The ethylene inhibitor, 1 methylcyclopropene (1-MCP), is used extensively in New York to maintain quality of the `Empire' apple cultivar through the marketing chain. However, the cultivar is susceptible to external CO2 injury, a physiological disorder that develops predominantly on the unblushed area of the apple skin. Injury is expressed as tan colored, smooth, water-soaked areas that become irregularly shaped, rough, depressed and wrinkled. The disorder usually occurs during controlled atmosphere (CA) storage. 1-MCP may increase susceptibility of fruit to external CO2 injury. Three experiments have been carried out to investigate postharvest manipulations that may attenuate the effects of 1-MCP on external CO2 injury of `Empire' apple. 1) The effect of CO2 concentration (1%, 2.5%, and 5%) and time of exposure to 2.5% and 5% CO2 during CA storage. 2) Delaying exposure of fruit to 5% CO2 after harvest to up to 14 d. 3) Using lower concentrations of diphenylamine (DPA), an antioxidant that is known to eliminate susceptibility at normal rates. The results show that higher external CO2 injury levels are associated with higher CO2 concentrations, but that 1-MCP does not increase the exposure period of susceptibility to injury during CA storage. Susceptibility to CO2injury is decreased markedly by delaying application of CA storage in untreated fruit. In contrast, high susceptibility to injury is maintained in 1-MCP-treated fruit as long as 14 days after harvest. DPA eliminated injury in 1-MCP-treated fruit, even at 250 ppm, 25% of commercial rates used for superficial scald control. Our data show that 1-MCP increases susceptibility of `Empire' apples to external CO2 injury and special care is therefore required to avoid fruit losses. Nonchemical means may reduce losses, but the only technology that has been shown to eliminate risk of injury is DPA treatment.
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