EVALUATION OF SUNFLOWER (HELIANTHUS-ANNUUS, L.) GENOTYPES DIFFERING IN EARLY VIGOR USING A SIMULATION-MODEL

High early vigour (plant dry matter in the early development stages) i n sunflower may be a desirable character under water-limited environme nts as it may contribute to higher transpiration efficiency and reduce d soil evaporation. However a high early vigour causes a more rapid us e of soil water, which may threaten crop water supply during seed fill ing. This is also influenced by the seasonal pattern of rainfall and g enotype season length. The objective of this research was to simulate the performance of cultivars of sunflower differing in season length a nd early vigour under a Mediterranean climate. A simulation model of t he sunflower crop, OILCROP-SUN, was modified and used to find the opti mum combination of early vigour and season length of the genotypes for different environments, Field experiments were carried out during 199 2, 1993 and 1994 in Cordoba, Spain (38 degrees N). Sunflower populatio ns with similar genetic background but with differences in early vigou r were used to study the association of this trait with other characte rs and with the genetic parameters required to run the model. Changes in early vigour were simulated by modifying leaf growth rate in the mo del, The field experiments showed that high early vigour, as measured by stem volume 425 degrees Cd after emergence, is not related to reduc ed root growth and is not associated with season length. Simulations s howed that the highest seed yield is obtained using genotypes with hig h early vigour, provided that their season length is long enough for t he growing conditions. (C) 1997 Elsevier Science B.V.