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

The olive tree is a traditionally nonirrigated crop that occupies quite an extensiveagricultural area inMediterranean-type agroecosystems.Improvements inwateruseefficiency of crops are essential under the scenarios of water scarcity predictedby global change models for the Mediterranean region. Recently, irrigation hasbeen introduced to increase the low land productivity, but there is little informationon ecophysiological aspects and quality features intended for a sagacious useof water, while being of major importance for the achievement of high-qualityproducts as olive oil. Therefore, deficit irrigation programmes were developed toimprovewater-use efficiency, crop productivity and quality in a subhumid zone ofSouthern Italy with good winter-spring precipitation. The response of matureolive trees to deficit irrigation in deep soils was studied on cultivars Frantoio andLeccino by examining atmospheric environment and soilmoisture, gas exchangeand plant water status, as well as oil yield and chemical analysis. Trees were notirrigated (rainfed) or subjected to irrigation at 66%and 100%of crop evapotranspiration(ETC), starting from pit hardening to early fruit veraison. Improvementsin the photosynthetic capacity induced by increasing soil water availability wereonly of minor importance. However, plant water status was positively influencedby deficit irrigation, with 66% and 100% of ETC treatments hardly differingfrom one another though consistently diverging from rainfed plants. Theeffect of water stress on photosynthesis was mainly dependent on diffusion resistancesin response to soil moisture. Leccino showed higher instantaneouswater-use efficiency than Frantoio. Crop yield increased proportionally to theamount of seasonal water volume, confirming differences between cultivars inwater-use efficiency. The unsaturated/saturated and the monounsaturated/polyunsaturated fatty acid ratios of the oil also differed between cultivars, whilethe watering regime had minor effects. Although irrigation can modify thefatty acid profile, polyphenol contents were scarcely affected by the watersupply. Irrigation to 100% of ETC in the period August-September might beadvisable to