2011 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.
Potato common scab seriously reduces potato marketability, especially in the upper Midwest and northeastern regions of the U.S., and there are no effective chemical controls for the disease. We examined the impact on common scab disease incidence and severity in potato varieties planted in fields with high disease pressure when non-disease-causing (biocontrol) strains of bacteria were added at the time of planting. In Michigan, the proportion of tubers with no scab was increased and the severity of the scab present was reduced by treatment with at least one of the three biocontrol strains in three potato varieties, though results were modest. The results suggest that biocontrol strains could offer a new method for reducing common scab.
The most effective control for potato common scab is the 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. In 2010, 22 potato varieties selected by potato breeders from 6 breeding programs in the U.S. were tested for common scab in 4 field locations which differ in soil and environmental conditions and in the bacteria responsible for the disease. Statistical analysis of the data from the tests is ongoing, but quick comparison of the tested potato breeding lines with resistant and susceptible standard check varieties shows that breeders selections are more scab-resistant than the susceptible varieties in all locations. Common scab is one of the most important potato diseases in the upper Midwest and northeastern United States, and the results of field-testing common scab resistance will be used to by potato growers to choose common-scab resistant varieties. Progress by Michigan State collaborators was monitored by regular telephone calls, exchange of e-mails, and receipt of a preliminary written report containing experimental results.