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United States Department of Agriculture

Agricultural Research Service

Title: Comparison of Visual Assessment to Polymerase Chain Reaction Assay Testing to Estimate the Incidence of the Huanglongbing Pathogen in Commercial Plantings in Florida

Authors
item Irey, Michael
item Gast, Tim - SOUTHERN GARDENS CITRUS
item Gottwald, Timothy

Submitted to: Proceedings of Florida State Horticultural Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 1, 2006
Publication Date: October 4, 2006
Citation: Irey, M.S., Gast, T., Gottwald, T.R. 2006. Comparison of visual assessment to polymerase chain reaction assay testing to estimate the incidence of the huanglongbing pathogen in commercial plantings in florida. Proceedings of Florida State Horticultural Society. 42:17-21.

Interpretive Summary: Huanglongbing (HLB), also called citrus greening, is one of the most serious diseases of citrus worldwide. The disease is caused by species of bacteria in the genus Candidatus Liberibacter and was discovered for the first time in the United States in Florida in August, 2005. Among the recommended control measures for HLB is the rouging of existing sources of HLB within an area in order to reduce the potential inoculum reservoir. In areas where HLB is endemic, rouging has been based primarily on the presence of visual symptoms. Molecular detection protocols are available for the detection of HLB, but it has generally been reported that molecular testing was limited to the confirmation of infections and not as useful for detecting infections in non-symptomatic plants. It is generally accepted that rouging based on visual symptoms does not remove all infected trees but there are little data available to document actual infection levels. In the study presented here, visual surveys were compared to the testing of the trees with a polymerase chain reaction-based protocol (PCR). Initial results indicate that the actual level on infection based on PCR testing may be up to two times the level of infection estimated based on presence of visual symptoms.

Technical Abstract: Huanglongbing (HLB), (synonym = citrus greening) is one of the most serious diseases of citrus worldwide. The disease is caused by species of bacteria in the genus Candidatus Liberibacter and was discovered for the first time in the United States in Florida in August, 2005. To date, the Asian form of HLB, caused by Candidatus Liberibacter asiaticus, is the only form of HLB that has been found in Florida. Among the recommended control measures for HLB is the roguing of trees expressing symptoms of HLB within an area in order to reduce the potential inoculum reservoir. In areas where HLB is endemic, roguing has been implemented based predominantly on the presence of visual symptoms. Molecular detection protocols are available for the detection of HLB, but due to the uneven distribution of the bacterium in the plant, the serological variability of the pathogen, and perceived limitations of testing methodology, generally it has been reported that molecular testing was limited to the confirmation of visual infections and not as useful for detecting infections in non-symptomatic plants. It is generally accepted that roguing based on visual symptoms does not remove all infected trees but there are little data available to document the actual incidence of infection. In the study presented here, visual surveys were compared to the testing of trees with a polymerase chain reaction-based protocol (PCR). Initial results indicate that the actual incidence of infection based on PCR testing may be up to two times the incidence of infection estimated based on the presence of visual symptoms alone.

Last Modified: 4/21/2014
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