Identification of Xanthones from the Mangosteen Pericarp that Inhibit the Growth of Ralstonia solanacearum.

Bacterial wilt caused by Ralstonia solanacearum is one of the most destructive bacterial diseases in agriculture. There is no effective control method, although chemical pesticides are used to prevent this disease, but they may lead to serious problems of environmental pollution. Natural products from plants can be rich and environmentally friendly sources for a broad spectrum biological control of bacteria. This study focuses on the pericarp of mangosteen (Garcinia mangostana) using bioactivity-guided analysis of different fractions and liquid chromatography-mass spectrometry combined with multivariate analysis to determine markers of active fractions. Six prenyl xanthones, including two new xanthones, garcimangosxanthones H and I, were isolated and identified by NMR and HRESIMS. The biomarker γ-mangostin displayed significant activity against the phytopathogen R. solanacearum with an IC₅₀ of 34.7 ± 1.5 μg/mL; γ-mangostin affected the bacterial morphology at a concentration of 16.0 μg/mL as seen with a scanning electron microscope image, and it significantly repressed the virulence-associated genes HrpB, FihD, and PilT of R. solanacearum. γ-Mangostin also reduced the symptoms of bacterial wilt disease effectively that is caused by R. solanacearum in tomato and tobacco seedlings in vitro. These results suggested that the use of γ-mangostin from the mangosteen pericarp against R. solanacearum may be used as a natural bacteriostatic agent in agriculture.