Constitutive differences in water use efficiency between two durum wheat cultivars

► Comparison of water use efficiency (WUE) of two durum wheat cultivars. ► The old cultivar Cappelli has higher WUE than the modern cultivar Ofanto. ► Differences are constitutive, persist throughout all growth stages. ► Higher WUE is associated with lower stomatal conductance. ► Identification of fast phenotyping methods for studies on the segregating population. This work was focused on the physiological analysis of the response to water availability in two durum wheat ( Triticum turgidum var. durum) parents of a mapping population, Cappelli and Ofanto, representing an old and a modern cultivar, respectively. We investigated if the two parents are constitutively different for traits related to water use efficiency ( WUE), a key step to prepare further studies on the large segregating population. Integrated WUE, as recorded by grain δ 13C, was studied in a 3-year field experiment conducted at Foggia (southern Italy) under irrigated and non-irrigated conditions. A growth chamber experiment was carried out to analyse the cultivars, at leaf and whole plant level in the vegetative growth phase under well watered and drought conditions. All measures consistently showed a higher WUE of the variety Cappelli than Ofanto. This trait was associated with lower stomatal conductance over a range of relative soil water contents tested in the growth chamber experiment. Carbon isotope discrimination ( CID) was confirmed as useful indicator of WUE when measured in grains harvested in the field trials. In addition, the consistent results obtained by CID analysis in the vegetative organs harvested in the growth chamber experiment, can facilitate the development of opportune phenotying approaches that, in perspective, can be employed for high sample numbers, as required for studies of the segregating population. Traits related to growth and biomass allocation in the map parents, indicative of different adaptive strategies for resource use of Cappelli and Ofanto, were also analysed.