Impact of Liberibacter-infective potato psyllids on different potato plant stages

Zebra Chip (ZC) disease of potato causes millions of dollars of losses annually in the U.S., Mexico, Central America and New Zealand. The disease is characterized by a necrotic pattern in tubers which becomes more pronounced after frying. Chips processed from infected tubers are commercially unacceptable. Recent studies have associated ZC with a previously undescribed species of liberibacter, designated ‘Candidatus Liberibacter solanacearum (=psyllaurous)’. This bacterium is transmitted by the potato psyllid, Bactericera cockerelli (Sulc). Plant stage or age has been shown to influence a vectored pathogen’s ability to cause disease. The objective of this study was to determine whether timing of infection by liberibacter influences ZC symptom expression in potatoes. Plants in small field cages were exposed to liberibacter-infective potato psyllids at five different growth stages. The insects were allowed to feed on the plants for a week before being killed with insecticides. The experiment was conducted at the USDA-ARS Research Farm in Moxee, Washington in 2009 and two potato varieties were used. Treatments consisted of five insect releases two weeks apart and a control which received no psyllids. Treatments were replicated four times each. At the end of the experiment, tubers were harvested and ZC incidence estimated. Preliminary results suggest that late infestation may produce ZC-free potatoes.