Rapid Screening of Apple Genotypes for Drought Tole rance by a Simplified Model of Canopy Conductance

Abstract

Expansion of apple growing to dry areas requires re liable approaches to select genotypes tolerant to water stress. We have simulat ed apple tree transpiration (Ec) from different commercial orchards and compared it with actual transpiration (Ea) derived from sap flow measurements. The modelling approach lies in rearranging a parameterized P–M Equation and incorporating in it a stomatal conductance model derived from meteorological variations. The model u ses diurnal courses of variables instead of commonly used daily means. We then wrote a complex P–M Equation which already includes the canopy conductance as the func tion of radiation and vapour pressure deficit. For model calibration, an extensive experi mental dataset of tree transpiration was collected from 2011 to 2013 in various sites of Alb ania and Kosovo, ranging from very warm to temperate. The daily pattern of canopy cond uctance for water vapour at canopy level provided by the model offers an unprecedented insight into rapid response to humidity of different cultivars as well as their li ght saturation levels. The satisfactory performance of this functional model should improve the precision of current empirical approaches followed to compute fruit tree water req uirements and can be a promising tool for early and quick evaluation of water stress tolerance in apple genotypes. Keywords: Irrigation, Modelling, Sap flow, Stomatal kinetics .