Effect of increased irrigation and additional nitrogen fertilisation on the concentration of green aroma compounds in Vitis vinifera L. Merlot fruit and wine

Abstract

Background and Aims: Green aroma compounds are considered undesirable when present at a high concentration in red wines. This study aimed to understand the effect of two irrigation levels and a higher than standard nitrogen fertilisation on the concentration of both 3-isobutyl-2-methoxypyrazine (IBMP) and six C6 compounds during fruit development. Methods and Results: Fruit samples were collected biweekly during the 2009 and 2010 seasons in a commercial Vitis vinifera L. Merlot vineyard in California, USA, where two irrigation levels (70 and 100% of crop evapotranspiration) and a higher than standard nitrogen fertilisation dose were implemented. The higher irrigation level and additional nitrogen promoted canopy growth and decreased fruit exposure, resulting in increased concentration of IBMP during fruit maturation. The concentration of the six measured C6 compounds, however, was not affected. Deficit irrigation increased fruit colour, quercetin glycosides and phenol-free glucose glycosides (i.e. aroma precursors), and decreased vine yield. The two irrigation levels did not differ on the sensory vegetal perception of the wines, but the additional application of nitrogen fertiliser at fruitset enhanced it. Significance of the Study: These findings confirm previous work showing that vineyard management practices influence fruit and wine concentration of IBMP, and demonstrate for the first time that the same practices have no significant impact on the concentration of six C6 compounds in grapes or on the concentration of hexanol in wines. Grapegrowers aiming to minimise IBMP concentration in fruit at harvest would probably benefit from a reduced application of water and nitrogen to the vineyard.