Résumé
Four non dormant cultivars (cvs) of Dactylis glomerata L., contrasting for summer drought survival, were compared to study the root system establishment of vegetative tillers in spring (irrigated) and summer (droughted). In two glasshouse experiments conducted in deep tubes (1.5 and 2.0 m), root biomass and depth, and root/shoot ratios, were significantly higher in drought resistant Mediterranean cvs Medly and Currie than in less resistant maritime cvs Cambria and Lutetia. Differences in root development were exhibited as well in spring under irrigation as during summer drought, resulting in much deeper root systems in Medly and Currie. Root extension of these two cvs was similar at moderate soil density d=1.50 g.cm-3, but reacted differently to soil compaction (-29% in Currie and -15% in Medly when d=1.70 g.cm-3). In a field trial, soil water profiles at the end of a long severe drought and autumn recovery following rehydration (density of surviving tillers, autumn herbage yield) were in accordance with rooting system features observed in the tubes (Medly>Currie>Lutetia).