External carbon dioxide injury and 1-methylcyclopropene (1-MCP) in the ‘Empire’ apple

The effects of several factors on the susceptibility of untreated and 1-MCP-treated ‘Empire’ apple (Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.) fruit to external CO2 injury have been investigated. These factors include CO2 partial pressure, the timing of elevated CO2 exposure, delays between harvest and exposure to elevated CO2, DPA concentration, and the timing of DPA treatment after exposure of fruit to 1-MCP. 1-MCP-treated fruit were more susceptible to external CO2 injury than untreated fruit when stored in 5 kPa, but not 1 kPa, CO2 (in 2 kPa O2). 1-MCP did not increase the period of highest susceptibility to injury during controlled atmosphere storage. The greatest sensitivity to injury occurred 0–3 weeks after harvest. Sensitivity to injury decreased when untreated fruit were kept in air for up to 14 days before exposure to 5 kPa CO2, but not for 1-MCP-treated fruit. DPA treatment prevented development of CO2 injury even at a level as low as 250 μL L−1. DPA treatment could be delayed for 4 days after 1-MCP treatment while fruit were exposed to 5 kPa CO2 in air without injury development. Overall the data indicate that 1-MCP enhances the risk of external CO2 injury, but this injury can be prevented by treatment of fruit with DPA at harvest. In the absence of DPA treatment, handling procedures such as maintaining low CO2 partial pressures in the storage atmosphere must be used.