Deficit irrigation affects seasonal changes in leaf physiology and oil quality of Olea europaea L. (cultivars Frantoio and Leccino)

The olive tree is a traditionally nonirrigated crop that occupies quite an extensive agricultural area inMediterranean-type agroecosystems.Improvements inwateruse efficiency of crops are essential under the scenarios of water scarcity predicted by global change models for the Mediterranean region. Recently, irrigation has been introduced to increase the low land productivity, but there is little information on ecophysiological aspects and quality features intended for a sagacious use of water, while being of major importance for the achievement of high-quality products as olive oil. Therefore, deficit irrigation programmes were developed to improvewater-use efficiency, crop productivity and quality in a subhumid zone of Southern Italy with good winter–spring precipitation. The response of mature olive trees to deficit irrigation in deep soils was studied on cultivars Frantoio and Leccino by examining atmospheric environment and soilmoisture, gas exchange and plant water status, as well as oil yield and chemical analysis. Trees were not irrigated (rainfed) or subjected to irrigation at 66%and 100%of crop evapotranspiration (ETC), starting from pit hardening to early fruit veraison. Improvements in the photosynthetic capacity induced by increasing soil water availability were only of minor importance. However, plant water status was positively influenced by deficit irrigation, with 66% and 100% of ETC treatments hardly differing from one another though consistently diverging from rainfed plants. The effect of water stress on photosynthesis was mainly dependent on diffusion resistances in response to soil moisture. Leccino showed higher instantaneous water-use efficiency than Frantoio. Crop yield increased proportionally to the amount of seasonal water volume, confirming differences between cultivars in water-use efficiency. The unsaturated/saturated and the monounsaturated/ polyunsaturated fatty acid ratios of the oil also differed between cultivars, while the watering regime had minor effects. Although irrigation can modify the fatty acid profile, polyphenol contents were scarcely affected by the water supply. Irrigation to 100% of ETC in the period August–September might be advisable to achieve high-quality yields, while saving consistent amounts of water.