Identification and Biological Activity of Antifungal Saponins from Shallot (Allium cepa L. Aggregatum Group)

The n-butanol extract of shallot basal plates and roots showed antifungal activity against plant pathogenic fungi. The purified compounds from the extract were examined for antifungal activity to determine the predominant antifungal compounds in the extract. Two major antifungal compounds purified were determined to be alliospiroside A (ALA) and alhospiroside B. ALA had prominent antifimgal activity against a wide range of fungi. The products of acid hydrolysis of ALA showed a reduced antifungal activity, suggesting that the compound's sugar chain is essential for its antifungal activity. Fungal cells treated with ALA showed rapid production of reactive oxygen species. The fungicidal action of ALA was partially inhibited by a superoxide scavenger, Tiron, suggesting that superoxide anion generation in the fungal cells may be related to the compound's action. Inoculation experiments showed that ALA protected strawberry plants against Colletotrichum gloeosporioides, indicating that ALA has the potential to control anthracnose of the plant.