The Effect of Irrigation-Initiation Timing on the Phenolic Composition and Overall Quality of Cabernet Sauvignon Wines Grown in a Semi-Arid Climate.

In semi-arid areas, vineyards grown for winemaking are usually mildly irrigated by drip irrigation systems in a manner maintaining drought stress. This practice ensures the proper development of vegetative and reproductive organs on the one hand, and on the other, the development of high-quality grapes which can be hampered by overly abundant water application. In previous work, we have developed and demonstrated an irrigation model suitable for high-quality grape production in semi-arid areas. Here, we tackle the question of proper irrigation initiation dates-should one wait for vines to develop drought stress before the initiation of irrigation, or rather commence irrigation earlier? Our results show that vines which undergo initial irrigation late in the growing season tend to develop a lower midday stem water potential even after irrigation initiation. In addition, these vines tend to produce a lower number of bunches per vine and smaller berry size, leading to lower yields. The wine produced from the late-irrigated treatments had a higher phenolic content, primarily due to higher levels of catechin and epicatechin. Their levels increased as irrigation initiation dates were delayed, while caffeic acid levels showed an opposite trend. Late irrigation also led to higher color intensities compared to those of irrigation at earlier stages, due to higher levels of most anthocyanins. Finally, we show that the overall wine sensory score, representing its overall quality, was approximately five points higher for wines made from delayed irrigation treatments compared to wines made from early season irrigation treatments.

Multi-seasonal water-stress memory versus temperature-driven dynamic structural changes in grapevine.

Perennial plants perpetually adapt to environmental changes in complex and yet insufficiently understood manner. We aimed to separate the intra-seasonal temperature effects on structure and function from perennial and annual water stress effects. This study focused on grapevine (Vitis vinifera L. 'Cabernet Sauvignon') petioles, which being a continuously produced organ, represent the current status of the plant. Field-grown mature plants subjected to multi-annual irrigation treatments (severe water stress, mild water stress and non-stressed) throughout the growing season were compared with greenhouse-grown plants under three temperature regimes (22, 28 and 34 °C). Physiological and functional anatomy parameters were measured. A generalized additive model (GAM) based on meteorological and lysimeter-based field data was applied to determine the relative influence of various meteorological parameters on evapotranspiration (ETc) during the growing season in the field experiment. At the beginning of the growing season, in May, petioles in the severe stress treatment showed a stress-related structure (decreased length, safer hydraulic structure and increased lignification), though having high values of stem water potential (SWP). As the season progressed and temperatures increased, all water availability treatments petioles showed similar changes, and at the end of season, in August, were structurally very similar. Those changes were independent of SWP and were comparable to high temperature-induced changes in the greenhouse. In contrast, stems hydraulic structure was strongly influenced by water availability. Regression analyses indicated a relationship between petioles xylem structure and stomatal conductance (gs), whereas gs (but not SWP) was temperature-dependent. The GAM showed that ETc was mainly dependent on temperature. Our results indicate a perennial water-stress memory response, influencing the petiole structure at the beginning of the following season. Intra-seasonally, the petiole's structure becomes independent of water status, whereas temperature drives the structural changes. Thus, ongoing climate change might disrupt plant performance by purely temperature-induced effects.

Water availability dynamics have long-term effects on mature stem structure in Vitis vinifera.

PREMISE OF THE STUDY: The stem of Vitis vinifera, a climbing vine of global economic importance, is characterized by both wide and narrow vessels and high specific hydraulic conductivity. While the effect of drought stress has been studied in 1- and 2-yr-old stems, there are few data documenting effects of drought stress on the anatomical structure of the mature, woody stem near the base of the vine. Here we describe mature wood anatomical responses to two irrigation regimes on wood anatomy and specific hydraulic conductivity in Vitis vinifera Merlot vines. METHODS: For 4 years, irrigation was applied constantly at low, medium, or high levels, or at alternating levels at two different periods during the growing season, either early spring or late summer, resulting in late season or early spring deficits, respectively. The following variables were measured: trunk diameter, annual ring width and area, vessel diameter, specific hydraulic conductivity and stem water potential. KEY RESULTS: High water availability early in the season (late deficit) resulted in vigorous vegetative growth (greater trunk diameter, ring width and area), wider vessels and increased specific hydraulic conductivity. High water availability early in the season caused a shift of the vessel population towards the wider frequency classes. These late deficit vines showed more negative water potential values late in the season than vines that received low but relatively constant irrigation. CONCLUSIONS: We concluded that high water availability during vegetative growth period of Vitis increases vessels diameter and hydraulic conductivity and causes the vines to be more vulnerable to drought stress late in the season.