Improved tissue sampling for reliable detection of Candidatus liberibacter asiaticus

Authors: HAJERI, SUBHAS - Central California Tristeza Eradication Agency; KUMAGAI, LUCITA - California Department Of Food And Agriculture; Yokomi, Raymond - Ray

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2023
Publication Date: 9/23/2023
Citation: Hajeri, S., Kumagai, L., Yokomi, R.K. 2023. Improved tissue sampling for reliable detection of Candidatus liberibacter asiaticus. Plants. 12(19). Article e3364. https://doi.org/10.3390/plants12193364.
DOI: https://doi.org/10.3390/plants12193364

Interpretive Summary: This report presents data from a 2-year study to determine the best source tissue for year around qPCR detection of 'Candidatus Liberibacter asiaticus' (CLas), the bacterium associated with Huanglongbing HLB) (aka citrus greening). The citrus tissue compared were mature leaves and various photoassimilate sink tissues (new flush, fruit peduncle, and feeder roots). DNA extracted from a single peduncle sample was more reliable than single or quadrant mature leaves or other sink tissues for qPCR detection of CLas. Quadrant peduncle samples were 10-20 percent more sensitive than other source tissues collected singly or as a quadrant sample. No statistical differences were found between seasons and tissue types for either positive or negative qPCR results. Therefore, the most reliable DNA sample for accurate detection of CLas from infected trees is from peduncle tissue.

Technical Abstract: Early detection and prompt response are key factors in both the eradication and suppression of the huanglongbing (HLB) epidemic in California. Due to the lack of visible symptoms, low titer, and uneven distribution of ‘Candidatus Liberibacter asiaticus’ (CLas) in an infected tree, selecting the best leaves to sample from a mature tree with more than 200,000 estimated leaves is a major hurdle for early detection by qPCR. Phloem-limited plant pathogens move in a source-to-sink fashion along with photoassimilates. The purpose of this two-year research project was to evaluate the titer of CLas in source tissues (mature leaves) and various sink tissues (new flush, fruit peduncle, and feeder roots) and determine the best tissue to test at the right time of the year for early CLas detection. In this study, we found that the peduncle tissue sample was the most reliable tissue type overall for accurately detecting CLas in trees known to be infected. Single peduncle samples were more reliable than single or quadrant mature leaves or other sink tissues. Quadrant peduncle samples were 10-20 percent more sensitive than other source tissues (single or quadrant mature leaf samples). No statistically significant relationship was found between season and tissue types for positive or negative qPCR results.