Detecting citrus greening in the field – a rapid new method published
27th February, 2026
A new rapid detection method for Candidatus Liberibacter asiaticus, the bacterium behind citrus greening (HLB), has just been published in Crop Protection, The Official Journal of the International Association for the Plant Protection Sciences.
Detecting Huanglongbing (HLB) early is one of the hardest problems in citrus protection. Once a tree is infected, there is no cure. Yield loss can range anywhere from 30% to a total loss. The pathogen distributes itself unevenly inside the plant, making laboratory diagnosis inconsistent. Current diagnostic tools such as polymerase chain reaction (PCR) and real-time PCR are sensitive, but they require thermal cyclers, fluorescence readers, trained staff and time. In field settings and at quarantine stations, all of these can be in short supply. A team at the Indian Council of Agricultural Research – Indian Agricultural Research Institute (ICAR-IARI) in New Delhi has now published a diagnostic tool that side-steps most of these constraints, working directly on crude citrus sap and returning a result in 25 minutes.
How the test works
The method combines two techniques. Recombinase polymerase amplification (RPA) is a fast, isothermal DNA amplification technology. Unlike PCR, it does not require thermal cycling and can be run at a constant temperature between 25°C and 45°C. It is resistant to common PCR inhibitors, and its reagents are stable in lyophilised form, which suits it for use outside the laboratory.
The team combined RPA with a lateral flow assay (LFA), the same underlying format as a pregnancy test or a rapid antigen test. The result is read visually as a coloured band on a paper strip. No fluorescence reader, gel electrophoresis or ultraviolet source is required.
The assay targets the conserved outer membrane protein (OMP) gene of Candidatus Liberibacter asiaticus, the most widespread species behind HLB. Runtime: 25 minutes at 37°C. The assay detected the bacterium at up to 10⁻⁴ dilution of crude sap and in 67 field samples across Indian citrus orchards, including symptomatic trees and apparently healthy ones.
When time is short
Time is everything with citrus greening. Once a tree shows the first symptoms, the bacterium has often been living inside it for months, spreading quietly to its neighbours. By the time a grower notices something is wrong, the disease has usually moved on.
That is what makes a fast, field-ready test so valuable. The RPA-LFA assay works directly on sap squeezed from a leaf, needs no refrigeration or specialised equipment, and returns a result during the same visit. For nursery managers, orchard inspectors and plant-health officers, that is a very different working day from one that ends with samples posted to a distant laboratory.
In citrus-growing regions where reliable laboratory access is limited, the change goes further still. Regular surveillance, once too slow or too expensive, becomes practical. Where citrus greening is already spreading, the test can speed up the removal of infected trees and slow further contamination. Where the disease has not yet arrived, it can help catch a single infected shipment at the border before it reaches a single orchard.
The CITRUSBUSTERS view
Early detection is the first line of defence against citrus greening, and one of the three integrated lines of action of CITRUSBUSTERS. Across our consortium, several partners are working on the same core question: how can the disease be detected before the tree looks sick?
In CITRUSBUSTERS’ Work Package 1, Bioclear Earth has built machine-learning models based on microbial signatures around leaves and roots, with preliminary accuracies of 71–79% in HLB detection. The Institute for Sustainable Plant Protection of the National Research Council of Italy (CNR-IPSP) is identifying the volatile chemical fingerprint of infected trees. AINIA has deployed a hyperspectral, thermal and LiDAR drone platform for large-scale orchard monitoring. And the Centro de Citricultura Sylvio Moreira – Instituto Agronômico (CCSM-IAC) in Brazil is providing field conditions for the future validation of selected project solutions.
The RPA-LFA assay from ICAR-IARI adds another approach to the same shelf: a paper-strip test, in the field, in 25 minutes.
CITRUSBUSTERS congratulates Damini Diksha and her colleagues at ICAR-IARI on the publication of this work. Different paths, same idea – a citrus sector that catches the disease before the disease catches the tree.
This article is based on: Diksha D., Wangkhem B., Sidharthan V.K., Sharma S.K., Baranwal V.K. (2025). Rapid detection of ‘Candidatus Liberibacter asiaticus’ through recombinase polymerase amplification-based lateral flow assay (RPA-LFA) in citrus using crude sap. Crop Protection.