Journal Article

Optical detection of downy mildew in grapevine leaves: daily kinetics of autofluorescence upon infection

Sébastien Bellow, Gwendal Latouche, Spencer C. Brown, Anne Poutaraud and Zoran G. Cerovic

in Journal of Experimental Botany

Published on behalf of Society for Experimental Biology

Volume 64, issue 1, pages 333-341
Published in print January 2013 | ISSN: 0022-0957
Published online December 2012 | e-ISSN: 1460-2431 | DOI: https://dx.doi.org/10.1093/jxb/ers338

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A 15-day survey of autofluorescence has been conducted upon infection by downy mildew [Plasmopara viticola (Berk. & M.A. Curtis) Berl. & de Toni] of leaves of a susceptible grapevine genotype. Different autofluorescence signals were followed from the cellular to the whole-leaf level by using four types of devices for fluorosensing: a macroscope, a spectrofluorimeter, a portable field optical sensor (the Multiplex 3), and a field fluorescence sensor prototype with 335nm excitation. It was shown for the first time, by the three different techniques and at three different scales, that the stilbene-dependent violet–blue autofluorescence (VBF) had a transitory behaviour, increasing to a maximum 6 days post-inoculation (DPI) and then decreasing to a constant lower level, nevertheless significantly higher than in the control leaf. This behaviour could be sensed from both sides of the leaf. On the abaxial side, VBF could discriminate the presence of infection from 1 DPI, and on the adaxial side from 3 DPI. There was a constant increase in blue-excited green fluorescence starting from 8 DPI, concomitant with a decrease in leaf chlorophyll content sensed by one reflectance and two fluorescence indices available on the Multiplex 3 sensor. These results show that a pre-symptomatic and symptomatic sensing of downy mildew is possible by autofluorescence-based sensors, and this is potentially applicable in the field.

Keywords: Disease diagnostics; optical proximal sensors; phenolic compounds; phytoalexin fluorescence; Plasmopara viticola; Vitis vinifera.

Journal Article.  6055 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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