2011 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 Unique germplasm derived from the wild potato species S. etuberosum and S. berthaultii has been shown to exhibit resistance to many insect pests of potatoes including green peach aphid, Colorado potato beetle, and wireworm. Based on the multiple insect resistances, this germplasm from our potato breeding program was identified as being a good candidate for resistance to potato psyllid, the vector of the bacterium associated with the Zebra Chip disease. Resistance to psyllid was identified by University of California-Riverside collaborators who found modified behavioral responses of potato psyllid placed on this unique germplasm. Relative to the potato variety Atlantic, significant reductions in psyllid probing occurrences and resting duration were observed in several of the evaluated breeding clones, suggesting resistance to potato psyllid; one clone also an increased duration of time off leaflet relative to Atlantic. In addition, the percentages of bacterium- infected plants were significantly reduced relative to Atlantic for three clones representing three backcross generations. Of interest, was the observation that clone A00ETB12-3, with no apparent psyllid resistance, was among the three clones identified as having the lowest percentage of infected plants. This observation suggests possible resistance to the bacterium and not just the psyllid vector may be contributing to reduced plant infection rates. Research results were accepted for publication in the Crop Protection Journal. Greenhouse and field trials of promising germplasm were continued in 2011 with researchers at the University of California-Riverside and with the USDA-ARS. 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. Monitoring of research activities included meetings, reports, and correspondence through e-mail and phone.