Maize Nitrogen Use Efficiency: QTL Mapping in a U.S. Dent x Argentine-Caribbean Flint RILs population

This study was aimed to identify quantitative trait loci (QTL) for nitrogen use efficiency(NUE) and related traits in a maize population derived from a cross between two lines with different genetic background (B100 and LP2). Recombinant inbred lines (181) from this population were evaluated under fieldconditions during two growing seasons, and significant(P < 0.01) phenotypic and genotypic variability was detected for most evaluated traits. Two different mapping methods were applied for detecting QTLs. Firstly, a trait by trait approach was performed on across environments, and 19 QTLs were identified.Secondly, a multi-trait multi-environment analysis detected seven joint QTLs. Almost all joint QTLs had inconsistent additive effects from one environment to another, which would reflectpresence of QTL × Environment interaction. Most joint QTLs co-localized with QTLs detected by indi-vidual mapping. We detected consistent additive effects for grain yield per plant and NUE, as well as for biomass and nitrogen harvest index in some joint QTLs, especially QTL-1 and QTL-6. These QTLs had positive and stable effects across environments, and presence of some genes within these QTL intervals could be relevant for selecting for both NUE and grain yield simultaneously. Up today, this is a firstreport on the co-localization of QTLs for enhan-ced allocation of biomass allocation to grains with NUE, and NUE candidate gene identificaion. Fine mapping of these regions could allow to detect additional markers more closely linked to these QTLs that could be used for marker assisted selection for NUE

Kernel weight in maize: genetic control of its physiological and compositional determinants in a dent × flint-caribbean RIL population

The genetic control of maize kernel weight (KW) determination could be studied through its physiological and/ or compositional determinants. Our objective was to dissect the genetic control of maize KW by analyzing its physiological (KGR: kernel growth rate; KFD: kernel filling duration) and compositional (protein, oil, starch) determinants in a dent×flint Caribbean RIL population, which combines a broad genetic background with grains of high added value for industry. An additional objective was to determine the stability of the genetic control under contrasting growing conditions, for which soil nitrogen offer was modified across experiments. Heritability (H2) values were high for KW (H2 = 0.74) and intermediate for the other traits (from 0.62 to 0.42). Kernel weight had a strong correlation with KFD (r = 0.69), KGR (r = 0.60) and protein concentration (r = 0.56). Ten joint QTL with inconsistent effects across years and seven epistatic interactions were detected. Despite changes in effect size, most QTL were significant under both environments. Nine QTL were associated with variations in potential KW (KW ), mean KW, KGR and oil concentration, eight with variations in protein and starch concentration and seven with KFD. Epistatic interactions were related to regions with significant main effects. The most important finding was the existence of a common QTL for KW , KGR and KFD on chromosome 5, for which there was no previous report. Results increased our knowledge on the genetic control of KW through its phenotypic and genetic correlation with KFD, confirming the need to explore different physiological strategies in different genetic backgrounds

Phenotypic plasticity for biomass partitioning in maize : genotype effects across a range of environments

El rendimiento en grano de maíz está determinado por el genotipo (G), el ambiente (E) y los efectos de la interacción G × E que influyen en la expresión de los rasgos a lo largo del ciclo del cultivo. Líneas endocriadas e híbridos pueden diferir en sus respuestas a las fluctuaciones ambientales, lo que determina cambios en los niveles de heterosis a través de los ambientes y, en consecuencia, en el ambiente objetivo para su evaluación. Los objetivos de este trabajo fueron (i) comparar rasgos relacionados con el rendimiento en grano, la producción de biomasa aérea y su partición en dos grupos genotípicos contrastantes (líneas e híbridos) y (ii) analizar su desempeño a través de ambientes para la evaluación de su plasticidad fenotípica, así como los efectos del ambiente sobre la expresión de la heterosis. Construimos un índice ambiental balanceado basado en el rendimiento en grano por planta normalizado (BEINPGY) de 14 ambientes contrastantes utilizando un diseño dialélico completo de 6 líneas endocriadas y analizamos la respuesta de los 12 rasgos evaluados a este índice para cada grupo genotípico. Este enfoque nos permitió (i) diferenciar entre rasgos con respuesta lineal (rendimiento de grano, biomasa total, número de granos, intervalo antesis-silking y eficiencia reproductiva de la planta), bilineal (índice de cosecha, peso individual del grano, prolificidad y eficiencia reproductiva de la espiga apical) o sin respuesta (tasas de crecimiento de la espiga y de la planta alrededor de floración, así como su relación) en la plasticidad fenotípica de cada grupo al BEINPGY , y (ii) agrupar rasgos de acuerdo a la respuesta de su heterosis absoluta (es decir, plasticidad de la heterosis) al BEINPGY, la cual varió en signo (positivo, nulo o negativo) según el rasgo. Hubo una relación clara y positiva entre la plasticidad de la heterosis absoluta y la plasticidad de los rasgos, que estuvo determinada principalmente por los híbridos. Los grupos genotípicos difirieron en los patrones de asociación de los valores de los rasgos per se, así como en sus plasticidades fenotípicas, indicativo de las diferentes bases genéticas que los determinan. El hecho de que el porcentaje de heterosis para el rendimiento en grano y otros rasgos secundarios relevantes no varió a través de los ambientes, mientras que se espera que la heredabilidad disminuya en condiciones de estrés, podría contribuir a orientar esfuerzos futuros del mejoramiento con el objetivo de desarrollar híbridos superiores con un desempeño exitoso, particularmente en los desafiantes escenarios ambientales futuros.Maize grain yield is determined by genotype (G), environment (E) and G × E interaction effects that influence the expression of traits along the crop cycle. Inbreds and hybrids may differ in their responses to fluctuations in environmental conditions, determining changes in heterosis levels across environments and consequently the target environment for their evaluation. The objectives of this work were (i) to compare traits related to grain yield, aboveground biomass production and its partitioning in two contrasting genotypic groups (inbreds and hybrids) and (ii) to analyze their performance across environments for the assessment of their phenotypic plasticity as well as environmental effects on the expression of heterosis. We built a balanced environmental index based on normalized plant grain yield (BEINPGY) from 14 contrasting environments using a 6-inbred complete diallel mating design and analyzed the response of the 12 evaluated traits to this index for each genotypic group. This approach allowed us to (i) differentiate among traits with simple linear (grain yield, total biomass, kernel numbers, the anthesis-silking interval and plant reproductive efficiency), bilinear (harvest index, individual kernel weight, prolificacy and apical ear reproductive efficiency) or no response (ear and plant growth rates around flowering as well as their relationship) in phenotypic plasticity of each group to the BEINPGY, and (ii) group traits depending upon their absolute heterosis response (i.e., heterosis plasticity) to the BEINPGY, which varied in sign (positive, null or negative) depending upon the trait. There was a clear and positive relationship between absolute heterosis plasticity and traits plasticities, which was mainly driven by hybrids. Genotypic groups differed in the association patterns of traits values per se as well as of their phenotypic plasticities, indicative of the different genetic bases that determine them. The fact that percent heterosis for grain yield and other relevant secondary traits did not vary across environments, whereas heritability is expected to decrease under stressful conditions, may contribute to guide future breeding efforts aiming to develop superior hybrids with successful performance, particularly in future challenging environmental scenarios.EEA PergaminoFil: Galizia, Luciana A. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Pergamino. Departamento de Ecofisiología; Argentina. Universidad de Buenos Aires. Facultad de Agronomía; Argentina.Fil: Munaro, Eugenia M. AgriScience; Estados UnidosFil: Cirilo; Alfredo Gabriel. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Pergamino. Departamento de Ecofisiología; ArgentinaFil: Otegui, María Elena. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Pergamino. Ecofisiología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Agronomía; ArgentinaFil: D'Andrea, Karina Elizabeth. Universidad de Buenos Aires. Facultad de Agronomía; Argentina. Consejo Nacional de investigaciones Científicas y Técnicas; Argentin