Cuticle and Cuticular Wax Development in the Sunflower (helianthus Annuus L.) Pericarp Grown at the Field under a Moderate Water Deficit

Wax in the sunflower (Helianthus annuus L.) pericarp is an important morphological feature that interferes with oil quality and varies with crop management and environmental conditions. We studied the effect of a moderate water deficit (MWD) generated from early to late anthesis on quantitative development of the cuticle, and qualitative and quantitative development of the cuticular waxes (CW) of the pericarp in two hybrids grown under field conditions. The experiment was repeated during two consecutive seasons (Exp-I and Exp-II). At harvest maturity (HM), plants grown under a MWD showed higher CW content (31 to 47%) and thicker cuticles (13%) in both experiments compared to controls. Epicuticular wax (ECW) crystals showed a granular morphology. Also a gradient of CW grain accumulation was observed along the pericarp surface, being higher in the exposed upper region. We determined a reduction of CW of 29% (mg CW/g pericarp), during the development of the fruit, from reproductive stage R6 (stage when ray flowers have lost their turgidity) to HM (stage when water content of the fruit was 11%) in Exp-I. This CW reduction reached 11% from R6 to R9 (physiological maturity) in Exp-II. This was very likely caused by an erosive action on the surface of the pericap by particulate solids carried by wind or rain. These results show how internal mechanisms and external variables regulate pericarp wax content, and that fruit dehydration affects both the quantity and quality of wax formation from the time of fertilization to maturity.