Postharvest applications of n-butanol increase greasiness in apple skins by altering wax composition via effects on gene expression

Abstract

The postharvest development of greasiness in apple skin has negative effects on fruit appearance and market quality and causes significant economic losses. The fluid wax constituents responsible for skin greasiness comprise mainly oleate and linoleate esters of (E,E)-farnesol and short-chain alcohols (C3-C5). Butyl esters are also key components. It is believed that accumulations of volatile alcohols affect the development of skin greasiness by offering substrates for the biosynthesis of the greasy esters. To demonstrate the putative role of volatile alcohols on apple skin greasiness, ‘Cripps Pink’ apples were treated with either 10 or 25 μL L−1 n-butanol (NBA) and then stored at 20 °C. The composition of each cuticular wax was analyzed, and the expression levels of the related genes were recorded. There was no significant difference in the time course of fruit ripening or senescence among the two NBA treatments and the control. As expected, accumulations of the fluid wax constituents were indeed promoted in the NBA-treated fruit. On day 42, compared with the control, the butyl ester contents of the skins of the 10 and 25 μL L−1 NBA-treated fruits were 1.7 and 2.9 times higher, respectively. Moreover, the 25 μL L−1 NBA-treated fruit showed higher greasiness levels and looked shinier than the fruit exposed to the lower NBA treatment or the control. Several genes were more highly expressed in the NBA-treated fruit than in the control. These included MdKASIII, MdSAD6, MdWSD1 (related to wax biosynthesis) and MdLTPG1 (related to wax export). We conclude that NBA had no significant effects on fruit ripening or senescence but promoted the development of skin greasiness.