A biotechnology solution to weeds

Plant breeders and researchers are working to produce crops that are resistant or tolerant to herbicides. This allows herbicides to be sprayed on the field, killing the weeds, but not harming the crop.

To do this, the genes responsible for herbicide tolerance need to be transferred into the crop plants.

There are four ways to create herbicide-tolerant plants.

1. By natural selection

If a large population of a plant species is sprayed with herbicide, a few plants will survive, flower and produce seed. Some of these seeds will contain the genes that allow the plant to tolerate the herbicide. This herbicide tolerance is passed on through generations of offspring. An increasing number of these plants will survive being sprayed by the herbicide.

If this process of allowing plants that survive exposure to the herbicide to develop and produce seed is carried out enough times, most seeds produced will be tolerant to the herbicide. The herbicide will no longer kill these plants.

For example, canola crops grown in Australia have some natural tolerance to herbicides. This natural tolerance has been enhanced by the process of selectively breeding herbicide-tolerant canola plants.

2. Using naturally occurring genes

TT canola – a conventionally bred strain of canola resistant to the herbicide triazine - is grown across Australia. In Western Australia, it makes up approximately 90 per cent of the total canola production in that state. This form of canola was bred by using genes that were already present in the canola's gene pool.

3. Using mutagenesis

Mutagenesis is the alteration of genes using chemicals or radiation. Mutagenesis can be used to create herbicide-tolerant plants. Then, using traditional cross breeding, crop plants with favourable characteristics and herbicide tolerance can be selected.

An example of a crop made using this technology is Clearfield® canola, marketed by BASF. Varieties of Clearfield® canola have been bred using conventional methods to be tolerant to imidazolinone herbicides, which include the marketed brand On Duty®. These conventionally-bred herbicide tolerant canola varieties are widespread across Australia. Similar herbicide tolerance systems have also been developed for wheat and maize.

4. Using gene technology

Glyphosate is a very effective herbicide. Only five species of plants worldwide are known to have developed resistance to glyphosate through natural selection. Developing herbicide tolerance in a wide variety of crop plants for this herbicide through natural selection is not likely to be easy.

A common soil bacterium gene, which causes a plant to be tolerant to the herbicide glyphosate, has been inserted into a line of canola. The Roundup Ready® canola variety will not be affected when the weeds in the same paddock are killed by spraying with glyphosate.

When using gene technology to modify plants, conventional breeding techniques still have to be used to breed the new trait into the commercial varieties for crops.

Not all herbicide-tolerant GM plants are resistant to glyphosate. The Bayer variety InVigor® canola has been created using gene technology, so that it is resistant to Liberty®, the Bayer glufosinate-ammonium herbicide. Rice is another glufosinate-ammonium resistant crop.