Search

Increasing wheat yield and grain quality is crucial for achieving profitable production systems. Genotype has an important role in determining potential grain end-use quality, because it defines the protein subunits stored in the endosperm. Nitrogen (N) and sulfur (S) availability modulate the expression of the genotype by determining variations in quantitative gluten composition. The aim of this work was to analyse the responses of grain quality to N and S fertilisation and relate them to the relative quantitative composition of different subunits of gliadins and glutenins in 24 Argentinean bread wheat cultivars differing in apparent S recovery (ASR), cycle length and protein pattern. Two field experiments were conducted in the Humid Pampas of Argentina. Gluten composition was analysed by electrophoresis and densitometry, and grain quality by N/S ratio, protein content, sedimentation test, and alveograms. Most genotypes presented high quality potential according to their pattern of high molecular weight glutenin subunits, although they differed in grain quality performance. Under an environment of low soil fertility (i.e. where the soil has a low capacity to supply N and S), N fertilisation reduced the sedimentation test values at low S level (67 vs 54 mm, on average) and increased this parameter at high S level (62 vs 81 mm, on average), with different responses among genotypes. Also, S fertilisation at high N level increased dough strength by 52% for long cycle genotypes and decreased it by 9% for those of short cycle. Genotypes with contrasting ASR, cycle length and protein pattern modified the responses of baking strength to S fertilisation in different ways (positive, neutral or negative), whereas genotype × N interaction modified the responses only in their magnitude. Outstanding genotypes (e.g. Klein Proteo) were identified according to baking quality stability. We conclude that S fertilisation had a notable effect on baking quality, especially in long cycle genotypes and a low soil-fertility environment, correcting S deficiency at high N availability. ASR was not a useful classificatory trait for predicting grain quality. Instead, the study of variants for the protein subunits coded by particular genes (e.g. Glu-A3, Glu-B3, Glu-D1x and Glu-D1y) that partially determine baking quality should be intensified, in order to optimise genetic improvement in wheat.

Wheat crop response to sulfur (S) depends on nitrogen (N) level, genotype and environmental conditions, demonstrating strong genotype×environment×nutrients interactions. The agronomic-use efficiency of both nutrients has not been evaluated in a wide range of modern genotypes differing in their cycle length and baking quality. The aim of this study was to analyse the effect of N and S fertilisation on yield components and use efficiency of both nutrients in 24 modern, high-yielding bread wheat genotypes (including long and short crop cycles) grown in contrasting environments in the Humid Pampa of Argentina. Two experiments were conducted under contrasting seasonal conditions on a Mollisol in Azul, Buenos Aires. Significant effects of N (range 15–200kgNha-1) on grain yield were observed in all genotypes. By contrast, responses to S (30–100kgSha-1) were found only at high N level in low soil-fertility environments, differing between long and short cycles. Genotype×fertilisation interaction was significant in the environment with higher soil fertility. Sulfur addition improved N-recovery efficiency (0.15 v. 0.32) and agronomic efficiency of the available N (84 v. 93gg-1) in the poor-fertility environment, characterised by their N and S deficiency and moderate level of organic matter. Grain N-recovery efficiency was largely explained by increases in grain number, whereas S recovery was also associated with increases in grain nutrient concentration. We conclude that genotype and environment strongly alter fertiliser-use efficiency, providing valuable information for ranking genotypes and optimising site-specific management of wheat crops in the Humid Pampa of Argentina. Grain S percentage may be useful as a physiological marker for selection of bread wheat genotypes with high apparent S recovery.

Improving wheat (Triticum aestivumL.) yield potential via higher grain number per unit area (GN) may reduce average grain weight and consequently the yield increment would be low. Thirty‐nine high‐yielding modern cultivars differing in spike fruiting efficiency (FE) (number of grains per gram of no‐grain spike) were grown under potential conditions during two temperature‐contrasting years to study the level of source limitation during grain filling and rank the main physiological determinants of potential grain weight (PGW) and actual grain weight. The response of grain weight to a 100% higher source ranged from 0 to 25%, depending on cultivar and year. No general relationship was observed between PGW and FE. The stabilized grain water content, which was partially correlated with the endosperm cell number per grain (r2= 48%, p< 0.05), was the main variable associated to grain weight variation (r2= 77%, p< 0.00001) in both temperate and warm years. Genetic improvement focused on increasing the sink strength through higher GN is still an alternative to increase yield potential in modern cultivars as no source limitation during grain filling was observed. The improvement of FE could be used to increase GN and yield as no general negative relationship was observed between PGW and FE.

It is well known that fatty acid biosynthesis in leaves is closely related to photosynthesis; although a residual synthesis is also detected at night. But less known is the effect of the day–night cycle in fatty acid biosynthesis in heterotrophic tissues such as developing seeds. Through the use of radioactive precursors, we detected variations in the metabolism of fatty acids and lipids during the day–night period in sunflower (Helianthus annuusL.) seeds. These oscillations have been observed both in the fatty acids bound to triacylglycerols and in polar lipids, indicating a fine regulation of the lipids biosynthetic activities in sunflower developing seeds. Additionally, in the triacylglycerol fraction, periodic variations were observed in the oleic and linoleic acids content as a consequence of qualitative variations in the biosynthetic machinery during the day–night period related to temperature changes. Analyzing the rate of oleic acid desaturation, we observed a significant increase in activity in the middle of the night, indicative of the importance of nocturnal desaturation. Similar variations were also observed in the stearoyl‐acyl carrier protein (ACP) desaturase activity. This study has shown the variation in the lipid biosynthetic capacity in sunflower developing seeds during the day–night cycle—including control over individual enzymes such as the stearoyl‐ACP desaturase—and the influence of diurnal and nocturnal temperatures in the quality (oleic/linoleic ratio) of the oil.