Predicting Berry Quality Attributes on Cv. Xarel·lo Rain-Fed Vineyards Using Narrow-Band Reflectance-Based Indices

Abstract

In rain-fed vineyards, water availability strongly influences vegetative and reproductive growth and, thus, berry quality. Narrow-band spectral indices might provide information on vine structure and physiological status and might be a useful tool for predicting berry quality. In the present study, the feasibility of the indices Normalized Difference Vegetation Index (NDVI) and Photochemical Reflectance Index (PRI) at assessing berry quality was tested. The study was carried out on five commercial vineyards (cv. Xarel lo) in 2009 and 2010. Measurements of predawn water potential (Ψ_pd), canopy to air temperature difference (ΔTm), fractional intercepted photosynthetic active radiation (fIPAR), exposed leaf area (ELA) and canopy reflectance were taken at veraison. Berry weight (BW), total soluble solids (TSS) and titratable acidity (TA) were determined at harvest. Values of Ψ_pd indicated mild to moderate water deficits. In our study, NDVI characterized the effects of water availability on vine vigor (fIPAR) while PRI was found to be related to water status (Ψ_pd). The extent of water deficits was found to be a key factor in determining the aptitude of spectral indices at estimating berry quality attributes. Thus, consistent with the influence of vine vigor and water status on berry quality attributes, NDVI was related to both TA (r² = 0.46) and IMAD (TSS/TA; r² = 0.27) whereas PRI was related to both TSS and IMAD (r² = 0.23 and r² = 0.34, respectively). In addition, PRI was positively related to berry weight (r² = 0.68). The results obtained suggest the potential of hyperspectral reflectance indices of canopy vigor (i.e., NDVI) and photosynthetic functioning (i.e., PRI) at estimating berry quality attributes in vineyards experiencing mild to moderate water deficits.