Potential application value of hydroxychalcones based on isoliquiritigenin in agricultural plant diseases

Abstract

To improve the fungicidal activity of the lead compound isoliquiritigenin, 33 hydroxychalcones were designed and prepared. Their in vitro antifungal activities against four pathogenic fungi (Rhizoctonia solani, Botrytis cinerea, Fusarium graminearum, and Sclerotinia sclerotiorum) were evaluated systematically. We found the most potent agricultural fungicides to be compounds LH-4, LH-5, LH-14 and LH-15 with EC₅₀ values in the range of 5.96 – 10.06 μg mL⁻¹, which are superior to the lead compound isoliquiritigenin and positive control azoxystrobin, with compound LH-4 displaying the best in vitro antifungal activity against R. solani with an EC₅₀ value of 5.96 μg mL⁻¹, approximately 6 times more potent than isoliquiritigenin (EC₅₀ = 36.91 μg mL⁻¹). Moreover, the preliminary antifungal mechanism of compound LH-4 illustrated that it could affect the hyphal morphology and ultrastructure feature of R. solani; its antifungal activity can be associated with the hyphal distortion that results from the disruption of the cell membrane integrity. Besides, SAR studies revealed that the chalcones with few hydroxyls on the A- and B-rings exhibited noticeable antifungal activity. However, chalcones with multi-hydroxyl groups showed unsatisfactory activity. Herein, we report and discuss hydroxychalcones based on isoliquiritigenin as bioactive compounds useful in treating agricultural plant diseases.