CO2 Injury in "Honeycrisp" Apple: Dose Response to Diphenylamine

‘Honeycrisp’ apple (Malus x domestica Borkh.) fruit are very sensitive to injury by controlled atmosphere (CA) storage, developing brown lesions and lens-shaped cavities in the cortex. The injury is in response to elevated CO₂ and, to a lesser extent, to low O₂. We know from previous work that diphenylamine (DPA) can prevent CA injury to 'Honeycrisp' when applied at commercial rates (1000 to 2000 µL·L^-1). However, the nature of the dose response of CO₂-related CA injury to DPA is unknown. To describe this relationship, we stored 'Honeycrisp' fruit with CO₂ levels of 0, 5, 10 and 20 kPa in combination with 3 kPa O₂ during storage at 3 °C. Prior to storage, fruit from each treatment were drenched for 30 s with DPA at concentrations of 1, 10, 50, 100, 250 and 1000 µL·L^-1. Fruit were assessed for CA injury incidence and severity after 4 months storage. CO₂ injury was evident for all treatments, including 0 kPa CO₂ in the absence of DPA. CO₂ injury declined as the concentration of DPA increased.  The concentration of DPA required to completely suppress CO₂ injury was 100, 250, and 1000 µL·L^-1 for 0, 5, and 10 kPa CO₂, respectively.  Injury for fruit stored in 20% CO₂ declined only slightly at higher DPA levels. The presence of CO₂ injury at 0 kPa CO₂ may be a result of low O₂ in combination with the low amounts of CO₂ that accumulate in the interior of the apple fruit.  The results suggest that some protocols for the CA storage of 'Honeycrisp' requiring low CO₂ for the first several weeks may not always sufficiently control this disorder if other means to suppress CO₂ injury (e.g., DPA or pre-storage conditioning) are not employed.