Abstract
The introduction of irrigation in vineyards of the Mediterranean basin is a matter of debate, in particular in those of the Douro Demarcated Region (DDR), due to the limited number of available studies. Here, we aimed to perform a robust analysis in three consecutive vintages (2018, 2019, and 2020) on the impact of deficit irrigation on the yield, berry quality traits, and metabolome of cv. ‘Touriga Nacional’. Results showed that in the peaks of extreme drought, irrigation at 30% crop evapotranspiration (ETc) (R30) was able to prevent a decay of up to 0.4 MPa of leaf predawn water potential (ΨPd), but irrigation at 70% ETc (R70) did not translate into additional protection against drought stress. Following three seasons of irrigation, the yield was significantly improved in vines irrigated at R30, whereas irrigation at R70 positively affected the yield only in the 2020 season. Berry quality traits at harvest were not significantly changed by irrigation, except for Total Soluble Solids (TSS) in 2018. A UPLC–MS-based targeted metabolomic analysis identified eight classes of compounds, amino acids, phenolic acids, stilbenoid DP1, stilbenoid DP2, flavonols, flavan-3-ols, di-OH- and tri-OH anthocyanins, and showed that anthocyanins and phenolic acids did not change significantly with irrigation. The present study showed that deficit irrigation partially mitigated the severe summer water deficit conditions in the DDR but did not significantly change key metabolites.
Highlights
Numerous highly important wine regions in the world are located in seasonally dry areas with high evaporative demand
The analysis of the agrometeorological conditions in the Douro Valley wine region revealed that the 2018 season was characterized by a dry winter, followed by relatively high precipitation and low temperatures during spring and early summer (Figure S1A)
At the end of July and beginning of August one heat wave occurred with temperatures above 40 ◦C for six consecutive days and peaking at 44.5 ◦C (Figure S1A)
Summary
Numerous highly important wine regions in the world are located in seasonally dry areas with high evaporative demand. Climate change scenarios are predicting an increase in temperature as well as more scarce and torrential rainfall episodes. This is the case in the Mediterranean basin, including the Douro Demarcated Region (DDR). Warmer temperatures increase sugar ripeness and reduce the acidity ( malic acid) and flavors, resulting in unbalanced wines [1,2]. Other impacts of increasing temperatures may include the raising of potential alcohol levels [3] and a reduction in anthocyanin accumulation [4]. Phenological stages with earlier onsets of budburst, flowering, and veraison may occur at warmer temperatures [5,6], which results in increased risks of frost damage during spring, as well as a higher incidence of grapevine-related pests and diseases [7–9]
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