In this work, we investigated the effect of intercepted PAR (photosynthetically active radiation) during seed filling on the weight of individual seeds and oil concentration in two hybrids, one with low and one with high oil concentration potential. Three experiments were carried out in three different years under good water and nutrient conditions.
Hybrids could differ in their oil concentration potential. Some (usually with black fruit pericarp [hull], as the one studied by Andrade and Ferreiro, 1996) are potentially able to produce high oil concentrations (480 g [kg.sup.-1] or more), whereas others (usually with stripped hull) typically produce low oil concentrations (440 g [kg.sup.-1] or less).
The objective of this work was to study the effect of intercepted PAR during seed filling on weight per seed and oil concentration in two sunflower hybrids, one with high oil concentration potential and black hulls, the other with low oil concentration potential and stripped hulls.
The K values in G-100 were greater than in NKT, indicating that partitioning into seeds was lower in the hybrid with low oil concentration potential. Relative differences between extreme values (shaded and thinned treatments) were similar in both hybrids (54 and 49%, in G-100 and NKT).
Our results suggest a significant role of intercepted PAR during seed filling in determining weight per seed in both hybrids and oil concentration in the hybrid with high oil concentration potential. More than 80% of the variability among treatments and experiments in these yield components was accounted for by variability in the solar radiation intercepted.