ARS | Publication request: Near-Infrared Spectroscopy for discrimination of huanglongbing-infected citrus leaves from uninfected leaves

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: July 6, 2010
Publication Date: April 18, 2011
Citation: Windham, W.R., Poole, G.H., Park, B., Heitschmidt, G.W., Gottwald, T.R., Lawrence, K.C. 2011. Near-Infrared Spectroscopy for discrimination of huanglongbing-infected citrus leaves from uninfected leaves. Proc. the 14th International Conference on NIR Spectroscopy: 235-239.

Technical Abstract: Citrus greening, also called Huanglongbing (HLB) or yellow dragon disease, is one of the more serious diseases of citrus and is a threat to the U.S. industry. An infected tree produces fruit that is unsuitable for sale as fresh fruit or for juice. The only definitive method of diagnosis of trees suspected of infection by citrus greening pathogens is by analysis of DNA. The purpose of this research was to investigate the use of near infrared spectroscopy to differentiate HLB infected leaves from uninfected leaves. Leaf samples were collected from orange and grapefruit trees that showed the various symptoms of HLB. Leaves were also collected from a controlled quarantined greenhouse and were used as a “negative” control. Samples were analyzed for the citrus greening pathogens DNA by real-time polymerase chain reaction (PCR). A critical Threshold (Ct) value was assigned from the PCR test that indicated whether a sample is positive or negative for HLB. Leaf spectra were collected from 400 to 2500 nm. PLS calibrations for HLB Ct values were developed with the visible region (400 -750 nm), visible plus the NIR region [(VNIR) 400 - 2500 nm)] and the NIR region (1100 - 2500 nm). All PLS models correctly predicted 100% of the leaves that were negative for HLB or uninfected. The visible, VNIR, and NIR models correctly predicted 94, 96, and 98%, respectively of the leaves that were HLB infected. The PLS loadings for the visible and VNIR models indicated absorption bands related to chlorophyll. The PLS loading for the NIR model indicated absorption bands related to carbohydrate and wax. The results indicate that NIR spectroscopy is a useful, rapid, and inexpensive tool compared to PCR in identification of citrus greening disease.