Transgenic glyphosate-resistant canola (Brassica napus) can persist outside agricultural fields in Australia

In the last two decades the cultivation of transgenic crops has steadily increased worldwide. In Western Australia transgenic glyphosate-resistant canola (GR) has been cultivated since 2009. This study was conducted to examine the potential for transgene persistence outside agricultural fields after commercialization of GR crops. Propagule pressure, population fluctuations and reproductive output of GR canola plants have been assessed in semi-natural (roadside) and natural environments over consecutive years. The estimation of demographic parameters (plant survival and fecundity) suggest that GR canola has low likelihood to become invasive, as plants are subjected to biological and abiotic stressors likely limiting the fitness. This was particularly evident in a natural environment in which a propagule of 300 GR canola plants accidentally introduced by a wind storm could persist for three years before extinction. Thus, in natural areas GR canola populations did not show a positive population turnover and declined overtime. Conversely, on roadsides the significant correlation (r = 0.975) between mean plant fecundity (seed rain) and the soil seedbank density in the following year suggests that local recruitment contributed to canola persistence for at least three years. As, no individual GR plants were found with stacked genes for multiple herbicide resistance we suggest that GR volunteer canola plants can be controlled by simple mixture of herbicide modes of action different to glyphosate although an integrated management including mechanical control operations would be the optimal strategy.