Changes in α-Farnesene and Phenolic Metabolism and the Expression of Associated Genes during the Development of Superficial Scald in Two Distinct Pear Cultivars

Author:Jingang He , Yunxiao Feng , Yudou Cheng , Thirupathi Karuppanapandian , Jinxiao Wang and Junfeng Guan

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 the expression of its related genes were investigated
      in two different pear cultivars, ‘Wujiuxiang’ (Pyrus communis L.) and ‘Yali’ (Pyrus bretschneideri R.),
      following 115 days of cold storage at 0 ◦C followed by 7 days of shelf life at 20 ◦C. The results
      indicated that the superficial scald occurred after 115 days of cold storage and became more severe
      during the shelf life of the ‘Wujiuxiang’ pear, whereas no scald was observed in ‘Yali’. The α-farnesene
      levels increased rapidly at first and then decreased, while the CTols contents increased significantly
      in ‘Wujiuxiang’ as compared to ‘Yali’, and the expression levels of the genes involved in α-farnesene
      and CTols metabolism (HMGR1, HMGR2, GSTU7, GPX5, and GPX6), as well as the phenolic synthesis (PAL1, PAL2, C4H1, 4CL2, C3H, and ANR) of the peel, were significantly up-regulated at the
      onset of the superficial scald. In addition, the relative conductivity and contents of catechin and
      epicatechin were higher, and the expression level of the laccase gene (LAC7) significantly increased
      with the development of superficial scald, while 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’ as
      compared to ‘Yali’. The results indicated that the onset and progression of superficial scald were associated with the accumulation of CTols, cell membrane breakdown, and higher catechin, epicatechin,
      and rutin contents, as well as the expression of associated genes of the peels of pear fruit.

Key words:pear; α-farnesene; conjugated trienols; phenolics; superficial scald