Genetic Diversity of Oilseed Rape Fields and Feral Populations in the Context of Coexistence with GM Crops

Abstract

Despite growing concern about transgenes escaping from fields, few studies have analysed the genetic diversity of crops in an agroecosystem over several years. Accurate information about the dynamics and relationship of the genetic diversity of crops in an agroecosystem is essential for risk assessment and policies concerning the containment of genetically modified crops and their coexistence with crops grown by conventional practices. Here, we analysed the genetic diversity of oilseed rape plants from fields and feral populations over 4 years in an agricultural landscape of 41 km2. We used exact compatibility and maximum likelihood assignment methods to assign these plants to cultivars. Even pure lines and hybrid cultivar seed lots contained several genotypes. The cultivar diversity in fields reflected the conventional view of agroecosystems quite well: that is, there was a succession of cultivars, some grown for longer than others because of their good performance, some used for one year and then abandoned, and others gradually adopted. Three types of field emerged: fields sown with a single cultivar, fields sown with two cultivars, and unassigned fields (too many cultivars or unassigned plants to reliably assign the field). Field plant diversity was higher than expected, indicating the persistence of cultivars that were grown for only one year. The cultivar composition of feral populations was similar to that of field plants, with an increasing number of cultivars each year. By using genetic tools, we found a link between the cultivars of field plants in a particular year and the cultivars of feral population plants in the following year. Feral populations on road verges were more diverse than those on path verges. All of these findings are discussed in terms of their consequences in the context of coexistence with genetically modified crops.

Glucosinolates promote initial population establishment of feral oilseed rape

“…Glucosinolate levels are known to vary both within and across Brassica populations (Hopkins, van Dam & van Loon 2009), yet little is known about chemical traits in feral oilseed rape. A subset of our feral populations displayed relatively high GS levels, which could have arisen as a result of founder effects (populations originating from high-GS cultivars), natural selection and/or hybridization (e.g., Charters, Robertson & Squire 1999;Pessel et al 2001;Bond et al 2004;Pivard et al 2008;Elling, Neuffer & Bleeker 2009;Pascher et al 2010;Schulze et al 2014;Bailleul, Ollier & Lecomte 2016). The relative importance of these nonmutually exclusive processes in shaping trait variation remains largely unresolved (Elling, Neuffer & Bleeker 2009).…”

“…While theoretical models have aimed at addressing this outstanding issue (Claessen et al 2005;Garnier & Lecomte 2006), demographic data encompassing the entire life cycle are scarce (Pessel et al 2001;Bagavathiannan & Van Acker 2008;Pascher et al 2010; but see : Crawley et al 1993;Crawley & Brown 1995;Crawley & Brown 2004;Hooftman et al 2015). This is an important knowledge gap as oilseed rape is a major crop for which transgenic lines have been developed (Ellstrand, Prentice & Hancock 1999;Hails & Morley 2005;Warwick et al 2008;Schafer et al 2011;Bailleul, Ollier & Lecomte 2016).…”

Evaluation of the Risks of Contaminating Low Erucic Acid Rapeseed with High Erucic Rapeseed and Identification of Mitigation Strategies

“…In an assessment of five study areas and 20 growing seasons, it was concluded that the distribution and persistence of feral B. napus is possible but the proportion of the population overall and their contribution to adventitious mixing is negligible [18]. Two studies both noted that feral populations of cultivars were not of the dominant genotype currently being grown in adjacent fields [55,56]. They showed instead to have greatest similarity with the cultivar grown the previous year.…”

“…They showed instead to have greatest similarity with the cultivar grown the previous year. Several studies have suggested that feral plants often survive for just one year even when self-seeding the previous year was prolific [54,55]. For example, it has been found that, in a given year, 35%-40% of feral B. napus plants resulted from the movement of seed from the adjacent field during the previous year [57].…”

“…For example, it has been found that, in a given year, 35%-40% of feral B. napus plants resulted from the movement of seed from the adjacent field during the previous year [57]. One potentially contradictory observation was that there was no sufficient distinction of a proportion of feral genotypes to allocate a specific cultivar to them, which would be expected if derived from a single cultivar grown in an adjacent field the previous year [55].…”