Induction od resistance against Penicillin expansum in harvested apple fruits using walnut green water extract

In this study, apple fruits were first treated with different concentrations (1.5, 3, 4.5 and 6×1000) of walnut green skin water extract and Penicillium expensum pathogen. The activity of defense enzymes including of phenylalanine ammonia-lyase, polyphenol oxidase, superoxide dismutase and β(1,3) glucanase were measured in the treated apple fruits in the sampling days, 3, 6, 9, 12, and 15 days after pathogen induction of fruit. Then, genes expression levels encoding these enzymes were assessed by Real-time PCR. The results showed that the activity of the studied enzymes increased from the third day of sampling to the 9th day and then decreased until the 15th day. Pathogen and walnut green skin both increased the enzyme activity. As the concentration of the walnut green skin extracts increased, the activity of the enzymes increased. The highest activity of PAL, PPO, SOD and Glu enzymes was observed at day 9 at concentrations of 6×1000 with values 11.28 (U per mg protein), 5.37 (∆OD per min per mg of total protein), 26.87 (U per mg mg protein) and 23.89 (∆OD per min per mg of total protein), respectively. The results of measurement of gene expression were also in accordance with the activity of enzymes. Exactly on the 9th day, the highest gene expression was observed for the genes expressing each enzyme and in the treatment of both pathogens and extracts. The gene expression levels of PAL, PPO, SOD and Glu enzymes at 9th day and in apple treated with pathogen and green walnut skin extracts were 121, 148, 150 and 148 times higher than those genes in the healthy apples as control, respectively.