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.
Highlights
A recent special issue in this journal (Ellstrand & Rieseberg, 2016) highlighted the potentially important applied consequences of gene flow
We focus on gene flow involving the domesticated sunflower, Helianthus annuus L. var macrocarpus (DC.), its wild progenitor, H. annuus, and a compatible wild relative, H. petiolaris Nutt. in Argentina
In light of extensive and well-documented hybridization and introgression between Helianthus species in North America, and phenotypic reports suggestive of hybridization in Argentina, we employed a genotyping-by-sequencing (GBS) approach to address the following two questions: (i) Are the wild species currently hybridizing in Argentina and does this account for observations of so-called off-type individuals in areas of sympatry? and (ii) Are domesticated sunflower alleles introgressing into wild Argentinian populations? Our results suggest that crop-wild gene flow is ongoing and highlight the future risk that edited sunflower genes will escape from farmer’s field
Summary
A recent special issue in this journal (Ellstrand & Rieseberg, 2016) highlighted the potentially important applied consequences of gene flow. The presence of H. annuus was reported around this time (Cabrera, 1974; Covas, 1964), the morphology did not match that of wild or weedy H. annuus, but rather escaped domestic sunflower It was another 40 years before wild H. annuus was described in Argentina (Poverene et al, 2002). Wild H. annuus has been occasionally used in breeding programs since the late 1940s (Bauer, 1988; Bertero de Romano & Vázquez, 2003), but escapes from breeding stations were deemed unlikely by Cantamutto, Torres, et al (2010) because ruderal populations or herbarium specimens of wild H. annuus have not been found nearby Both species currently occur as far as 500 km from the presumptive site of introduction in the center of the country.
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