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 plant 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 ionization coupled to high-resolution mass spectrometry to analyze EW in developing olives of nine varieties. The proportions of EW fractions [wax esters (WEs), diacylglycerols, triacylglycerols (TAGs), triterpenic acids, and aldehydes] strongly depended upon the olive cultivar and, in only a few cases, were 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 chain length of the WEs evolved throughout the 4 weeks prior to the olive turning color.

Chemical Composition and Crystal Morphology of Epicuticular Wax in Mature Fruits of 35 Pear (Pyrus spp.) Cultivars

“…It is noteworthy that 1-monopalmitin and 1-monostearin were the only two glycerides compounds simultaneously detected in all 35 pear cultivars in this study (Supplementary Table S1 ). Glycerides were interesting ester compounds which have been rarely detected in waxes, till now, they have only been detected in the cuticular waxes of potato tuber and olives fruits ( Vichi et al, 2016 ; Guo and Jetter, 2017 ). In addition, the epicuticular wax of fruits, esters were also detected as being the smallest proportion of the total wax in many species, including plums (8.2%) ( Ismail et al, 1977 ), grapes (<5.1%) ( Casado and Heredia, 1999 ) and apple fruits (1.39–4.85%) ( Veraverbeke et al, 2001 ), while esters were not detected in blueberry ( Chu et al, 2017 ) or peach fruits ( Belge et al, 2014 ).…”

Chemical Composition and Water Permeability of Fruit and Leaf Cuticles of Olea europaea L.

“…The turning stage is considered to be important for the tolerance and/or resistance to biotic and abiotic environmental factors. 21 However, the contribution of the cuticular components to cuticle functions, particularly the transpiration barrier properties, have not been comprehensively studied.…”

Role of Fruit Epicuticular Waxes in Preventing Bactrocera oleae (Diptera: Tephritidae) Attachment in Different Cultivars of Olea europaea

“…In this context, studies clarifying the attachment ability of B. oleae in relation to the different physico-chemical features of the EW in different O. europaea cultivars could contribute to deepen the knowledge about this important insect pest, thus helping to develop control methods alternative to the use of pesticide harmful for human health. In particular, starting from the results of the present investigation highlighting that B. oleae friction force and pull off force on the olive fruit surface varied significantly depending on the olive cultivar, in consideration that EW morphology and chemical composition can change during fruit development [21,62,72,73] and could be affected by environmental abiotic factors potentially changing the surface micro-and nanostructure that in turn influence the degree of porosity, wettability of surface as well as the ability of the fly terminal contact elements to form real contact area with these surfaces [10], further investigations on the mechanical ecology of the olive fruit fly adhesion to the olive fruit surface are advisable.…”

“…The EW of ripe olive is mainly composed of triterpenic acids, alkanes, alcohols, aldehydes, alkyl esters, benzyl esters, triacylglycerols, and fatty acids [62][63][64][65][66][67]. A chemical analysis of EWs of olives in different cultivars has revealed the presence of various fractions consisting of chemicals from the above reported compound families, whose proportions depended strongly upon the olive cultivar [21,67]. Our data on the attachment ability of B. oleae females to the ripe fruit surface of different cultivars of O. europaea revealed that both friction force (force preventing sliding of two contacting bodies) and pull off force (force resisting separation of two contacting bodies) varied significantly depending on the olive cultivar and these effects were similar for both above forces.…”

“…In particular, Neuenschwander et al [18] attributed this reduction of susceptibility to the thickness of the waxy coverage, able to shield the attractant chemicals in the olive cultivars. Vichi et al [21] observed differences in the chemical composition of the EWs of nine olive varieties grown in the same geographical area, and hypothesized a possible relationship between EW composition and varietal resistance to several biotic and abiotic factors, highlighting the need of further investigations to elucidate the role of EWs in olive varietal resistance to insect pests and environmental conditions.…”