Wild radish can resist all by itself by Alex Nicol

Super Radish

GOOD NEWS! Concerns that herbicide-tolerant canola would cross with wild radish and produce a super weed are misplaced in Australian paddocks - although growers need to remember that wild radish and other weeds don't need any help to become resistant to herbicides.

Concern about the possibility of a race of super weeds developing has been heightened by French research that shows a significant flow of genes from canola to wild radish. Working at Adelaide University with the CRC for Australian Weed Management and with backing from the GRDC, Mary Rieger first checked the methods used by the French scientists and then set up her own research trials under Australian conditions.

She found that the French work had not replicated the sort of conditions most farmers would come across in a weedy paddock. They had interspersed wild radish between rows of canola rather than scattering the weeds at random. Dr Rieger set up two separate research trials, one with four wild radish plants per square metre, and the other with one every square metre. "It's the sort of situation you're likely to find in Australian paddocks;' she said.

Dr Rieger was relieved to find fewer hybrid plants than she expected but she warns that wild radish can become resistant to herbicides without any help if herbicides are overused.

"Continual rotation of herbicide groups is the key to keeping resistant weeds at bay," she said.

Her research looked for the transfer of genes from herbicide-resistant wild radish to herbicide-susceptible canola and from herbicide-tolerant canola to susceptible strains of radish. She used the presence of molecular markers, differences in chromosome numbers and the morphology or general appearance of the plant, as well as herbicide tolerance in testing for hybrids.

Wild radish pollination of herbicide-resistant canola produces herbicide-resistant hybrids at a rate of I in 26 million. This is less than the chance of having wild radish develop resistance in the paddock through herbicide overuse.

"It appears that canol a will accept foreign pollen and be fertilised by it," Dr Rieger said, "but this seems less likely for wild radish. Results show that it is much more likely to be fertilised by pollen from another wild radish plant. This breeding barrier is natural protection against the transfer of genes. What growers need to remember is that wild radish has a higher chance of developing herbicide resistance without any help if the same herbicide group is used frequently in the same paddock.

"Growers should also understand the importance of using fresh canol a seed every year," she advised. "Even if no herbicide-resistant hybrids are produced, the quality of their oil could be inferior due to pollination with wild radish."

Contact: Dr Mary Rieger 08 8303 7298 email mary.rieger@adelaide.edu.au

Region North, South, West