Abstract:Alternaria alternata was inoculated on the large nets，small nets，and areas without nets of postharvest Jiashi melon，and the disease resistance among different nets and different tissues was compared based on the activities of enzymes involved in phenylpropanoid metabolism and cell wall degradation.The incidence was significantly higher in the large-net group than in other groups.On the 18th day after infection，the incidence was 89.00% ，83.33% ，and 78.00% in the large-net，small-net，and no-net groups，respectively.Activities of phenylalanine ammonia lyase（PAL），4-coumaroyl-Coa ligase（4CL），chitinase（CHT），and β-1，3-glucanase（GLU）showed an initial increase followed by a decrease in the inoculation groups，all of which were higher than those in the control group（p＜0.05）.The peak PAL activity in the exocarp（135.16 U/g）and endocarp（221.81 U/g）of the no-net group was higher than that of the large-net and small-net groups，respectively，and the PAL peak in the pulp（44.42 U/g）was higher in small-net group than in large-net and no-net groups.The peak 4CL activity in the exocarp（44.42 U/g），endocarp（131.28 U/g），and pulp（221.13 U/g）in no-net group was higher than that in the large-net and small-net groups.The peak activities of CHT（170.30 U/g，153.60 U/g，121.48 U/g，re-spectively） and Glu（29.84 U/g，19.27 U/g，and 15.71 U/g，respectively） in exocarp，endocarp，and pulp were higher in the no-net group than in the large-net and small-net groups.The activities of PAL，4CL，CHT，and Glu could reflect the resistance of Jiashi melon to A.alternata.The resistance was in the order of no net>small net>large net and exocarp>endocarp>pulp.