stem elongation phase (SEP) duration is critical for grain number (GN) per unit of area determination, as it is the phase in which the spikes grow. Lengthening SEP, for instance by photoperiodic sensitivity, without altering the cycle to anthesis (AT) has been proposed as an alternative way to increase spike dry weight, and in turn GN. As most works supporting this idea have modified only SEP by artificial manipulation (e.g. photoperiod extensions), it is relevant to evaluate this hypothesis in populations segregating for this attribute in natural conditions. The aim of this work was to analyse the variability in SEP duration relative to AT in two F4 populations; in order to select contrasting phenotypes to evaluate the impact of this attribute on grain yield components and to analyse the selection response of this attribute. These segregating populations (Las Rosas INTA × Triguero 230 (A) and Klein Estrella × ProINTA B. Alazan (B)) were derived from parental lines with similar flowering time but different relative duration of their pre-anthesis phases. Two field experiments with previous vernalization treatment in cool chamber were carried out. In 2006, F4 populations were characterized and from one of them (population B, which presented higher variability) four groups were selected, which presented contrasting phenotypes in the attribute under study. Progenies of these groups (F5), together with remnant F4 full-sib of each one, were studied during 2007. Grain yield per plant was higher, due to GN increases, when duration of the SEP was lengthened. However, selection response to longer SEP with similar cycle to AT could not be found, possibly as the result of a high environmental influence on this attribute. The phenotypic variability evidenced in this attribute was not clearly associated with major adaptation genes evaluated (i.e. Ppd and/or Vrn), suggesting that other minor genes could be associated.

The present work analysed whether grain weight is affected by changes in source:sink ratio in twenty-four durum wheat cultivars from Italy and Spain released through the 20th century grown under Mediterranean conditions. For this purpose, a field experiment was conducted during the 2002 growing-season in southeastern Spain. Sink strength was modified by removing half of the spikelets, of one side of the spike, one week after anthesis. Spikelet trimming had different effects on both average grain weight and individual grain weight at different positions within the spike. While old cultivars did not respond positively to spikelet trimming, and appear to be mainly sink-limited, intermediate and modern cultivars from Spain increased their grain weight in response to sink reductions, suggesting co-limitation by the sink and source. On the contrary, grain weight of intermediate and modern Italian cultivars remained relatively unchanged suggesting a sink-limitation to grain yield. The differential response to source-sink manipulations observed between Italian and Spanish cultivars could be attributed to their different genetic background, which determines their level of adaptation to harsh Mediterranean environments. Fil: Rharrabti, Y.. Universidad de Granada; España 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 Fil: Martos, V.. Universidad de Granada; España Fil: García Del Moral, L.F.. Universidad de Granada; España

Nitrogen (N) fertilization plays a central role for improving yield in wheat and high N use efficiency (NUE) is desired to protect ground and surface waters. Several studies showed that sulfur (S) fertilization may increase NUE, but no attempts have been made to explain whether this increase is due to greater recovery efficiency (RE), an enhanced internal efficiency (IE) or by an improvement of both efficiencies. The aim of this study was to analyze the effects of different N and S fertilizer rates, and their interaction on N uptake, its partition at maturity, NUE and its main components. Field experiments were carried out during two consecutive growing seasons in the Argentinean Pampas using a single bread-wheat genotype grown under different combinations of N and S fertilizer rates. Additional experiments were performed in farmer fields using N and S fertilization evaluating different genotypes in order to analyze the components of NUE in other environmental conditions. Plant N uptake increased linearly in response to N addition until rates of ca. 80 kg N ha −1 . Sulfur addition showed no effect at the lowest N fertilizer rate, but N uptake was increased when S was applied at the highest N rate, revealing a synergism between both nutrients. At the lowest S rate RE was 42%, and increased to 70% when S fertilizer was added. No changes in IE in response to S fertilization were observed. These results were also observed in farmer field experiments, in genotypes that showed different IE. This study showed that S addition increased NUE mainly by increasing the N recovery from the soil. Thus, the concurrent management of N and S is important for reducing the potential pollution of residual soil nitrate by increasing N recovery from the soil while sustaining high nitrogen use efficiency.

The critical period for yield determination in barley ( Hordeum vulgare L.) is situated in the pre-heading phases. During the latest part of the critical period one of the most important yield components (i.e. the number of grains per spike) is set in two- and six-rowed barley. In wheat, much is known about the role of the spike in assimilate acquisition for the establishment of grains per spike, but not in barley. This paper evaluates how biomass partitioning between vegetative and reproductive organs impacts floret development and primordia survival in response to radiation during different periods in the crop cycle, in barley lines. Field experiments were carried out using two- and six-rowed near isogenic barley lines differing only in spike type. Shading treatments were applied at different periods during the crop cycle (from 60 to 15 days before and after heading) reducing the intercepted radiation (ca. 70%). Dynamics of floret primordia initiation and mortality and of floret development for different spikelet positions along the spike were measured, and biomass partitioning between vegetative and reproductive structures was calculated. Pre-heading shading reduced fertile florets per spike ( P The amount of assimilates partitioned to the spike at heading affected the number of fertile florets per spike in both barley types. However, when spike biomass at heading was corrected by nitrogen concentration, the fitness of the relationship did not improve in relation to the first one. In relative terms, radiation restrictions during the immediate pre-heading phase increased the amount of biomass partitioned to the growing spike.

In barley no studies have attempted to pinpoint the critical period for grain number determination, and it is frequently stated that the critical period is similar to that of wheat. However, there are important differences between the species and among barley genotypes (i.e. two- and six-rowed types) suggesting that this assumption requires testing. The objectives of this paper were (i) to determine the critical period for grain number determination in two- and six-rowed barleys, and (ii) to identify which yield components were more sensitive to changes in incident radiation during that period. Two field experiments were conducted using two pairs of near isogenic lines differing only in the spike type. Shading was imposed at different periods throughout the crop cycle (from 60 days before heading to 15 days after) to reduce incident solar radiation approximately 70%. The critical period for grain number determination tended to be slightly earlier in two- (ca. between 40 and 10 days before heading) than in six-rowed barleys (ca. between 30 days before heading until that stage). In terms of the external phenology, the beginning of the critical period for setting grains was 10 days after the beginning of stem elongation, and 10 days before flag leaf appearance in two- and six-rowed lines, respectively. Changes in the number of grains per unit area were correlated with crop growth rate during the critical period for yield determination.

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.

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.

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.

Soybean (Glycine max (L.) Merrill) exposure to long days during the post-flowering phase increases total biomass, nodes, pods and seeds per plant, and also the post-flowering duration, increasing the radiation offer. This work aims to identify the main mechanisms responsible for yield increases in response to long days, separating direct photoperiodic effects on yield determination, from the indirect effect associated with changes in cumulative radiation when the crop cycle is modified by photoperiod. Two field experiments were conducted with an indeterminate soybean cultivar. A factorial combination of two radiation levels (unshaded and shaded), and two or three photoperiod regimes (control, extended 1.5 and 3 h) was imposed from flowering to maturity. Yield tended to be reduced by shade and increased by extended photoperiod mainly through their effects on nodes per m2, and thereby affecting pods and seeds per m2. Photoperiod extension increased node number due to both increased cumulative radiation (indirect effect) and delayed reproductive development (direct effect). As a result, more pods were established per unit of cumulative radiation under extended photoperiod. The results suggest that photoperiod extension enhanced yield radiation use efficiency due to the alleviation of intra-nodal interferences. The direct post-flowering photoperiodic effect on node number and the resultant effects on pod and seed number, provide evidence of direct photoperiodic effects on soybean yield determination. Fil: Nico, Magalí. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cultivos Industriales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina 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 Fil: Kantolic, Adriana Graciela. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cultivos Industriales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

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

Although floret abortion is related to a shortage in assimilates acquisition by the spikes, differences in floret abortion and grain setting has been reported between two- and six-rowed barley types. However, the origin of those differences has not been studied until now. This study was designed to explore the dynamics of floret development and to analyze the coordination between floret primordia development and growth of vegetative and reproductive organs in near isogenic barley lines differing only in the lateral spikelet fertility gene (Vrs1). Two field experiments using four near isogenic lines differing only in the spike type were carried out. Floret primordia development together with stem and spike growth were studied. In both barley types floret primordia mortality starts at the beginning of the spike active growth phase and continued when stem and spike growth were at their maximum rate. A reduced contribution of fertile florets in apical and basal spikelet positions explained the lower floret survival in six-rowed barleys. The chance to reach the fertile floret stage at heading was highly dependent on the floral development stage attained at the start of floret primordia mortality. Floret development stage at the beginning of active floret primordia mortality was higher for all spikelet positions in two- than six-rowed barleys. Grain setting was lower in six- than two-rowed genotypes associated to a lower grain setting in distal spikelet positions. Smaller carpels in six- than two-rowed genotypes in those positions could be associated with a reduce chance of those florets to set grains. The lower grain survival within the spike in six-rowed genotypes was caused by (i) a lower floret survival due to a lower degree of floret development in distal and lateral spikelet positions at the beginning of the floret primordia mortality stage and (ii) a reduced establishment of the fertile florets initially formed.

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

Lengthening the late reproductive phase (LRP) of stem elongation in wheat (Triticum aestivumL.), by changing its photoperiod sensitivity independently of the preceding phases, would improve the yield potential through increasing spike weight and the number of fertile florets at anthesis. This paper presents results of a two-year field experiment designed to determine the impact of Ppd-D1and Ppd-B1on (i) the duration of three pre-anthesis developmental phases, and (ii) spike weight and the number of fertile florets at anthesis under two photoperiods during the LRP (natural and an extension of six hours over that). Near isogenic lines of Mercia and single chromosome recombinant lines of Cappelle Desprez were used. Under natural photoperiod, Ppd-D1hastened time to anthesis ca. 500∘C d in both backgrounds by reducing each of the three pre-anthesis phases. Ppd-B1hastened the time to anthesis under natural photoperiod by 178∘C d, mainly by reducing the early reproductive phase. The response to photoperiod of the LRP under extended daylength depended on the Ppdlocus present: Ppd-D1was insensitive while Ppd-B1and the recessive controls were sensitive. For all lines, photoperiod treatments and years, the number of fertile florets was associated with spike dry weight at anthesis (R 2≅ 80%, p< 0.01) which, in turn, was positively related to the intercepted radiation accumulated during the LRP (R 2 45%, p< 0.05). Changing the duration of the LRP through extended photoperiod or through Ppd-D1produced similar results in both backgrounds and years. Thus, altering the duration of the LRP by manipulating photoperiod sensitivity may be an alternative to changing the fertile floret number in wheat. Nevertheless, as no particular allele was responsible for the photoperiod sensitivity only during the LRP, new alleles should be studied to identify the control of photoperiod sensitivity of individual phases to fine-tune the pre-anthesis wheat development.

The present study was designed to analyse the effect of the length of exposure to a long photoperiod imposed c. 3 weeks after sowing in spring wheat (cv. UQ189) and barley (cv. Arapiles) to (i) establish whether the response to the number of cycles of exposure is quantitative or qualitative, (ii) determine the existence of a commitment to particular stages well before the stage has been observable, and (iii) study the interrelationships between the effects on final leaf number and phyllochron when the stimulus is provided several days after seedling emergence. Both wheat and barley seemed to respond quantitatively to the number of long-day cycles they were exposed to. However, wheat showed a requirement of approximately 4 long-day cycles to be able to produce a significant response in time to heading. The barley cultivar used in the study was responsive to the minimum length of exposure. The response to extended photoperiod cycles during the stem elongation phase was due to the ‘memory’ photoperiod effects being related, in the case of wheat, to the fact that the pre-terminal spikelet appearance phase saturated its photoperiod response well before that stage was reached. Therefore, the commitment to the terminal spikelet appearance in wheat may be reached well before this stage could be recognized.As the response in duration to heading exceeded that of the final leaf number, and the stem elongation phase responded to memory effects of photoperiod, the phyllochron of both cereals was responsive to the treatments accelerating the average phyllochron when exposed to longer periods of long days. The response in average phyllochron was due to a switch from bi-linear to linear models of leaf number v. time when the conditions were increasingly inductive, with the phyllochron of the initial (6–8) leaves being similar for all treatments (within each species), and from then on increased.

The manipulation of photoperiod sensitivity during stem elongation (terminal spikelet initiation—anthesis) has been suggested as a means to increase wheat yield potential. Nevertheless, photoperiod sensitivity and the interaction with vernalization during that phase have not been previously explored under field conditions. Thus, a field study was carried out (i) to assess whether duration of stem elongation is sensitive to photoperiod experienced only during that phase, and if so (ii) to evaluate whether vernalization interacts with this photoperiod response and (iii) to determine if altering duration of stem elongation may influence wheat yield and its components. The experiment was a factorial combination of two vernalization treatments (15 (V15) or 50 (V50) days at 4±1 °C and 8 h photoperiod), two photoperiod regimes during stem elongation (natural daylength in the field (NP+0) and one daylength extension of 6 h (NP+6)) and three cultivars (Buck Manantial (BM), Eureka Ferrocarril Sur (EFS), and ProINTA Puntal (PP)). The stem elongation phase responded to the actual photoperiod experienced during that phase in the three cultivars, increasing its duration with shorter photoperiod. In the vernalization-sensitive cultivars EFS and PP, plants vernalized 50 days showed greater response to photoperiod than those vernalized 15 days. In the most photoperiod-sensitive cultivar (BM), as duration of stem elongation lengthened by exposure to less inductive photoperiod, a higher number of fertile florets at anthesis was achieved leading to an increased grain number and thereby to a higher wheat yield. These results reinforce the idea that a longer duration of stem elongation may offer an alternative avenue to improve yield potential in wheat.

A longer duration of stem elongation (from terminal spikelet initiation to anthesis) would result in a higher wheat yield potential as a consequence of the increase in both spike dry weight and number of fertile florets at anthesis. It is not clearly understood, however, which processes are involved in the increased spike dry weight and whether this variable accounts for the higher number of fertile florets when duration of stem elongation is modified by photoperiod treatments. As vernalization interacts with photoperiod during the stem elongation phase, a better understanding of the role of vernalization is also required. A field experiment was carried out using two wheat cultivars (Buck Manantial (BM) and Eureka Ferrocarril Sur (EFS)) subjected to diverse periods of vernalization (V 15 and V 50 , plants vernalized for 15 and 50 days, respectively) and exposed to different photoperiods (NP+0 and NP+6, natural and 6 h extended photoperiod, respectively) only during the stem elongation phase. Floret development together with stem and spike growth during the stem elongation phase were studied. When the stem elongation phase was exposed to short photoperiod (i) duration of spike growth increased without any change in its growth rate, and (ii) most of the spike growth occurred during minimum stem growth rate as the onset of maximum stem growth rate was delayed. In EFS, the vernalization-sensitive cultivar, the former (i) and (ii) was true only when vernalization requirements were met. For both cultivars, the survival of the initiated floret primordia under short photoperiod increased, independently of vernalization. Both partitioning of assimilates to the spike and a direct photoperiod effect seemed to have been involved in the survival of floret primordia when the stem elongation phase was exposed to short photoperiod.

It has been established that photoperiod influences the rate of wheat development well beyond the end of the vegetative phase. Conversely, vernalization effects are still assumed to be mainly during the vegetative phase. The aim of the study was to assess the effects of different combinations of vernalization and photoperiods on the developmental characteristics of wheat pre-flowering reproductive phases under field conditions. For this purpose, three high yielding cultivars (ProINTA Puntal, ProINTA Super and Klein Pegaso) were subjected to two vernalization treatments (unvernalized (V0) and vernalized during 56 days in a cool chamber (V56)) and four photoperiod regimes. The photoperiod treatments consisted of the natural photoperiod of the season (NP+0) and daylength extensions over that of 2 (NP+2), 4 (NP+4), and 6 (NP+6) hours. Photoperiod influenced the duration of early (collar—first node detectable) and late (first node detectable—heading) pre-flowering reproductive phases, reducing their durations as photoperiod increased. When cultivars with strong vernalization response (ProINTA Puntal and ProINTA Super) were not vernalized, duration of the early and late pre-flowering reproductive phases increased and the rate of spikelet initiation decreased. Thus, when vernalization requirements were not satisfied, the spikelet initiation rate was even slower than the leaf initiation rate (both expressed in a thermal time base). Results showed significant interactions between photoperiod and vernalization (vegetative phase), or clear, though non-significant, trends to interactive effects (late pre-flowering reproductive phase). Thus, the length of vegetative and late pre-flowering reproductive phases changed in response to photoperiod depending on the level of satisfaction of the vernalization requirements. The relationship between the cumulative number of leaves on the main stem and thermal time fitted a bi-linear model whenever the final leaf number (LNf) was large, e.g. when photoperiod was not extended or vernalization requirements not satisfied. Thus, responses during the pre-flowering reproductive phases were accompanied by an increased phyllochron for leaves emerging after the first 7–8 leaves. This study demonstrated with field grown plants that the length of the late pre-flowering reproductive phase in wheat is sensitive to photoperiod and that the response to this environmental factor could be changed by the level of satisfaction of the vernalization requirements.

In the Pampean region of Argentina, farming systems are based on intensive land use, wheat/soybean double cropping being a key component of these agricultural systems. However, during the last years farmers have been replacing wheat for barley due to its earlier maturity date, reducing yield penalization in soybean as a consequence of delays in its sowing date, and improving the economic profits of the double cropping system. To maximize the benefits of barley/soybean double cropping system, the proper timing of key barley ontogenic stages should be easily identifiable by farmers. The objectives of the present study were to (i) characterize crop phenology through thermo-photoperiod models in response to different sowing dates, (ii) use the algorithms calculated in point (i) to generate a simple model for predicting phenology, using historical climatic series, and (iii) validate the model with independent data. Barley cultivars used in the present study did not show vernalization requirements. Variations in phenology, measured in thermal time, were mainly associated with variations in photoperiod sensitivity during the emergence-heading phase. Significant differences in photoperiodic sensitivity, from −65 °Cd h−1 (Scarlett) to −344 °Cd h−1 (Q. Ayelen), were observed among cultivars. However, cultivars did not show significant differences in critical photoperiod or intrinsic earliness. The slope of the relationship between heading time and date of emergence, calculated from the algorithms used to build the model, based on thermo-photoperiodic response, varied between locations and cultivars. When the model was tested with an independent data set, predictions for the sowing-flowering phase showed a root mean square error lower than 4% (similar to that observed using more complex models). The algorithms used in the model were masked into a friendly frame and outputs were shown in a simple and attractive manner for users. The model was uploaded to the web site of the University of Buenos Aires to be used by students, advisors, professionals and farmers barley. Fil: Alzueta, Ignacio. 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. Cátedra de Cerealicultura; Argentina Fil: Arisnabarreta Dupuy, Sebastián. Monsanto Company. Production Research; Argentina 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; Argentina 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. Cátedra de Cerealicultura; Argentina

Two cultivars of each bread wheat ( Triticum aestivum L.), malting barley ( Hordeum vulgare L.) and spring rapeseed ( Brassica napus L.), were grown in a wide range of different sowing dates in Buenos Aires, Argentina. The aims of this study were (i) to analyse how the number of leaf primordia and the rate of leaf emergence interact to modify the duration of different pre-flowering phases and (ii) to establish how different yield components initiated during those phases are affected when the duration of these phases are modified by wide range of sowing dates. The results showed interactions between photoperiod and temperature for wheat and rapeseed producing different combination for the length of the pre-flowering phases. Barley reached floral initiation earlier than wheat and rapeseed and had a shorter ‘intrinsic earliness’. Plastochron and phyllochron varied among different sowing dates in the three species. In most cases the relationship between the cumulative number of leaves on the main shoot of wheat and barley and thermal time was describe by a bilinear model with the earlier leaves emerging faster than the later ones. However, the opposite pattern was observed for rapeseed which showed a slower rate of leaf emergence for the first than for the lasts leaves. The changes observed in the rate of leaf emergence throughout plant ontogeny, might delay or hasten the duration of the later reproductive phase during which the spikes grow and some of the initiated floret primordia becoming fertile. Extending the duration of the stem elongation phase in wheat and barley produced more fertile florets per spikelets.

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 effects of Rht1 and Rht2 alleles on the dynamics of floret development in isogenic lines (dwarf, DD; semi-dwarf, SD and standard height, SH) of spring wheat were investigated. Studies were conducted on wheat grown in the field in each of 4 years and where water and nutrients were non-limiting. The number of grains per spike was significantly greater in the lines with Rht alleles than in the SH lines. Grain number for each line was such that DD>SD>SH. Grains per spike varied with the number of grains per spikelet rather than number of spikelets per spike. Grains per spikelet in turn varied with the number of fertile florets at anthesis. Florets were considered fertile when male and female reproductive organs had developed green anthers and bifidum stigma, respectively. The dwarfing genes had no effect on the percentage of fertile florets setting grain. Increased number of fertile florets per spikelet due to the presence of Rht1 and Rht2 alleles in the genome was a consequence of the higher number of relatively distal primordia, to progress to the stage of fertile floret at anthesis in the DD and SD than in the SH lines. This ability to allow that a greater proportion of distal florets maintain a normal rate of development was related to the fact that Rht alleles produced a more favourable assimilate partitioning to the spike during the pre-anthesis period associated with the reduction in stem growth imposed by Rht alleles. This allowed a higher proportion of the later-initiated floret primordia to produce fertile florets at anthesis.

Three near isogenic lines of spring wheat grown to determine whether Rht dwarfing alleles alter radiation interception. A field study (involving two sowing dates in two growing seasons) with lines containing different allelic dosage of Rht1 and Rht2 (i.e. dwarf, DD; semi-dwarf, SD and tall SH), was conducted without water and nutritional deficiencies. Dwarfing genes did not modify the timing of occurrence of phenological events. Above-ground biomass at anthesis was reduced by 22% in the DD line in relation of the rest of the lines. However, at maturity accumulated biomass of the DD and SH lines were not significant different. Dwarfing genes increased the light attenuation coefficient (k, with values of 0.48, 0.62 and 0.78 for the SH, SD and the DD line respectively). A similar trend was followed to the leaf thickness (estimated by the specific leaf weight, SLW). Despite the differences observed among the lines, both in k and SLW values, they did not differ significantly in the proportion of incoming radiation intercepted by the canopy, nor in the cumulative intercepted radiation during the pre and post-anthesis periods. Radiation use efficiency (RUE) differed significantly among the lines. While RUE during pre-anthesis was the lowest in the DD line, from anthesis to maturity the lines with Rht alleles showed higher RUE values than the SH line. The low pre-anthesis RUE in the DD lines could be associated with (i) poor canopy architecture due to reductions in leaf sheath and internode lengths and/or (ii) reduced canopy CO2 exchange rate. Post-anthesis RUE was lower than that recorded pre-anthesis in all lines. But the magnitude of the reduction was inversely related to the doses of the Rht alleles. Post-anthesis RUE appeared to be closely and positively associated with the number of grains set per unit biomass at anthesis. This relationship suggests a regulatory effect of the sink size on the efficiency of the crop to convert radiation into biomass during this period.