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Bacterium identified as potato disease culprit

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.

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
they’re cut and fried to make chips or fries. However, eating them poses no
consumer danger, according to Joseph Munyaneza, an Agricultural Research
Service (ARS) entomologist who’s 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 ZC.

According
to Munyaneza, with the ARS Yakima 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
didn’t know what actually caused the disease – only that it correlated to
psyllid feeding. Now, with evidence pointing to a Candidatus species, growers
have more information to go on.

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 ZC’s severity. For example, 90 percent of potatoes planted
in mid-December were infected with ZC by harvest in April, versus 25 to 30 per
cent infected when planted in mid-January or mid-February and harvested in May.

Read
more about this research in the October 2009 issue of Agricultural Research
magazine, available online by clicking here.