Sunflower fruit hullability and structure as affected by genotype, environment and canopy shading

Removal of the hull (pericarp) in sunflower (Helianthus annuus L.) reduces fibre and increases protein in seed meals. Thus, high hullability (H), the ease with which the pericarp is mechanically separated from the seed (kernel) is desirable. This study assessed how different hybrids, field environments and canopy shading modified fruit H, and how that was related to morphology, anatomical structure and chemical composition of pericarps in three high oil‐producing hybrids that share a common female parent (Monsanto®, Argentina): Contiflor 9 (Zeneca S.A.), Dekalb Dekasol (DK) 3900 and DK4030. DK4030 had higher H than Contiflor 9 and DK3900. This was mainly associated with a lower frequency of parenchyma radii, which was stable across environments (locality‐year) and among shading treatments. This showed that parenchyma radii were genetically determined and promising for breeding. Fruit volume was positively correlated with H only when the fruits had similar densities and the pericarps with comparable anatomical structures. Preanthesis shading reduced fruit volume, increased slightly the number of sclerified layers and cell wall thickness of the pericarp, but did not affect H. Postanthesis shading reduced the thickness and the amount of material deposited in the cell walls of the pericarp and, consequently, fruit H. In the shading experiments, H was positively correlated with fruit hull content and the number of sclerified cell layer and the thickness of the cell walls of the pericarp. The wide range of fruit variables analysed in the present study identified critical fruit traits that determine differences in fruit H in high oil‐producing hybrids, and how they are modified by the growing environment. Relation among physical, chemical and anatomical fruit variables and hullability in sunflower. H differences between hybrids were related to ray frequency which is promising for breeding. H correlated positively with fruit volume when fruit had similar pericarp anatomical structure. Preanthesis shading reduces fruit volume but not fruit hullability and pericarp sclerification. Postanthesis shading decreases pericarp cell wall thickness and fruit H but not fruit volume.