Autofluorescence of grape berries following Botrytis cinerea infection
Résumé
Gray mold is caused by Botrytis cinerea (anamorph of an ascomycete fungus) infecting over 200 plant species worldwide and causing tremendous harvest losses in vineyards. Even though all grapevine cultivars (Vitis vinfera L.) are susceptible to the disease, defense mechanisms are induced to counteract or slow down infection and colonization by the pathogen. One of the key inducible defense molecule is resveratrol, a blue fluorescent stilbenic compound. Considering early fungal detection as a crucial step in disease control strategies, we evaluated the potential of plant fluorescence to achieve early detection of B. cinerea in grapevine berries. By comparing control and artificially inoculated berries, images of fluorescence were taken in the laboratory at six combinations of emission/excitation wavelengths (F440/UV, F520/UV, F690/UV, F740/UV, and F690/436-blue F740/436-blue). Data treatments include proper image correction, interest area selection, fluorescence ratios computation and edge detection. In the early stages, before 3 DAI (days post inoculation), the discrimination (of - between ?) wounded and symptomatic berries could not easily be achieved using blue fluorescence solely (440 nm). However, using blue out of red fluorescence ratio (F440/F740), it was possible to detect infected berries starting as early as 4 DAI. Using image analysis and edge detection over UV-epidermal transmittance measured at 690 nm, it was possible to detect botrytised berries as early as 6 hours after inoculation. The potential of these detection methods for use in the epidemiological field are discussed.
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