Where do the feral oilseed rape populations come from? A large‐scale study of their possible origin in a farmland area

Abstract

Summary 1.Many cultivated species can escape from fields and colonize seminatural habitats as feral populations. Of these, feral oilseed rape is a widespread feature of field margins and roadside verges. Although considered in several studies, the general processes leading to the escape and persistence of feral oilseed rape are still poorly known. Notably, it remains unclear whether these annuals form transient populations resulting mainly from seed immigration (either from neighbouring fields or during seed transport), or whether they show real ability to persist (either through self-recruitment or seed banks). 2. We conducted a 4-year large-scale study of factors involved in the presence of feral oilseed rape populations in a typical open-field area of France. The results were subjected to statistical methods suitable for analysing large data sets, based on a regression approach. We subsequently addressed the relative contribution of the ecological processes identified as being involved in the presence of feral populations. 3. Many feral oilseed rape populations resulted from seed immigration from neighbouring fields (about 35-40% of the observed feral populations). Immigration occurred at harvest time rather than at sowing. Around 15% of such populations were attributed to immigration through seed transport. 4. The other half resulted from processes of persistence, mainly through persistent seed banks (35-40% of the observed feral populations). This was all the more unexpected because seed banks have not yet been documented on road verges (despite being frequent within fields). Local recruitment was rare, accounting for no more than 10% of the feral populations. 5. Synthesis and applications . Understanding the dynamics of feral oilseed rape populations is crucial for evaluating gene flow over an agro-ecosystem. Our results show that, while many feral populations do come from annual seed dispersal, a significant number also result from seeds stored in the soil for several years. In the current context of coexistence and management of transgenic with non-transgenic crops, feral persistence and, especially, the seed bank contribution to the dynamics of feral populations need to be considered seriously. The latter, combined with selfrecruitment, indicates a high potential for the persistence of transgenes and the possible emergence of gene-stacking.

Persistence of Feral Populations of Brassica napus Originated from Spilled Seeds around the Kashima Seaport in Japan

“…In these countries, the feral and volunteer plants originating from cultivated B. napus seeds have established around agricultural lands, and the population persistence of B. napus has been intensively examined 3,4,7,11,14,15 . In Japan, the cultivated acreage of B. napus is not so large and the feral plants have not been viewed as an agricultural problem.…”

Fitness and beyond: Preparing for the arrival of GM crops with ecologically important novel characters

“…Deployment of life-history modeling approaches has proved a popular and informative strategy to address this need, and has generally confirmed a tendency towards extinction and emphasized the importance of seedbank dynamics and fresh spillage (Aono et al, 2006;Garnier et al, 2006;Pivard et al, 2008aPivard et al, , 2008bSaji et al, 2005;Kowarik, 2007a, 2007b;Yoshimura et al, 2006). These data are useful because they provide a valuable baseline comparator for any transgenic crop.…”

Feral genetically modified herbicide tolerant oilseed rape from seed import spills: are concerns scientifically justified?

“…Few studies have been able to define the proportion of populations derived from fresh spills, but at the study site of Selommes in France, 15% of feral populations were attributed to immigration through seed transport, potentially including seed imports to the area, as opposed to 35-40% originating from seed from neighbouring fields (Pivard et al, 2008a).…”

“…Even though observations from demographic studies across Europe showed that seed yield of feral plants is often much smaller than that of the crop due to the less suitable habitat than agricultural fields, seed from mature plants is still likely to replenish the soil seedbank and contribute to population persistence (Squire et al, 2011). One of the few direct estimates in Europe is by Pivard et al (2008a) who found that local seed input from resident feral oilseed rape is rare, accounting for less than 10% of subsequent feral populations in the study site of Selommes. Other data, relying on the existence of feral plants bearing seed, are mostly circumstantial and indicate that the proportions of feral plants having pods ranged between 30 to 48% in northwest Germany (Elling et al 2009).…”