Fig. 1. Relationships between oil-corrected grain yield and (A) oil-corrected biomass at physiological maturity, and (B) harvest index, for nine sunflower hybrids grown in October (S1) and December (S2) sowing dates at Venado Tuerto during 1996-1997 and 1998-1999. Dashed arrows highlight some contrasting genotypic responses to S2, which underlie G x S interactions (Genotype 1, triangles; Genotype 9, circles). Genotype groups derived from cluster analysis of a multienvironment trial (de la Vega et al., 2001), i.e., G1: Northern adapted, G2: Central adapted, G3: broadly adapted. See Table 1 for genotype group membership.