2010 Annual Report 1a.Objectives (from AD-416) 1. Evaluate potential biologically active control measures in controlled conditions and the field. 2. 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) Potato seed pieces of 3 popular but scab-susceptible varieties (Yukon Gold, Ranger Russet and Atlantic) will be treated with several individual non-pathogenic isolates of Streptomyces, and planted in Pennsylvania and Michigan fields with high common scab pressure. Treatments will be planted in 4 replicates in a randomized block design, and evaluated at harvest for incidence and severity of common scab. Field test varieties for scab resistance in multiple locations. 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 4 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 4 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. 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. Research was conducted in summer 2009 to investigate whether several non-pathogenic strains of Streptomyces that were originally isolated from potatoes might work to counter-act pathogenic Streptomyces strains that cause potato common scab. Five potential biocontrol strains were tested in triplicate hills of three potato cultivars that are highly susceptible to common scab were planted in common scab nurseries (fields with high natural common scab disease pressure) in Michigan and Pennsylvania. All 5 strains decreased the severity of common scab in at least one of the three potato cultivars in Michigan, where natural common scab disease pressure was low. Four of the 5 strains decreased common scab severity on at least one cultivar in Pennsylvania, where the natural disease pressure was very high. These tests are being repeated in the summer of 2010. 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. Comparisons and common scab susceptibility rankings will be made available to growers to help them select the most scab-resistant cultivars for their region. The impact of this research is that it provides much-needed new information on controlling potato common scab. A new biocontrol method of controlling common scab disease is being evaluated at two locations, and 20 potato cultivars or breeding lines are being evaluated for common scab resistance in multiple locations each year. Progress was monitored by regular telephone calls, exchange of e-mails, and receipt of a preliminary written report containing experimental results.