Bacterium Identified as Potato Disease Culprit
By Jan Suszkiw
October 13, 2009
Studies tying a new species of
Candidatus Liberibacter bacteria to zebra chip (ZC) disease in potato
should speed efforts to better protect the tuber crop from costly outbreaks.
Zebra chip is so-named because afflicted tubers form dark, unsightly stripes
when theyre cut and fried to make chips or fries. However, eating them
poses no consumer danger, according to
Munyaneza, an Agricultural Research
Service (ARS) entomologist whos studied zebra chip since its
detection in southern Texas in 2000.
The disease, which has spread to Arizona, California, Nevada and other
western states, has caused millions of dollars in losses. In 2007, an ARS-led
team completed studies identifying the potato psyllid, Bactericera
cockerelli, as an insect that transmits ZC. Then, in early 2008, New
Zealand researchers, followed by University of
California-Riverside scientists, announced their discovery of genetic
evidence suggesting that a new species of Candidatus bacterium causes
According to Munyaneza, with the ARS
Agricultural Research Laboratory in Wapato, Wash., potato growers had been
spraying their crops with insecticides to prevent psyllids from transmitting
ZC. But until the 2008 discovery, they didnt know what actually caused
the diseaseonly that it correlated to psyllid feeding. Now, with evidence
pointing to a Candidatus species, growers have more information to go
For example, testing psyllid populations for ZC at known overwintering sites
could give growers located at the insects summer migration destinations
early warning that potato crops there could be in danger of infection.
Predicting psyllid migration could also help time the use of natural enemies.
Munyaneza and colleagues current studies include examining whether
altered planting dates could diminish ZCs severity. For example, 90
percent of potatoes planted in mid-December were infected with ZC by harvest in
April, versus 25 to 30 percent infected when planted in mid-January or
mid-February and harvested in May.
more about this research in the October 2009 issue of Agricultural
ARS is the principal intramural scientific research agency of the
U.S. Department of Agriculture.