XYLEM DYNAMICS OF DIFFERENT ROOTSTOCK/SCION COMBINATIONS OF APPLE UNDER A HOT, SEMI ARID MEDITERRANEAN CLIMATE
New apple plantations in Albania have descended from the mountain areas of Eastern Albania to the hot and dry Western Plain demanding an evaluation of different cultivars and rootstocks adaptable for such a climate. Moreover, best practice in terms of water use efficiency (WUE) requires an irrigation regime which is temporally and spatially adjusted for each cultivar within the same orchard. The object of this study was to assess the behavior of these rootstock/scion combinations this climate regime to properly design an irrigation strategy. The study was conducted in a commercial apple orchard, trained in a central leader system, in their 2nd year of growth. Sap flow sensors based on the stem heat balance method (SHB) were installed on the main leader at 30 cm height, from August to September on 2 trees for each of the following rootstock/scion combinations: Golden Delicious/Pajam2, Fuji/Pajam2 and I dared/Pajam2. Soil water potential was measured at two different depths. A portable meteorological station measured meteorological variables enabling the calculation of vapour pressure deficit (VPD) and potential evapotranspiration (PET) Trunk Cross Sectional Area (TCSA) was measured for rootstock, trunk, individual and all branches. Length of branches was measured too. A linear regression analysis was undertaken to study different regression models which better predict sap flow by measuring environmental variables. Irrigation of the orchard was withheld in order to create extreme water stress levels. The results show clearly that cultivar 'Fuji' on Pajam 2 rootstock has lower levels of transpiration compared to other cultivars, as a results of a more favorable ratio between the reproductive and vegetative growth, which makes it more adaptable for this arid area of cultivation. From the regression models studied, it can be concluded that sap flow was best predicted by ET. Global radiation and even air temperature are useful climatic variables for predicting SF reference values because are easily measured.