The ‘stacking’ of multiple herbicide tolerance traits through outcrossing between the two GM herbicide tolerant canolas and non-GM herbicide tolerant canola varieties could also occur at a low frequency, and would have implications for herbicide choices for the control of canola volunteers. In 2005–2006, approximately 75% of the canola crop in Australia comprised non-GM imidazolinone tolerant (Clearfield®) and triazine tolerant (TT) varieties (Norton & Roush 2007).
Note that because the triazine tolerance trait in TT canola is maternally inherited, and so cannot be spread by pollen movement, stacking of the glyphosate or glufosinate ammonium tolerance traits will only occur in the direction of Roundup Ready® or InVigor® canola to TT canola, and not vice versa.
Hybridisation between the existing non-GM herbicide-tolerant canola varieties, InVigor® canola and Roundup Ready® canola could result in accumulation or ‘stacking’ of genes for tolerance to up to four different herbicide groups within the same plant. However, development of canola plants with all four herbicide tolerance traits would only be expected to occur at an extremely low frequency because it would require at least three separate hybridisation events (two crosses between different pairs of herbicide tolerant canolas and a cross between the progeny of these).
Attention to volunteer management, proper crop rotation and herbicide management practices should limit the frequency of productive hybridisation between different herbicide tolerant canola varieties and hence the development of multiple herbicide tolerant canola in Australia (Rieger et al. 2001; Downey 1999; Salisbury 2002c). If multiple-herbicide tolerant canola plants were to occur, they are unlikely to be more invasive or persistent than non-herbicide tolerant canola plants and could be controlled by other herbicides or other agricultural practices.
Gene transfer to other sexually compatible species
Canola can cross with other B. napus groups or subspecies (including vegetable forms), B. oleracea,B. juncea and B. rapa under natural conditions.Naturally occurring hybrids between B. napus and R. raphanistrum, H. incana and S. arvensis have also been reported at very low frequencies (Salisbury 2002b; Warwick et al. 2009). All of these species are naturalized in Australia and weedy forms are known to be present (Groves et al. 2003). B. juncea,H. incana, R. raphanistrum and S. arvensis are problematic weeds in commercial canola growing regions of Australia. Therefore, it is likely that some or all of these sexually compatible species may be found growing at or near sites where the parental GM canola lines are grown. Hybridisation requires synchronicity of flowering between the parental GM canola lines and sexually compatible species to enable cross-pollination and gene flow to occur.
The RARMPs prepared for DIR 020/2002 and 021/2002 assessed the risks associated with gene flow from the parental GM canola lines to B. rapa,H. incana, R. raphanistrum and S. arvensis as very low, while the risks associated with gene flow to B. napus vegetables and forage rape, B. oleracea or B. juncea were assessed as negligible.
B. napus vegetables or forage are generally harvested or used for forage before flowering. B. napus vegetable seed production crops are isolated from other B. napus vegetable or canola crops to prevent outcrossing. Of the other sexually compatible Brassica species, hybridization offurs most readily between canola and B. rapa. Hybrids are often observed when the two species are grown in close proximity (Simard et al. 2006) and the transfer of traits from commercially grown canola to wild populations of B. rapa has been observed in Canada (Warwick et al. 2003). Warwick et al. (2008) showed that a herbicide tolerance trait from a commercial canola crop was transferred to, and stably maintained in, a wild B. rapa population for at least six years. The trait persisted despite the fact that the corresponding herbicide had not been applied during this period and, hence, no selective pressure had been applied.
The research of Warwick et al. (2008) illustrates that, if plants are growing in close proximity with synchronous or overlapping flowering periods, gene flow to sexually compatible species can occur. However, all interspecific hybrids have reduced fertility and low seed set due to the genetic barriers that exist (Jorgensen & Andersen 1994; Jorgensen et al. 1998; Salisbury 2002a; Warwick et al. 2003; Salisbury 2006). With the exception of the relatively productive interspecific hybridisation that occurs between Brassica species that contain the A genome (B. napus, B. juncea and B. rapa), most other interspecific hybridisation events occur at very low frequency.
Gene transfer from the parental GM canola lines to brassicaceous weeds would have implications for the choice of herbicide(s) for control of brassicaceous weeds. Glyphosate or glufosinate ammonium tolerant hybrids can be effectively controlled using a range of alternative herbicides and other non-chemical management techniques currently used for the control of Brassicaceous weeds. In addition, glyphosate or glufosinate ammonium would not be used for weed control in or adjacent to paddocks where Roundup Ready® or InVigor® canola has been grown because it would be ineffective in controlling the GM herbicide tolerant canola volunteers. Measures taken to control GM herbicide tolerant canola volunteers would also eliminate any herbicide tolerant hybrids.
The GMO, nature and effect of the genetic modification
Introduction to the GMO
The InVigor® x Roundup Ready® canola that Bayer intends to commercialise in Australia in the current application is derived from conventional breeding between InVigor® canola lines MS8 and RF3 and Roundup Ready® canola line GT73.
The InVigor® x Roundup Ready® canola would most likely be produced by crossing a MS8 x GT73 hybrid with RF3, but Bayer may also produce it by crossing a RF3 x GT73 hybrid with MS8, or by crossing the two hybrids together (RF3 x GT73 and MS8 x GT73). Hybrids MS8 x GT73 and RF3 x GT73 would therefore be grown by Bayer for breeding and seed production purposes. In addition, Bayer has indicated that it may use the RF3 x GT73 hybrid for cropping in the future.
Although they are not intended for commercial release, Bayer is also seeking approval from the Regulator for release of GM canola hybrids derived from conventional breeding between GM Roundup Ready® line GT73 and the remaining GM canola lines authorised for release under licence DIR 021/2002 i.e. T45, Topas 19/2, MS1, RF1 and RF2.
Based on the conventional crosses, the introduced genes present in the GM canola hybrids proposed for release are listed in Table . The InVigor® x Roundup Ready® canola that Bayer intends to commercialise will contain the barnase and barstar genes that comprise a hybrid breeding system; two copies of the bar gene conferring tolerance to glufosinate ammonium; and the cp4 epsps and goxv247 genes thatconfer tolerance to glyphosate.
Table : The introduced genes present in the GM canola hybrids proposed for release
GM canola
Hybrid breeding system
Glufosinate ammonium tolerance
Glyphosate tolerance
Antibiotic resistance
MS8 x RF3 x GT73 (InVigor® x Roundup Ready® canola)
barnase and barstar
2 copies of bar
cp4 epsps and goxv247
-
MS8 x GT73
barnase
bar
cp4 epsps and goxv247
-
RF3 x GT73
barstar (2 copies)
bar
cp4 epsps and goxv247
-
T45 x GT73
-
pat
cp4 epsps and goxv247
-
Topas 19/2 x GT73
-
pat (2 copies)
cp4 epsps and goxv247
nptII (2 copies)
MS1 x GT73
barnase
bar
cp4 epsps and goxv247
nptII
RF1 x GT73
barstar
bar
cp4 epsps and goxv247
nptII
RF2 x GT73
barstar
bar
cp4 epsps and goxv247
nptII
Characterisation of the GMO
Extensive data characterising the parental GM canola lines were provided with licence applications DIR 020/2002 and 021/2002. A brief summary of these analyses is provided below, with details available in the RARMPs prepared for these applications. In addition, Bayer has provided five reports characterising the InVigor® x Roundup Ready® canola proposed for commercial release. These reports are described in detail below.
