Submitted to: Journal of Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2006
Publication Date: 9/20/2007
Citation: Lacava, P.T., Li, W., Araujo, W., Azevedo, J., Hartung, J.S. 2007. The endophyte curtobacterium flaccumfaciens reduces symptoms caused by xylella fastidiosa in catharanthus roseusan endophytic bacterium from citrus. Journal of Microbiology. 45(5):388-393. Interpretive Summary: Plant diseases pose a direct threat to the U.S. Citrus Industry. Citrus variegated chlorosis is a disease of sweet orange caused by the bacterium Xylella fastidiosa. All varieties of sweet orange are susceptible to this disease, and the severity of the disease is increasing in Brazil, where it reduces the yield of usable fruit. However, in some severely diseased groves, individual trees are sometimes observed to be infected by Xylella fastidiosa without showing severe disease symptoms. These trees are not genetically resistant to the pathogen, because when new trees are propagated from them by bud grafting, they are just as susceptible to the disease as any other sweet orange. What is protecting these trees from the disease in the groves? We isolated Xylella fastidiosa as well as other bacteria from these trees. These bacteria were used to inoculate periwinkle plants in a greenhouse. Periwinkle plants are a convenient host for experiments with Xylella fastidiosa. We show in this work that one of these bacteria isolated from healthy appearing, but infected sweet orange, can colonize periwinkle plants after experimental inoculation. Plants inoculated with Curtobacterium flaccumfaciens and Xylella fastidiosa did not develop symptoms typical of Xylella fastidiosa infection. We also developed a sensitive test for the presence of Curtobacterium flaccumfaciens in inoculated plants. Our results will be of interest to scientists working on biologically based controls for plant diseases.
Technical Abstract: Citrus variegated chlorosis (CVC) is a disease of sweet orange (Citrus sinensis (L.)) caused by Xylella fastidiosa subsp. pauca, a phytopathogenic bacterium that can infect all sweet orange cultivars. Sweet orange trees are sometimes observed to be infected by Xylella fastidiosa without showing severe disease symptoms, while other trees in the same grove do show severe disease symptoms. The principal endophytic bacterial species isolated from such CVC-asymptomatic citrus plants is Curtobacterium flaccumfaciens. Madagascar periwinkle (Catharanthus roseus (L.)), is a model plant used to study X. fastidiosa in greenhouse environments. To study the interactions of X. fastidiosa and C. flaccumfaciens, periwinkle plants were separately inoculated with C. flaccumfaciens, X. fastidiosa and with both bacteria together. The number of flowers produced by the plants, the height of plants and disease symptoms were evaluated. PCR-primers for C. flaccumfaciens were designed to confirm the presence of this endophytic bacterium in plant tissue and to complement an existing assay for X. fastidiosa. These primers were able to detect C. flaccumfaciens in periwinkle in the presence of X. fastidiosa. X. fastidiosa caused stunting and reduced the number of flowers produced by periwinkle. When C. flaccumfaciens was inoculated together with X. fastidiosa, stunting was not observed. The number of flowers produced by our doubly- inoculated plants was intermediate between the number produced by plants inoculated with either bacterium separately. Our data suggest that C. flaccumfaciens interacted with X. fastidiosa in C. roseus, and reduced the severity of disease symptoms induced by X. fastidiosa. Periwinkle provides an excellent experimental system to study the interaction of C. flaccumfaciens and other endophytic bacteria with X. fastidiosa.