Abstract: With the seedlings of 19 pumpkin cultivars as test materials, this paper studied the variations of Na⁺, K⁺, Ca²⁺, Na⁺/K⁺, Na⁺/Ca²⁺, S_Na⁺,K⁺ and S_Na⁺,Ca²⁺ in their shoots and roots under the stress of 300 mmol NaCl·L^-1. The results showed that after an 8-day exposure to 300 mmol NaCl·L^-1, the Na⁺ content in the seedlings increased significantly while the K⁺ content decreased, resulting in the brokenness of ion balance. The root Na⁺ content, shoot Na⁺/K⁺ and Na⁺/Ca²⁺ ratios, and S_Na⁺,K⁺ and S_Na⁺,Ca²⁺ of Cucurbita moschata (Q₁) were significantly higher than those of C. maxima (H₂) and C. ficifolia (H₃). The variation tendency of these parameters of different pumpkin cultivars’ seedlings were nearly consistent with the salt injury index of the seedlings under NaCl stress, which further proved that the strong salttolerance of Q₁ was related to the lower values of shoot Na⁺/K⁺, Na⁺/Ca²⁺, S_Na⁺,K⁺ and S_Na⁺,Ca²⁺, and the high contents of K⁺ and Ca²⁺, while the saltsensitivity of H₂ and H₃ was related to the higher values of shoot Na⁺/K⁺, Na⁺/Ca²⁺, S_Na⁺,K⁺ and S_Na⁺,Ca²⁺, and low contents of K⁺ and Ca²⁺ under NaCl stress.

Key words: GF-2, C50 decision tree, random forest, tree species classification, temporal stage selection, support vector machines