The potential of spectral reflectance technique for the detection of Grapevine leafroll-associated virus-3 in two red-berried wine grape cultivars

The detection of viruses in plants involves destructive sampling followed by testing by enzyme-linked immunosorbent assay (ELISA) and/or reverse transcription-polymerase chain reaction (RT-PCR). In this study, we have investigated the potential of leaf spectral reflectance changes between virus infected and uninfected grapevines (Vitis vinifera L) in developing non-invasive techniques for field-based 'real-time' diagnosis of grapevine leafroll disease (GLD). In situ leaf reflectance spectra were taken with a portable spectrometer using detached leaves from uninfected and Grapevine leafroll-associated virus-3 (GLRaV-3) infected plants of two wine grape cultivars (Cabernet Sauvignon and Merlot). Specific differences in vegetation indices and wavelength intervals were observed between virus-infected and uninfected leaves in the green peak (near 550 nm), the near infrared (near 900 nm) and in the mid-infrared (near 1600 nm and 2200 nm). Results of reflectance spectra and classification analysis suggest that different vegetation indices and/or individual wavelength bands may differ in their ability to detect GLD depending on whether there are visible symptoms in the virus-infected leaves. The differences in leaf reflectance measurements at specific wavelength intervals between virus-infected and uninfected grapevines and their correlation with RT-PCR results for the presence of GLRaV-3 suggest spectral reflectance technique as a promising tool for cost-effective, nondestructive method for diagnosis of GLD in the field. To our knowledge this represents the first study to report the potential of using leaf spectral data for virus disease diagnosis in a perennial crop. (C) 2008 Elsevier B.V. All rights reserved.