Relationship between hybridization frequency of <i>Brassica juncea</i> × <i>B. napus</i> and distance from pollen source (<i>B. napus</i>) to recipient (<i>B. juncea</i>) under field conditions in Japan

Abstract

Several imported transgenic canola (Brassica napus) seeds have been spilled and have grown along roadsides around import ports. B. juncea, a relative of B. napus with which it has high interspecific crossability, is widely distributed throughout Japan. There is public concern about the harmful impacts of feral B. napus plants on biodiversity, but spontaneous hybridization between spilled B. napus and weedy B. juncea populations is hardly revealed. We evaluated the relationship between the hybridization frequency of B. juncea × B. napus and their planting distance in field experiments using the mutagenic herbicide-tolerant B. napus cv. Bn0861 as a pollen source for hybrid screening. The recipient B. juncea cv. Kikarashina was planted in an experimental field with Bn0861 planted in the center. No hybrids were detected under natural flowering conditions in 2009. However, the flowering period was artificially kept overlapping in 2010, leading to a hybridization frequency of 1.62% in the mixed planting area. The hybridization frequency decreased drastically with distance from the pollen source, and was lower under field conditions than estimated from the high crossability, implying that spontaneous hybridization between spilled B. napus and weedy B. juncea is unlikely in the natural environment.

Long-term monitoring of feral genetically modified herbicide-tolerant <i>Brassica napus</i> populations around unloading Japanese ports

“…Consequently, hybridization may be prevented by physical isolation. When both species are cultivated together in large fields, the crossing rates was 0.1–3.29% ( Bing et al 1991 , 1996 , Huiming et al 2007 , Jørgensen et al 1998 ); when they grew together on unintended terrain the crossing rate was 1.62% ( Tsuda et al 2012 ). The largest number of B. juncea populations we encountered were located in Nagoya (in 2006), but only 41 populations occurred in a 5 km radius.…”

“…Were they to cross with B. napus , there is a risk that the hybrids would have elevated fitness levels and invade the surrounding vegetation. However, the average crossing rate of B. juncea and B. napus is only 1.62% even when they are planted together ( Tsuda et al 2012 ). Furthermore, GM B. napus distributions are limited to port environs and roads leading from them ( Aono et al 2006 , 2011 , Kawata et al 2009 , Mizuguti et al 2011 , MAFF 2012 , Saji et al 2005 ).…”

Genetically modified seeds and plant propagating material in Europe: potential routes of entrance and current status

“…Even though spread of GM plants is often hypothesized to occur through cross-pollination with compatible non-GM crop plants or wild species, the literature search reported only a limited number of cases demonstrating transfer of transgenic pollen, e.g., for maize in South Africa (Viljoen and Chetty, 2011) or oilseed rape in Japan (Tsuda et al., 2012). In summary, even though it is possible that imported GM seed material can be inadvertently introduced to the EU environment and, in some cases, depending on species fitness, can establish persisting plant populations, e.g., oilseed rape, the available evidence suggests that probability of gene transfer from persisting population to crop plants via hybridization is very low (Belter, 2016; Devos et al., 2012).…”

Possibilities of direct introgression from <i>Brassica napus</i> to <i>B. juncea</i> and indirect introgression from <i>B. napus</i> to related Brassicaceae through <i>B. juncea</i>

“…Spontaneous hybridization frequency is greatly influenced by the field experimental design, such as the size of the pollen donor and the isolated distance from the donor ( Scheffler et al 1993 , Tsuda et al 2012a ). This section summarizes the effects of distance between the donor and the recipient on spontaneous hybridization frequency ( Table 1 ).…”

“…In mixed cultivation experiments, spontaneous hybridization frequency varied from 0.13 to 5.91% in B. juncea × B. napus ( Bing et al 1991 , 1996 , Heenan et al 2007 , Huiming et al 2007 , Jørgensen et al 1998 , Liu et al 2010 , Tsuda et al 2012a ). On the other hand, the frequency in B. napus × B. juncea ranged from 1.1 to 1.3% ( Bing et al 1991 , 1996 , Heenan et al 2007 , Jørgensen et al 1998 ).…”