Solar Radiation Intercepted during Seed Filling and Oil Production in Two Sunflower Hybrids

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Abstract
The expression of the components of oil yield in sunflower (Helianthus annuusL.) could depend on environmental conditions during the seed filling period. 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. Intercepted PAR was modified by shading or thinning to reduce plant population and by the combination of shading and thinning. The treatment application date corresponded to 46 ± 2°C days (base temperature = 6°C) after R6. Greater intercepted PAR increased weight per seed in both hybrids. Oil concentration was affected in `Dekalb G‐100' (G‐100, high oil concentration and black hull) but remained unaffected in `Northrup King Tordillo' (NKT, low oil concentration and stripped hull) although the thinned treatments intercepted up to 7.5 times the amount of radiation per plant than the shaded ones. About 84 (G‐100) and 80% (NKT) of the variability among treatments and experiments in weight per seed was accounted for by the PAR intercepted during seed filling. The variation in oil concentration in G‐100 was related to intercepted solar radiation (r2= 0.93). Our results suggest that intercepted PAR during seed filling plays a primary role in determining oil production in sunflower, and considering genotypic differences may be important when using relationships between weight per seed or oil concentration and intercepted PAR as modeling tools.