Abstract:Root injection and foliar spray were adopted to study induced resistance and physiological and biochemical mechanisms of chitosan on Botrytis cinerea Pers.of cucumber, Cucumis sativus L., and disease index, defense enzyme activities and disease resistance-related substance contents in cucumber seedlings were determined. The results showed that chitosan decreased disease index of cucumber seedlings by 39.4%, increased phenylalanine ammonia lyase (PAL), peroxidase (POD) and polyphenol oxidase (PPO) activities, enhanced total polyphenol, flavonoid and lignin content. Chitosan played an important role in inducing disease resistance of cucumber seedlings with the optimum concentration at 200mg·L-1.