University of Georgia
As far as plant enemies go, it’s one of the world’s toughest. A
scientist in Athens, Ga., wants to know how and why it’s so
deadly efficient, in hopes of finding ways to control it in the
future.
Ralstonia solanacearum is a bacterial pathogen that attacks a
plant from within, destroying it, said Tim Denny, a research
plant pathologist with the University of Georgia College of
Agricultural and Environmental Sciences.
Global enemy
Most bacterial pathogens are problems to a specific region. But
this one causes damage worldwide.
“Part of the reason this pathogen is found all over the globe
is that it has an exceptionally wide host range,” he said.
There are many different strains of Ralstonia salanacearum.
They can infect and kill hundreds of plant species, including
important agricultural crops, landscape trees, flowers and
shrubs.
The bacterium gets into the plant through the roots. It then
migrates quickly throughout the plant, eating and reproducing
as it goes. This causes the plant to wilt and die.
“Disease is really the byproduct of this organism’s desire to
thrive,” he said.
In greenhouse experiments, young plants purposely infected with
this bacterium die within a week, he said.
New threat
One nasty type Ralstonia solanacearum (race 3, biovar 2) has
the United States Department of Agriculture concerned. It
recently entered the country in a shipment of geraniums from
Kenya. The strain can kill major U.S. farm crops, like
potatoes,
vegetables and nursery stock. The USDA is
quarantining suspect plants and areas to control its spread.
“Once a field has been infested, it’s extremely hard to get rid
of this pathogen,” Denny said.
Like humans, plants “are covered with microorganisms all the
time,” he said. “But they usually don’t get sick. But this
pathogen has learned how to defeat a plant’s natural defense
processes to use the plant as a food source.”
This unusual ability of Ralstonia solanacearum interests
Denny.
Know the enemy
Using genetic, microscopic, biochemical and many other research
tools, Denny is studying the pathogen in as many ways as he
can. He’s trying to understand how it lives and interacts with
the plants it kills and the ones it can’t.
For example, Denny altered some strains of the pathogen to make
bacteria flourescent under certain light wavelengths. Using
these strains, he can track their progress as they colonize a
plant. This is important in understanding how they move so
quickly.
There are no cures for the diseases caused by Ralstonia
solanacearum. The only effective way to combat it is through
crop rotation: farmers plant crops that aren’t susceptible to
the bacterium. This can reduce but not eliminate it from a
field. But it can be impractical and economically hard for
farmers to do.
Denny has learned that the bacterium secretes proteins that
help it colonize a plant quickly. He believes plants could be
genetically engineered to turn off the bacteria’s secretion
system, stopping it before it makes a meal of the plant.
