Minimal pruning increases the concentration of aromatic precursors in viognier grapes

Abstract

Aromatic composition of grapes is essential to wine quality. A study was conducted over four years, under Mediterranean conditions in southern France, to assess the impact of different training systems on aromatic precursors in fruit of Viognier B. grapevines. Two training systems [vertical shoot positioning (VSP) and minimal pruning (MP)] were investigated during the 2010, 2011, 2013 and 2014 seasons. At harvest, 18 different compounds corresponding to 4 families of grape aromatic glycoside precursors were quantified in grapes and musts by Gas Chromatography with flame ionization detector (GC-FID): monoterpenes, C6 compounds, aromatic alcohols and C₁₃-norisoprenoids (the latter only analysed in 2013 and 2014). MP significantly increased grape aromatic glycoside precursors concentrations, expressed in µg of 4 nonanol per kg of grapes, of C6 compounds (+38%), aromatic alcohols (+46%) and C₁₃-norisoprenoids (+133%). The differences between MP and VSP were greater in 2014, a year with diminished potential of aromatic glycoside precursors (2014 < 2010 <2013< 2011). This difference between years was negatively correlated with the Cool night index (CI). This study confirms that the MP training system presented a greater aroma potential of grapes than VSP, mainly due to a positive effect on the concentration of aromatic glycoside precursors by a reduction in berry size. In fact, biosynthesis of aromatic precursors, expressed in nanograms of 4 nonanol per berry, was similar for both training systems.