Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/4/2010
Publication Date: 5/1/2010
Citation: Paret, M. L., Cabos, R., Kratky, B. A., and Alvarez, A. M. 2010. Effect of plant essential oils on Ralstonia solanacearum race 4 and bacterial wilt of edible ginger. Plant Dis. 94:521-527. Interpretive Summary: Bacterial wilt causes severe reduction in yields of edible ginger in Hawaii and many other sub-tropical and tropical regions of the world. Once a field is infested with the pathogen it becomes unsuitable for further ginger cultivation due to the persistent survival of the bacterium in plant debris and weeds. Due to the current restrictions on the use of methyl bromide, farmers have limited options for the management of this disease. Plant essential oils have potential to control bacterial wilt by eliminating the disease-causing bacteria in field soil. The results of this study show that palmarosa and lemongrass oils were effective in significantly reducing the bacterial wilt pathogen in both laboratory and greenhouse studies. In addition, none of the essential oil treatments reduced the growth or yield of the edible ginger test plants.
Technical 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 bio-fumigants for treating pathogen- infested edible ginger (Zingiber officinale R.) fields. Three concentrations of the oils (0.04, 0.07 and 0.14 % v/v) were evaluated by culture amendment assay, epifluorescence microscopy, and pot studies. Culture amendment assay indicated complete inhibition of growth of the bacterium on the medium with palmarosa and lemongrass oils at 0.07 % and above. At 0.04 %, both oils significantly reduced the growth of the bacterium compared to the control. Eucalyptus oil at all concentrations did not reduce the growth of the bacterium. Epifluorescence microscopic observations showed 95-100 % cell death when treated with palmarosa and lemongrass oils at all concentrations and eucalyptus oil at 0.14 % in a direct contact assay indicating its bactericidal effect. Eucalyptus oil treatments at 0.04 and 0.07 % had bacteriostatic effects on cells. The pathogen was not detected in R. solanacearum- infested potting medium after treatment with palmarosa and lemongrass oils at 0.07 % and above in any of the experiments. None of the treatments reduced the growth or yield of edible ginger.