The use of Fourier Transform Infrared Spectroscopy in phenotyping berries from the grapevine Vitis vinifera L.

Abstract

Phenotyping is an increasingly important issue in plant biology, in particular when studying the genetic basis of complex traits, in the context of genotype*environment interactions. The composition of grape berries is a key target for fruit and wine quality. Although an increasing number of samples need to be analysed, grape berry metabolites are not easily accessible and their measurement sometimes involves time consuming protocols. The volume of available grape juice can also be a limiting factor for metabolic phenotyping of grape berries. Fourier Transform Infrared Spectroscopy (FTIR) may provide an accurate and rapid estimate for a whole range of metabolites while using a limited amount of grape juice (15 mL). However, calibration curves must be established for each individual metabolite determined using reference analyses. An important question is whether these curves are variety-specific or not. Another issue is whether calibration curves remain valid through a wide range of maturity levels. In this study, grape juice was obtained weekly over several years from veraison to harvest for 52 varieties of Vitis vinifera L. (31 red and 21 white varieties) with 5 replicates for each sampling date. Each sample was then analyzed using FTIR technology (WineScan™, FOSS). Values for Brix, total acidity, tartrate, malate, pH and Yeast Assimilable Nitrogen (YAN) were compared with reference analyses, such as enzymatic assays. Results obtained by FTIR were highly correlated with reference analyses for Brix, total acidity and malate (R² values > 0.97). For these variables, no specific calibration beyond the one provided by WineScan^TM seems necessary, whatever the variety or the ripening stage. However, calibration was less reliable for tartrate and YAN (0.7<R² values<0.8). Nevertheless, our results indicate that using the FTIR technology is very promising for accurate and high-throughput phenotyping of major grape berry components.