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Abstract: Gene flow can have several different applied consequences, ranging from extinction to the escape of transgenes to the evolution of weedy or invasive lineages. Here, we describe patterns of hybridization and gene flow involving domesticated and wild sunflowers in Argentina. To address the risks of introgression of variants from the cultivated sunflower into invasive wild Helianthus, we used genotyping‐by‐sequencing (GBS) to genotype 182 samples from 11 sites in Argentina, along with previously published data from samples from the native range (North America), to determine the native source populations of the Argentinian samples and to detect admixture. We unexpectedly discovered two distinctive forms of H. petiolaris in Argentina, one from H. petiolaris subsp. petiolaris as expected, but the other from an unknown source. Extensive admixture was observed among Argentinian sunflowers, largely confirming phenotypic predictions. While many hybrids are F1s, there were signals consistent with introgression from the domesticated sunflower into H. petiolaris. Whether this introgression is incidental or a causal driver of invasiveness is not yet clear, but it seems likely that genes found in the domesticated sunflower genome (whether engineered or not) will quickly find their way into wild Argentinian sunflower populations. [ABSTRACT FROM AUTHOR]

Abstract: Wild sunflower, Helianthus annuus, is an open-pollinated species that can be a major weed in several crops. If it hybridizes with cultivated sunflower the following generations can generate crop-wild hybrids that could evolve into invasive populations. The objective of this study was to morphologically characterize F1 hybrids between inbred lines and wild sunflower, their F2, BC1 and BC2 progenies with domestic sunflower to assess the risk of these plants evolving into invasive biotypes. Crop-wild hybrids were easily identified as off-type plants. F1 plants were taller, branched with several heads, smaller disks and phyllaries, stigma and pale anthocyanins, and a longer flowering period compared to cultivated sunflower. None of the F2 plants were similar to wild sunflower plants, but morphologically closer to the cultivated materials. These results showed the improbability that crop-wild off-type plants give rise to plants morphologically similar to wild sunflowers and therefore the risk of developing invasive populations by their introduction. [Copyright &y& Elsevier]

Agricultural weeds are plants well-adapted to agricultural environments interfering directly and indirectly with crop production and causing important economic losses worldwide. Crop-wild hybridization is one of the main forces that have ruled weed evolution along with adaptation to agricultural (or benign) environments. Considering the competing demands for resources in any plant, adaptation to agricultural environments might result in an increase in growth but with lower tolerance to stress. In Argentina, most of the non-native H. annuus populations grow on roadsides, ditches, fences, hedgerows (ruderals), but there are also a few cases of H. annuus growing in agricultural field as weeds (agrestals). We asume that weediness of these agrestal biotypes came after crop hybridization as result of growth-stress tolerance trade-offs. Ruderal, agrestal (with evidence of crop introgression), and crop biotypes were contrasted under studies of drought and defoliation stresses, as well as for plant growth under non-stressful conditions and sequences of stress-related genes. The agrestal biotype was less tolerant to defoliation and drought than the ruderal biotype. Drought tolerance variation was largely explained by plant height rate (growth) and defoliation tolerance variation was mainly explained by biomass accumulation (resource allocation). Agrestal biotype sequences of two genes encoding transcription factors involved in stress response, DREB2 and NAC , showed evidence of positive selection in the crop direction. Therefore, selection in the agricultural environment combined with crop hybridization driver the evolution of a well-adapted genetic variant of H. annuus with fast growth but reduced stress tolerance. [ABSTRACT FROM AUTHOR]