Cultivated Helianthus annuus (Asteraceae) volunteers as a genetic “bridge” to weedy sunflower populations in North America

Abstract

In many crops, unharvested seeds can create populations of volunteer plants that increase opportunities for crop-to-wild gene flow. Pollen-mediated gene flow between cultivated and wild sunflower (both Helianthus annuus, Asteraceae) is well documented, but the role of seed dispersal and volunteers has not been investigated. We compared flowering times and other phenotypic traits of volunteers from both ''normal'' and ''off-type'' (multi-headed) crop plants with those of wild sunflowers. Normal and off-type volunteers typically had a maternally inherited, crop-specific DNA marker. Seedlings of wild plants, normal volunteers, and off-type volunteers from Colorado were cultivated in a greenhouse and at a field site in Ohio. We used a classification tree approach to differentiate the three plant types and identify phenotypic traits that can be used to recognize volunteers in the field in future surveys. In greenhouse and field experiments, we observed sufficient overlap in flowering times to allow gene flow among the three plant types. Volunteers from off-type crop plants were more likely to cross-pollinate with wild plants than volunteers from normal crop plants. Our results suggest that both types of crop volunteers have the potential to act as conduits for gene exchange between cultivated and wild sunflowers.

Chromosomal Evolution and Patterns of Introgression inHelianthus

“…The genus Helianthus, which is composed of 49 species native to the Americas (Timme et al 2007) and includes cultivated sunflower (Helianthus annuus L.; 2n = 2x = 34; hereafter referred to as ANN), has emerged as a model for genetic studies of adaptation, hybridization, and speciation (Rieseberg et al 1995a,b;Lai et al 2005;Reagon and Snow 2006;Massinga et al 2009;Gutierrez et al 2010;Vekemans 2010;Roumet et al 2013). Insight into the nature and extent of reproductive barriers within Helianthus will provide valuable understanding of how these species arose and will also aid in the development of strategies for the introgression of beneficial alleles from related wild species (e.g., silverleaf sunflower and the Algodones Dune sunflower) into the cultivated sunflower gene pool.…”

“…As such, detailed information on karyotypic differences between species provides insight into the nature of reproductive isolation and, more pragmatically, informs attempts to introgress beneficial alleles from wild species into crop gene pools (Chetelat and Meglic 2000;Foulongne et al 2003;Dirlewanger et al 2004). An improved understanding of synteny across species can also facilitate the identification and localization of functionally important genes in a taxon of interest through the extrapolation of gene order from model species (e.g., Choi et al 2004;Dilbirligi et al 2006).The genus Helianthus, which is composed of 49 species native to the Americas (Timme et al 2007) and includes cultivated sunflower (Helianthus annuus L.; 2n = 2x = 34; hereafter referred to as ANN), has emerged as a model for genetic studies of adaptation, hybridization, and speciation (Rieseberg et al 1995a,b;Lai et al 2005;Reagon and Snow 2006;Massinga et al 2009;Gutierrez et al 2010;Vekemans 2010;Roumet et al 2013). Insight into the nature and extent of reproductive barriers within Helianthus will provide valuable understanding of how these species arose and will also aid in the development of strategies for the introgression of beneficial alleles from related wild species (e.g., silverleaf sunflower and the Algodones Dune sunflower) into the cultivated sunflower gene pool.…”

CMS Lines for Evaluation of Pollen Flow in Sunflower Relevance for Transgene flow Mitigation

“…A number of studies documented the introgression and persistence of cultivar alleles in wild relatives (1,8,9,14,17). Several factors assist exchange of genes between wild and cultivated sunflowers: overlapping of flowering time, shared pollinators, self-incompatibility of wild sunflower, self compatibility of domesticated sunflower, and high rate of outcrossing.…”

Genetic and Ecological Consequences of Transgene Flow to the Wild Flora

“…Finally, an additional potential source of transgenes is represented by first and subsequent generations of hybrids between GE crops and wild relatives, which can act as "genetic bridges" between the parental species [5,9].…”

“…The concerns related to the cultivation of GE crops, in particular those dealing with the possibility of transgene escape into the wild flora, have generated a multitude of studies on crop-to-wild gene flow [1][2][3][4][5][6][7][8][9]. While these studies have shown that such gene flow exists for almost all of the most important crops cultivated worldwide, only recently have new studies focused and are focusing on its ecological and genetic consequences [9][10][11]. Yet, in order to better assess the ecological and agronomic risks associated with the transgene flow to the wild flora, it is fundamental to understand the mechanisms and the consequences of such gene flow [12].…”