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Forum -- Getting to the Root of Wheat Take-All

I'll never forget walking into the laboratory one Monday in April 1970.

The table was covered with clear plastic bags of green wheat from a field experiment near Puyallup, Washington. Plants in four bags had white, healthy roots. Plants in the other 32 bags had black, dead roots.

The experiment site was heavily infested with the fungus that causes the wheat root disease called take-all. The plants with white roots were from four plots with special soil.

In 1968, we had mixed into the native soil a small amount of soil from a wheat field in Quincy, about 150 miles east of Puyallup. The soil came from a field where take-all was being controlled naturally and mysteriously—a process reported a few years earlier in Europe as "take-all decline".

I knew there was something in the Quincy soil so powerful that it kept roots white when they should have been black. I also figured that the protective factor in the soil could multiply on wheat roots. If I did nothing else for the rest of my career, I was going to find out what was in that soil.

We have since learned that natural bacteria, selectively favored by wheat roots, produce antibiotics that suppress take-all. Now advances in fermentation technology are helping to create a commercial seed treatment that will soon be available to fanners.

A story in this issue [p. 4] describes our success in isolating the microorganisms that produce the antibiotics and using them to control take-all. We're also enhancing the bacteria's natural antibiotic production with genetic techniques. And we have molecular methods to measure the frequency of these antibiotic-producing strains' occurrence in soil.

Disease control is important because wheat with root diseases not only yields poorly, it also leaves nitrogen fertilizer unused in the soil, is less competitive with weeds, and does not take full advantage of available water supplies.

In addition, root diseases make it more difficult for farmers to adopt erosion-controlling practices such as no-till and minimum-till.

The very conditions needed to hold soil in place—little or no soil disturbance from tillage and standing plant stubble from the previous crop—provide the perfect environment for take-all and other root diseases like Rhizoctonia and Pythium to thrive.

Another research program at Pullman, called STEEP, successfully tackles the many issues and technical problems associated with conservation tillage systems.

The take-all and STEEP research share two approaches that help account for their success.

First, both use nature as a guide to solve real-world problems.

Take-all decline was observed in nature years before basic research revealed how it worked and how to take advantage of the beneficial organisms responsible. Our results can be translated into field applications because the work started in the field.

STEEP researchers realized that soil eroded differently in the Northwest than in other areas of the country. Field tests and observations allowed them to modify the Universal Soil Loss Equation developed by ARS in 1958. It now gives land managers an accurate tool to predict erosion for this unique area.

Second, both programs rely on grower participation.

Our ability to commercialize a biological control for take-all is fueled by farmers who have seen their yields decline—even while increasing fertilizer. We're providing the technology, and they're conducting large-scale testing on their farms.

STEEP has more formalized grower input, along with an advisory committee, an on- farm testing program, and follow-up surveys.

Solutions to the problems of conservation farming systems have come slowly, and there are still more questions than answers. Nevertheless, the goals of STEEP and of our work on biological control of take-all are clear: more economical farming, a cleaner environment, and protection of the natural resource base upon which agriculture depends.

R. James Cook

Plant Pathologist
Agricultural Research Service
Pullman, Washington


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