Bacterium breakthrough

Researchers at Oregon State University have taken a major step toward developing an on-site detection tool for crown gall disease, an incurable malady that affects numerous species of plants, including many of economic importance to Oregon.

The researchers developed molecular tools to work with commercially available kits that allow the user to quickly and effectively test plants for the disease, using a dipstick that reveals the presence of the pathogen within minutes.

Crown gall disease is caused by a soil bacterium that modifies the plant’s genome and causes large, cancer-like tumors (galls) to grow at its base. The soil-borne pathogen, Agrobacterium tumefaciens, affects woody and herbaceous plants, including fruit and nut trees, grapevines and roses.

The findings are published in the journal Phytopathology. OSU has filed for a patent for the molecular tools.

Big numbers illustrate the importance of the research. The greenhouse and nursery, fruit and nut and wine grape industries total $1.75 billion in economic activity each year, according to the Oregon Department of Agriculture.

The researchers developed probes so sensitive that they can detect the pathogen from a tiny sample. Traditional methods of detection of Agrobacterium take several hours using specialized equipment.

Early and rapid detection of Agrobacterium is key to the management of crown gall because there is no cure for the disease, says Jeff Chang, associate professor, and Elizabeth Savory, postdoctoral researcher, in OSU’s College of Agricultural Sciences and coauthors of the study.

“Growers can’t predict when it will strike, and once it has, the disease cannot be cured because the plant is permanently genetically modified and will form the tumors,” Chang says. “These growths can be lethal to young plants and they are also grotesque, so they compromise the aesthetic value of these plants. Nurseries typically go through extreme protocols to keep their sites clean, but once infection occurs, the only solution is to throw away diseased plants and clean up the site.”

Agrobacterium species penetrate plants through fresh wounds, which can be caused by pruning, cultivating, chewing insects, or often by freezing.

When the bacteria infect, they genetically modify plants, Chang says. A fragment of their DNA is clipped and transferred into the plant. Once inside, the DNA fragment integrates into the genome of the plant and brings in genes that cause the galls and the transformed plant cells to make a unique food source for the bacteria.

Skylar Fuller, a recent OSU graduate, designed the detection mechanism under the mentorship of the study’s coauthors. Collaborators included Alexandra Weisberg, a postdoctoral fellow, and Melodie Putnam, director of the OSU Plant Clinic, as well as their students. The gene sequences the team used were variations of those originally developed by OSU Professor Walt Ream.

The study was funded by the U.S. Department of Agriculture’s National Institute of Food and Agriculture and Fuller was supported by OSU’s Department of Botany and Plant Pathology.

Chris Branam is a communications specialist at the Oregon State University Extension Service.