Induces Resistance Against Blue Mould Of Apple Fruit By Postharvest BTH Treatment And Challenged Inoculation

Blue mold caused by Penicillium expansum is major disease of apples during postharvest.In this study,the apple cultivar ‘Fuji’ was used as materials.The fruit was dipped in 100mg/L BTH,then inoculated with P.expansum after 24 hours of treatment.The control effect was assayed against blue mould of treated fruit.Cells and organelle were observed under the peel after treatments.The key enzymes activities and contents related with metabolism were analyzed,on reactive oxygen,energy and phenylpropanoid metabolisms.The results showed that as follow:1.BTH treatment significantly inhibited the expansion of the lesion area of inoculated fruit,increased activity of phenylalanine ammonia-lyase（PAL）,and the content of total phenolic,flavanoid and lignin.The challenge with P.expansum enhanced furthermore activity of PAL in treated fruit,increased the content of total phenolic,flavanoid and lignin.Although the control had increase responses after challenged,however,the intensity was weaker and the duration was shorter than the treated fruit.2.BTH significantly increased the content of ATP and ADP,enhanced EC level in fruit.The treatment also increased activity of succinate dehydrogenase（SDH）,cytochrome c oxidase（CCO）and Ca²⁺-ATPase of mitochondria.The challenge inoculation enchanced furthermore the activity of SDH,CCO,H+-ATPase and Ca²⁺-ATPase in treated fruit,more accumulation was also found in ATP,ADP and EC.Although the control had increased response after challenge,however,the intensity was weaker and the duration was shorter than the treated.In addition,BTH maintained the quantity and integrity of mitochondria in fruit.3.BTH maintained the membrane integrity by decreasing and membranes permeability and the malondialdehyde（MDA）content.BTH resulted in an increase in the activity of NADPH oxidase（NOX）,Ssuperoxide dismutase（SOD）,peroxidase（POD）and polyphenoloxidase（PPO）.BTH decreased the activity of catalase（CAT）and ascorbic peroxidase（PAX）.Furthermore,the challenge inoculation enhanced the activity of NOX,SOD,POD and PPO,decreased the activity of CAT and APX.Although the control had increase responses after challenged,however,the intensity was weaker and the duration was shorter than the treated fruit.4.BTH induced ROS brust of cells under the peel,significantly increased the production of O2-and H₂O₂ in fruit.The challenge inoculation furthermore enchanced accumulation of O2-and H₂O₂ in treated fruit.Although the control had increase responses after challenged,however,the intensity was weaker and the duration was shorter than the treated fruit.In conclusion,BTH significantly inhibited the expansion of the lesion area of inoculated apples.The inhibition elicited by BTH is closely related with increased the related enzymes activity of ROS,energy and phenylpropanoid metabolisms,promoting the energy level,ROS accumulation,and the content of total phenolics,flavonoids and lignin in fruit.