Résumé
In rainfed Mediterranean areas, summer drought is the main factor affecting the persistence of perennial grasses. Most available cultivars of Dactylis glomerata (cocksfoot) exhibit low persistence in this environment; therefore, research is needed on the relationships between plant physiology and recovery after severe drought. In the field, we subjected a large range of populations and cultivars of cocksfoot to 3 months of drought followed by 3 weeks of rewatering. Principal component and cluster analysis discriminated 3 groups of genotypes: (1) late heading populations and cultivars of temperate origin (ssp. glomerata) that exhibited high tiller mortality in summer; (2) early heading populations of Mediterranean origin (ssp. hispanica) that survived well but had a low growth potential; (3) very early heading Mediterranean cultivars (ssp. glomerataxhispanica) that survived and recovered actively. The study of bases of youngest enclosed leaves (surviving organs) showed that osmotic potential in living bases was not significantly different between groups of populations; dry matter content was higher in bases of hispanica populations at the onset of drought; total water-soluble carbohydrate and fructan contents increased as drought progressed and reached 35-40% of dry matter in bases at the end of the drought. Drought survival was best correlated with both the ratio between low and high weight fructans in July (summer) and the heading date (R-2 = 0.75, P < 0.001). Recovery yield after autumn rewatering was highly correlated with both of these variables and the dry matter content in leaf bases in June (R-2 = 0.75, P < 0.001), which may be associated with levels of summer dormancy These results emphasise the role of ontogeny in drought resistance and carl be used to predict plant survival in a large range of populations of cocksfoot.