We investigated alpha-mangostin (α-mangostin, α-MG), a xanthone natural product extracted from the pericarp of mangosteen (Garcinia mangostana), for its antifungal activities and possible mechanism against Colletotrichum gloeosporioides, which causes mango anthracnose. The results demonstrated that α-MG had a relatively high in vitro inhibitory activity against C. gloeosporioides among 20 plant pathogenic fungi. The median effective concentration (EC50) values of α-MG against mycelial growth were nearly 10 times higher than those of spore germination inhibition for both strains of C. gloeosporioides, the carbendazim-sensitive (CBD-s) and carbendazim-resistant (CBD-r). The results suggested that α-MG exhibited a better inhibitory effect on spore germination than on the mycelial growth of C. gloeosporioides. Further investigation indicated that the protective effect could be superior to the therapeutic effect for mango leaves for scab development. The morphological observations of mycelium showed that α-MG caused the accumulation of dense bodies. Ultrastructural observation further revealed that α-MG caused a decrease in the quantity and shape of the swelling of mitochondria in the mycelium cells of C. gloeosporioides. In addition, bioassays disclosed that the inhibitory activity of α-MG on spore germination was reduced by adding exogenous adenosine triphosphate (ATP). These results suggested that the mode of action of α-MG could be involved in the destruction of mitochondrial energy metabolism. The current study supports α-MG as a natural antifungal agent in crop protection.
Keywords: Colletotrichum gloeosporioides; alpha-mangostin; antifungal activity; mitochondria; spore germination.