Abstract: In order to further study the inhibiting activity and mechanism of ethyl acetate extracts of introduced Trichoderma harzianum strain T28 fermentation liquid to the growth of Phytophthora infestans, we investigated bacteriostasis of the extracts in different concentrations on P. infestans and their effects on several enzyme activities in the pest physiological metabolism. The results indicated that all the studied concentrations of the extracts had inhibiting effects on the growth, sporangium germination and spore released zoospores of P. infestans, and among the concentrations the 10 and 100×diluted had slightly better effects without significant differences. The activities of protective enzymes (SOD, CAT, POD and GSH-Px) of P. infestans treated with the extracts in 48 hours reduced by 89.06%, 86.96%, 97.47% and 97.63%, respectively. Meanwhile, the activities of carbohydrate metabolic enzymes(HK、PK and LDH)and TCA aerobic catabolic enzymes (SDH and MDH)also decreased by 93%, 89.56%, 88.5%, 97.66% and 97.43%, energy-metabolic enzyme activities (ATP) decreased by 98.5% and 98.67%. The MDA contents enhanced 60.98%. This research determined that the ethyl acetate extract from fermentation liquid of T. harzianum strain T28 was able to reduce the metabolic enzyme activities of P. infestans and increase the MDA contents. The extracts could cause the damage to P. infestans and prevent from normal working of its glycometabolism, tricarboxylic acid cycle, energy metabolism and etc, which may be one of inhibiting mechanisms of ethyl acetate extracts of T. harzianum strain T28 on the growth of P. infestans.

Key words: Trichoderma harzianum strain T28, extract, Phytophthora infestans, inhibiting mechanism