Epicuticular Wax in Developing Olives (Olea europaea) Is Highly Dependent upon Cultivar and Fruit Ripeness

Abstract

The epicuticular wax (EW) layer is located on the surface of most of plants organs. It provides the cuticle with most of its properties and is the primary barrier against biotic and abiotic stress. Despite the importance of Olea europaea cultivation, few studies have characterized the EW covering leaves and olives, which could be involved in resistance to both infection and environmental conditions. In the present study, wide-ranging screening was carried out using direct-injection electrospray ionisation coupled to high-resolution mass spectrometry to analyse EW in developing olives of nine varieties. The proportions of EW fractions (wax esters (WEs), diacylglycerols, triacylglycerols (TAGs), triterpenic acids and aldehydes) strongly depended on the olive cultivar, and in only a few cases were they influenced by the sampling date. The specific compositions of the major fractions, WEs and TAGs, were strictly related to the cultivar, while the degree of unsaturation and the chain length of the WEs evolved throughout the four weeks prior to the olive colour turning.