-Photosynthetic activity of cereals has traditionally been studied using leaves, thus neglecting the role of other organs such as ears. Here, we studied the effects of water status and genotypes on the photosynthetic activity of the flag leaf blade and the ear of durum wheat. The various parameters related to the photosynthetic activity were analysed in relation to the total above-ground plant biomass and grain yield at maturity. Four local varieties plus two cultivars adapted to the semiarid areas of South Morocco were grown in pots in a greenhouse. Five different water treatments were maintained from the beginning of stem elongation to maturity, when shoot biomass and grain yield were recorded. The net photosynthesis (A), stomatal conductance (g s ) and transpiration (T) of the ear and the flag leaf were measured at anthesis. In both organs these factors decreased significantly with water deficit, whereas the A/T and A/g s ratios increased. The genotype effect was also significant for all traits studied. Whole-organ photosynthesis was much higher in the ear than in the flag leaf in well-watered conditions. As water stress developed, photosynthesis decreased less in the ear than in the flag leaf. Whole-ear photosynthesis correlated better than flag leaf photosynthesis with biomass and yield. Nevertheless, the relationships of the whole flag leaf with biomass and yield improved as the water stress became more severe, suggesting a progressive shift of yield from sink to source limitation. For all water regimes the ratios A/g s and A/T of the ear also showed a higher (negative) correlation with both biomass and yield than those of the flag leaf. The results indicate that the ear has a greater photosynthetic role than the flag leaf in determining grain yield, not only in drought but also in the absence of stress. durum wheat / ear / flag leaf / photosynthesis / yield / drought Résumé -Comparaison des relations entre photosynthèse de la feuille étendard et de l'épi avec la biomasse et le rendement en grain chez le blé dur sous différents régimes hydriques. Traditionnellement, lorsque l'activité de la photosynthèse de céréales est étudiée, l'importance est attribuée aux feuilles, négligeant ainsi le rôle d'autres organes comme l'épi. Ici, une étude comparative de l'effet du statut hydrique sur l'activité photosynthétique au niveau de la feuille étendard et de l'épi ainsi que leurs relations avec la biomasse totale aérienne et le rendement en grain à maturité a été menée chez le blé dur. Quatre variétés locales et 2 cultivars adaptés aux zones semi-arides du sud du Maroc ont été mis en croissance dans des pots en conditions de serre. Cinq différents régimes hydriques ont été instaurés du début de l'élongation des tiges jusqu'à maturité. La biomasse et le rendement en grain sont alors enregistrés. Des mesures de la photosynthèse nette (A), de la conductance stomatique (g s ) et de la transpiration (T) ont été effectuées au niveau de l'épi et de la feuille à l'anthèse. Pour les deux organes, on note une diminut...