En Argentina, la normativa vigente establece cuatro años de evaluación de rendimiento para cualquier nuevo cultivar comercial de trigo pan. El objetivo de este trabajo fue determinar la cantidad óptima de años de evaluación en ensayos comparativos de rendimiento de cultivares de trigo pan, condicionando dicho óptimo al grupo de calidad, ciclo de crecimiento y manejo fitosanitario. Se estimaron componentes de varianza (REML) con los datos de la Red de evaluación de cultivares de trigo pan de Argentina (RET), correspondientes a diez sitios experimentales. Se consideraron los tres grupos de calidad (GC1, GC2 y GC3), la primera y tercera época de siembra (E1 y E3), y manejo con y sin fungicida (CF y SF). Los resultados muestran que se requieren tres años de ensayos para evaluar el rendimiento de los diferentes grupos de calidad y ciclos de crecimiento manejados CF. Para el SF, se requieren cuatro años, excepto para GC1 en E3 y GC2 en E1, que demandan tres y más de cinco años, respectivamente. Estos resultados indican que la norma actual es apropiada para la mayoría de los casos; incluso, podría reducirse a tres CF, para mejorar la calidad de los ensayos y aumentar el número de repeticiones.

The thickness of wheat (Triticum aestivum L.) glumes and lemmas (T-GL) influences their thermal insulation properties, which in turn, may influence reproductive frost susceptibility. The objectives of this study were to (i) determine the variability in T-GL in bread wheat cultivars, (ii) quantify the frost susceptibility of cultivars with different T-GL under field conditions and natural frosts, and (iii) find out, based on the estimation of the heat transfer through the glume + lemma, if differences in frost susceptibility are associated with differences in T-GL. T-GL was evaluated in 11 long-cycle and 11 short-cycle cultivars and frost susceptibility in five cultivars with contrasting T-GL was also determined. Additionally, the thermal properties of the glumes and lemmas were measured and the heat transfer through them was estimated. Significant and consistent differences in T-GL were measured among cultivars. It was estimated that as T-GL increased the inner side of the lemma would cool more slowly. However, differences in frost susceptibility of cultivars were not associated with variation in T-GL. The research also showed that frost susceptibility does differ among Argentine cultivars. Further work is needed to confirm and understand the physiological basis of the variation in frost susceptibility of wheat.

A partir del año 2000 la tasa de aumento de rendimiento (RTO) de trigo pan en Argentina alcanzó 46.0 kg ha-1 año-1, mientras que el norte de Santa Fe mantuvo la misma tasa desde los años 1970. Para indagar el origen de la diferencia, se analizó si en las dos últimas décadas hubo algún cambio climático relevante, cuál fue la brecha tecnológica departamental, y cuál fue el aporte del mejoramiento genético al cultivo. Los datos de la estación meteorológica de INTA Reconquista mostraron que el aumento del déficit de presión de vapor ponderado (DPVP) promediado desde 20 d antes a 10 d después del 1-sep. (fecha óptima de espigazón), fue la variable de cambio climático más desfavorable, entre la serie de años recientes (2000-2018) y previos (1971-1999). Se estimó que al aumento del DPVP correspondería una caída de 16% en el RTO cuando el nivel de estrés hídrico fue 45%; por lo cual, los cambios climáticos implicarían una reducción del 51% en la tasa de aumento de RTO entre el norte de Santa Fe. Se encontró que la brecha entre el RTO promedio de la RET-INASE de INTA Reconquista y el promedio departamental fue 66% y que la brecha respecto de los cultivares de mayor RTO fue 125%. El avance genético se analizó comparando el RTO los cultivares evaluados en la RET con el RTO de cultivares testigos. No se encontró evidencia de avance genético continuo en los últimos 10-13 años. Un mayor avance genético podría impulsar la difusión del cultivo para superar el 22% de la superficie agrícola del norte de Santa Fe que ocupa actualmente.

Lodging is the permanent displacement of plant shoots from an upright position and represents a major obstacle to reaching yield potential in bread wheat (Triticum aestivum L.). Breeding programs would benefit from the identification of lodging-related traits amenable to easy and rapid screening, even in the absence of lodging. However, no locally tested lodging model is available for the Pampas region of Argentina, and most lodging models are based on measurements before crop maturity. We adapted two existing models and generated a new one, using easily measurable traits at crop maturity in 24 cultivars (14 for model fit and 10 for model validation) grown in plot trials with no nutritional, water or disease restrictions in three crop seasons at Balcarce, Argentina. Of 17 traits evaluated, 16 showed differences between cultivars (P<0.05), and in 11 of these traits, no genotype×environment interaction was detected (P>0.05). Estimations of the safety factor against stem lodging, proposed by Crook et al., and the wind velocity that produces lodging, proposed by Berry et al., showed a high correlation with lodging score (R2=0.60 and 0.72, respectively), but when the estimators were tested with another set of cultivars there was no association. A new empirical regression model was based on three traits measured at maturity: plant height, spike dry weight, and the inertia moment of the stem base (stem resistance to bending estimated from stem diameter and wall thickness). The model was then simplified by replacing the third trait with basal stem diameter, and it showed an even better fit (R2=0.90). These models were satisfactorily validated by rank correlations with a different cultivar set. The regression model proposed in this study can easily be applied to the evaluation of commercial cultivars and may be used to screen breeding materials. Measurements at maturity are convenient and easy to combine with other traits of possible selective advantage.

Frosts may damage wheat (Triticum aestivum L.) spikes and severely reduce their yield. The objective of this study was (i) to quantify the level of susceptibility to frost at different spike developmental stages, and (ii) to develop a theoretical-empirical model to estimate successive frosts damage on grain number (GN) at different spike and crop developmental stages based on the meteorological characteristics of the event. Three experiments were performed under field conditions at Balcarce (Argentina), using Klein Roble and Floripan 100 spring cultivars, sown on seven dates, The proportion of aborted grains in spikes was evaluated at different spike developmental stages, from stem elongation to the beginning of grain filling, with all spikes receiving the same natural frosts. The higher the frost severity (defined as the number of hours with temperatures < -1.5 degrees C and the minimum temperature reached), the higher the damage on GN (28 to 88%, depending on the experiment). The duration of the period in which maximum damage on GN was registered was variable, but it always included anthesis. Based on collected data, a theoretical-empirical model to estimate successive frosts damage on GN at different spike or crop developmental stages was proposed and validated. This study provides a detailed quantification of the damage caused by natural frosts under field conditions and it allows to achieve a better estimation of frost effect on crop.

BACKGROUND:Increasing wheat (Triticum aestivum L.) production is required to feed a growing human population. In order to accomplish this task a deeper understanding of the genetic structure of cultivated wheats and the detection of genomic regions significantly associated with the regulation of important agronomic traits are necessary steps. To better understand the genetic basis and relationships of adaptation and yield related traits, we used a collection of 102 Argentinean hexaploid wheat cultivars genotyped with the 35k SNPs array, grown from two to six years in three different locations. Based on SNPs data and gene-related molecular markers, we performed a haplotype block characterization of the germplasm and a genome-wide association study (GWAS).RESULTS:The genetic structure of the collection revealed four subpopulations, reflecting the origin of the germplasm used by the main breeding programs in Argentina. The haplotype block characterization showed 1268 blocks of different sizes spread along the genome, including highly conserved regions like the 1BS chromosome arm where the 1BL/1RS wheat/rye translocation is located. Based on GWAS we identified ninety-seven chromosome regions associated with heading date, plant height, thousand grain weight, grain number per spike and fruiting efficiency at harvest (FEh). In particular FEh stands out as a promising trait to raise yield potential in Argentinean wheats; we detected fifteen haplotypes/markers associated with increased FEh values, eleven of which showed significant effects in all three evaluated locations. In the case of adaptation, the Ppd-D1 gene is consolidated as the main determinant of the life cycle of Argentinean wheat cultivars.CONCLUSION:This work reveals the genetic structure of the Argentinean hexaploid wheat germplasm using a wide set of molecular markers anchored to the Ref Seq v1.0. Additionally GWAS detects chromosomal regions (haplotypes) associated with important yield and adaptation components that will allow improvement of these traits through marker-assisted selection.

It has been demonstrated that soybean (Glycine max) produces lower yields at relay intercropping with wheat (Triticum aestivum) than if it is sown as a sole crop. However, most studies considered wider or irregular soybean row spacing, compromising its capacity to recover after wheat harvest. This work studied the stress effects in relay soybean intercropping and suggests narrowing row spacing to improve soybean performance. The aims were (i) to compare growth and yield of two planting patterns and (ii) to separate the effect of water stress (WS) from the effects of other stress factors (OSF) induced by wheat on intercropping soybean. WS was evaluated comparing above-ground dry and grain yield of irrigated and non irrigated intercropping soybean, and OSF was evaluated comparing intercropping soybean with another treatment in which wheat straw (aerial biomass) was eliminated at soybean emergence, both irrigated treatments. In wheat, similar yields were obtained in treatments with an intercropping planting pattern with two rows for wheat and one for soybean (2:1) compared to three rows for wheat and one row for soybean (3:1). However, intercropping soybean at narrow row spacing (52 cm; 2:1) improve yielded 23% more than intercropping at 70 cm (3:1). During wheat-soybean coexistence, OSF prevailed on soybean and this effect persisted in later stages. After wheat harvest, OSF reduced the amount of light interception from R1 to R5 and depressed the crop growth rate (CGR) in 34%. However, in this period, WS also affected the radiation use efficiencies (RUE) which explained the greater fraction (66%) of the total stress induced by wheat in soybean CGR. Intercrop soybean yielded 182 g m-2 less compared to the unstressed sole crop control. Considering the wheat effects on soybean growth, 63% (116.5 g m-2) of the total yield lost were due to WS. Therefore, most of the performance of relay intercropping soybean was linked with water disponibility since early stages. However, at optimum water condition wheat competition by light and resources also affected soybean yield (OSF: 37%).

Increasing grain yield is a key breeding goal in bread wheat. Several authors have suggested that a spike fertility index (SF), that is the quotient between grain number per unit spike (GNS) and spike chaff dry weight (SCDW), could be used as a yield-related selection criterion, especially if molecular markers were available. Here, the effects of Ppd-B1 and Ppd-D1 genes on SFm, GNSm and SCDWm (measured at maturity) and the relationship between these variables were analysed in field experiments carried out during three crop seasons at Balcarce, Argentina, on an association mapping population of 100 bread wheat cultivars of diverse origin released in Argentina between 1927 and 2010. Results show that both Ppd-B1 and Ppd-D1 are associated with SFm with similar effects. Cultivars with insensitive alleles at both genes showed a mean SFm 9.2% greater than those with sensitive alleles at both genes; at each gene, difference in SFm between insensitive and sensitive alleles was similar to 4.5%. In turn, each gene showed a differential effect on GNSm and SCDWm, as Ppd-B1 was more related to SCDWm, whereas Ppd-D1 was only related to GNSm. Although more research needs to be carried out in order to ascertain the physiological pathway by which these genes affect spike fertility, this study represents a first approximation in order to elucidate the molecular and genetic basis underlying SF and related physiological traits.

Grain yield in wheat is generally considered to be sink-limited during grain filling. But is this limitation inherent to the crop species or a consequence of the breeding process? A way to ascertain this is by using genetic materials not subject to selection. Grain yield could be analyzed as the product between: (i) grain number per unit area, (ii) the potential grain weight (i.e. weight per grain obtained without source limitation); and (iii) the degree of sink limitation (DSL). The product of the first two components defines the crop sink capacity (SICA), and the DSL could be assessed as the quotient between weight per grain and its potential weight. Such an analysis was carried out in a RIL population derived from the cross between Baguette 10 and Klein Chaja (Argentinean cultivars with contrasting grain number). Three field experiments were conducted at Balcarce, Argentina during the 2013, 2014 and 2015 crop seasons, under non-limiting conditions; 146 recombinant inbred lines (RILs), the parental cultivars and other commercial cultivars were evaluated. At maturity, grain yield and grain weight were determined. The potential grain weight was obtained by thinning rows at the beginning of grain filling. Grain number m(-2) was calculated as grain yield/grain weight. Grain yield was highly associated with SICA; the slope of the relationship between grain yield and SICA was lower than the expected 1:1 ratio above similar to 8 tons ha(-1), indicating that the source for grain filling becomes a limiting factor when SICA increases, particularly in the RILs. This suggests that much of the sink limitation observed in modern wheat cultivars may be the result of genetic improvement.

SUMMARYGrain yield in bread wheat is often tightly associated with grain number/m2. In turn, spike fertility (SF), i.e., the quotient between grain number and spike chaff dry weight, accounts for a great proportion of the variation in grain number among cultivars. In order to examine the potential use of SF as a breeding target, (1) variation for the trait was assessed in six datasets combining commercial cultivars under different environmental conditions, (2) trait heritability was estimated in a set ofF1hybrids derived from controlled crosses between cultivars with contrasting SF and (3) SF distribution pattern was analysed in twoF2segregating populations. Analysis of commercial cultivars revealed considerable variation for SF, under both optimal and sub-optimal conditions. In addition, genotypic variation was consistently larger than genotype × environment interaction variation in all datasets. Narrow sense heritability, estimated by the mid-parent-offspring regression of 20F1hybrids and their respective parents, was 0·63. Data from twoF2populations exhibited bell-shaped and symmetric frequency distributions of SF, with a SF mean intermediate between the parental values. Substantial transgressive segregation was detected in bothF2populations. In conclusion, SF appears to be a heritable trait with predominantly additive effects. This warrants further investigation on the feasibility of using SF as an early selection criterion in wheat breeding programs aimed at increasing grain yield.

The yield potential of a crop can be defined as its expected yield, in an adapted environment with nutrients or water non-limiting, and under full control of any kind of adversity or stress. Rapeseed winter cultivars usually out-yield the spring types; that is why introgression of winter germplasm into spring hybrids has achieved an increase in the yield of the latter. In our region there have been yield differences between winter and spring cultivars; however it seems unclear whether these are actually due to differences in their yield potential. The objective of this paper was to assess 4 rapeseed cultivars, 2 winter types and 2 spring types, under non-limiting conditions, to verify their yield differences.

In wheat, grain number is considered as the product of spike dry weight (SDW) and the number of grains per unit of SDW, that is an indicator of spike fertility (SF). The aim of this study was to determine the heritability of SF and the effect of early selection for high SF on its relationship with other spike yield components. Two field experiments were conducted in the south-eastern Pampas (Argentina) with 400 F-2 and F-2:3 families obtained from two crosses between varieties with contrasting SF (PIG/SSN and B10/KCJ). Heritability estimates in PIG/SSN and B10/KCJ were, respectively, 0.60 and 0.51 by variance component analysis, 0.43 and 0.43 by F-2 : F-3 parent-offspring regression and 0.30 and 0.28 by realized heritability analysis. The existence of transgressive segregation (i.e. the occurrence of families with SF values that were more extreme than those of the parents) was observed. The top 25% F-3 families with the highest SF had 12% more grains per spike, despite a 13% and 5% decrease in SDW per spike and weight per grain, respectively, than the remaining families. These results give support to the application of early selection for high SF.

Es sabido que la soja intersembrada en trigo tiene bajo crecimiento inicial, lo cual podría afectar negativamente la formación de nódulos fijadores de nitrógeno (N) y limitar el crecimiento de la soja luego de la cosecha del trigo. En este trabajo se propuso: (i) corroborar si soja intersembrada en trigo tiene respuesta a la fertilización nitrogenada y (ii) evaluar la dosis de N óptima de una soja intersembrada. Se condujeron dos experimentos de soja intersembrada en trigo bajo riego en Balcarce, con tratamientos de niveles de fertilización nitrogenada. En el primer año los niveles de fertilización fueron cero y una dosis equivalente a los requerimientos de N del cultivo (530 kg N ha-1). En el segundo año se evaluaron cuatro niveles de fertilización calculados como una proporción de la dosis de indiferencia (204 kg N ha-1): 0, 51, 102 y 204 kg N ha-1. A la madurez del cultivo de soja, se midió rendimiento, índice de cosecha, peso/grano, peso seco total y número de granos m-2. Los resultados obtenidos muestran que existieron respuestas significativas de la soja a la fertilización nitrogenada. Bajas dosis de N (equivalentes a 1/4 de la dosis de indiferencia) fueron suficientes para maximizar el rendimiento. Ambos experimentos confirman que el aumento de rendimiento a causa del N aplicado generó un incremento en el aporte de biomasa al sistema.

Wheat grain protein content (GPC) is important for human nutrition and has a strong influence on the quality of pasta and bread. The objective of this study was to analyse the introduction of the Gpc-B1 allele into two Argentinean bread wheat cultivars. Near-isogenic lines were developed in ProINTA Oasis and ProINTA Granar using marker-assisted selection. Gpc-B1 lines showed a significant (P = 0.01) increase in GPC and a significant (P = 0.001) decrease in grain weight in comparison with control lines without Gpc-B1. Differences in yield were not significant (P = 0.49) between lines. Gpc-B1 lines significantly reduced (P = 0.02) straw nitrogen concentration at maturity and significantly increased (P = 0.02) the nitrogen harvest index. When data were analysed by genotype and environment, differences in some analysed parameters were found, indicating that Gpc-B1 expression may be affected by different genetic backgrounds and environmental conditions. These results suggest that the introgression of the Gpc-B1 allele into Argentinean wheat germplasm could be a valuable resource for improving GPC with no detrimental effect on grain yield.

El fósforo (P) es uno de los macronutrientes menos disponible en el suelo. Se predijo para los próximos años un incremento en el uso de fertilizantes fosforados debido al crecimiento de la demanda de alimentos. Una de las prácticas que puede contribuir a un uso más sustentable de los fertilizantes fosforados es la selección de cultivares con baja concentración de P en los granos. Para saber si existen diferencias en la concentración de P en los cultivares de trigo utilizados actualmente en la Argentina, se compararon 66 cultivares durante las campañas 2008/09 y 2009/10, en Balcarce. Hubo diferencias entre cultivares en la concentración de P, el rendimiento y la exportación de P (los rangos fueron 0,22 - 0,38%; 5170 - 9740 kg/ha y 13 - 29 kg P/ha, para concentración de P en grano, rendimiento y P exportado respectivamente). Para el productor las implicancias económicas de utilizar cultivares con menor concentración de P no resultan relevantes, ya que sólo representan diferencias en el costo menores al 2% del rendimiento. Sin embargo, a largo plazo y en el país, estas diferencias cobran una dimensión considerable.Phosphorus (P) is one of the least available macronutrients in soil and a rise in the use of phosphate fertilizers was predicted due to the growing food demand. A practice that can contribute to a more efficient use of P fertilizers and reduce soil P extraction is the selection of cultivars with low concentration of P in grains. In order to find out if there are differences in P concentration in wheat cultivars that are currently used in Argentina, 66 cultivars, grouped in two sowing dates, during 2008/09 and 2009/10, were compared in Balcarce, under potential conditions. There were differences between cultivars in P concentration, P exportation and yield (ranges were: 0.22 - 0.38%; 5170 - 9740 kg/ha and 13 - 29 kg P/ha) for P concentration in grains, yield and P export, respectively). However, when considering the economic implications for farmers of using cultivars with lower P concentration, these differences between cultivars were not relevant, since the differences in cost were less than 2% yield, while at long-term and for country (Argentina), these differences have another dimension.

SUMMARYWheat grain yield is often associated with grain number/m2. Spike fertility (SF), i.e. the quotient between grain number and spike chaff dry weight, is a major component of grain number/m2determination. Several methodologies have been proposed in the literature for field determination of SF, but they are tedious and expensive. Also, no comparison between methodologies has been done. The feasibility of using wheat SF as a selection criterion in a breeding programme or as a variable of interest in crop physiology studies depends largely upon the availability of a simpler and faster method for collecting and processing samples. Thus, the objective of the present study was to determine: (1) the association between SF calculated with the non-grain spike dry weight at anthesis (reference method) or at crop maturity, (2) the association between SF evaluated at the plot level (i.e. both non-grain spike dry weight and grain number determined as per area unit) and at the individual spike level and (3) the minimum number of individual spikes that should be sampled for the development of a screening method that can be applied in wheat breeding programmes or in crop physiology studies. Associations between variables were determined by correlation analysis of treatment means, and by a test of agreement for categorical rating (low, medium and high SF) between individual data of each variable. Four experiments (BY95, BC96, BC97 and ML07) were performed with five, ten, eight and eight wheat cultivars, respectively, under no environmental limitations, except for experiment ML07 which was not irrigated. In the first three experiments, SF was determined both at the beginning of grain filling and at maturity, in plot-size samples (0·8 m2/plot). In experiments BC96 and BC97, SF was determined both in plot-size samples and in individual spikes (five spikes per plot), at the beginning of grain filling. In experiment ML07, increasing numbers of individual spikes were sampled at maturity to assess SF. As a result: (1) a significant association (R2=0·78;P<0·001;d.f.=20) was detected between SF determined at the beginning of grain filling and at maturity, and the test of agreement for categorical rating showed that the classification of data into categories of SF was equivalent between methods (P>0·05); (2) when comparing SF determined in large plot-size samplesv.in small samples of individual spikes, a good adjustment (R2=0·77;P<0·001;d.f.=6) was also observed, with no significant cultivar×experiment interaction and a good agreement between methods in the classification of data into categories of SF (P>0·05); and (3) increasing sample size from 5 to 40 spikes gradually decreased the average relative standard error of the mean (from 0·034 to 0·012, respectively). In conclusion, wheat SF can be determined in a fairly accurate way by sampling a small group of individual spikes at crop maturity, thereby allowing the evaluation of a large number of treatments in a timely fashion and the screening of breeding material from early generations.

El fósforo (P) es uno de los macronutrientes menos disponible en el suelo. Se predijo para los próximos años un incremento en el uso de fertilizantes fosforados debido al crecimiento de la demanda de alimentos. Una de las prácticas que puede contribuir a un uso más sustentable de los fertilizantes fosforados es la selección de cultivares con baja concentración de P en los granos. Para saber si existen diferencias en la concentración de P en los cultivares de trigo utilizados actualmente en la Argentina, se compararon 66 cultivares durante las campañas 2008/09 y 2009/10, en Balcarce. Hubo diferencias entre cultivares en la concentración de P, el rendimiento y la exportación de P (los rangos fueron 0,22 - 0,38%; 5170 - 9740 kg/ha y 13 - 29 kg P/ha, para concentración de P en grano, rendimiento y P exportado respectivamente). Para el productor las implicancias económicas de utilizar cultivares con menor concentración de P no resultan relevantes, ya que sólo representan diferencias en el costo menores al 2% del rendimiento. Sin embargo, a largo plazo y en el país, estas diferencias cobran una dimensión considerable.