Changes induced by water stress on water relations, stomatal behaviour and morphology of table grapes (cv. Crimson Seedless) grown in pots

Abstract

The response of different deficit irrigation strategies on physiological and morphological parameters on table grapes (cv. Crimson Seedless) grown in pots was studied three times a day to evaluate how such strategies could be safely used for hardening and to ascertain their tolerance to drought. Five preconditioning treatments were applied: (i) CTL-1 and CTL-2; both irrigated daily to field capacity; (ii) DI, watered to 50% of CTL-1; (iii) PRDFIX, permanently watered to 50% of CTL-1 in a pot, and (iv) PRDALT, the root was split into two pots, and the pots alternatively watered to 50% of CTL-1 when the volumetric substrate water content (θv) reached 12%. 30 days after the application of the preconditioning treatments, vines were subjected to drought for 7 days, except for CTL-1. After that, vines were re-irrigated and their recovery was studied for 7 days. Crimson Seedless displayed different responses to water stress, depending on the diurnal course. At predawn (t1) and early morning (t2), the cultivar showed near-anisohydric behaviour, through a less effective stomatal control of drought, whereas at midday (t3) the behaviour was near-isohydric. Although the total amount of irrigation water was the same for DI, PRDALT and PRDFIX, the vines from the last had a reduced photosynthetic activity, probably due to a limited sap flow. Water stress conditions induced avoidance mechanisms to drought such as stomatal closure, partial defoliation and a reduction in leaf insertion angle. Osmotic adjustment was only observed in un-preconditioned vines (CTL-2) but it was not enough to reach full turgor. In addition, PRDFIX and CTL-2 vines suffered serious dehydration damages to biomass accumulation and vine quality, regardless of the recovery of gas exchange parameters. PRDALT and DI can be used as safe techniques for irrigation scheduling in the nursery stage, because of their adaptability to water stress and so improve the survivability of the young table grapes plantations.