Kinetic Modeling of Sunflower Grain Filling and Fatty Acid Biosynthesis

Grain growth and oil biosynthesis are complex processes that involve various enzymes placed in different sub-cellular compartments of the grain. In order to understand the mechanisms controlling grain weight and composition, we need mathematical models capable of simulating the dynamic behavior of the main components of the grain during the grain filling stage. In this paper, we present a non-structured mechanistic kinetic model developed for sunflower grains. The model was first calibrated for sunflower hybrid ACA855. The calibrated model was able to predict the theoretical amount of carbohydrate equivalents allocated to the grain, grain growth and the dynamics of the oil and non-oil fraction, while considering maintenance requirements and leaf senescence. Incorporating into the model the serial-parallel nature of fatty acid biosynthesis permitted a good representation of the kinetics of palmitic, stearic, oleic, and linoleic acids production. A sensitivity analysis showed that the relative influence of input parameters changed along grain development. Grain growth was mostly affected by the specific growth parameter (μ′) while fatty acid composition strongly depended on their own maximum specific rate parameters. The model was successfully applied to two additional hybrids (MG2 and DK3820). The proposed model can be the first building block toward the development of a more sophisticated model, capable of predicting the effects of environmental conditions on grain weight and composition, in a comprehensive and quantitative way.Fil: Durruty, Ignacio. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Departamento de Ingeniería Química. Grupo de Ingeniería Bioquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; ArgentinaFil: Aguirrezábal, Luis Adolfo Nazareno. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Balcarce; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; ArgentinaFil: Echarte, Maria Mercedes. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Balcarce; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentin

Post flowering assimilate availability regulates oil fatty acid composition in sunflower grains

Fatty acid composition of Helianthus annuus L. (sunflower) oil depends on intercepted solar radiation per plant (ISR) during grain filling. This effect could be accounted by the assimilate availability for the grains (the source-sink ratio). However, the current physiological-biochemical knowledge does not consider any effect of carbon availability on oil fatty acid composition. The objective of this work was to address the regulation of fatty acid composition by assimilate supply to sunflower grains. A wide range of source-sink ratios was obtained by manipulating either the source or the sink during grain filling. Assimilate supply was also modified by injecting sucrose to the receptacle of sunflower capitula. Grain weight and oil content depended on both ISR and source-sink ratio in a curvilinear manner. When sink size was decreased by grain excision, ISR failed to explain oil fatty acid composition while source-sink ratio appropriately described it. Sucrose injection significantly increased grain weight, oil content and oleic acid percentage of shaded plants. It is concluded that effects of ISR on fatty acid composition are a consequence of changes in assimilate availability for grain oil synthesis. To explain these results a conceptual model is proposed: when assimilate supply limits grain growth and oil synthesis, mainly linoleic acid is synthesized. As the assimilate supply increases, oleic acid desaturation process gets saturated and oleic acid accumulates.Fil: Echarte, Maria Mercedes. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; ArgentinaFil: Alberdi, Ignacio. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; ArgentinaFil: Aguirrezábal, Luis Adolfo Nazareno. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentin

Procesos asociativos e innovación para la solución de problemáticas energético ambientales: el caso de una pequeña comunidad rural en el sudoeste bonearense

Actualmente la resolución de problemáticas energético-ambientales ocupa un lugar cada vez más importante en el ámbito académico, en las agendas de los decisores de política públicas y en la comunidad en general. Sin embargo, a nivel institucional las vinculaciones entre sector científico académico, sociedad civil y gobierno local en torno a esta problemática son recientes y enfrenta desafíos tanto por los recursos humanos y materiales asignados, como por las capacidades, niveles de organización y gestión que demandan para que perduren en el tiempo. En este contexto, la demanda global de energía y los problemas ambientales derivados del uso de combustibles fósiles, visibilizan a la biomasa y los residuos orgánicos derivados de las actividades productivas como fuentes de generación de energía de carácter renovable, potencialmente sustentable y de relativamente bajo impacto ambiental. En este contexto la producción de biogás representa una tecnología clave para el uso sostenible de los recursos a la vez que presenta alta flexibilidad y puede ser adaptado a necesidades específicas a partir de los recursos disponibles a nivel local. El biogás puede ser una alternativa energética central en las pequeñas comunidades rurales de Argentina, ya que la matriz actual en las mismas es compleja y dependiente de áreas urbanas donde esta se centraliza. En particular, estas comunidades suelen contar con gran cantidad de recursos potencialmente transformables en bioenergía, derivados de actividades agrícola-ganaderas, aunque esta tecnología aún no se ha difundido como se podría esperar para mejorar las economías rurales, la calidad de vida y las condiciones medioambientales. Derivado de esta situación, en el año 2016 se comenzó la construcción de una experiencia articulada entre investigadores, docentes y funcionarios de nivel nacional, provincial y local. Estos decidieron llevar a cabo una experiencia conjunta con la población de la localidad de Los Pinos, municipio de Balcarce Buenos Aires, Argentina con el fin de construir una Unidad Demostrativa para la producción de Biogás (UDB).A partir del desarrollo de esta experiencia, el objetivo de este trabajo es analizar la trayectoria sociotécnica y la articulación de los actores (universidad, instituciones de I+D, municipio y comunidad rural) y artefactos para la construcción de (UDB) mediante la utilización residuos de la actividad agropecuaria.Fil: Iriarte, Liliana Beatriz. Universidad Nacional de Mar del Plata; ArgentinaFil: Carrozza, Tomás Javier. Universidad Nacional de Mar del Plata; ArgentinaFil: Echarte, Maria Mercedes. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; ArgentinaFil: Costa, Ana Maria. Universidad Nacional de Mar del Plata; Argentin

Bioprospecting for fast growing and biomass characterization of oleaginous microalgae from South-Eastern Buenos Aires, Argentina

As part of pioneering efforts to assess the potential of native microalgae as biofuel feedstock in South–Eastern Buenos Aires, 34 monoalgal cultures (corresponding to the Phylum Chlorophyta) were established and 21 were selected for further growth and biomass composition characterization. Novel RNA sequences in the ITS1-5.8S-ITS2 region were identified. Some strains showed desirable traits as biodiesel feedstock such as (i) apparent maximal doubling times of 6 h, (ii) lipids accumulation of up to 43% of their dry biomass, (iii) high ration of mono-unsaturated to poly-unsaturated fatty acids, (iv) high response to CO2 supplementation, and (v) complete sedimentation in 4 h. Data of the outdoors performance of some strains suggested they might represent valuable resources for future research towards the regional development of the technology for microalgae-based biofuels.Fil: Do Nascimento, Mauro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Biodiversidad y Biotecnología; ArgentinaFil: Ortiz Marquez, Juan César Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Biodiversidad y Biotecnología; ArgentinaFil: Sánchez Rizza, Lara. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Biodiversidad y Biotecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; ArgentinaFil: Echarte, Maria Mercedes. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; ArgentinaFil: Curatti, Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Biodiversidad y Biotecnología; Argentin

Exchange of microtubule molecular motors during melanosome transport in Xenopus laevis melanophores is triggered by collisions with intracellular obstacles

The observation that several cargoes move bidirectionally along microtubules in vivo raised the question regarding how molecular motors with opposed polarity coordinate during transport. In this work, we analyzed the switch of microtubule motors during the transport of melanosomes in Xenopus melanophores by registering trajectories of these organelles moving along microtubules using a fast and precise tracking method. We analyzed in detail the intervals of trajectories showing reversions in the original direction of transport and processive motion in the opposite direction for at least 250 nm. In most of the cases, the speed of the melanosome before the reversion slowly decreases with time approaching zero then, the organelle returns over the same path moving initially at a very high speed and slowing down with time. These results could be explained according to a model in which reversions are triggered by an elastic collision of the cargo with obstacles in the cytosol. This interaction generates a force opposed to the movement of the motor-driven organelle increasing the probability of detaching the active motors from the track. The model can explain reversions in melanosome trajectories as well as other characteristics of in vivo transport along microtubules observed by other authors. Our results suggest that the crowded cytoplasm plays a key role in regulating the coordination of microtubules-dependent motors. © 2008 Humana Press Inc.Fil: Bruno, Luciana. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Echarte, Maria Mercedes. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires; ArgentinaFil: Levi, Valeria. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin

Assessing the mechanisms underlying sunflower grain weight and oil content responses to temperature during grain filling

Temperature and solar radiation during grain filling are the main drivers of grain weight and composition in several crops. While significant progress has been done on the effect of solar radiation intercepted by the plants (ISR) on grain weight (GW, mg) and oil content (OC, mg grain−1) of sunflower (Helianthus Annus L.), the effects of temperature on these traits are far from clear. As temperature affects the rate of plant development, increasing temperature would shorten grain filling duration and so, the critical period for ISR effect on GW and OC (indirect effect of temperature). However, direct effects of temperature non-mediated by ISR accumulation could also affect these traits. The objectives of this work were a) to characterize the responses of grain weight and oil content to mean temperature during grain filling in two traditional sunflower hybrids and b) to determine whether these responses can be exclusively explained by changes in ISR or any direct effect of temperature should also be considered. Two experimental approaches have been used to address these objectives: i) temperature manipulation at constant incident radiation in growth chambers; ii) modification of radiation interception in the field in different locations and years (different mean temperatures). Growth chamber experiments showed that GW and OC respond to temperature in a plateau lineal shape. At low incident radiation such as that of growth chambers, temperature effects on GW can be exclusively explained by reductions in ISR, while both direct and indirect effects of MT are evident on OC. Results obtained in field experiments confirmed this behavior at low radiation. Both GW and OC exponentially increased up to a maximum with ISR disregarding MT. Mathematical models were established to describe the responses of GW and OC to MT and ISR. These models consider MT x ISR interactive effects on GW; and MT - ISR additive effects on OC. The combination of growth chamber and field experiments observations allowed to unravel different mechanisms underlying the responses of GW and OC to temperature: at low incident radiation intensity, increasing temperature decreased GW exclusively by reducing ISR accumulation (indirect effects) while at higher radiation, temperature displays both direct (non-mediated by ISR) and indirect (ISR mediated) effects on GW. OC is affected by temperature in both direct and indirect way disregarding ISR. This work constitutes an important contribution towards understanding the effect of temperature during grain filling on sunflower yield and its relationship to solar radiation effects.Fil: Angeloni, Patricia Norma. Universidad Nacional del Nordeste; ArgentinaFil: Aguirrezábal, Luis Adolfo Nazareno. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Innovación para la Producción Agropecuaria y el Desarrollo Sostenible - Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Balcarce. Instituto de Innovación para la Producción Agropecuaria y el Desarrollo Sostenible; ArgentinaFil: Echarte, Maria Mercedes. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Innovación para la Producción Agropecuaria y el Desarrollo Sostenible - Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Balcarce. Instituto de Innovación para la Producción Agropecuaria y el Desarrollo Sostenible; Argentin

Assessment of the critical period for the effect of intercepted solar radiation on sunflower oil fatty acid composition

The fatty acid composition of sunflower (Helianthus annuus L.) oil closely depends on the environmental conditions during grain filling. Temperature and solar radiation are the main environmental factors driving oil fatty acid composition. Minimum night temperature and intercepted solar radiation per plant (ISR) during grain filling independently affect oleic acid percentage of traditional sunflower oil. Critical period for temperature effect on this trait has been shown to be placed between 100 and 300ºC day after flowering (ºCd af). The period of maximal sensitivity of fatty acid composition to ISR remains unknown. The aim of the present work was to identify the time window of high sensitivity (critical period) of fatty acid composition to ISR of sunflower oil. For this, ISR was modified by shading (50 or 80%) or thinning (50%) field grown sunflower hybrid DK3820 during different periods of grain filling. The timing of maximal sensitivity of fatty acid composition to source variations at post flowering periods was explored and analyzed by two widely used approaches: i) evaluation of the relative oleic acid percentage under short shading treatments in relation to the control; ii) window-pane analysis of the response of oleic acid percentage to ISR. The first approach provided different critical periods depending on the level of radiation reduction. By the second approach, a developmental interval during which oleic acid was most sensitive to ISR regardless of the radiation level was determined. The critical period began at 350ºCd af and ended at 450ºCd af. Critical period of radiation effect on oleic acid concentration differed from radiation effect on grain weight and oil concentration and from the critical period of temperature effect on oil fatty acid composition. Different critical periods for different traits and specific environmental factors are indicative of the complexity of the interaction between environmental conditions and grain growth and oil synthesis dynamics.Fil: Echarte, Maria Mercedes. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires. Estación Experimental Agropecuaria Balcarce. Area de Investigación en Agronomía; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata; ArgentinaFil: Puntel, Laila Alejandra. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata; ArgentinaFil: Aguirrezábal, Luis Adolfo Nazareno. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias. Departamento de Producción Vegetal; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata; Argentin

Sunflower evapotranspiration and water use efficiency in response to plant density

This study quantified sunflower (Helianthus annuus L.) water use efficiency for seed (WUEg) and for oil yield (WUEo) and their components (i.e., evapotranspiration [ET], seed and oil yields) in response to plant density increments and studied, in particular, the underlying processes relevant to the responses of crop ET to plant density (i.e. water uptake pattern, intercepted photosynthetically active radiation [iPAR], and soil water depletion profile). Sunflower was grown at 3, 6, and 9 plants m−2 in Season 1 and at 2, 3 and 6 plants m−2 in Season 2. Measurements included (i) soil water content and iPAR during the whole growing season, and (ii) seed and oil yield at physiological maturity. Crop ET was estimated by means of a water balance, and it was analyzed during three different periods (i.e. vegetative, critical period for seed set, and seed filling period). Increasing sunflower plant density from 2 to 9 plants m−2 did not modify seasonal ET, but it changed the water uptake pattern through the season; it increased ET during the vegetative period by depleting more water from deep soil layers (i.e., 41–140 cm), but it reduced ET during the seed-filling period. Increments in plant density increased seed and oil yield in accordance with significant iPAR increments, whereas harvest index remained stable. Sunflower WUEg ranged from 4.8 to 9.4 kg ha−1 mm−1, WUEo ranged from 1.8 to 4.5 kg oil ha−1 mm−1 across plant densities, and they were positively and closely associated with seasonal iPAR.Fil: Echarte, Laura. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Balcarce; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; ArgentinaFil: Echarte, Maria Mercedes. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Balcarce; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; ArgentinaFil: Cerrudo, Diego. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; ArgentinaFil: Gonzalez, V. H.. No especifíca;Fil: Alfonso, C.. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; ArgentinaFil: Cambareri, M.. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; ArgentinaFil: Hernandez, M.. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; ArgentinaFil: Nagore, Maria Luján. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; ArgentinaFil: Della Maggiora, A.. No especifíca

Sunflower evapotranspiration and water use efficiency in response to plant density

This study quantified sunflower (Helianthus annuus L.) water use efficiency for seed (WUEg) and for oil yield (WUEo) and their components (i.e., evapotranspiration [ET], seed and oil yields) in response to plant density increments and studied, in particular, the underlying processes relevant to the responses of crop ET to plant density (i.e. water uptake pattern, intercepted photosynthetically active radiation [iPAR], and soil water depletion profile). Sunflower was grown at 3, 6, and 9 plants m−2 in Season 1 and at 2, 3 and 6 plants m−2 in Season 2. Measurements included (i) soil water content and iPAR during the whole growing season, and (ii) seed and oil yield at physiological maturity. Crop ET was estimated by means of a water balance, and it was analyzed during three different periods (i.e. vegetative, critical period for seed set, and seed filling period). Increasing sunflower plant density from 2 to 9 plants m−2 did not modify seasonal ET, but it changed the water uptake pattern through the season; it increased ET during the vegetative period by depleting more water from deep soil layers (i.e., 41–140 cm), but it reduced ET during the seed-filling period. Increments in plant density increased seed and oil yield in accordance with significant iPAR increments, whereas harvest index remained stable. Sunflower WUEg ranged from 4.8 to 9.4 kg ha−1 mm−1, WUEo ranged from 1.8 to 4.5 kg oil ha−1 mm−1 across plant densities, and they were positively and closely associated with seasonal iPAR.Fil: Echarte, Laura. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Balcarce; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; ArgentinaFil: Echarte, Maria Mercedes. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Balcarce; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; ArgentinaFil: Cerrudo, Diego. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; ArgentinaFil: Gonzalez, V. H.. No especifíca;Fil: Alfonso, C.. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; ArgentinaFil: Cambareri, M.. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; ArgentinaFil: Hernandez, M.. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; ArgentinaFil: Nagore, Maria Luján. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; ArgentinaFil: Della Maggiora, A.. No especifíca

Kernel number determination in argentinean maize hybrids released between 1965 and 1993.

Grain yield and the stability of harvest index are greater in newer than in older Argentinean maize (Zea mays L.) hybrids. The objective of this study was to elucidate mechanisms underlying the superior yield and harvest index stability of newer Argentinean maize hybrids using the relationship between kernel number per plant (KNP) and plant growth rate during the period bracketing silking (PGRs). Three experiments were performed at Balcarce, Argentina, during two growing seasons (1998–2000). Maize was grown under a wide range of plant densities (from 2 up to 30 plants m−2) to generate contrasting availability of resources per plant. Growth of individual plants during the period bracketing silking was estimated through a nondestructive method on the basis of relationships between actual shoot dry matter and morphometric variables, including stem and ear diameters and ear length. Detasseling and silk pollination synchronization treatments were imposed in one experiment to also modify available resources per kernel and kernel sink strength. Newer hybrids set more kernels per unit PGRs than older hybrids as is indicated by (i) the lower threshold PGRs for kernel set and (ii) greater potential kernel number at high availability of resources per plant, for newer than for older hybrids. At low and intermediate PGRs, the greater kernel set per unit PGRs in newer vs. older hybrids was attributable to greater partitioning of dry matter to the topmost ear during the period bracketing silking, whereas number of kernels set per unit of ear growth rate did not differ. In contrast, kernel set per unit of ear growth rate was greater in newer than in older hybrids when PGRs was high. Results of this study indicate that genetic yield improvement in maize is attributable, in part, to increased partitioning of dry matter to the ear during the critical period bracketing silking.Fil: Echarte, Maria Mercedes. Instituto Nacional de Tecnología Agropecuaria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Andrade, Fernando Héctor. Instituto Nacional de Tecnología Agropecuaria; ArgentinaFil: Vega, Claudia Rosa Cecilia. Universidad de Buenos Aires. Facultad de Agronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Tollenaar, M.. University of Guelph; Canad