The role of domestication and maternal effects on seed traits of crop–wild sunflower hybrids (Helianthus annuus)

Abstract

Hybridization between crops and their wild relatives may promote the evolution of weeds. Seed germination and dormancy are the earliest life-history traits and are highly influenced by the maternal parent. However, the ecological role of the maternal effect on seed traits in the evolution of crop-wild hybrids has received little attention. In this study, we test the relative importance of maternal and hybridization effects on seed traits of the first generation of crop-wild sunflower hybrids (Helianthus annuus). Seed germination was tested in two wild populations with contrasting dormancy, two cultivated materials and their reciprocal crosses at four different times after harvest and three different temperatures. Seed germination at each of the four times, after ripening response and secondary dormancy were recorded along with four morphological traits. Additionally, the pericarp anatomy was analysed with light and scanning electron microscopy. We observed strong maternal effects on all seed traits. Seed germination, morphology and pericarp anatomy differed largely between the crop and wild seeds and these traits in the crop-wild hybrids resembled their<br />female parent. Slight but significant hybridization effects were observed in germination, mainly in seeds produced on wild plants. Crop hybridization changed seed germination, the after ripening response and secondary dormancy in the crop direction. Morphological and anatomical traits associated with domestication strongly correlated with the observed differences in seed germination and dormancy in crop-wild sunflower hybrids. The large maternal effects along with the evolutionary divergence in seed traits were responsible for the large phenotypic differences observed in crop-wild hybrids with the same genetic composition. Wild-like seed traits of hybrids suggest that there are no barriers to crop gene introgression at the seed level whereas crop-like seed traits could be strongly selected against, conditioning the selection of traits expressed later in the life cycle and in the next generations.