The chromatograms detected by HPLC both in standard chemicals and root exudates.

The peaks from left to right in the Standards represent the following standard compounds: 1, gallic acid; 2, coumaric acid; 3, β-hydroxybenzoic acid; 4,chlorogenic acid; 5, vanillic acid; 6, caffeic acid; 7, syringic acid; 8, ferulic acid; 9, benzoic acid; 10, salicylic acid; 11, cinnamic acid. The peaks identified by HPLC in the root exudates collected from own-root bottle gourd, grafted-root watermelon and own-root watermelon were showed by the corresponding numbers.