Soil water availability effects on plant growth, yield and fruit quality in grapevine and olive tree

Grapevine (Vitis vinifera L.) and olive tree (Olea europaea L.) are the most cultivated fruit tree crops in the Mediterranean Basin where it is produced more than half of the world production of wine and olive oil. However, the climate change is particularly concern for all the Mediterranean region where its effects are particularly severe. The increasing mean air temperature is accompanied by a decreasing tendency in the annual total precipitations, threatening viticulture and olive growing which are often not irrigated in many areas. Irrigation management in vineyards and orchards trough suitable strategies, represents one of the main agronomic practices to cope with climate change maintaining high quality productions in their traditional vocated areas. The main objective of this work was to evaluate the response of grapevine and olive tree to different irrigation regimes, in terms of plant physiology, vegetative growth, yield components and fruit quality. A specific objective for grapevine was to evaluate the effect of water deficit, in terms of timing and level of stress imposed on important secondary metabolites such as volatile organic compounds (VOCs), whereas on olive tree a possible use of remote sensing techniques for supporting precision irrigation management in the olive orchard was tested. In grapevine, water deficit applied before veraison affected vines physiology (leaf gas exchange and fluorescence) and reduced vines vegetative growth (trunk diameter, total leaf area, canopy volume), berry fresh weight and fruit yield. Post-veraison water deficit did not affect fruit yield at harvest and increase the sugars accumulation rate. Berry total anthocyanins and total flavonols concentration were enhanced when the water stress was applied before veraison. Similarly, the water deficit applied between fruit-set and veraison increased berries VOCs concentration at harvest, and it showed a positive correlation with the water stress intensity. Moreover, just few days of water deficit applied during lag-phase induced significantly higher VOCs in berries than full irrigation. Similar results were obtained for monoterpenes and other classes of aroma compounds. The seasonal patterns of berry endogenous hormones concentration may suggest a key role of the jasmonic acid derived compounds as regulators or activator of the berry VOCs accumulation. In olive, deficit irrigation allowed to save more than 50% of water compared to full irrigation with limited or no effect on fruit and oil yield. Deficit irrigation was also beneficial for oil quality, inducing higher antioxidant power compared to oils from fully irrigated trees. A significant relationship between the remoted sensed crop water stress index derived from thermal images and the stem water potential was found. The RGB images by UAV allowed to estimate tree canopy volume, highlighting differences in canopy growth pattern between irrigation regimes. Our results suggest a possible use of the RGB-thermal images from UAV to monitor both the tree water stress and its effect on canopy growth, yield and oil quality at field level, for a more efficient irrigation management in the olive orchard. We also tested the combined use of remote and proximal sensing techniques to discriminate different clusters within the orchard, with different productivity and vegetative performances. Remotely and proximally sensed indices was able to identify the soil-plant variability of the entire orchard, allowed to determine that: i) the effect of different irrigation regimes on tree performance and water productivity depended on the soil characteristics within the orchard; ii) tree vigour played a major role in determining the final fruit yield under optimal soil water availability, whereas soil features prevailed under rainfed conditions.