Les tournesols adventices : un exemple d’évolution d’une mauvaise-herbe apparentée à une espèce cultivée – Synthèse des recherches menées sur les populations adventices de tournesol en France depuis 2004

Weedy sunflowers have been officially reported in South-Western France in 2004. They display a combination of phenotypic traits of the wild and domesticated forms of the species and infest between 15 and 20% of fields of sunflower crop in this area, although at variable levels. When the infestation is strong, it affects seed yield and oil quality. Molecular studies showed that weedy sunflowers most probably resulted from accidental crop-wild hybridization during the seed production process and from the introduction of the resulting hybrids into commercial seed lots. Multiple independent introductions were at the source of the number of infested fields observed nowadays. The temporal dynamics of the infestation of a field and the detailed conditions for its success remain largely unknown. The flowering synchrony between crops and weeds is substantial, even if a variable fraction of the weeds (15-55%) flower completely outside the crop flowering period. Molecular survey of adult weedy plants and their progenies showed that crop-toweed gene flow occurs, at a rate that can reach 35 %on average, at the peak of the crop flowering period. We draw perspectives on the durability of herbicide-tolerant sunflower varieties as a solution to control these weeds, and call for more studies tackling weed management from an evolutionary lens.