Fungicidal activity of curcumol against Phytophthora capsici via inhibiting phosphatidylcholine biosynthesis and its systemic translocation in plants

Phytophthora capsici is an infamously soil-borne pathogen that poses a serious threat to agricultural production. Curcumol is a natural plant-derived sesquiterpene lactone, whose antimicrobial effect against plant pathogens remains unclear. In this study, curcumol exhibited pronounced antifungal activity against a diverse range of plant pathogens, particularly against plant pathogenic oomycetes, which including P. capsici, Phytophthora infestans, Phytophthora parasitica, and Phytophthora sojae. The median effective concentration values of curcumol against P. capsici for spore germination and mycelial growth were 4.75 and 2.11 μg mL⁻¹, respectively. After treatment with curcumol, mycelia of P. capsici exhibited morphological and ultrastructual defects, which included swelling, hyperbranching, dissolution of plasma membrane, and loss of organelles. In addition, curcumol effectively inhibited the synthesis of phosphatidylcholine (PC), a primary component of cell membrane, by downregulating the expression levels of genes participated in PC synthesis such as Phospholipid N-methyltransferase and Cholinephosphotransferase. This inhibition decreased the accumulation of PC and phospholipids within the cell, thereby increasing the cell membrane permeability and damaging its integrity. In the in vivo antifungal tests, curcumol reduced the disease incidence of P. capsici on tomato leaves as well as pepper seedlings. The systemicity tests further validated the strong phloem and xylem mobility of curcumol in both upward and downward directions. Taken together, these results indicated that curcumol could effectively combat diseases caused by P. capsici and had the potential for development into a novel fungicide for P. capsici management.