Abstract: In order to clarify the combined toxicity of Macleaya cordata alkaloids and tea saponins against three food crop pathogens, namely Fusarium graminearum, Magnaporthe grisea, and Exserohilum turcicum （Pass） Leonard et Suggs, the semi-effective concentration（EC₅₀）, toxicity ratio, and optimal combination toxicity of macleaya alkaloids, tea saponins, and their different mixtures against the three food crop pathogens were determined by the growth rate method. The results showed that the EC₅₀ of macleaya alkaloids against Fusarium graminearum, Magnaporthe grisea and Exserohilum turcicum Pass, were 60.626, 24.933 μg/mL and 83.152 μg/mL, respectively; the EC₅₀ of tea saponins against Fusarium graminearum, Magnaporthe grisea, and Exserohilum turcicum Pass were 194.978, 565.427 μg/mL and 440.656 μg/mL, respectively; the combined toxicity screening of the best ratio represented that the mixture of macleaya alkaloid and tea saponin with a mass ratio of 1∶3.2 showed a synergistic effect on Fusarium graminearum, and the synergistic coefficient was 2.517. The mixture of macleaya alkaloid and tea saponin with a mass ratio of 1∶9.7 and 1∶15.1 showed a synergistic effect on the pathogen of Magnaporthe grisea, with a synergistic coefficient of 2.650 and 1.656, respectively. The mixture of macleaya alkaloid and tea saponin with a mass ratio of 1∶3.5 and 1∶5.3 showed a synergistic effect on the pathogen of Exserohilum turcicum Pass, with a synergistic coefficient of 2.522 and 2.440, respectively. It was shown that the combination of macleaya alkaloid and tea saponin had an obvious synergistic effect on Fusarium graminearum, Magnaporthe grisea, and Exserohilum turcicum Pass.

Key words: Macleaya cordata, alkaloids, tea saponin, food crop, pathogens, combined virulence