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ARS Home » Pacific West Area » Parlier, California » San Joaquin Valley Agricultural Sciences Center » Crop Diseases, Pests and Genetics Research » Research » Publications at this Location » Publication #380386

Research Project: Characterization and Management of Citrus Pathogens Transmitted by Phloem-Feeding Insect Vectors

Location: Crop Diseases, Pests and Genetics Research

Title: Improvements to HLB and stubborn testing

item Yokomi, Raymond - Ray
item SELVARAJ, VIJAYANADRAJ - Foreign Agricultural Service (FAS, USDA)
item MAHESHWARI, YOGITA - Foreign Agricultural Service (FAS, USDA)
item RATTNER, RACHEL - Cooperative Agricultural Support Services
item GODFREY, KRISTINE - University Of California, Davis
item Chen, Jianchi
item HAJERI, SUBHAS - Central California Tristeza Eradication Agency

Submitted to: Citrograph
Publication Type: Trade Journal
Publication Acceptance Date: 1/7/2021
Publication Date: 3/16/2021
Citation: Yokomi, R.K., Selvaraj, V., Maheshwari, Y., Rattner, R., Godfrey, K.E., Chen, J., Hajeri, S. 2021. Improvements to HLB and stubborn testing. Citrograph. 12(2):64-68.

Interpretive Summary:

Technical Abstract: Huanglongbing (HLB) control in California is based, in part, on testing citrus trees and eradicating ‘Candidatus Liberibacter asiaticus’ (CLas)-positive trees. This is complicated by the presence of Spiroplasma citri, which is the causal agent of citrus stubborn disease (CSD), since CSD symptoms can resemble those of HLB. These trees will test negative for CLas, but this may raise concern that this is a false negative result. The objective of this study was to develop a protocol to detect and differentiate both pathogens in a single test. Using specific primers and different fluorescent probes for each pathogen, a duplex qPCR assay was developed that detects and differentiates both pathogens simultaneously. Because conventional qPCR assays provide only a relative quantity of the pathogen target, a duplex droplet digital (ddPCR) assay was developed that measures the exact number of DNA targets in the sample and can serve as a confirmation test. These tests can be used by regulators and diagnosticians to improve reliable detection of CLas. In addition, whole genome sequencing of seven strains of S. citri were determined and examined for new gene targets to improve detection of S. citri.