Solar radiation intercepted during seed filling and oil production in two sunflower hybrids

The expression of the components of oil yield in sunflower (Helianthus annu us L.) could depend on environmental conditions during the seed filling per iod. In this work, we investigated the effect of intercepted PAR (photosynt hetically 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 d ifferent years under good water and nutrient conditions. Intercepted PAR wa s modified by shading or thinning to reduce plant population and by the com bination of shading and thinning. The treatment application date correspond ed to 46 +/- 2 degreesC days (base temperature = 6 degreesC) after R6. Grea ter intercepted PAR increased weight per seed in both hybrids, Oil concentr ation was affected in 'Dekalb G-100' (G-100, high oil concentration and bla ck hull) but remained unaffected in 'Northrup King Tordillo' (NKT, low oil concentration and stripped hull) although the thinned treatments intercepte d up to 7.5 times the amount of radiation per plant than the shaded ones, A bout 84 (G-100) and 80% (NKT) of the variability among treatments and exper iments In weight per seed was accounted for by the PAR intercepted during s eed filling. The variation in oil concentration in G-100 was related to int ercepted solar radiation (r(2) = 0.93), Our results suggest that intercepte d PAR during seed filling plays a primary role in determining oil productio n in sunflower, and considering genotypic differences may be important when using relationships between weight per seed or oil concentration and inter cepted PAR as modeling tools.