COMPOST CAN CUT PESTICIDE USE, IMPROVE DISEASE CONTROL
COLUMBUS, Ohio -- Researchers at Ohio State University have found that beneficial microorganisms in composts induce disease resistance in plants.
The findings could lead to a major reduction in pesticide use by gardeners and farmers, the scientists said. Even better, they might offer ways to control plant diseases that currently can't be prevented.
"This gets to the claims of sustainable agriculture and organic farmers: that organic matter makes plants healthier," said Harry Hoitink, co-author of the study and a professor of plant pathology at the Ohio Agricultural Research and Development Center in Wooster, associated with OhioState University.
Hoitink conducted the research with Weizheng Zhang, a visiting scholar, and Warren Dick, a professor of natural resources, both at OARDC. The study was published in a recent issue of the journal Phytopathology.
The researchers found significantly enhanced diseaseresistance in plants grown in soils with compost. This resistance is communicated throughout the plant, a mechanism known as systemic acquired resistance. Dick said it works like a smallpox inoculation in humans.
"When you get yourself scratched for a smallpox inoculation, it turns on a system in your body that makes you become resistant to the smallpox disease," he said. "What we found is that certain organisms in compost interact with the root, and the biochemistry of the plant is changed so it becomes resistant.
Compost is decomposed organic matter -- dead plants, animal waste and so on. It's been used since the early 1970s to control certain root diseases. Nursery growers have replaced the fungicide methyl bromide with compost-amended potting mixes, for example.
The result is biological control of root diseases, and beneficial microorganisms are the key. In some cases, these good microorganisms eat the bad ones -- the pathogens. Sometimes they out-compete the bad ones. And sometimes they produce antibiotics.
But sometimes compost controls leaf diseases, too. And sometimes it benefits roots that aren't directly touching compost, as with those Ohio rhododendrons. The Ohio State team wanted to explain this.
For their study, the scientists compared disease severity and peroxidase activity in cucumber plants. Peroxidase, an enzyme, is a molecular marker for enhanced systemic acquired resistance in cucumber. The plants were germinated in two types of potting mixes -- spruce or pine bark composts that suppressed Pythium root rot, and a peat mix that didn't.
After 35 days, the scientists rated the severity of root rot in the Pythium-inoculated peat and compost. They found that plants germinated in compost had the best health, and that root rot in the disease-inoculated peat was much less severe on roots paired with compost, even though these roots did not directly touch the compost.
"This shows that a plant communicates within itself," Hoitink said. "You need only part of a plant in compost to make the whole plant resistant."
Also in the study, plants germinated in compost were tested for resistance to anthracnose, a leaf disease. Three weeks after planting, plants grown in compost were much healthier than those grown in peat.
Finally, the scientists measured peroxidase activity. They found that it was significantly enhanced in plants grown in compost, and that it was enhanced even further when the plant was inoculated with the pathogen that causes anthracnose.
Based on this, the scientists said the interaction of compost and pathogen appears critical for the rapid activation of systemic acquired resistance.Written by Kurt Knebusch, (330)263-3776; Knebusch.1@osu.edu
Contact: Harry Hoitink, (330) 263-3848; Hoitink.1@osu.edu
Warren Dick, (330) 262-3877; Dick.5@osu.edu
Weizheng Zhang, (330) 263-3878; Zhang.105@osu.edu