Effects of Low Oxygen and 1-Methylcyclopropene on Storage Disorders of 'Empire' Apples

The objective of this study was to investigate the effects of low-oxygen storage and 1-methylcyclopropene (1-MCP) on disorders and quality of 'Empire' apples. For 2 years, 'Empire' apples were obtained from commercial orchards during their harvesting period. After cooling overnight at 3 degrees C, the apples were treated with or without 1-MCP (1 mu L.L-1) for 24 hours and subsequently stored in controlled atmosphere (CA) with 2.5 kPa O-2 (+2 kPa CO2) or 1.5 kPa O-2 (+1.2 kPa CO2) for 8 months at 1.5 and 3 degrees C for the first and second year, respectively. In the second year, a third group of the 'Empire' apples was also held in respiratory quotient (RQ)-based dynamic CA storage (SafePod) that reached 0.6 kPa O-2 (+0.5 kPa CO2), and half of these apples were treated with 1-MCP (1 mu L.L-1) for 24 hours at 3(degrees)C upon removal after 8 months. All apples were then evaluated for disorders and quality after 1, 7, or 14 days at room temperature (RT, 23 to 24 degrees C). Substantial external CO2 injury, flesh browning, and core browning (up to 38% incidence) developed in 'Empire' stored in 2.5 and 1.5 kPa O-2 during both years of study. Storage in 1.5 kPa O-2 reduced flesh browning in the first year and core browning during the second year in apples without 1-MCP, as compared to storage in 2.5 kPa O-2. 1-MCP-treated apples stored in 2.5 or 1.5 kPa O-2 had higher overall incidence of disorders than similar fruit without 1-MCP. In contrast, there was negligible incidence (0% to 1%) of these disorders in 'Empire' apples held in 0.6 kPa O-2, regardless of 1-MCP treatment upon removal. Storage in 0.6 kPa O-2 also resulted in the greatest fruit firmness retention while at RT for 14 days. This regime can provide flexibility to postpone 1-MCP treatment until after storage, to prevent increased susceptibility to disorders during storage, without compromising fruit quality. However, results from the RQ-based dynamic CA with 0.6 kPa O-2 were from a single season, and further research is needed to confirm these observations.