Evidence for gene flow via seed dispersal from crop to wild relatives inBeta vulgaris(Chenopodiaceae): consequences for the release of genetically modified crop species with weedy lineages

Abstract

Gene flow and introgression from cultivated to wild plant populations have important evolutionary and ecological consequences and require detailed investigations for risk assessments of transgene escape into natural ecosystems. Sugar beets (Beta vulgaris ssp. vulgaris) are of particular concern because: (i) they are cross-compatible with their wild relatives (the sea beet, B. vulgaris ssp. maritima); (ii) crop-to-wild gene flow is likely to occur via weedy lineages resulting from hybridization events and locally infesting fields. Using a chloroplastic marker and a set of nuclear microsatellite loci, the occurrence of crop-to-wild gene flow was investigated in the French sugar beet production area within a 'contact-zone' in between coastal wild populations and sugar beet fields. The results did not reveal large pollen dispersal from weed to wild beets. However, several pieces of evidence clearly show an escape of weedy lineages from fields via seed flow. Since most studies involving the assessment of transgene escape from crops to wild outcrossing relatives generally focused only on pollen dispersal, this last result was unexpected: it points out the key role of a long-lived seed bank and highlights support for transgene escape via man-mediated long-distance dispersal events.

Hybrids between cultivated and wild carrots in natural populations in Denmark

“…Largescale transportation of seeds may thus create a gene flow between wild populations and cultivars in very different parts of the world. This dynamic has so far only been described in carrots and in cultivated and wild beets (Arnaud et al, 2003;Van Dijk, 2004). In beets, this has created serious problems with weedy beets in northern Europe, supporting the idea that hybridization between cultivated and wild plants may lead to increased weediness (Ellstrand and Schierenbeck, 2000;Campbell et al, 2006).…”

“…A similar route of hybridization, via seed production regions, has been described for cultivated beets (Beta vulgaris) (Arnaud et al, 2003;Van Dijk, 2004). Another possibility for hybridization and gene transfer between cultivated and wild plants is a direct transfer of pollen from cultivar plants into wild populations.…”

Genetic use restriction technologies and possible applications in the integrated pest management

“…vulgaris) and sea beets (B. vulgaris ssp. maritima), sorghum (Sorghum bicolor) and S. propinquun and cultivated rice (Oryza sativa) and weedy red rice (O. sativa) (ELLSTRAND et al, 1999;ELLSTRAND & SCHIERENBECK, 2000;GRESSEL, 2000;ARNAUD et al, 2003). The introgression of glyphosate tolerant gene from GM canola has been reported in other brassicas wild plants (WARWICK et al, 2008).…”

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

“…In CWH complexes where the crop is harvested or mowed before flowering occurs (e.g., beet, radish, lettuce, turf grass), volunteers may be the only viable pathway for gene flow. This has been shown to be the case in sugar beet: a recent study of weed beet populations in France found that crop seed dispersal and backcrossing from volunteers was the primary pathway for crop-to-wild gene flow (Arnaud et al, 2003).…”

“…Most studies of gene flow within CWH complexes have focused on the dispersal of pollen rather than seeds (Ellstrand et al, 1999;Ellstrand, 2003), in part because of difficulties in separating the effects of pollen and seed dispersal and the prevailing view that pollen movement is mostly responsible for genetic subdivision among plant populations (Cain et al, 2000). As a result, only a few studies have examined the role of seed dispersal in determining gene flow rates in CWH complexes (Arnaud et al, 2003). However, if certain types of transgenic crops are designed to minimize pollen flow from the crop, for example by having male sterility or maternally inherited transgenes, it will also be important to gain a better understanding of seed-mediated gene flow (NRC, 2000).…”