ξ current address : Financière agricole du Québec -Développement international, 1400, boulevard de la Rive-Sud, Saint-Romuald, Québec, G6W 8K7, Canada 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 Author-produced version of the article published in International Journal of Remote Sensing, 2011, 32 (14), 3835-3849. The original publicatioin is available at http://www.tandfonline.com doi:10.1080/01431161003782064Page 2 fluorescence ratio (F 440 /F 740 ), it was possible to detect infected berries starting as early as 4DAI. 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.Key words: Bunch rot, detection, epidemiology, fluorescence, remote sensing, phytoalexins, precision viticulture, Vitis vinifera.
IntroductionGray mold of grapevines is caused by Botrytis cinerea Pers.:Fr., the anamorph of an ascomycete fungus (Botryotinia fuckeliana Whetzel). This cosmopolitan fungus is a necrotrophic pathogen attacking over 200 plant species (Jarvis, 1980). In grapevine, it can infect leaves, in spring, where it grows in a concentric way at the margin of the blade and inflorescences which are highly susceptible, particularly dehiscent floral parts (Pezet et al. 2004). Various infection pathways have been described to establish epidemiological relationships between these first attacks, occurring early in the season, and the typical infections of maturing berries (Elmer and Michailides, 2004). Gray mold development on grape berries depends on the genetic structure of the pathogen population (Martinez et al., 2005), but is also driven by some key factors, including climatic conditions, cluster architecture and berry susceptibility (Pezet...
