One of the major problems of confection sunflowers is low seed set. We studied the relationship between seed set and the origin of pollen, either self or cross, and the effects of stigmatic sprays of calcium nitrate, boric acid and polyphenols on seed set. In a screen-house experiment, seed set was analyzed for three predetermined regions in the sunflower capitulum: distal, median and proximal. Cross-pollination combined with calcium nitrate or boric acid spray significantly improved seed set in the distal region compared with cross-pollination alone or with cross-pollination combined with self-pollination. Neither spray had a significant effect on seed set in the median or proximal regions. Cross-pollination of the proximal region only, with either fresh pollen or 24-h-old pollen, did not improve seed set compared with cross-pollination of the whole capitulum. We found no direct link between pollen germination on the stigma and seed set. However, each region of the capitulum responded differently to self- or cross-pollination. In two open-field experiments, stigmatic applications of calcium nitrate significantly increased seed set by approximately 9% compared with open pollination alone, while stigmatic applications of polyphenols significantly increased seed set by approximately 9% only once, suggesting that commercial yields may be increased by using similar applications. © 2008 Elsevier B.V. All rights reserved.
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