Maturation of sunflower

Maturation of sunflowers was recorded in two field sowings at Armidale, New South Wales. Measurements were made to define anthesis, the accumulation of dry weight, oil and fatty acids in the achenes and to determine moisture contents and crop appearance associated with achene maturation. It is suggested that anthesis may be described either as its mid-point, i.e. when 50% of capitula exhibit anthesis over half their area, or by its spread, i.e. the time between 50% of capitula commenced anthesis and 50 %completed anthesis. Maximum achene dry weight was reached in the field when the achene moisture content was about 40 and the capitulum moisture content was about 70%. Both achene oil content and the content of the major polyunsaturated fatty acid (linoleic) reached their maxima at about the same time as achene dry weight in the field and this point was thus defined as 'physiological' maturity for sunflowers. It corresponded to when about ten per cent of capitula had turned brown. Production of linoleic and oleic acid was found to predominate in the later stages of achene maturation in both field sowings.