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Wheat is a crop of vital importance for food security. In contrast to the accumulated knowledge for yield determination, the effect of variations in the source/sink (S/S) ratio on grain quality, and its interaction with the genotype and fertilization level, have received little attention. This work aimed to analyze the incidence of S/S ratio changes during post-flowering on grain weight and commercial quality in bread wheat genotypes with contrasting baking aptitude, as well as to evaluate its interaction with early nitrogen-sulfur fertilization. It is hypothesized that modern wheat genotypes bred for high-yield and contrasting baking aptitudes differ in their responses to variations in the availability of assimilates during post-flowering. Rainfed field trials were carried out in the Humid Pampas of Argentina during two years. Six wheat genotypes belonging to different quality groups were used, to which manipulative S/S treatments in post-flowering (shading, defoliation, thinning, trimming) and different levels of nitrogen-sulfur fertilization were applied. Regressions between S/S ratio (growth per grain) and grain variables (grain weight, protein content per grain, protein concentration, and test weight) were analyzed. Grain weight responses ranged from − 42% to + 31% relative to control compared to variations in S/S ratio from − 81% to + 56%, varying with the year and genotype. Relative changes of grain weight and S/S ratio were linearly associated, showing differences in stability (slope range: 0.29–0.80) among genotypes (the lower the slope, the greater the stability). Protein content per grain increased linearly with increases in the S/S relationship only for fertilized crops with N and S. As expected, protein concentration decreased when the S/S ratio increased, while test weight was the opposite. Importantly, responses varied among genotypes and fertilization levels, regardless of baking quality group. Grain weight to S/S ratio after flowering relationships differed between bread wheat genotypes, even within the same quality group, while protein content stability did not differ significantly. Therefore, for the conditions of this study in high-yielding environments in the Humid Pampas, the different protein concentration responses were due to genotypic differences in grain weight stability against variations in assimilates availability during grain filling. Nitrogen-sulfur fertilization early at the crop cycle did not modify the grain weight responses to variations in the S/S ratio, although it increased their influence on the commercial quality parameters. These findings are relevant to genetic improvement for high yield that can increase the co-limitation by source and sinks, and the occurrence of farm adversities that restrict the source capacity during post-flowering. • The impact of source/sink ratio on wheat grain weight and their quality were assessed. • Genotypes differed in their grain weight stability to source/sink ratio changes. • Test weight was more stable for genotypes with the best baking quality. • N-S fertilization increased responses of protein percentage and test weight to source/sink ratio. [ABSTRACT FROM AUTHOR]

Soil water constraints in La Pampa province, Argentina occur mainly during September each year, just when wheat (Triticum aestivum L.) is at the stage of stem elongation under field conditions. Overall, the yield response of such cereal crop to hydric stress has been studied at anthesis and grain filling stages. The aim of this work was to study the effect of low water availability at the beginning of stem elongation, on weight and protein concentration of wheat grain. The experiment was performed under controlled conditions with three wheat cultivars: Buck Malevo, ACA 315 and Baguette Premium 11. Hydric stress treatment was assessed by interruption of irrigation for a period of 15 days following to the beginning of stem elongation. As a result of irrigation withdrawal, leaf relative water content decreased and greenness index increased. Plants grown under water limitations showed a significant reduction in number of grains per spike, as well as a decrease in grain weight of 22% in Malevo Buck, 51% in ACA 315 and 37% in Baguette Premium 11. Besides, grain protein concentration was increased by 43% in ACA 315 and 17% in Baguette Premium 11, but was not significantly altered in Buck Malevo. Grain nitrogen content was reduced by 31% in ACA 315 and 26% in Baguette Premium 11, but did not vary significantly in Malevo Buck. These results suggest that, under soil hydric limitations at the start of stem elongation, the simultaneous occurrence of grain weight reduction and grain protein concentration increment depend on wheat genotype, with a response pattern being similar to that observed when water deficiency happens in a more advanced period of the crop cycle. [ABSTRACT FROM AUTHOR]

Abstract: The Argentinean Pampas are considered among the most productive areas of the world. However, few research has been done to explore its potential and constraining factors for wheat production. The objective of this paper was to evaluate variability of wheat yield and yield components potential in the Pampas. For this purpose, a modelling approach was used using 30 years climatic series of various locations distributed along the Pampas. Two biologically founded assumptions related to wheat yield determination were used: (1) potential grain number (GN) is associated with a photothermal quotient (PTQ); and (2) potential grain weight (GW) depends on mean temperature during the grain filling period (TGF). Mean wheat yield potential in the Pampas varied between 5000kgha−1 in northern locations to 7300kgha−1 in southern ones. GN showed greater variability than GW both, among locations (spatial scale) and years (temporal scale). Anthesis date appeared as a strong yield potential determinant factor; A 10-day delay in anthesis date produce substantial changes in GN and GW, depending on location latitude. This was related to the specific combination of crop phenological development and radiation and temperature changes in the region. A temporal decrease in PTQ during the period 1971–2002 was observed. This decrease was more associated with a radiation decrease than with a temperature increase during this period. TGF did not show any trend during the same period. The importance of estimating wheat yield potential yield and yield-gap reduction is discussed. [Copyright &y& Elsevier]

Temperature is one of the most important factors affecting grain quality in the majority of cereal growing areas. It has been shown that brief periods of high temperature during grain filling can reduce grain weight and quality. However, it is not known whether breeding for increased yields has altered the sensitivity to high temperatures after flowering. Four malting barley cultivars, chosen from previous studies to represent a series of successful breeding releases in Argentina, were sown under field conditions. The high temperature treatments consisted of increasing the spike temperature by about 5°C for 6 h/day (from 10 am to 4 pm) for 20 days starting nine days after flowering (DAF), or for two periods of 10 days each, between 9 to 19 DAF or from 20 to 29 DAF. In all cultivars, grain weight and screening percentages decreased significantly with the treatments. In general, the two more modern cultivars (Q. Pampa and Q. Ayelén) were more sensitive to heat stress than the older ones (Heda and Unión). A similar pattern was found for malt extract. Thus it appears that breeding for higher yields has concomitantly increased sensitivity of grain weight (and yield) and quality to the episodes of high temperatures during the grain-filling period in barley. [ABSTRACT FROM AUTHOR]