2012 Annual Report 1a.Objectives (from AD-416): Provide unique germplasm for the assessment of resistance to Zebra Chip and the insect vector of the disease. On the basis of the screenings, develop commercially acceptable germplasm with resistance to Zebra Chip 1b.Approach (from AD-416): Unique germplasm developed by the ARS-Potato Breeding Program at Aberdeen, Idaho, will be evaluated for resistance to Zebra Chip disease and the insect vector of the disease. Individuals identified as resistant to the Zebra Chip disease and/or insect vector will be used in the breeding program as parents for the generation of progeny. Resistant progeny will be evaluated for agronomic performance and those with acceptable agronomics will be evaluated for acceptability for commercial production and further utilized in developing Zebra Chip resistant potato varieties. 3.Progress Report: The ARS potato breeding program at Aberdeen, Idaho, provided unique potato germplasm derived from the wild potato species Solanum etuberosum and S. berthaultii to University of California-Riverside collaborators for an assessment of potato psyllid feeding behavior; potato psyllid being the insect that transmits Zebra Chip (ZC) disease. Of eleven breeding clones evaluated, five had a significantly reduced number of probing (feeding) occurrences relative to the potato cultivar, Atlantic. The potato cultivar GemStar Russet, also displayed a reduced number of feeding occurrences confirming previous observations of possible psyllid resistance. Average resting duration of psyllids also was significantly reduced relative to Atlantic for four breeding clones. A breeding clone was also identified having a significantly increased duration of potato leaflets relative to Atlantic, possibly indicating a non-preference by psyllids relative to other germplasm entries. The percentage of Liberibacter-infected plants was also found to be significantly reduced for three breeding clones relative to Atlantic. Infection for these three clones was 30%, whereas the infection rate of Atlantic was 80%- indicative of possible reduced transmission/ resistance to Liberibacter. Research results were published in a peer-reviewed journal in 2011. Two breeding clones, originating from the ARS potato pre-breeding program, Madison, Wisconsin, were also submitted for screening for ZC resistance under controlled field cage conditions by an ARS collaborator in Wapato, Washington. These two breeding clones had previously been used in parental hybridizations for improvement of cold-sweetening resistance at Aberdeen, Idaho, and are unique in having the wild potato species S. raphanifolium in their pedigrees. Screening results from 2011 were promising with respect to both clones showing resistance to ZC with both again entered in the 2012 field cage screening. The goal of this project is the identification and use of potato germplasm resistant to the Zebra Chip disease which contributes directly to Objectives 1 and 2 of the in-house project.