Relationship between oil tocopherol concentration and oil weight per grain in several crop species

The objectives of this work were (i) to analyse the effect of intercepted solar radiation (ISR) per plant during grain filling on oil tocopherol concentration in soybean, maize and rape and (ii) to investigate in these species if variations in oil tocopherol concentration are well accounted for by variations in oil weight per grain. Field experiments were conducted with genotypes of soybean, maize and rape. A genotype of sunflower was included as 'control species' as its behaviour was known from previous works. ISR was modified during grain filling by shading or thinning plants. Plants were harvested at physiological maturity and oil tocopherol concentration was determined by high performance liquid chromatography. Samples from other field or growth chamber experiments were also processed. In the four species, increasing radiation increased the oil and tocopherol weight per grain. Increasing ISR reduced oil tocopherol concentration in sunflower, soybean and rape but not in maize. The oil tocopherol concentration would be reduced by ISR in those species, with high oil contents in their grains, where the oil synthesis is more increased than tocopherol synthesis. The variations in oil tocopherol concentration were accounted for by variations in oil weight per grain only in those species with high and variable oil concentration.