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Starch accumulation sensor for early detection of HLB

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Research by Dr. Alireza Pourreza, Department of Biological and Agricultural Engineering, University of California, Davis
Article written by Alireza Pourreza, Elizabeth Grafton-Cardwell, Peggy G. Lemaux, & Lukasz Stelinski.
Revised June 21, 2018.

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What is the technique?

This techniques uses starch accumulation in Clas bacteria-infected leaves as an early indication of huanglongbing (HLB) disease in citrus. Starch rotates the polarization plane of light. The sensor has a monochrome camera with a linear polarizing filter set perpendicularly to the polarizing film of the illumination system, which can then be used to visually detect patterns of starch deposition. 

Early detection sensor prototype

Starch accumulation in an HLB-infected leaf generates a blotchy mottle, asymmetrical yellowing pattern. Deficiency of nutrients, like Mg and Zn, cause more uniform yellowing symptoms in the leaf.   

Leaf symptoms of HLB and Zn deficiency

The sensor, mounted on a gator vehicle, was tested in a Florida citrus grove. Polarized images were taken from healthy, HLB-infected, and Zn-deficient canopies. The sensor could detect and differentiate between HLB-infected and nutrient deficient plants.


Polarized images from healthy, HLB, and HLB with Zn deficiency

The polarized imaging methodology was also studied to determine the earliest time after infection HLB can be detected. In one study, two-year old Valencia orange plants were inoculated using a disk of infected leaf tissue grafted into a healthy leaf.

Citrus leaf graft-inoculated with disk tissue from an HLB-infected leaf

Time-lapse polarized images of leaves from inoculated citrus plants were taken weekly. HLB symptoms (viewed as starch accumulation) became visible in the polarized images five weeks after inoculation, while plants were still not showing symptoms. 

Time-lapse images of a leaf from HLB-infected plant collected weekly after infection
Time-lapse images of a leaf from HLB-infected plant collected weekly after infection

Who is working on the Project?

Alireza Pourreza, Department of Biological and Agricultural Engineering at the University of California, Davis, is part of a team of researchers (Won Suk Lee, John Schueller, Reza Ehsani, Ed Etxeberria, Bill Gurley, and Arunava Banerjee at the University of Florida and Eran Raveh at ARO Gilat Research Center, Negev, Israel) that developed and are testing the sensing system to measure starch accumulation in leaves resulting from infection by the CLas, bacterium, that causes HLB in citrus.

What are the challenges and opportunities?

Currently, the team is focusing on improving accuracy, determining how early in the infection this sensor can detect the disease, and developing a commercialized product for in-field diagnosis. This affordable tool will help citrus growers determine which trees are infected withCLas and, with tree removal, help growers to more effectively eliminate HLB from their groves in the early stages of infection.

Funding source: This project is funded by the Citrus Research and Development Foundation (CRDF)