Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/13/2011
Publication Date: 9/1/2011
Citation: Zhang, M.Q., Powell, C.A., Zhou, L., He, Z., Stover, E., Duan, Y. 2011. Chemical compounds effective against the citrus huanglongbing 'Candidatus Liberibacter asiaticus' in planta. Phytopathology. 101:1097-1103. Interpretive Summary: Citrus huanglongbing (HLB) is an extremely damaging citrus disease throughout the world, and is now the greatest threat facing the Florida citrus industry. There is no reported cure for this disease. A new antibiotic combination was screened to see if it would control the citrus HLB bacterium. The antibiotic combination killed or suppressed the HLB bacterium and kept it at levels below those causing disease for a longer time than the separate antibiotics used alone. The combination of antibiotics also makes it much less likely that antibiotic resistance will develop in the HLB bacterium. In periwinkle, an easily studied plant that also allow the HLB bacterium to multiply well and shows disease, bacterial levels decreased greatly following root-soaking or foliar-spraying with the antibiotic combination. Application of the antibiotic combination through trunk injection or root-soaking also killed or suppressed the HLB bacterium in infected citrus plants and may provide a useful tool for HLB management.
Technical Abstract: Citrus huanglongbing (HLB) is one of the most destructive diseases of citrus worldwide, and is threatening the survival of the Floridian citrus industry. Currently, there is no established cure for this century-old and emerging disease. The new antibiotic combination of penicillin and streptomycin (PS) was screened as one of the control options against the citrus HLB bacterium, ‘Candidatus Liberibacter asiaticus (Las)’ using our newly developed propagation test system with Las-infected periwinkle and citrus. The results demonstrated that the PS was more effective to eliminate or suppress the Las bacterium and remained at a therapeutically effective level for a much longer period of time than when administering the same amount of penicillin or streptomycin alone. When treated with the PS, Las-infected periwinkle cuttings achieved 70% rooting, vs. less than 50% from the other treatments. The Las bacterial titer indicated by quantitative real-time PCR (qPCR) decreased significantly following root-soaking or foliar-spraying with PS in the infected periwinkle. Application of the PS via trunk injection or root soaking also eliminated or suppressed the Las bacterium in the HLB-affected citrus plants, and may provide a useful tool for HLB management.