Postharvest Heat Treatments Control Blue Mould In Apple Fruit And Its Partial Mechanism

Apple is an important temperate fruit, the fruit could be infected by various fungi during postharvest, and blue mould caused by Penicillium expansum is the most serious postharvest disease. The objective of this study is to investigate the effect of hot water dips on controlling blue mould of apples under different treatment temperature and time, to study the possible mechanism of hot treatment controlling decay by observing the changes of vital rate and ultrastructure of treated pathogens, and resistance of treated fruits. The results showed that:1. Fruit inoculated with P. expansum was dipped in hot water at 45, 50 and 55℃for 1, 3, 5, 10, 15 and 25 min, the lesion diameter of fruit was significantly reduced by the treatment at 45, 50 and 55℃for 5～15 min, and the treatment at 50℃for 10 min showed the best effect.2. In vitro, the pathogenicity of P. expansum spores was significantly reduced by HWD at 45, 50 and 55℃; the germination or growth of spores was delayed by treatment at 50 and 55℃, and the treatment at 55℃had a better effectiveness. On the contrary, spores germination was promoted by treatment at 45℃.3. The observations of ultrastructure showed that heat treatment at 50 and 55℃damaged cell wall, nucleus and mitochondria of spores, made the cell wall dented, collapsed, even ruptured, and resulted in deformation of nucleus and mitochondria.4. The treatment at 50℃for 10 increased activity of POD, PPO and PAL, and accumulated the content of total phenolic, flavanoid and lignin in treated fruits. The challenge with P. expansum enhanced activity of GLU and CHT, increased furthermore activity of POD, PPO and PAL, and more accumulation was also found in content of total phenolic, flavanoid and lignin in treated fruits.It is suggested that the treatment of hot water dips could effectively control blue mould of apples through inhibitation vital rate of P. expansum, and inducement the resistance of fruits by increasing activity of defanse enzymes and accumulation of antifungal compounds.