Further Evidence that Zebra Chip Potato Disease in the Lower Rio Grande Valley of Texas is Associated with Bactericera cockerelli

Abstract

Zebra chip (ZC) is an important and emerging potato disease that is causing millions of dollars in losses to both potato producers and processors in the southwestern United States, Texas in particular. This disease is characterized by symptoms that develop in fried chips from infected potato tubers and that consist of a striped pattern of necrosis in tuber cross-section. Zebra chip plant symptoms resemble those caused by potato purple top and psyllid yellows diseases. To increase the understanding of the role of the potato psyllid (Bactericera cockerelli Sulc) and phytoplasmas in the expression of ZC, controlled exposure and exclusion field experiments using cages were conducted in the Lower Rio Grande Valley of Texas, where the psyllid is common and abundant and the disease is very damaging. Also, potato tubers exhibiting ZC symptoms were tested for phytoplasmas by PCR. Results indicated that there was a strong association between the potato psyllid and ZC. Plants exposed to psyllids developed typical ZC symptoms in both raw tubers and fried chips. At harvest, potato plants exhibiting ZC symptoms in raw tubers averaged 79.2, 37.5, and 48.6% for uncaged plants, caged plants exposed to Texas field-collected psyllids, and caged plants exposed to laboratory-reared psyllids, respectively. Incidence of ZC increased when the harvested tubers were processed into fried chips. No single potato plant in the cages without psyllids (controls) showed ZC symptoms in raw tubers or fried chips, suggesting that the observed ZC symptoms were due to psyllids. No phytoplasmas were detected in tubers with ZC symptoms, suggesting that these pathogens are not involved in ZC.