Planting ryegrass may be the answer

IN A twist that might surprise many of Australia's 33,000 graingrowers and 'ryegrass haters' , a new school of thought suggests sowing more ryegrass may help to fight herbicide resistance with this weed.

The theory, developed by Professor Steve Powles of the WA Herbicide Resistance Initiative and GRDC-supported PhD student David Ferris, cleverly exploits plant reproductive behavionr.

When a diploid * plant crosses with a tetraploid* plant, their genetic incompatibility often leads to the production of triploids*. which are sterile and so do not progress any more generations.

(*'Diploid' refers to the normal chromosome make-up of plants and animals with two copies of each chromo.some. 'Tetraploid' refers to fonr copies of each chromosome, the by-prodnct of occasional crossing of different species. 'Triploids' contain three copies of each chromosome.)

Using this technique in the field would require the development of an earJymaturing herbicide-susceptible tetraploid ryegrass, with the same flowering time as resistant and naturally diploid ryegrass weeds. If such a variety can be developed and then planted during a pasture break in nnmbers large enough to overwhelm resistant diploid ryegrass during pollination, the overall level of resistance could be cut by up to 90 per cent within three to five years.

Program 3 Contact: Mr David Ferris 08 9690 2000