Spectral Signatures Dataset of Loureiro Grapevine Leaves Affected by Downy Mildew

The present dataset provides a set of spectral reflectance measurements of grapevine leaves (Vitis vinifera L. cv. Loureiro) collected in an experimental vineyard located in Ponte de Lima, within the Vinhos Verdes sub-region (northwestern Portugal), during the 2023 and 2024 growing seasons. The measurements were conducted in situ on grapevine leaves using a portable ASD FieldSpec® 4 spectroradiometer (Analytical Spectral Devices, Boulder, USA). This instrument covers the 400–2500 nm spectral range with a 1 nm spectral resolution. The instrument was operated with a contact probe equipped with an internal halogen light source, ensuring constant illumination and minimising interference from ambient light. The experimental design was implemented in a vineyard plot for the collection of data from leaves with downy mildew symptoms as well as leaves with no visual symptoms. The measurements were performed at multiple phenological stages across the two growing seasons. The spectral signature of each leaf were measured on three consecutive occasions, and the recorded value corresponds to the mean of the three reflectance readings for each wavelength. The data have been organised by year, sampling date, and experimental condition, in Excel (.xlsx) format. This dataset is representative of raw leaf reflectance data, devoid of any additional analytical processing, and can be used in studies addressing the use of spectroscopy for plant physiology, spectral response to biotic stress.