In vivo fungicidal properties of Diospyros kaki-isolated compound and its analogues

Fungicidal effects of active component purified from Diospyros kaki roots and its analogues against Erysiphe graminis, Botrytis cinerea, Pyricularia grisea, Puccinia recondite, Rhizoctonia solani, and Phytophthora infestans were investigated using a whole-plant method. Active constituents isolated from the chloroform fraction of D. kaki roots were characterized as plumbagin, using various spectroscopic analyses. To establish the structure-activity relationships, the fungicidal effects of plumbagin and its structural analogues were bioassayed against phytopathogenic fungi. At 0.25, 0.125, and 0.0625 g/L, plumbagin had a greater fungicidal effect than p-naphthoquinone, juglone, lawsone, 2-methoxy-p-naphthoquinone, or menadione against P. grisea, B. cinerea, R. solani, and E. graminis. Our results suggest that the methyl and hydroxyl functional groups at the 5'- and 2'-positions of p-naphthoquinone play key roles in its fungicidal effect against six phytopathogenic fungi. Therefore, plumbagin and its analogues may be suitable as antifungal agents to control plant diseases.