Agrestal Environments and Maternal Genetic Effects Weaken the Ecological Barriers for Crop to Wild Introgression in Sunflower

Admixture between crops and their wild relatives may lead to the evolution of aggressive weeds in agricultural and natural habitat. As many crops and their wild relatives belong to the same species, admixture is common, and the low fitness of crop-wild hybrids is the main ecological barrier for introgression. However, fitness of hybrids can vary between environmental conditions, genetic background of recipient and donor populations, and maternal genetic effects. Here, we study how these three factors influence the phenotypic variation of crop-wild sunflower hybrids in the field. To this end, we measured seven variables related to fitness throughout the life cycle in eight populations (including reciprocal crop-wild hybrids and their parents) in two agrestal (wheat and maize plantings) and one ruderal (natural vegetation in a human-disturbed area) environments over 2 years. Overall, high out-of-season germination was observed in the first year but declined in the second across all environments. In ruderal habitats, flowering was delayed, and fitness was lower compared to agrestal ones. Hybrids exhibited similar or lower fitness than wild plants in agrestal habitats, but the differences were larger in ruderal habitats. Hybrids with maternal crop parents displayed higher fitness than their reciprocal crosses across all environments in the first year, but differences disappeared the second year. Our findings suggest that agrestal conditions and crop maternal parent favor the establishment of crop-wild hybrids, weakening the ecological barriers for crop introgression.