Symbiotic incompatibility inhibited the growth of cucumber/pumpkin grafted seedlings. A PPO activity. B PAL activity. C Plant phenotype 25 days after grafting. Scale bar: 10 cm. D Fresh weight. E Dry weight. F SPAD value. Phenotype, PPO activity, PAL activity, and SPAD value were measured 25 days after grafting, and biomass was measured at 70 days. Data represent mean ± standard deviation (n = 3). According to Tukey’s test, means with the same letter did not differ significantly at P < 0.05. FW, fresh weight; NG, non-grafted; SG, self-grafted; CG, compatible combination; IG, incompatible combination.