OSU to study diseases affecting nursery plants

By Peg Herring

Oregon State University plans to use a $3 million grant to study two groups of bacteria that result in millions of dollars in losses annually to the nation’s nursery industry.

Researchers will study Agrobacterium tumefaciens and Rhodococcus fascians, which deform hundreds of common landscape plants, including hostas, Shasta daisies, petunias and pansies.

These bacterial pathogens are of particular concern in Oregon, where the greenhouse and nursery industry contributes more than $745 million to the Oregon economy annually. Some growers report losses of up to $100,000 a year to gall-forming bacterial diseases.

The four-year grant, from the USDA's National Institute of Food and Agriculture, will help determine how these pathogens are introduced into nurseries and how they establish and persist; develop new approaches to improve detection and control; and help nursery workers recognize and prevent the spread of the pathogens.

For more than a decade Melodie Putnam, chief diagnostician at OSU's Plant Clinic, has been working with Oregon nurseries to correctly identify these bacterial pathogens that are responsible for tumor-like galls and cancer-like leaf growth in infected plants. Correct identification of the bacterial pathogen is a necessary first step to preventing disease, Putnam said.

“It is difficult to combat a problem if you don’t recognize it for what it is,” she said.

These two types of bacteria have “wily life histories that help them evade detection,” Putnam added. R. fascians can grow on the surface of plants without causing any symptoms for months before moving into plant tissue and triggering a proliferation of leafy galls, deforming the plant and making it unmarketable. The ubiquitous R. fascians has been found in environments such as cheese rinds, glacial ice cores, the stomach of Atlantic hagfish and the backs of fly-bitten sheep.

A. tumefaciens infects plants by injecting and integrating a portion of its DNA into the genome of the host plant. Scientists have long used non-pathogenic variants of A. tumefaciens in the process of plant genetic engineering. Using the bacteria's natural infection process, it is possible to genetically modify plants to express novel traits such as increased synthesis of vitamin A in rice to combat nutrient deficiencies.

Long before its remarkable biology was fully understood, A. tumefaciens was known to cause crown gall disease, which alters plant metabolism and swells tissues into tumors, called galls.

“A. tumefaciens has caused up to 40 percent reductions in yield in some perennial crops, and as much as 100 percent loss in roses,” Putnam said.

Despite the obvious disease symptoms, both of these pathogens can be easily misdiagnosed, Putnam said, which slows the response to a spreading infection.

“Unfortunately, there is no treatment for either A. tumefaciens or R. fascians at this time," she said. "Therefore, steps must be taken to prevent disease.”

 Image above: Photo by OSU Plant Clinic Agrobacterium tumefaciens creates cancer-like galls on the roots of plants, in this case on the Gaillardia.

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