Abstract: 2,6-dichloroisonicotinic acid（INA） induces plant tolerance to a wide spectrum of diseases. But whether the compound induced the deseases-tolerance in postharvest fruits and vegetables remains to be clarified. We investigated the effects of INA on diseases-tolerance in harvested banana（Musa AAA Group‘Brazil’）and the possible mechanism. The results showed that INA treatment effectively reduced the disease spot sizes on the peel of banana fruit when inoculated with spore suspension of Collectotrichum musae during 24 h after INA treatment and cultured for 8 d. H2O2，a type of reactive oxygen species（ROS），and the involved enzymes were analysed and it was found that the content of H2O2 and activity of NADPH oxidase，an enzyme catalyze the production of ROS，were stimulated at 3 h，6 h and 12 h after INA treatment，respectively. In addition，INA treatment decreased CAT and APX activities obviously，and suppressed the both genes expression to a certain extent. We also analysed the defence enzyme of chitinase（CHI）and found that activity of intro-CHI and extro-CHI were enhanced at 0–12 h and 0–24 h after INA treatment，espectively，and the expression of CHI1 and CHI2 genes were enhanced lightly at 3–6 h and 0–3 h after INA treatment，respectively. These results strongly suggest that elevated H2O2 levels，resulting from enhanced NADPH oxidase activity and suppressed CAT and APX activities，and the enhanced CHI activity are involved in the INA-induced disease tolerance.

Key words: banana, fruit, 2, 6-dichloroisonicotinic acid, Collectotrichum musae, reactive oxygen species, defense-related enzyme