Agricultural Research Division of IANR


Date of this Version



Phytopathology 103:1235-1242.


U.S. Government Work


Potato zebra chip (ZC), caused by the bacterial pathogen ‘Candidatus

Liberibacter solanacearum’, which is vectored by the potato psyllid

(Bactericera cockerelli), has caused widespread damage to U.S. potato

production ever since its first discovery in south Texas in 2000. To

determine the influence of environmental factors and management

practices on ZC occurrence, data on management and meteorological

variables, field locations, and psyllid counts were collected over a 3-year

period (2010 to 2012) from six locations across the central United States

(south Texas to Nebraska). At these locations, ZC-symptomatic plants

were counted in 26 fields from systematically established 20 m × 30 m

plots around the field edges and field interiors. Mean numbers of symptomatic

plants per plot were classified into two intensity classes (ZC ≤ 3

or ZC > 3) and subjected to discriminant function and logistic regression

analyses to determine which factors best distinguish between the two ZC

intensity classes. Of all the variables, location, planting date, and maximum

temperature were found to be the most important in distinguishing

between ZC intensity classes. These variables correctly classified 88.5%

of the fields into either of the two ZC-intensity classes. Logistic regression

analysis of the individual variables showed that location accounted

for 90% of the variations, followed by planting date (86%) and maximum

temperature (70%). There was a low but significant (r = –0.44983, P =

0.0211) negative correlation between counts of psyllids testing positive

for pathogen and latitudinal locations, indicating a south-to-north declining

trend in counts of psyllids testing positive for the pathogen. A

similar declining trend also was observed in ZC occurrence (r = –0.499,

P = 0.0094).