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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 #390560
Research Project: Identification of Novel Management Strategies for Key Pests and Pathogens of Grapevine with Emphasis on the Xylella Fastidiosa Pathosystem

Location: Crop Diseases, Pests and Genetics Research

Title: Studying bacterial population in ACP and citrus samples - improvements of HLB diagnostic accuracy

Author
item Chen, Jianchi

Submitted to: Citrograph
Publication Type: Trade Journal
Publication Acceptance Date: 2/1/2021
Publication Date: 4/1/2022
Citation: Chen, J. 2022. Studying bacterial population in ACP and citrus samples - improvements of HLB diagnostic accuracy. Citrograph. 13(2):58-60.

Interpretive Summary:

Technical Abstract: Huanglongbing (HLB) is associated with an unculturable bacterial pathogen, ‘Candidatus Liberibacter asiaticus’ (CLas). HLB was found in southern California in 2012, and the current management strategy is based on suppression of the Asian citrus psyllid (ACP) that transmits CLas, and removal of confirmed CLas-positive trees. CLas in ACP and citrus is detected using polymerase chain reaction (PCR) technology based on the characteristic sequence of DNA, typically 16S rDNA1, in the CLas genome. Recent research has shown that in ACP and citrus, there can be bacteria other than CLas present, some which are close relatives of CLas and may interfere with PCR detection of CLas. Most of these non-CLas bacteria are not well known or completely unknown. We recently developed a procedure using a technology called metagenomic analysis to detect and identify non-CLas bacteria in samples being tested for CLas. With assistance from the California Department of Food and Agriculture (CDFA) and the Citrus Research Board (CRB), five ACP and two citrus samples were obtained from HLB quarantine zones. From these samples, ten bacteria different at genus level were identified with high confidence based on the presence of full or partial genome sequences. Two of these bacteria, called Bradyrhizobium sp. and Mesorhizobium sp., were known to be closely related to CLas. These bacteria, if present in high concentrations, could interfere with current 16S-rDNA-based PCR for CLas detection and result in a false positive result. Therefore, the use of this metagenomic technology will improve the specificity of HLB diagnosis in California.