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

Abstract

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.