Non-destructive fluorescence sensing for applications in precision viticulture

A portable fluorescence device was used for the non-destructive sensing of winegrape (Vitis vinifera L.) maturity and plant vigor, directly in the vineyard. The sensor assesses target molecules such as chlorophyll and phenolic compounds (anthocyanins and flavonols), which markedly change during fruit maturity and plant stress conditions. Different excitation wavelengths were provided by LED sources, in the UV (375 nm) and visible (630 nm red, 520 nm green and 450 nm blue) spectral bands, and the acquisition was performed in the red (680-690 nm) and far-red (730-780 nm) regions. The far-red to red chlorophyll fluorescence ratio is an index of the chlorophyll content. The red-to-UV fluorescence (far-red) excitation ratios was used as index of flavonols. Fluorescence mapping was carried out at the `Fattoria di Magliano' winery (South Tuscany, Italy) in 2013, on Vermentino and Merlot cvs. detecting manually vine leaves at the bunch closure phenological stage and grape bunches just before harvest, on a 15×15m grid. The spatial distribution of flavonols in Vermentino and anthocyanins in Merlot were reported as colorimetric maps, showing the heterogeneity of phenolic maturity. The chlorophyll index, inversely correlated to the sugar content of berries, allowed representing the heterogeneity of technological maturity. Maps of the chlorophyll-flavonols combined index, correlated to the leaf nitrogen content, were used to control the vine growth status within and among vineyards. These information provided in a sustainable, rapid and non-destructive way, are useful in precision viticulture to support producer decisions and improve the wine quality.