Under-vine Zulla cover crop: Effect on glycosidic aroma precursors of Vitis vinifera L. cv Syrah musts

The employment of cover cropping has been developed in vineyards to mitigate soil erosion and the massive use of herbicides, but the effects on crop yields and berry quality have been little explored. Glycosidic aroma precursors constitute the aroma potential of grapes and have remarkable relevance in neutral grapes, such as Syrah. These compounds tend to be affected by environmental conditions and stressors; therefore, the influence of cover crops on aroma precursors has been studied for the first time. For this purpose, bound aroma compounds from Syrah cv. must obtained from conventional and organic vineyards, subjected to soil tillage and to the influence of different amounts of Zulla cover crop, were extracted and analysed. This experiment was carried out over three consecutive harvests (2019, 2020 and 2021). 40 aglycones were detected, mainly C13-norisoprenoids and terpenes. The last harvest (2021) accounted for the highest amount of precursors, owing to the exceptional amount of isodurene, naphthalene and 2-methylnaphtalene. The year Zulla was planted (2019), treatments with lower Zulla "pressure" increased aroma precursors. In the second vintage (2020), the general impact of Zulla was negative. Decreasing the amount of aglycones with the largest amount of cover crop increased the presence of aglycones in the must. In the last harvest (2021), the two highest levels of Zulla resulted in an increase of the aromatic precursors determined in the must. These results show that the effects of the presence of Zulla are strongly vintage-dependent and probably on the development of the roots. Furthermore, the last vintage results indicate that the employment of Zulla cover crops could be favourable for varieties such as Syrah, a neutral aroma grape, where bound forms are largely responsible for the potential aroma in the resulting wines.