2010 Annual Report 1a.Objectives (from AD-416) Monitor the location-specific variation in scab resistance of potato breeding material and newly released cultivars by field testing (national trials). 1b.Approach (from AD-416) A total of 20 newly-released potato cultivars and advanced breeding selections plus four popular cultivars as checks (Atlantic, Ranger Russet, Russet Burbank, and Superior) will be tested in common scab nurseries in four locations, embodying a range of environmental conditions and different pathogen populations. Locations are in Aberdeen, ID, Becker, MN, E. Lansing, MI, and University Park, PA. A randomized complete block with three replications of four hills will be planted for each clone. At harvest, each tuber will be rated for percent surface area covered with lesions and type of lesion. Data from cooperating sites will be analyzed by our investigator. The resulting comparison and ranking of susceptibility to predominant Streptomyces isolates will be made available to growers to help them select the most scab-resistant cultivars for their region. 3.Progress Report No reliable methods of controlling common scab are currently available. The best method of limiting common scab damage to potatoes would be the use of resistant cultivars. To identify potato lines with stable resistance to common scab and to determine the importance of genotype x environment interactions on the expression of scab resistance, we conducted field tests at four locations that have different environmental conditions and pathogen populations. Four standard check cultivars and 21 cultivars and breeding lines were tested in Aberdeen, ID, Becker, MN, E. Lansing, MI, and University Park, PA. Data from the 2009 locations are being analyzed, and 20 new varieties, together with check cultivars, are being tested in the same four locations in the 2010 summer field season. The impact of this research is that it provides new information on cultivar resistance to common scab in multiple locations. Common scab susceptibility rankings will be made available to growers to help them select the most scab-resistant cultivars for their region. Progress was monitored by telephone calls, exchange of e-mails, and receipt of a preliminary written report containing experimental results.