Grain position affects grain macronutrient and micronutrient concentrations in wheat
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Little is known about nutrient distribution within the spike of bread wheat (Triticum aestivum L.). This knowledge is important for determining breeding strategies aimed at increasing grain yield without affecting nutritional quality. The objective of this study was to gain a better understanding of how grain position affects nutrient concentration, dry matter distribution, and water dynamics of grains. An experiment using two sowing dates was performed under field conditions. Dry weight and concentrations of macronutrients (Ca, Mg, K, P, and S) and micronutrients (Cu, Fe, Mn, and Zn) in grains from the basal (BS), central (CS), and apical spikelets (AS) of two cultivars and one synthetic hexaploid line were determined. Grain water dynamics and nutrient and dry matter concentrations were also measured throughout the grain-filling period for the second sowing date. Genotypes showed different distributions of dry matter in different grain positions. Grain macronutrient and micronutrient concentrations in all genotypes decreased at grain positions more distal from the rachis. This reduction was as great as 30% (Ca) but varied by nutrient (e.g., Zn = -18%; S = -10%; K = +1%). Grain water content did not differ between grains. The observed differences in grain weight and nutrient concentration between grain positions could have important implications for wheat breeding. They suggest that it might be more effective to select for higher grain yield by increasing individual grain weight rather than grain number, a strategy that, in addition, would be less likely to affect the balance of nutrient concentrations within the spike.
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