Abstract: Davidia involucrate, a relic species of paleotropical kingdom in Tertiary period and belonging to Davidiaceae with a single genus, is one of the first-class protective plants in China. In this paper, a pot culture experiment with quadratic general rotation design was conducted to study the effects of CaCl₂,salicylic acid (SA), and a water-retention agent on the drought resistance of D. involucrate seedlings. The results showed that all test reagents had positive effects, and synergistic effect existed among them. CaCl₂ and SA improved the water utilization efficiency of D. involucrate at the initial stage of water stress, while water-retention agent maintained higher soil moisture content when the drought stress developed so as to improve the drought resistance of D. involucrate and alleviate the effects of water stress. The optimum combination of management practice in improving drought resistance of D. involucrate seedlings was 839.400-1256.520 mg·L^-1 CaCl₂, 44.015-69.306 mg·L^-1SA, and 618-700 ml·pot^-1 water-retention agent.

Key words: Pseudoperonospora cubensis, Temperature, Humidity, Potentiality of producing sporangia