Raman Spectroscopy an Option for the Early Detection of Citrus Huanglongbing

Abstract

This research describes the application of portable field Raman spectroscopy combined with a statistical analysis of the resulting spectra, employing principal component analysis (PCA) and linear discriminant analysis (LDA), in which we determine that this method provides a high degree of reliability in the early detection of Huanglongbing (HLB) on Sweet Orange, disease caused by the bacteria Candidatus Liberibacter asiaticus. Symptomatic and asymptomatic plant samples of Sweet Orange (Citrus sinensis), Persian Lime (C. latifolia), and Mexican Lime (C. aurantifolia) trees were collected from several municipalities, three at Colima State and three at Jalisco State (HLB presence). In addition, Sweet Orange samples were taken from two other Mexican municipalities, one at San Luis Potosí and the other at Veracruz (HLB absent). All samples were analyzed by real-time PCR to determine its phytosanitary condition, and its spectral signatures were obtained with an ID-Raman mini. Spectral anomalies in orange trees HLB-positive, were identified in bands related to carbohydrates (905 cm(-1), 1043 cm(-1), 1127 cm(-1), 1208 cm(-1), 1370 cm(-1), 1272 cm(-1), 1340 cm(-1), and 1260-1280 cm(-1)), amino acids, proteins (815 cm(-1), 830 cm(-1), 852 cm(-1), 918 cm(-1), 926 cm(-1), 970 cm(-1), 1002 cm(-1), 1053 cm(-1), and 1446 cm(-1)), and lipids (1734 cm(-1), 1736 cm(-1), 1738 cm(-1), 1745 cm(-1), and 1746 cm(-1)). Moreover, PCA-LDA showed a sensitivity of 86.9 % (percentage of positives, which are correctly identified), a specificity of 91.4 % (percentage of negatives, which are correctly identified), and a precision of 89.2 % (the proportion of all tests that are correct) in discriminating between orange plants HLB-positive and healthy plants. The Raman spectroscopy technique permitted rapid diagnoses, was low-cost, simple, and practical to administer, and produced immediate results. These are essential features for phytosanitary epidemiological surveillance activities that may conduct a targeted selection of highly suspicious trees to undergo molecular DNA analysis.

Root samples provide early and improved detection of Candidatus Liberibacter asiaticus in Citrus

“…Early detection of CLas has long been a goal of the Citrus community 31 , 32 . A number of researchers have focused efforts on improving the rate of detection using a wide variety of methods including: differences in spectra 41 or polarization of light reflected from leaves using portable devices 42 , 43 or satellite imagery 44 ; the presence of CLas secreted proteins 45 ; and the presence of salivary sheaths from Asian citrus psyllid (ACP) 46 . However, commercial growers have been hesitant to adopt methods not approved by regulators, and regulators require direct evidence of the pathogen’s presence (i.e., its genome).…”

Raman-Based Diagnostics of Biotic and Abiotic Stresses in Plants. A Review

“…The remaining inelastically scattered photons are directed into the spectrometer, where photons are dispersed on a grating according to their energies prior to their appearance on the CCD. Typically, researchers use near-Infrared (near-IR; 785 and 830 nm) laser sources for RS on biological species (Vallejo-Pérez et al, 2016;Farber et al, 2019bFarber et al, , 2020cMandrile et al, 2019;Sanchez et al, 2019c. This wavelength choice is based on a phenomenon that is known as "biological window. "…”

Identificación de tecnologías y métodos para la detección temprana del Huanglongbing (HLB) a través de cienciometría en artículos científicos y patentes

“…Esta es una técnica óptica no invasiva, fácil de llevar a cabo y que solo requiere una conguración muy compacta, lo que signica que puede ser portátil (Pérez et al, 2016). Esta técnica mide la dispersión de luz inelástica basada en una fuente monocromática, proporcionando información sobre la composición química del objeto analizado (Pérez et al, 2016).…”