Ear photosynthesis in C3 cereals and its contribution to grain yield: Methodologies, controversies, and perspectives

In C3 cereals such as wheat and barley, grain filling was traditionally explained as being sustained by assimilates from concurrent leaf photosynthesis and remobilization from the stem. In recent decades, a role for ear photosynthesis as a contributor to grain filling has emerged. This review analyzes several aspects of this topic: (i) methodological approaches for estimation of ear photosynthetic contribution to grain filling; (ii) the existence of genetic variability in the contribution of the ear, and evidence of genetic gains in the past; (iii) the controversy of the existence of C4 metabolism in the ear; (iv) the response of ear photosynthesis to water deficit; and (v) morphological and physiological traits possibly related to ear temperature and thermal balance of the ear. The main conclusions are: (i) there are a number of methodologies to quantify ear photosynthetic activity (e.g. gas exchange and chlorophyll fluorescence) and the contribution of the ear to grain filling (individual ear shading, ear emergence in shaded canopies, and isotope composition); (ii) the contribution of ear photosynthesis seems to have increased in modern wheat germplasm; (iii) the contribution of the ear to grain filling increases under resource-limitation (water deficit, defoliation, or pathogen infection); (iv) there is genetic variability in the contribution of the ear in wheat, opening up the possibility to use this trait to ameliorate grain yield; (v) current evidence supports the existence of C3 metabolism rather than C4 metabolism; (vi) the ear is a 'dehydration avoider organ' under drought; and (vii) thermal balance in the ear is a relevant issue to explore, and more research is needed to clarify the underlying morphological and physiological traits.Fil: Tambussi, Eduardo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Maydup, Maria Luján. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Carrión, Cristian Antonio. Universidad Nacional de Tierra del Fuego. Instituto de Ciencias Polares, Recursos Naturales y Ambiente; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Guiamet, Juan José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Araus, José L.. Universidad de Barcelona; Españ

Analysis of early vigour in twenty modern cultivars of bread wheat (Triticum aestivum L.)

Fast development of seedling leaf area is a relevant trait in order to increase early resource acquisition. The use of semi-dwarf genotypes of wheat has decreased early vigour of modern cultivars. We studied early vigour of 20 cultivars cropped in Argentina, and our main objectives were: (i) to analyse the genotypic variability in early vigour; (ii) to study morphological traits that can be good indicators of early vigour, such as seed mass, leaf width, and specific leaf area; and (iii) to determine whether increased dry mass allocation to roots impacts negatively on early vigour. Experiments with non-size-selected and size-selected seeds were carried out in a greenhouse. A field trial was also conducted in order to test the reliability of the greenhouse results. Seeds mass was the main parameter related to early vigour. However, results from the experiment with seeds selected by size (45-50mg seed-1) showed that seed mass per se only partially explains early vigour, since a significant coefficient of determination was observed between the seedling leaf area of each cultivar in both experiments (i.e. with randomly chosen or size-selected seeds). We observed a high coefficient of determination between net assimilation rate and changes in the ranking of early vigour of the cultivars with time after transplant. Root biomass was positively correlated with leaf area, indicating that the traits were not mutually exclusive. We built simple models by multiple regression to predict early vigour, including some parameters that were easy to measure. Seed mass and leaf width taken together showed better fit than seed mass or leaf width alone. We found a significant coefficient of determination between early vigour in greenhouse and field experiments; thus, screening for early vigour under semi-controlled conditions may be feasible.Fil: Maydup, Maria Luján. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Graciano, Corina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Guiamet, Juan José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Tambussi, Eduardo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; Argentin

The contribution of the awns of bread wheat (Triticum aestivum L.) to grain filling: Responses to water deficit and the effects of awns on ear temperature and hydraulic conductance

The awns of the ear have been reported as important sources of assimilates in wheat. However, their actual importance in grain filling is not well known. We examined several aspects of the awns and their role in the grain filling, and the objectives of this work were: (i) to study their photosynthetic activity during grain filling, comparing flag leaf, ear body and awns in two cultivars differing in ear contribution to grain filling, (ii) to estimate the influence of awns on the temperature and the hydraulic conductance of the ear, (iii) to analyze the response of the flag leaf versus awns to water deficit, particularly regarding relative water content and photosynthetic activity, (iv) to analyze if there is a correlation between awn size versus ear and awn contribution to the grain filling in six modern Argentinean cultivars, and, (v) to explore if awn size and awn contribution have changed during the past century, analyzing old and modern Argentinean cultivars. In this paper we show that: (1) during late grain filling, ear parts (particularly the body of the ear) maintained a higher photosynthetic activity than the flag leaf, (2) awns showed some ‘tolerance’ to water deficit, maintaining a higher relative water content and electron transport rate than the flag leaf under drought, (3) awns increase water conductance of the ear (particularly in the cv. K. Escudo), decrease the ear temperature during the morning, but increase ear temperature after midday (4) there is a moderately positive relationship between awn size and contribution of the ear to grain filling, and (5) in the retrospective analysis we did not find a clear tendency in awn size and awn contribution to grain filling along the years. However, in general terms modern cultivars seem to have a higher awn contribution (and higher awns size) than old ones. In summary, awns may have positive (increased photosynthetic area and activity, tolerance to drought) and negative (increased ear temperature) effects on grain filling, and their final impact on yield will depend on the interaction between these effects and prevailing environmental conditions.Fil: Maydup, Maria Luján. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Antonietta, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Graciano, Corina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Guiamet, Juan José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Tambussi, Eduardo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; Argentin

Methodological aspects and impact on grain weight of source reduction through shade meshes during grain filling of bread wheat

In crop studies, shading is a common approach for reducing source activity (i.e. assimilates produced by photosynthesis); however, if source reduction is not directly proportional to the degree of light attenuation, estimations could be flawed. We analysed the effects of shading at three levels on light transmittance, air and canopy temperatures, and actual photosynthetic activity at different times of day, and on grain weight in a modern genotype of bread wheat (Triticum aestivum L.). The treatments were imposed 10 days after anthesis and comprised three levels of shading with meshes: 80%, 50% and 10% transmittance during midday. The decrease in midday photosynthetic activity (electron transport rate, ETR; and CO2 assimilation, An) in the shading treatments compared with control plants did not fit a 1: 1 relationship with light transmittance of the meshes; for example, the reduction in ETR and An was <50% under the mesh with 50% light transmittance. The decrease in light transmittance and photosynthesis caused by the meshes was higher during the morning and afternoon than midday. In the grain-filling period, midday ETR showed a progressive, age-dependent decrease in control plants compared with shading treatments. Initial differences in photosynthetic activity between treatments were attenuated throughout the grain-filling period. The diurnal course of air temperature showed a progressive decrease from control to shade treatments, mainly during midday. This pattern was confirmed by infrared thermometry of canopy temperature, with severe shade showing the lowest temperature. Greenness measurements at 19 days after anthesis showed delayed senescence in shaded plants, possibly due to the decrease in temperature under shade. Grain weight per ear was reduced in shading treatments (mainly with 50% and 10% light transmittance). The decrease in grain weight per ear plotted against the decrease in photosynthesis (evaluated through ETR or An) did not fit a 1: 1 relationship. This could be explained in part by an observed increase in dry matter retranslocation from the stem. In summary, estimations of source reduction on the basis of light attenuation could be biased, because the photosynthesis decrease is less than proportional, and photosynthesis differences are attenuated throughout grain filling.Fil: Maydup, Maria Luján. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Antonietta, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Rouillet, Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Cano, Maria Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Guiamet, Juan José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Tambussi, Eduardo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; Argentin

New avenues for increasing yield and stability in C3 cereals: exploring ear photosynthesis

Small grain cereals such as wheat, rice and barley are among the most important crops worldwide. Any attempt to increase crop productivity and stability through breeding implies developing new strategies for plant phenotyping, including defining ideotype attributes for selection. Recently, the role of non-foliar photosynthetic organs, particularly the inflorescences, has received increasing attention. For example, ear photosynthesis has been reported to be a major contributor to grain filling in wheat and barley under stress and good agronomic conditions. This review provides an overview of the particular characteristics of the ear that makes this photosynthetic organ better adapted to grain filling than the flag leaf and revises potential metabolic and molecular traits that merit further research as targets for cereal improvement. Currently, the absence of high-throughput phenotyping methods limits the inclusion of ear photosynthesis in the breeding agenda. In this regard, a number of different approaches are presented.Fil: Sanchez Bragado, Rut. Universidad de Barcelona. Facultad de Biología; EspañaFil: Vicente, Rubén. Universidad de Barcelona. Facultad de Biología; EspañaFil: Molero, Gemma. Universidad de Barcelona. Facultad de Biología; EspañaFil: Serret, Maria Dolors. Universidad de Barcelona. Facultad de Biología; EspañaFil: Maydup, Maria Luján. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Araus, José Luis. Universidad de Barcelona. Facultad de Biología; Españ

Balance de P en el cultivo de soja: ¿Fertilizar o no fertilizar? Esa no es la cuestión

En la zona núcleo sojera los niveles de P disponible han caído por debajo del valor crítico para soja (14.3 ppm) entre 1980 y la actualidad como consecuencia de un balance de P negativo. Realizamos un análisis con datos obtenidos en lotes de productores asociados a CREA en soja de primera durante 3 campañas (2017-19) y en 3 regiones: Oeste, Oeste Arenoso y Sudeste (n=2302). Más de un 80% de los lotes presentaron valores de P Bray1 menores a 15 ppm. La fertilización con P tendió a ser mayor en lotes propios que en arrendados. Se detectaron diferencias en rendimiento de hasta un 25% entre lotes fertilizados con P y no fertilizados. El balance de P más negativo se detectó en el Oeste Arenoso (-17 Kg P ha-1) y el menos negativo en la región Sudeste (-6 Kg P ha-1) en línea con los menores niveles de P disponible. La respuesta del rendimiento al P podría promover la práctica de fertilización dependiendo de la relación costo-beneficio. Una agricultura sustentable no puede alcanzarse sin repensar el flujo lineal de P desde las minas hacia los océanos pasando por los campos.In the soybean core zone, available P soil levels have decreased below critical values for soybean (14.3 ppm) between 1980 and present due to negative P balances. We analyzed soybean data obtained in farmer fields associated to CREA during 3 years (2017-19) in 3 regions: West, Sandy West and Southeast (n=2302). Above 80% of the lots had P Bray1 values below 15 ppm. Higher P doses were observed in owned compared with rented fields. Yield differences of up to 25% were detected between P- fertilized and non-fertilized plots. Most negative P balances were detected in Sandy West zone (-17 Kg P ha-1) whereas the least negative were detected in the Southeast (-6 Kg P ha-1) in line with its lower levels of available P. Yield response to P may promote fertilization practices depending on the cost-benefit relationship. In any case, sustainable agriculture cannot be achieved without rethinking the linear flux of P from mines to oceans passing through the fields.Fil: Antonietta, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Girón, Paula. Instituto Nacional de Tecnologia Agropecuaria. Centro Regional Buenos Aires Norte. Estacion Experimental Agropecuaria General Villegas. Agencia de Extension Rural General Villegas.; ArgentinaFil: Martini, Gustavo. Asociacion Argentina de Consorcios Regionales de Experimentacion Agricola.; ArgentinaFil: Maydup, Maria Luján. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Micheloud, José Roberto. Asociacion Argentina de Consorcios Regionales de Experimentacion Agricola.; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cerealicultura; ArgentinaFil: Paolini, Maria Sol. Asociacion Argentina de Consorcios Regionales de Experimentacion Agricola.; ArgentinaFil: Guiamet, Juan José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Satorre, Emilio Horacio. 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. Asociacion Argentina de Consorcios Regionales de Experimentacion Agricola.; Argentin

Andean maize in Argentina: physiological effects related with altitude, genetic variation, management practices and possible avenues to improve yield

In the Argentinean Andean region, maize is a main staple being cropped up to27 3900 meters above the sea level. Yields are limited by the sharp decrease in temperature28 associated with altitude but also by a lack of management and breeding technologies to29 underpin traditional practices. In this review we discuss (i) the main physiological changes30 of increasing altitude using experimental reports up to 2650 meters above the sea level31 (masl) plus own experiments up to 3300 masl; (ii) available genetic diversity within local32 races; (iii) maize cropping systems based on literature and own data from 23 surveys; and33 (iv) possible avenues for improving yield. Among physiological traits, major penalties are34 associated with delayed phenology reducing light capture, and low temperatures inhibiting35 photosynthesis and kernel growth rate. As a result, yields can be reduced up to 85% at36 3300 masl compared with 2300 masl in contrast to increases at lower latitudes. Local races37 are characterized by a high genetic diversity that is aiming to be preserved by both in situ38 and ex situ conservation initiatives. However, little is known about phenotypic variation,39 impairing the exploitation of these genetic resources in breeding programs. Breeding40 strategies could consider tillering ability (to buffer stand heterogeneity) and41 photosynthetic recovery rates from chilling as important target traits, whereas plant42 density management could overcome penalties related with delayed plantings and43 phenology. Water availability is currently insufficient, especially at higher altitudes where44 most farmers rely on water from thaw, and climate change projections suggest this will45 worsen; thus improving water use efficiency also deserves further work.Fil: Salve, Diego Antonio. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación y Desarrollo Tecnológico para la Agricultura Familiar; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ferreyra, Mariana J.. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Salta-Jujuy. Estación Experimental Agropecuaria Salta; ArgentinaFil: Defacio, Raquel Alicia. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Norte. Estación Experimental Agropecuaria Pergamino; ArgentinaFil: Maydup, Maria Luján. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Lauff, Diana Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Tambussi, Eduardo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Antonietta, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; Argentin