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Background and Aims The pericarp weight comprises Methods Two spring wheat cultivars contrasting in kernel weight (Bacanora and Kambara) were sown in field conditions during seasons 2012–13 and 2014–15. Both genotypes were grown under contrasting plant density (control, 370 plants m–2; and low plant density, 44 plants m–2) and night temperatures, i.e. at ambient and increased (>6 °C) temperature for short periods before and after anthesis. From anthesis onward, grains were harvested every 3 or 4 d. Grain samples were measured and the pericarp was removed with a scalpel. Whole grain and pericarp fresh and dry weight were weighed with a precision balance. At harvest, 20 grains from ten spikes were weighed and grain dimensions were measured. Key Results Fresh weight, dry matter and water content of pericarp dynamics showed a maximum between 110 and 235 °Cd. Maximum dry matter of the pericarp ranged between 4.3 and 5.7 mg, while water content achieved values of up to 12.5 mg. Maximum values and their timings were affected by the genotype, environmental condition and grain position. Final grain weight was closely associated with maximum dry matter and water content of the pericarp. Conclusions Maximum pericarp weight is a determinant of grain weight and size in wheat, which is earlier than other traits considered as key determinants of grain weight during grain filling. Better growing conditions increased maximum pericarp weight, while higher temperature negatively affected this trait.

Two experiments were carried out with three isogenic lines (standard height, semi-dwarf and double dwarf) of wheat under field conditions without water and nutritional stresses, with the objective of assessing the effects of Rht1 and Rht2 leaf alleles on leaf appearance and leaf blade area development. Possession of dwarfing genes did not affect phenological development, final number of leaves nor the rate of leaf appearance on the mainstem. The relationship between number of appeared leaves and thermal time could be described by a bi-linear model with an inflection point at the sixth-leaf stages independently of any particular ontogenic stage. Rht alleles caused significant reduction in the growth of leaves and stems, but did not affect internode diameter. Rht alleles were also associated with decreased individual leaf blade area, mainly through reductions in leaf blade length caused by reduced rates rather than durations of extension. The data presented confirm that Rht alleles affect internode growth more than leaf blade expansion; two hypotheses are discussed.

Several studies have analysed the effects of wheat breeding on dry matter accumulation and partitioning, but little has been done to understand the effects on nutrient economies. The objective of this study was to identify the changes produced by wheat breeding in the economy of nitrogen and phosphorus under field conditions. Two experiments were carried out with seven genotypes (including a commercial hybrid) representing different eras of plant breeding. Wheat breeding has increased grain nitrogen and phosphorus yield but total absorbed nutrients have not shown any trend during this century. The main attribute closely related to the increase in grain nitrogen and phosphorus yields was their harvest indices. The higher nutrient partitioning in the newer cultivars was associated with lower grain nitrogen and phosphorus concentrations in their grains. Therefore, there was a negative effect of genetic improvement in grain nitrogen and phosphorus concentrations. The main cause for the decreased concentration of these nutrients in the grains of the modern cultivars appeared to be a dilution by an even more increased dry matter partitioning. It is suggested that future breeding should be aimed to select for higher nitrogen uptake as a way to increase the level of this nutrient in grain.