Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 1/25/2012
Publication Date: 5/25/2012
Citation: Rashad, A., Workneh, F., Paetzold, L., Wallis, C.M., Rush, C.M. 2012. Zebra chip disease severity and ‘Candidatus Liberibacter solanacearum’ titer load of the potato hosts inoculated throughout the field season. In: Workneh F. Rashed A. Rush CM (eds). Proceedings of the 11th annual SCRI zebra chip reporting session. Fredric Printing, Aurora, NY. p.27-31. Interpretive Summary: Zebra chip disease (ZC) is a new challenge that potato growers in the United States and elsewhere are now facing. ZC symptoms leave tubers unmarketable. Current management for ZC involves spraying pesticides throughout the potato growing season to manage potato psyllids, vectors for the putative causal agent 'Candidatus Liberibacter solanacearum' (Lso). This study aimed to determine the necessity of a season-long spray program by inoculating potato plants at various times throughout the summer. Potato plants inoculated earlier in the season developed more severe foliar and tuber symptoms than plants inoculated closer to the end of the season. Lso population sizes within plants inoculated earlier were greater in leaf tissues; however, Lso population sizes in tuber tissues were reduced in plants inoculated earlier. Furthermore, in tubers, Lso population sizes unexpectedly were negatively correlated with symptom severity. Tubers inoculated as little as two weeks prior to harvest developed ZC; however, those inoculated one week prior to harvest did not.
Technical Abstract: The study investigated end-of-season ‘Candidatus Liberibacter solanacearum’ (Lso) titers in potato tuber and foliar tissues inoculated at different times during the growing season. Potato plants inoculated earlier in the season expressed more severe foliar symptoms and bacterial titers when compared to those inoculated later. Tuber symptoms were also more pronounced in plants inoculated earlier in the season. However, Lso titers within tubers were not greater in early-infested plants and were actually negatively correlated with disease severity. In a separate study, asymptomatic, Lso-positive tubers inoculated two weeks before harvest developed Zebra chip symptoms during a 3-month storage period at 40°F. However, plants inoculated one week before harvest did not develop disease symptoms and tested negative for Lso. These findings suggest that vector control is needed until a week before harvest.