CONICET | Buscador de Institutos y Recursos Humanos

It has been suggested that the maximum volume of grain could determine its potential dry weight, and that grain water content can be used as a surrogate of grain volume, but this issue has not been investigated in sunflower. The aim of this work was to examine the relationships between final achene weight and the dynamics of achene volume and achene, pericarp and embryo water contents. Seven experiments were conducted between 2002-6 in Argentina, testing a total of 10 sunflower genotypes. Achenes were collected every 2-3 days, and the fresh and dry weights of the achene, pericarp and embryo, achene dimensions (length, breadth, width) and volume were determined. The pericarp played a dominant role in achene water content throughout grain filling. Maximum achene and pericarp water contents were reached early in development, and these maxima were good predictors of final achene and embryo dry weights across genotypes. Achene water content and volume showed parallel increases between anthesis and peak achene water content, but achene volume and dimensions continued to increase for a few days after the time of peak achene water content. We have concluded that the relationship between final achene dry weight and peak values for achene water content is not causal, and that the strong correlation between these variables arises because of the correlation between achene water content and volume during the phase where both variables increase together and the fact that, at the time of peak achene water content, the achene has reached close to 90% of its final volume. Key words: sunflower- achene size- water content- pericarp- achene dimensions.