In vitro and in vivo antifungal activities of decursin and decursinol angelate isolated from Angelica gigas against Magnaporthe oryzae, the causal agent of rice blast

Blast is considered the most important fungal disease of rice due to its wide distribution and destructiveness under favorable conditions. Development of new effective and environmentally benign agents against the causal pathogen, Magnaporthe oryzae , is of great interest. In the course of a search for natural antifungal compounds in medicinal plants, we found that the methanol extract of Angelica gigas roots showed a potent control efficacy against rice blast caused by M. oryzae . We isolated antifungal coumarins from the extract, and they were identified as decursin and decursinol angelate. Antifungal activities of these compounds, along with kasugamycin, were tested on M. oryzae in vivo and in vitro . In an in vivo assay, the three compounds effectively suppressed the development of rice blast at concentrations more than 100 μg/mL. Coumarins showed relatively weak inhibitory effect on fungal mycelial growth when compared to kasugamycin. However, they strongly inhibited M. oryzae spore germination, which was not observed in kasugamycin treatments. This is the first report demonstrating that decursinol angelate can provide control against rice blast and that the two coumarins inhibit M. oryzae spore germination. In addition, the wettable powder formulation of the crude extract of A. gigas prohibited the development of blast symptoms on rice plants more effectively than liquid concentrate formulation of kasugamin, a commercial fungicide. Based on our study, we propose that coumarin compounds as well as the A. gigas root crude extract can be used as natural, benign fungicides for controlling rice blast.