Increased residual activity controls disease in 'Red Fuji' apples (Malus domestica) following postharvest heat treatment

The efficacy of hot air treatment (38 degrees C, 4 days) on the development of residual activity to control diseases in stored apples (Malus domestica 'Red Fuji') was investigated. The study included three separate trials involving apples with artificial wounds and/or with natural micro-wounds. It was found that heat treatment can accelerate the healing of artificial wounds and melt the epicuticular wax to fill in natural micro-wounds. During storage, these two effects provide a strong physical barrier to defend against fungal re-invasion through wounds. Results showed that heat treatment increased chitinase (CHI), phenylalanine ammonia-lyase (PAL), and peroxidase (POD) activity levels. In addition, phenolic compounds and lignin content increased during the later storage period. Heat treated 'Red Fuji' apple fruit showed reduced decay development, indicating disease resistance. It was concluded that heat treatment can induce increased residual activity to control disease in 'Red Fuji' apple fruit, via the beneficial effects on wound healing and inducing disease resistance.