Physiological response of post-veraison deficit irrigation strategies and growth patterns of table grapes (cv. Crimson Seedless)

To determine whether partial root-zone drying (PRD) offers physiological advantages compared with regulated deficit irrigation (RDI), a 3 year long-experiment was conducted on a commercial vineyard of 'Crimson Seedless' table grapes (Vitis vinifera L.). Four different drip irrigation treatments were imposed: (i) a Control treatment irrigated at 110% of seasonal crop evapotranspiration (ETc), (ii), a regulated deficit irrigation (RDI) treatment irrigated similar to Control before veraison and at 50% of the Control treatment post-veraison, (iii) a partial rootzone drying (PRD) irrigated similar to RDI but alternating (every 10-14 days) the dry and wet side of the rootzone, and (iv) a null irrigation treatment (NI) which only received the natural precipitation and occasional supplementary irrigation when midday stem water potential (psi(s)) dropped below - 1.2 MPa. Post-veraison, PRD vines accumulated greater localized soil and plant water deficit at midday than RDI vines, but maintained similar pre-dawn water potential (psi(pd)) values. Stomatal conductance (g(s)) of PRD vines remained high, likely because there was sufficient root water uptake from irrigated soil. Xylem ABA concentration ([ABA](wylem)) did not change yet intrinsic WUE (WUEi) decreased compared to RDI vines, probably because PRD induced greater root density and root development at depth, allowing greater water uptake from roots in the wet part of the soil profile. Vegetative growth was only decreased by severe deficit irrigation (NI) although total leaf area index (LAI) was also affected by PRD in the 1st and 3rd year.. PRD can be considered a useful strategy in semiarid areas with limited water resources because sustained water use maintained assimilation rates despite greater stress than conventional RDI strategy, which may be related to root and morphological adjustment.