Project Number: 8072-42000-093-002-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Oct 1, 2020
End Date: Aug 30, 2021
Huanglongbing (HLB) is a devastating citrus disease with no known cure. It’s spread by an insect present in most citrus-producing areas of the US. Therefore, locations like California that do not presently have the disease in commercial groves are on high alert, spending millions of dollars annually for prevention. Early disease detection can help identify efficient strategies for deploying the limited resources critical for effective containment. The current industry standard for detection involves a lab-based real-time PCR method. To aide producers, ARS proposes to develop a device that can be utilized in the field for early detection of Huanglongbing. The device can potentially be used to screen trees on-site to more effectively identify areas that merit further evaluation.
The Pulse Electric Field (PEF) is a multilayer cantilever device that measures the stress-strain responses of composite materials using the piezoelectric effect. Voltage applied to a driving piezoelectric layer within the device generates a force that places the cantilever tip. The induced voltage of the sensing piezoelectric layer in the device, which correlates with the displacement, is measured with and without the sample to quantify the stiffness and the elastic modulus of the sample. The measurement duration is on the order of seconds, and within minutes a heat map of measured stiffnesses can be produced for a scanned area. Further the orientation of the device relative to the sample can be varied to accommodate measurements of shear modulus. Cantilever tip geometries and orientation can be varied in an array format to simultaneously collect measurements under specific, well controlled conditions. Laboratory PEF prototypes will be constructed for assessing a broad range of leaf samples The technology will be benchmarked against the state-of-the-art RT-PCR assays, and response operator characteristic (ROC) curves will be used to assess the rate of false positive and negatives. Proof-of-concept studies will focus around differentiating HLB-affected plants from those that are healthy or affected by other biotic/ abiotic stresses such as phytophthora infection and zinc-deficiency. Determining exactly how early infection can be detected will also be investigated. Importantly, the aim of the research is not to identify the cause of the changes to leaf stiffness, but simply establish that the changes can reliably distinguish HLB-affected trees. Using the information collected regarding the leaves with the stiffness response from an array of PEF, mathematical models will be constructed to interpret the appropriate responses that will not be confounded by extraneous variables such age, seasonal variations, and/or underlying pathogens not related to HLB. Additional funding will be used to support the transition of laboratory devices to hand-held prototype PEF arrays that are controlled and monitored using software installed on a smart phone or tablet, similar to the iBE device commercialized for breast cancer screening. Prototypes will be provided to stakeholders and extension programs focused on rapid screening for pilot studies.