Résumé
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