GM canola on horizon a primer for farmers

Photo of a GM crop in flower

Monsanto has applied to the Office of the Gene Technology Regulator in Canberra for a licence to commercially release Roundup Ready® canola. Aventis has even more recently done the same for InVigor® canola, which uses a hybrid technology that may give greater yield potential, and is also tolerant to the herbicide glufosillate (marketed in some uses as 'Basta' Liberty®).

The Office of the Gene Technology Regulator is llOW ill the process of assessillg these applications. Growers and the public will be able to comment in upcoming months (see separate story p26).

Ground Cover asked scientists from the Australian Weed Mallagement CRC to address some of the issues that surround the potential introductioll of these varieties alld provide us with the latest research results on agronomic concerns such as pollen drift. We also asked that GM canola be put in perspective with currently available herbicide-resistant varieties - why might you consider switching to a GM variety?

Weed management options in canola - the current situation

Due to the difficulty of weed management in canola, many Australian growers currently use triazine-tolerant (TT) canola, which now accounts for 60- 70 per cent of Australia's canola-producing area. Some growers are also using Clearfield canola, which is resistant to the imidazolinone herbicides.

Both resistance types were bred by 'classical' means, that is, they are not GM. However, TT canola has a significant penalty in yield and oil content, which is a direct cost of the resistance mechanism. Further, atrazine use is potentially under threat from recent research in the USA suggesting that low concentrations can harm frogs.

Clearfield canola may be an option for some growers, but resistance to 'imi' herbicides can be selected with 4-5 uses of Group B herbicides. Resistance has already occurred in annual ryegrass in many areas of SA and WA.

These concerns open the door for further options. Roundup Ready® and InVigor®canol a varieties will provide additional incrop herbicide options for the control of weeds and, in the case of In Vigor, possible higher-yield potential (see Gene Scene for agronomic benefits listed by Canadian growers - Ed).

In sum, GM canola will increase the range of types of tolerance available in canola and widen the range of weed and crop management options available to graingrowers.

What about weed resistance and GM canola?

Weed resistance to herbicides, including glyphosate, has come about as a result of repeated usage of the same herbicide in conventional crops - selecting for resistant weeds. Resistance to glyphosate in annual ryegrass has now been found in at least 14 sites across southern Australia (including three more in July 2002), mostly in horticulture.

Growers will still face issues of weed resistance with GM varieties. This is one of the reasons why Monsanto and Aventis will market their GM varieties with detailed management packages attached. Based on our research, if Roundup Ready® canola is adopted, we strongly recommend that growers avo id the use of glyphosate either the year before or the year after growing a Roundup Ready® canola crop. This would allow susceptible weeds from the seed bank to escape glyphosate selection after germination and dilute resistance.

There is increasing evidence that glyphosate-resistant annual ryegrass competes poorly with susceptible ryegrass in the absence of glyphosate use (Preston, unpublished), but there have to be periods when the herbicide is not used for the susceptible plants to suppress resistance.

In Vigor® hybrid canola may be attractive to graingrowers who can maintain good weed control with their current management practices. The herbicide glufosinate ammonium will control some weeds and has potential to suppress seed set in annual ryegrass and perhaps other weeds, but may disappoint as a stand-alone herbicide in a weed management program.

Research on other management issues

The CRC for Weed Management Systems has investigated other public concerns about GM canola, including the potential for herbicide-tolerant canola volunteers in subsequent crops and crossing between herbicide-resistant crops and weeds.

There has been a report of multipleresistant canola volunteers evolving from crosses among different canola varieties in Canada. In this case three types of resistant canola were separated no further apart than a farm road. Controlling volunteers will require careful management, but we suspect many growers will control canola volunteers with applications of herbicides for radish and other broadleaf weeds in cereal crops.

World's largest pollen-flow study

Canola is recognised internationally as one of the crops most likely to spread viable pollen. In contrast, cereal crops, cotton and pulses pollinate only over short to very short distances.

With the help of agrichemical company BASF, we measured the potential for pollen flow between crops following the commercial introduction of Clearfield canola in 2000. In the largest and most comprehensive study of pollen flow in canola ever conducted anywhere in the world, Mary Rieger of the Australian Weed Management CRC led the collection of 48 million seeds from 63 non-resistant canola fields surrounding 20 Clearfield canola fields.

The seeds were then grown and tested for herbicide resistance to measure the extent of pollen flow. The average level of pollination in all of the surrounding canola fields was 0.009 per cent. Not even fields that were 10 metres away showed an average pollination of greater than 0.07 per cent. Cross-pollination was not found at greater than 3 km.

There have been claims that crosspollination caused a farmer to be sued in Canada (the Percy Schmeiser case). But the court record indicates that the farmer deliberately saved Roundup Ready® seed obtained in some other way (see http://decisions.fct-cf.gc.ca/fct/2001/2001fct256.html).

GM-free zones and pollen flow

There is a lot of discussion in Australia about GM-free zones and buffer zones between GM and non-GM canola crops. It 's important to consider what are the goals of such zones in the light of our data on pollen flow and market considerations. Internationally, standards for unintentional mixing of GM with non-GM food ingredients have been set for labelling purposes at 0.5-1 per cent, which is at the practical limit of detection by DNA testing methods. Our studies show that mixing by pollen flow would be 50 times lower than this.

Provided that seed supplies and shipping retained segregation of GM and non-GM canola, even having a GM crop in the next paddock would not prevent conventional canola from being accepted as non-GM.

Organic farmers leading GM-free push

Organic farming programs, however, have set a zero threshold for cross-pollination, even for canola. In contrast, many organic certification systems have thresholds for accidental contamination with pesticides. The zero threshold set by organic growers will continue to be a contentious issue. However, our data indicate that no pollination could be detected at 3 km from the pollen source, which should prove to be useful in any effort to reach a compromise.

Gene transfer to weeds?

Another concern is that herbicide-resistance genes could be transferred from crops to weeds. Canola can potentially hybridise with (and transfer genes to) wild radish. Mary Rieger, Chris Preston and Steve Powles of the Australian Weed Management CRC have studied the potential for hybridisation between canola and wild radish in largescale field experiments that also used herbicide resistance to identify potential hybrids.

These experiments, which screened more than 50 million seeds, found two plants that were hybrids. Thus, glyphosate or glufosinate resistance could move from GM canola to wild radish. However, what would be the implications? We now believe the answer is 'not much', because neither glyphosate nor glufosinate would be preferred as the stand-alone treatment for wild radish management.

GM canola, promising but no magic bullet

Herbicide-tolerant crops could become a component of integrated weed management strategies, but will require considerable care and record keeping to live up to their potential. Growers will need to implement the management packages to realise their potential on a sustainable basis. Even then, with the continuing evolution of resistance in weeds, herbicide-resistant crops should not be relied upon as the primary long-term solution to weed problems.

Other applications of biotechnology will also be important, especially the more sustainable use of crop cultivars that are highly competitive with weeds. In the end, there will be no substitute for the continued and expanded integration of a range of weed management tactics for any sustainable successes.