Phytophthora capsici is an important plant pathogenic oomycete that causes great losses to vegetable production around the world. Antofine is an important alkaloid isolated from Cynanchum komarovii Al. Iljinski and exhibits significant antifungal activity. In this study, the effect of antofine on the mycelial growth, morphology, and physiological characteristics of P. capsici was investigated using colorimetry. Meanwhile, the activity of mitochondrial respiratory chain complexes of P. capsici was evaluated following treatment with a 30% effective concentration (EC30), as well as EC50 and EC70, of antofine for 0, 12, 24, and 48 h. The results showed that antofine had a significant inhibitory effect against P. capsici, with an EC50 of 5.0795 μg/mL. After treatment with antofine at EC50 and EC70, the mycelia were rough, less full, and had obvious depression; they had an irregular protrusion structure; and they had serious wrinkles. In P. capsici, oxalic acid and exopolysaccharide contents decreased significantly, while cell membrane permeability and glycerol content increased when treated with antofine. Reactive oxygen species (ROS) entered a burst state in P. capsici after incubation with antofine for 3 h, and fluorescence intensity was 2.43 times higher than that of the control. The activities of the mitochondrial respiratory chain complex II, III, I + III, II + III, V, and citrate synthase in P. capsici were significantly inhibited following treatment with antofine (EC50 and EC70) for 48 h compared to the control. This study revealed that antofine is likely to affect the pathways related to the energy metabolism of P. capsici and thus affect the activity of respiratory chain complexes. These results increase our understanding of the action mechanism of antofine against P. capsici.
Keywords: Phytophthora capsici; antofine; biological characterization; mycelia morphology; respiratory chain complexes.