The origin and evolution of a recent agricultural weed: population genetic diversity of weedy populations of sunflower (Helianthus annuus L.) in Spain and France

Abstract

The recurrent evolution of crop-related weeds during agricultural history raises serious economic problems and challenging scientific questions. Weedy forms of sunflower, a species native from America, have been reported in European sunflower fields for a few decades. In order to understand their origin, we analysed the genetic diversity of a sample of weedy populations from France and Spain, and of conventional and ornamental varieties. A crop-specific maternally inherited marker was present in all weeds. At 16 microsatellite loci, the weedy populations shared most of their diversity with the conventional varieties. But they showed a large number of additional alleles absent from the cultivated pool. European weedy populations thus most probably originated from the unintentional pollination of maternal lines in seed production fields by wild plants growing nearby, resulting in the introduction of crop-wild hybrids into the farmers’ fields. The wide diversity and the low population structure detected were indicative of a multiplicity of introductions events rather than of field-to-field propagation. Further studies are required to understand the local evolutionary dynamics of a weedy population, and especially the respective roles of crop-to-weed gene flow and selection in the fate of an initial source of crop-wild hybrids.

How to escape from crop‐to‐weed gene flow: phenological variation and isolation‐by‐time within weedy sunflower populations

“…As shown previously by Muller et al . (), varieties had a lower allelic richness relative to weedy populations: 70 alleles were detected over all 15 loci in the database of varieties (i.e. C alleles), against 235 alleles in the weedy pool.…”

“…Molecular methods for DNA isolation, genotyping and allele scoring were as described in Muller et al . ().…”

The red queen in the corn: agricultural weeds as models of rapid adaptive evolution

“…Sunflowers are native to North America, where the crop is often grown in proximity to wild Helianthus populations. Weedy sunflower strains in European fields most likely originated in seed plots in the US, where nearby populations of wild sunflower contributed pollen to cultivated sunflowers, producing weedy hybrids (Muller et al, 2011). These hybrid seeds were likely exported with cultivated seeds to Europe and established as weeds in the field.…”

Estimation of mating system parameters in an evolving gynodioecous population of cultivated sunflower (Helianthus annuus L.)

“…If conducted for further generations, a manipulation of the selective pressures will be needed to observe a significant evolution (see, for example, David and Pham, 1993). Finally, natural populations of weedy sunflowers, fixed for the male-sterile cytoplasm and submitted to recurrent gene flow from cultivated fields (bringing recurrently Rf and rf alleles, Muller et al, 2011), could constitute an interesting case study in relation with models including gene flow in the evolution of gynodioecy (Dufay and Pannell, 2010).…”