Occurrence of spilled genetically modified oilseed rape growing along a Japanese roadside over 10 years

Abstract

To map the distribution of feral oilseed rape (Brassica napus L.) in Japan, we conducted a roadside survey along 19 km of Route 51 for 10 years, from 2005 to 2014. We found more than 2,000 plants in the first 2 years. The number decreased to 150–305 from 2007 to 2010, and to only 27 in 2014, likely owing to extensive road repairs. Three areas of high frequency were found. One area features frequent hills. The second was where the road narrows, likely where seeds spill from trucks as they decelerate or accelerate. The third is in a fenced patch, showing that if spilled seeds fall in places where they cannot be managed, they can perpetuate. Our survey confirms that feral oilseed rape has nearly disappeared from this road. The proportion of genetically modified (GM) oilseed rape in the feral population was low, and it decreased as the total number of rape plants decreased. Therefore, we conclude that the distribution of GM oilseed rape growing along Route 51 has no effect on biodiversity such as suppression of other species' distribution and introgressive hybridization with wild relatives. This is the first report of a long-term survey on the fate of oilseed rapes growing along transportation route in Japan.