The trial was carried out in two years (1992 and 1993) at two different locations in the centre of Italy (Pisa and Grosseto) and the main aim was to evaluate the influence of four different environmental conditions (Pisa, 1992; Grosseto, 1992; Pisa, 1993 and Grosseto, 1993) and the effects of two different water availabilities (without and with irrigation) on six sunflower hybrids: Ares, Cisa, Granada and Oleica, with high oleic acid content, and Gloriasol and Select, conventional hybrids (high linoleic), used as controls. The experimental scheme adopted was a split-block experimental design with five replications. The following characteristics were observed: duration of main phenological periods, plant height, leaf area index at flowering, aboveground biomass and seed yield per plant, harvest index, growing degree-days, water use and water use efficiency.

The water use efficiency for seed yield per plant was highest at Pisa, 1993 under rainfed conditions (1.02 g/l) and at Grosseto, 1993 under both water treatments (1.00 g/l). The irrigation treatments led to an increase of the harvest index in all environments except for the wettest environment (Pisa, 1992). In the four environments examined, the growing degree-days ranged from 789 to 1108℃ and from 1612 to 2036℃ for the sowing-flowering and sowing-maturity periods, respectively. Seed yield per plant in all high oleic hybrids, with the exception of Ares, were not significantly different from those of Select and Gloriasol in all environments, with the exception of Pisa 1993, which was characterized by a limited water availability during flowering-maturity period, where all high oleic hybrids showed a significant decrease of seed yield per plant.