Inhibitory Activity and Control Efficacy of 23 Medicinal Plant Extracts against Tobacco Powdery Mildew

Purpose To explore the control effects of different medicinal plant extracts on tobacco powdery mildew, providing a theoretical basis for developing plant-derived fungicides.

Methods A spore germination assay was conducted to assess the indoor inhibitory effects of ethanol extracts from 23 medicinal plants on Erysiphe cichoracearum. Subsequently, field trials were performed to evaluate the control efficacy of selected extracts.

Results The determination of virulence indoors showed that: when the mass concentration of the extract was 6 mg/mL, the spore germination of tobacco powdery mildew was inhibited by the extracts of 22 medicinal plants except Portulaca oleracea. Field experiments showed that: when the mass concentration of the extract was 3 mg/mL, the Cnidium monnieri extract exhibited a preventive efficacy of 73.85%, which was not significantly different from that of triadimefon (82.05%); the therapeutic efficacies of C. monnieri, Macleaya cordata, and Angelica dahurica were 66.67%, 68.52% and 66.67%, respectively, which were comparable to that of triadimefon (66.67%). The regression analysis of virulence showed that: the preventive median effective concentration (EC₅₀) of C. monnieri extract (0.003 mg/mL) was obviously lower than its therapeutic EC₅₀ value (0.733 mg/mL); conversely, M. cordata extract displayed a lower therapeutic EC₅₀ (0.690 mg/mL) compared to its preventive EC₅₀ (1.148 mg/mL); and the therapeutic EC₅₀ of A. dahurica was 0.897 mg/mL. Thus, C. monnieri extract demonstrated superior preventive potential, whereas M. cordata extract exhibited stronger therapeutic effects.

Conclusion Considering the inhibitory activity of medicinal plant extracts on spore germination of tobacco powdery mildew, the stability of indoor inhibitory activity and the cost of medicinal plants, the ethanol extracts of C. monnieri, M. cordata, and A. dahurica are effective in controlling tobacco powdery mildew and have the to be developed as green fungicides.