Bacteria in wheat roots combat take all by Chris Franco et al*

Electron microscope image of actinomycete filaments growing out of a wheat root fragment

TAKE-ALL costs the Australian wheat industry $100 million a year in lost productivity. Other than avoidance through strict crop rotation schedules, take-all has few chemical control measures, and the severity of the disease is increased in paddocks where fanners are trying to adopt more 'green' or 'environmentally sustainable' farming practices.

Stubble retention can promote the fungus that causes take-all. It is able to survive and multiply on stubble from year to year, and thrives in undisturbed soil. This puts Australian wheat fanners in a no-win situation, where they have to choose between low disease levels but high erosion and low fertility, or to improve the soil with the adoption of sustainable practices, but run the risk of disease.

New research by the Biotechnology Group at Flinders University has found actinomycete bacteria th at live within healthy wheat and barley plants. Actinomycetes is the collective name given to a particular kind of filamentous bacteria that are recognised as prolific producers of antibiotics and other useful chemicals. (Today over 60 percent of the a ntibiotics that we use in medicine are derived from actinomycetes.)

This project began with the idea that if the actinomycetes were able to live in the plant tissue, they may protect the plant by producing chemicals that can kill the fungi that cause disease.

We isolated actinomycetes from within the root tissue of the plant.

These organisms have already demonstrated the ability to colonise the host plant , hence are protected from competing soil organisms, and are more likely to be effective. In return for this ecological niche provided by the plant, the organisms may produce a ntibiotics or other bioactive compounds in side the plant where they should benefit the host plant.

Bacteria or fungi such as these, which can colonise plants and lead to a beneficial associatio,. are known as endophytes (endo meaning within and phyte meaning plant).

The next step was to see if the actinomycetes were able to protect the wheat plant from root diseases through the production of anti -fungal compounds or some other mechanism. More than 400 actinomycete endophytes were isolated from healthy wheat and barley plants collected from across the SA and WA cereal belts. After extensive screening we found that many of these were able to inhibit both Rhizoctonia and take-all. We also found that a number of isolates increased the growth o f wheat plants.

With this information in hand, it was decided to select the most effective endophytes via field trials, at an early stage, because many microbial inoculanls fail when used under tield conditions. The most promising actinomycetc endophytes will be tested singly, in combinations and at different inoculum levels in the coming growing season.

This technology has the potential to improve the economic returns to Australian wheat farmers, while at the same lime improving the environmental sustainability of cereal· farming in Australia.

(See also our story on the previous page for all other approach to disease suppression - Ed. )

* Dr Chris Franco1, Dr Justin Coombss, Mr Philip Michelsen ' and Dr Margaret Roperz 1 Flinders University. Adelaide SA 08 8204 5764 2 CSIRO Plant Industry, Florea! WA 08 9333 6668

Program 4 Contact: Dr Chris Franco 08 8204 5764 email Chris.Franco@flinders.edu.au