1a. Objectives (from AD-416):
Develop reliable high throughput methods of phenotyping common scab resistance. Accelerate selection of breeding lines combining chip processing, late blight and scab resistance.
1b. Approach (from AD-416):
In cooperation with Sklarczyk Minitubers, Johannesburg, MI, a hydroponic tuberization system (nutrient film technology or NFT) has been set up at Michigan State. Initial experiments will be conducted to examine how nutrient solution pH, inoculum concentration and timing of inoculation influence scab lesion development on a set of four lines that differ in their scab reaction under field conditions. The validated NFT system will be further used to evaluate commonly grown varieties and breeding material, as well as for phenotyping scab tolerance in populations developed during other research projects. Evaluation of 117 crosses comprising about 500 selections segregating for common scab resistance, late blight resistance and chip-processing will allow selection of optimal lines with good agronomic traits that also combine these three characteristics for further advancement in the ARS breeding program. In addition, 53 lines that may combine scab resistance, late blight resistance and chip-processing will be evaluated in replicated trials for agronomic performance in 2009 and also screened in replicated trials for late blight and scab resistance.
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. More efficient high-throughput methods for testing common scab resistance are greatly needed. A nutrient film technology method for producing minitubers has so far been difficult to apply to large-scale screening, but is providing a useful way to explore the mechanisms of common scab resistance. These results are likely to provide new potential targets for control of common scab, for which there are currently no consistently effective chemical or biological control methods. The only consistently reproducible control for potato common scab is the use of resistant potato varieties. Scab infection and severity have been compared at a new Michigan State nursery (MRC) and a near-by commercial site in northern Michigan. In both years the commercial site had extreme levels of pitted scab lesions on susceptible lines, making the tubers unmarketable. Of 15 lines common to the two sites that were classified as resistant at MRC, 11 were also classified as resistant at the commercial site. The most resistant lines were not free of scab infection, although only surface lesions were noted. Based upon the data collected, the level of scab resistance is increasing in the Michigan State potato breeding program.This information is valuable to the breeding program in Michigan and the upper Midwest in determining which advanced lines to consider for commercial release.