Selection on domestication traits and QTL in water-stressed sunflower crop-wild hybrids

Renewed interest in the consequences of gene flow between crop and wild plant populations was initially generated with the widespread commercialization of transgenic crops. Although crop-wild hybridization is observed in most cultivated species, how ecological factors influence the likelihood that a crop allele will persist in wild populations remains unclear. Given that environmental factors influence strength of selection, crop-wild hybridization must be studied under locally relevant conditions in order to determine the risks associated with transgenic crops. Previous risk assessments have considered a range of biotic factors but not the arid conditions prevalent in agricultural regions of Washington. In this study, sunflower (Helianthus annuus) crop-wild hybrids were field-grown in an arid region of Washington, utilizing divergent water treatments simulating irrigated (high-water) and native (low-water) conditions. Known phenotypic differences between crop and wild sunflowers were measured at plant senescence, and quantitative trait loci (QTL) were mapped for each trait. Crop-like traits for leaf size, head size, and flowering were strongly associated with fitness (seed-production) under low-water conditions. Significant QTLs for crop-like traits in the low-water treatment were detected with some overlapping with fitness QTLs. These results suggest that some crop-like traits may be advantageous in a wild environment and should be considered in future risk assessments