Texture-related soil water-holding capacity modulates ABA effects on grapevine adaptation to increasing drought levels and berry quality.

In rain-fed vineyards, soil controls the productive potential additively to and even more than rootstock and scion. Soils with different texture, imposing specific conditions of water availability, could override the genotype effect, either of rootstock or scion, in the long term adaptability processes. In these contexts, xylem anatomy and whole plant hydraulic conductance are both influenced by genotype and water-holding soil capacities. The aim of this work was to understand whether in rain-fed vineyard conditions an ABA related drought signal, putatively influenced by the texture related to water-holding capacity of the soil, drives ecophysiological plant adaptation to seasonal water availability. To this aim, the field trial was followed during two consecutive and climatically different years. A parallel one-year pot experiment designed with the same variety of the vineyard trial (‘Nebbiolo’) and two different substrates, showing sand/clay ratios at the extremes of the field textures, was carried on. In the presence of higher percentage of clay, ‘Nebbiolo’ response to water deprivation switched from aniso- toward iso-hydric control, maintaining water potential during drought periods through ABA-related stomatal regulation. In parallel, in berries, anthocyanin accumulation was faster and total concentration at harvest was higher; the berry anthocyanin profile differed in terms of hydroxylation and acylation. Also the accumulation of free volatiles, especially terpenes, was affected by texture related soil water-holding capacity. Mild water stress conditions experienced by grapevines in vineyards were prolonged in clayey soils, driving ABA-related plant responses both at the leaf (stomatal regulation) and at the berry (secondary metabolism induction) levels. Consequences on metabolite accumulation in berries increased must quality.