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

Xiao Wu,Hao Yin,Shaoling Zhang,Xin Qiao,Peng Cao,Zebin Shi,Kaijie Qi,Guoming Wang,Yangyang Chen

doi:10.3389/fpls.2018.00679

Abstract

An evaluation of fruit wax components will provide us with valuable information for pear breeding and enhancing fruit quality. Here, we dissected the epicuticular wax concentration, composition and structure of mature fruits from 35 pear cultivars belonging to five different species and hybrid interspecies. A total of 146 epicuticular wax compounds were detected, and the wax composition and concentration varied dramatically among species, with the highest level of 1.53 mg/cm2 in Pyrus communis and the lowest level of 0.62 mg/cm2 in Pyrus pyrifolia. Field emission scanning electron microscopy (FESEM) analysis showed amorphous structures of the epicuticular wax crystals of different pear cultivars. Cluster analysis revealed that the Pyrus bretschneideri cultivars were grouped much closer to Pyrus pyrifolia and Pyrus ussuriensis, and the Pyrus sinkiangensis cultivars were clustered into a distant group. Based on the principal component analysis (PCA), the cultivars could be divided into three groups and five groups according to seven main classes of epicuticular wax compounds and 146 wax compounds, respectively.

Highlights

Cuticular wax is the product of a complex mixture of very-long-chain (VLC) aliphatic compounds and their oxygenated derivatives, including fatty acids, alkanes, alcohols, esters, aldehydes, ketones, and triterpenes (Kolattukudy, 1996)
The amount of wax obtained from the 35 pear varieties varied dramatically (Figure 1 and Supplementary Tables S1, S2), and the wax concentrations ranged from 0.46 ± 0.03 mg/cm2 (‘Huagai’, P. ussuriensis) to 2.44 ± 0.41 mg/cm2 (‘Docteur Jules Guyot’, P. communis) (Figure 1A)
The concentrations of alkanes, primary alcohols, fatty acids, esters and other epicuticular wax compounds were much higher in P. communis than in the other four species and hybrid interspecies (Supplementary Figures S2B,D,F,L,N), whereas the hybrid cultivars and P. ussuriensis had the highest concentrations of terpenoids and aldehydes, respectively (Supplementary Figures S2H,J)

Summary

Introduction

Cuticular wax is the product of a complex mixture of very-long-chain (VLC) aliphatic compounds and their oxygenated derivatives, including fatty acids, alkanes, alcohols, esters, aldehydes, ketones, and triterpenes (Kolattukudy, 1996). It has been widely reported that wax plays important roles in moderating gas exchange, limiting non-stomatal water loss, protecting plants against ultraviolet (UV) radiation and extreme temperature damage, self-cleaning behavior and providing mechanical support to maintain the integrity of plant organs (Wang et al, 2016). More and more studies have suggested that the fruit cuticular wax layer acts as the first protective barrier against fruit splitting and plays pivotal roles in the reduction of pathogenic and insect attacks, protection against mechanical damage (Chu et al, 2017). The removal of the natural wax of blueberry fruits can accelerate the postharvest water loss and decay, reduce the sensory and nutritional qualities, and shorten the fruit shelf-life (Chu et al, 2018). As one of the most important quality factors determining consumer demand, the apple’s appearance during the postharvest storage were determined by the Comparative Analysis of Pear Wax physical and chemical properties of wax composition (Glenn et al, 1990)

Methods

Results

Conclusion