Changes in Α-Farnesene and Phenolics Metabolism and Expression of Associated Genes During the Development of Superficial Scald in Two Distinct Pear Cultivars
Superficial scald is a postharvest physiological disorder that occurs in pear during and after cold storage. In this study, the superficial scald index, α-farnesene, and its oxidation products conjugated trienols (CTols), phenolic content, and expression of its related genes were investigated in two pear cultivars, ‘Wujiuxiang’ (sensitive to scald) and ‘Yali’ (less sensitive to scald), following 115 days of cold storage at 0 °C and followed by 7 days shelf life at 20 °C. The results indicated that the superficial scald occurred after 115 days of cold storage and became more severe during shelf life in ‘Wujiuxiang’ pear, whereas no scald was observed in ‘Yali’, the α-farnesene levels increased rapidly at first and then decreased while CTols contents increased significantly in ‘Wujiuxiang’ as compared to ‘Yali’, and the expression levels of genes involved in α-farnesene and CTols metabolism ( HMGR 1 , HMGR 2 ), GSTU 7 , GPX 5 , and GPX 6 , as well as phenolic synthesis ( PAL 1 , PAL2 , C4H1 , 4 CL2 , C3H , and ANR ) of the peel were significantly up-regulated at the onset of superficial scald. In addition, the relative conductivity and contents of catechin and epicatechin were higher, and the expression level of laccase gene ( LAC7 ) was significantly increased with the development of superficial scald, while the lower contents of chlorogenic acid, arbutin, and isorhamnetin-3-3-glucoside, as well as the lower expression levels of a phenolic synthesis-related gene ( C4H3 ) , and polyphenol oxidase genes ( PPO1 and PPO5 ) were noticed in ‘Wujiuxiang’ than those in ‘Yali’. The results indicated that the onset and progression of superficial scald were associated with the accumulation of CTols, cell membrane permeability, higher catechin, epicatechin, and rutin contents and associated genes expression in pear fruit.