S23 - Session P6 - Superficial scald induction in `Granny Smith´ apples subjected to different storage practices

Authors: Monja Gerber *, Thirupathi Karuppanapandian, Daniel Viljoen, Anel Botes, Ian Crouch, Elke Crouch

Superficial scald is a postharvest oxidative stress disorder that develops in susceptible apple cultivars during prolonged low-temperature storage. Scald development consists of an induction period, that initially occurs during refrigerated air (RA) storage and is characterized by irreversible physiological changes, followed by symptom expression, characterized by browning of the peel during or following RA or low-oxygen storage. This negatively impacts the fruits fresh market value and contributes to significant annual losses. Therefore, the South African export industry routinely employs low-oxygen storage practices, such as controlled atmosphere (CA) and dynamic controlled atmosphere monitored by chlorophyll fluorescence (DCA-CF) storage, to delay scald induction and maintain fruit quality. However, symptoms expression usually occurs during the extended shipment and shelf-life period. Here were sought to determine the efficacy of different storage practices in combination with diphenylamine (DPA) and 1-methylcyclopropene (1-MCP) to control superficial scald. To determine this, 'Granny Smith' apples were subjected to 10 different storage practices for 4, 8, 16, 24, and 33 weeks (W) cold storage (1 °C) followed by a 6W RA shipment period (-0.5 °C) and 10 days at 20 °C shelf-life (10d SL). These storage practices include RA, DPA+RA, 1-MCP+RA, CA (1.5% O 2 and 1.0% CO 2 ), 1-MCP+CA, DCA-CF (≈0.4% O 2; 1% CO 2 ), 1-MCP+DCA-CF, 1-MCP+CA+(1-MCP), 1-MCP+CA+(DCA) and 1-MCP+CA+(DCA+1-MCP). The results for the 2019n2020 season indicate that scald induction was effectively delayed during 33W CA and DCA-CF storage however, symptoms developed following 16W+6W RA+10d SL and 24W+6W RA+10 d SL, respectively. The combination treatment with 1-MCP offered a higher degree of control against superficial scald for fruit stored under RA, CA and DCA-CF with symptom expression following 33W+6W RA+10 d SL. Alpha-farnesene metabolism, internal ethylene and reactive oxygen species levels indicate the degree of scald induction as well as, the efficacy of these storage practices.