1a. Objectives (from AD-416):
Evaluate potential biologically active control measures in controlled conditions and the field. 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 three 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 four replicates in a randomized block design, and evaluated at harvest for incidence and severity of common scab. 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. 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:
Potato common scab is one of the most important potato diseases in the upper midwest and northeastern United States, because it seriously reduces potato marketability, in both fresh-market sales and in chip and French fry processing. There are no effective chemical or cultural controls for common scab. The most effective control is use of potato varieties resistant to the disease, and potato breeders routinely test their newly developed lines in field trials to establish levels of susceptibility or resistance to the disease. We received notice that the project was funded too late in the spring of 2012 (late May) to repeat the previous 2 years field biocontrol experiments, but we have submitted for publication the results of two years’ repetition of the experiment, in which we observed a general decrease in common scab by the biocontrol strains. Responses varied by potato variety, location and year, but some variety-biocontrol strain combinations could be useful for reducing common scab severity. Twenty-four potato varieties selected by potato breeders from 6 breeding programs in the U.S. were tested for common scab in 4 field locations (one field each in Pennsylvania, Michigan, Minnesota, and Idaho). The 4 sites differ in soil and environmental conditions and in the Streptomyces bacteria responsible for the disease. Statistical analysis of the data from 3 locations is ongoing, but quick comparisons of the tested potato breeding lines with resistant and susceptible standard check varieties show that some breeders’ selections are more scab-resistant than the susceptible check varieties in all locations. The final results of field-testing potato varieties for their common scab resistance will be used by potato growers to choose the most common-scab resistant varieties for their areas, and will be made available on our USDA website. Some results of common scab field and greenhouse tests are now posted at http://www.ars.usda.gov/pandp/docs.htm?docid=22336.