Salicylic Acid Spray Delays Sand Pear Fruit Senescence during Room Temperature Shelf Life by Regulating Antioxidant Capacity and Senescence-Related Genes

‘Whangkeumbae’ (<i>Pyrus pyrifolia</i>) is a variety of sand pear fruit well-known for its smooth surface and good taste. However, the fruit quality is adversely affected by postharvest ethylene production. Therefore, improving postharvest shelf life by regulating fruit senescence is critical to promoting the ‘Whangkeumbae’ fruit industry. Here, we investigated the effect of salicylic acid (SA) spray on fruit senescence in sand pears during room temperature shelf life. Exogenous SA reduced polyphenol oxidase (PPO) activity and malondialdehyde (MDA) content during room temperature shelf life. Additionally, SA effectively maintained the fruit skin coloration and increased the activity of antioxidant enzymes, such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX). SA treatment inhibited <i>PpPPO1</i> expression and upregulated <i>PpSOD1</i>, <i>PpAPX6</i>, and <i>PpGST2</i> expression. Furthermore, SA application downregulated the expression of <i>PpACO2</i>, <i>PpEIN3a</i>, <i>PpNCED1</i>, and <i>PpAOC2</i>, while upregulating <i>PpNPR-1</i>, <i>PpTAR2</i>, and <i>PpCOMT1</i> during room temperature shelf life. SA treatment also influenced cell wall metabolism and modification genes by inhibiting <i>PpPG1</i>, <i>PpPME2</i>, and <i>PpCEL3</i> and inducing <i>PpPGIP1</i> expression. Additionally, SA treatment affected sugar and acid metabolism genes and increased the expression of <i>PpSPS1</i>, <i>PpSUS1</i>, <i>PpSOT1</i>, <i>PpTMT4</i>, <i>PpSWEET15</i>, and <i>PpcyNAD-MDH,</i> but suppressed the expression of <i>PpcyNADP-ME</i>. The Pearson correlation analysis indicated that PPO activity and MDA content were positively correlated with the expression of <i>PpPPO1</i>, <i>PpACO2</i>, <i>PpEIN3a</i>, <i>PpNCED1</i>, <i>PpAOC2</i>, <i>PpPG1</i>, <i>PpPME2</i>, <i>PpCEL3</i>, and <i>PpcyNDA-MDH</i>. Conversely, these factors were negatively associated with the activities of SOD, POD, CAT, and APX, as well as the expression levels of <i>PpSOD1</i>, <i>PpPOD1</i>, <i>PpCAT1</i>, <i>PpAPX6</i>, <i>PpGST2</i>, <i>PpNPR-1</i>, <i>PpTAR2</i>, <i>PpCOMT1</i>, <i>PpPGIP1</i>, <i>PpSPS1</i>, <i>PpSUS1</i>, <i>PpSOT1</i>, <i>PpTMT4</i>, <i>PpSWEET15</i>, and <i>PpcyNAD-MDH</i>. Our results reveal that exogenous SA could delay fruit senescence in sand pear fruit by regulating various biochemical and molecular mechanisms and can be used to effectively extend fruit shelf life during room temperature storage. However, further research is necessary to determine whether the fruits sprayed with SA are suitable for direct human consumption.