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Summer dormancy in perennial grasses is a major trait conferring plant survival and persistence in Mediterranean areas. The aim of the present study was to characterize the effect of summer dormancy on dehydration tolerance in six Moroccan ecotypes and two cultivars “Kasbah” and “Porto” of Dactylis glomerata in a glasshouse experiment. Measurements included the ratio of green/senescent aerial tissues, soil water evolution, water content in survival organs and plant survival rate. D8 and D9 ecotypes showed high senescence when soil moisture was 5%, while Kasbah (dormant cultivar) was at 52% of areal senescence. Proportion of senescent tissue reached 98% for all ecotypes at soil humidity of 1.9%. Under severe drought, water content of apices decreased to reach 0.31 g H20 g–1 dry weight, which was a lethal value for four tested ecotypes and cv. Porto. Except for Kasbah, D1 and D6, which remained alive with little hydrated apices. The soil moisture associated with 50% of plant mortality was 2.5% for Porto and D8 but decreased to 1.9% for D14. Kasbah, D1 and D6 could survive until 1% soil moisture. These results are ascribed to efficient strategies of both dehydration avoidance and tolerance in the best surviving genotypes., La dormance estivale chez les graminées pérennes est un trait majeur conférant la survie et la persistance dans les régions méditerranéennes. Le but de ce travail est de caractériser la dormance et la tolérance à la déshydratation de six écotypes marocains et de deux cultivars de Dactylis glomerata en conditions contrôlées. La progression de la sénescence foliaire, de la teneur en du sol, l’hydratation des organes de survie et le taux de survie des plantes ont été mesurés. La sénescence a atteint 98 % pour l’ensemble des écotypes à l’humidité de sol de 1,9 %. Sous sécheresse extrême, le contenu d’eau des apex a diminué drastiquement jusqu’à 0,31 g H20 g-1 MS considérée comme létale pour quatre écotypes et Porto, à l’exception de Kasbah, D1 et D6, qui ont maintenu une survie avec des apex faiblement hydratés. L’humidité de sol associée à 50 % de mortalité est 2,5 % pour Porto et D8, mais seulement de 1,9 % pour D14 alors que Kasbah, D1 et D6 ont survécu jusqu’1% d’humidité du sol. Ces résultats sont attribués à une efficace combinaison d’évitement et de tolérance à la déshydratation chez les écotypes les plus résistants.

International audience; Extensive livestock is a basic socio-economic feature of the Mediterranean region whose environmental and economic sustainability depends on the ability of forage resources to withstand climatically stressful conditions. Perennial forages such as tall fescue can be a valuable alternative to annuals, if they can survive across successive summer droughts. Three-year dry matter yield and plant survival of five cultivars of Mediterranean-type tall fescue were evaluated in six sites of Algeria, France, Italy, Morocco and Portugal, with the following objectives: (i) modelling adaptive responses and targeting cultivars as a function of environmental factors associated with genotype x location interaction; and (ii) defining plant ideotypes, adaptation strategies and opportunities for international co-operation for regional breeding programmes. Site mean yield and winter temperatures were positively correlated, whereas sward persistence was positively correlated to lower site heat and drought stress. Cultivar adaptation was adequately modelled by factorial regression as a function of site spring-summer (April-September) drought stress (long-term potential evapotranspiration minus actual water available) for yield, and annual drought stress for final persistence. Specific-adaptation responses to high- or low-stress environments emerged which were consistent with drought-stress levels of cultivar selection environments. However, the wide-adaptation response of cultivar Flecha suggested that breeding for wide adaptation can be feasible