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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Citrus and Other Subtropical Products Research » Research » Publications at this Location » Publication #354415
Title: A new diagnostic real-time PCR method for huanglongbing detection in citrus root tissue

Author
item PARK, JONG-WON - Texas A&M University
item LOUZADA, ELIEZER - Texas A&M University
item BRASWELL, W. EVAN - Animal And Plant Health Inspection Service (APHIS)
item STANSLY, PHILIP - University Of Florida
item DA GRACA, JOHN - Texas A&M University
item McCollum, Thomas
item RASCOE, JOHN - Animal And Plant Health Inspection Service (APHIS)
item KUNTA, MADHURABABU - Texas A&M University

Submitted to: Journal of General Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/23/2018
Publication Date: 6/13/2018
Citation: Park, J., Louzada, E.S., Braswell, W., Stansly, P.A., Da Graca, J.V., McCollum, T.G., Rascoe, J.E., Kunta, M. 2018. A new diagnostic real-time PCR method for huanglongbing detection in citrus root tissue. Journal of General Plant Pathology. https://doi.org/10.1007/s10327-018-0793-4.
DOI: https://doi.org/10.1007/s10327-018-0793-4

Interpretive Summary: Huanglongbing is the most destructive of all citrus diseases and poses a serious threat to the continued existence of commercial citrus production worldwide. Huanglongbing is associated with infection by Candidatus Liberibacter asiaticus, a non-culturable, insect vectored, phloem limited bacterium. Currently there are no preventive or therapeutic treatments for Huanglongbing. One of the cornerstones of Huanglongbing management is removal of infected trees to prevent spread of the pathogen. Unfortunately, confirmation of infection is especially challenging because there is a lag between the time of infection and subsequent appearance of disease symptoms. Detection of Candidatus Liberibacter asiaticus infections prior to appearance of symptoms has the potential to improve Huanglongbing management. Results of previous reports indicate that following transmission of Candidatus Liberibacter asiaticus into citrus shoots, it moves into roots and roots may prove to be a more reliable diagnostic sample than leaves in infected, but asymptomatic trees. In this study, the diagnostic reliability of roots was compared with leaves from citrus growing in Florida and Texas were compared. Results indicate that there was a greater incidence of Candidatus Liberibacter detection in roots than in leaves, confirming that roots provide an effective diagnostic sample for trees infected, but prior to the appearance of Huanglongbing symptoms in citrus canopies. Use of roots as diagnostic samples has the potential to enhance diagnostics and as a consequence result in improved management of Huanglongbing.

Technical Abstract: Citrus fibrous root tissue was evaluated as an alternative source material for Huanglongbing (HLB) diagnosis by real-time PCR using primer-probe set TXCChlb, developed in the present study based on 16S rDNA of “Candidatus Liberibacter asiaticus” (CLas). Real-time PCR data obtained with DNA samples prepared from leaf and fibrous root tissue collected from mature (> 10 years old) and young (4–5 years old) citrus trees growing in Texas and Florida confirmed that root HLB test is more sensitive than the leaf HLB test in terms of the detection rate of HLB positive trees. In addition, the current study confirmed that HLB can be diagnosed at the pre-symptomatic stage using the root HLB test to facilitate efficient removal of HLB-positive, asymptomatic trees that could serve as a source for HLB. The new HLB diagnostic method using root tissue described in the current study can assist in deploying a more efficient disease management strategy to deter HLB spread, especially at the pre-symptomatic stage.