Effects of Preharvest Aminoethoxyvinylglycine (AVG) Treatment on Fruit Ripening, Core Browning and Related Gene Expression in ‘Huangguan’ Pear (<i>Pyrus bretschneideri</i> Rehd.)

‘Huangguan’ pear (<i>Pyrus bretschneideri</i> Rehd. cv. Huangguan) is a widely planted cultivar in China. However, it is susceptible to core browning after harvest. In this study, aminoethoxyvinylglycine (AVG) was applied at 200 mg L⁻¹ one and two weeks prior to harvest, and its effects on fruit quality, ripening and core browning were investigated during fruit storage at ambient temperature (25 ± 1 °C). The results showed that there was higher firmness, soluble solids content (SSC) and titratable acid (TA) content, but a lower ethylene production rate and core browning index in AVG-treated fruit than in control (water). Compared with the control fruit, AVG treatment decreased the malondialdehyde (MDA) content and polyphenol oxidase (PPO) activity, delayed the peak of chlorogenic acid (CGA) content in the core tissue, and significantly inhibited the expression of genes such as ACC synthase (<i>PbACS2</i>, <i>PbACS3a</i>, <i>PbACS5a</i> and <i>PbASC5b</i>), ACC oxidase (<i>PbACO1</i> and <i>PbACO2</i>), ethylene receptors (<i>PbETR2</i> and <i>PbERS1</i>), ethylene response factor (<i>PbERF1</i>), phenylalanine ammonia lyase (<i>PbPAL1</i>), cinnamate 4-hydroxylase (<i>PbC4H4</i>), 4-hydroxycinnamoyl- CoA ligase (<i>Pb4CL2</i>), hydroxycinnamoyl- CoA shikimate hydroxycinnamoyl transferase (<i>PbHCT1</i> and <i>PbHCT3</i>), and polyphenol oxidase (<i>PbPPO1</i> and <i>PbPPO5</i>), as well as phospholipase D (<i>PbPLD</i>) and lipoxygenase (<i>PbLOX1</i> and <i>PbLOX5</i>). Thus, these results suggested that the reduction in core browning by preharvest application of AVG might be due to an inhibitory effect on the expression of genes associated with ethylene biosynthesis and signaling pathways, CGA biosynthesis, PPO and cell membrane degradation in ‘Huangguan’ pear.