Effect of Plant Essential Oils on Ralstonia solanacearum Race 4 and Bacterial Wilt of Edible Ginger

Palmarosa (Cymbopogon martini), lemongrass (C. citratus), and eucalyptus (Eucalyptus globulus) oils were investigated for their effects on Ralstonia solanacearum race 4 and their potential use as biofumigants for reducing bacterial wilt disease of edible ginger (Zingiber officinale). Three concentrations of the oils (0.04, 0.07, and 0.14% vol/vol) were evaluated by culture amendment assays, epifluorescence microscopy, and studies in potting medium. In culture amendment assays with palmarosa and lemongrass oils at 0.04%, both oils significantly reduced the growth of the bacterium compared with the control, and at 0.07 and 0.14% they showed complete inhibition of bacterial growth. Epifluorescence microscopic observations showed cell deterioration in 95 to 100% of the cells at all concentrations of palmarosa and lemongrass oils, indicating its bactericidal properties. Eucalyptus oil treatments at 0.04 and 0.07% had bacteriostatic effects on the cells. The pathogen was not detected in R. solanacearum-infested potting medium after treatment with palmarosa and lemongrass oils at 0.07 and 0.14% in any of the experiments. Bacterial wilt incidence on edible ginger was significantly reduced when planted in essential oil-treated potting medium. None of the essential oil treatments reduced the growth or yield of edible ginger grown for 180 days in 5-liter pots.