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La pollinisation entomophile du tournesol est souvent mentionnée comme un facteur contribuant au rendement et à la qualité de cette culture. Alors que les rendements stagnent depuis une trentaine d'années en France, l'amélioration de la pollinisation des tournesols de consommation constitue une piste pour les relancer en conditions agricoles. Notre étude visait à évaluer l'impact d'un front d'insectes pollinisateurs (colonies d'abeilles domestiques installées dans une bande fleurie disposée sur une bordure de parcelles agricoles longue de plus de 550 m de long). Cet impact a été mesuré à différentes distances de ce front d'insectes pollinisateurs sur la fréquentation des capitules par les insectes floricoles, la charge en pollen des stigmates, le rendement et la teneur en huile des graines. Nous avons bien observé un gradient négatif d'activité des abeilles domestiques en fonction de l'éloignement au front de colonies et aussi une diminution du rendement et de la teneur en huile chez le tournesol. Nous présentons la méthodologie originale utilisée ainsi que les premiers résultats obtenus. more...

The sunflower crop provides an important honey flow for beekeepers. In France, beekeepers observed a decrease in honey yield from this crop these past years compared to the 1980s–1990s. They suspect the new cultivars to be less productive in nectar compared to the older ones, but no data is available to support this, and it is known that climate conditions have a strong impact on nectar secretion. This study aimed to explore the effect of abiotic environmental conditions on nectar secretion in sunflower, as well the range of variation of this secretion in a sample of current cultivars. Thirty-four current sunflower hybrid cultivars were sampled in test plots for their nectar secretion under varying conditions of temperature, air humidity and soil moisture. Air humidity controlled the sugar concentration of nectar, and thus its volume. To study nectar secretion independently from this effect, analyses subsequently focused on nectar sugar mass per floret. The nectar sugar mass increased with temperature up to an optimum of 32 °C, while the variation range of soil water tension was not sufficient to detect an effect on nectar sugar mass. This varied by up to 100% among the 34 cultivars (from 101 to 216 μg sugar per staminate floret in average), with a similar range to those reported in the literature for older cultivars. Likewise, oleic cultivars, a new type introduced since the early 2000s, were found to secrete the same amounts of nectar as linoleic cultivars, an older conventional type. The more self-fertile cultivars also showed no reduction in nectar secretion. Finally, we tested the method that measures the nectar gross secretion rate in one hybrid, and we observed that this hybrid secreted in average 28 μg sugar per hour per staminate floret. The potential benefits of this method were discussed. more...