2004 Annual Report 4.What were the most significant accomplishments this past year? This report serves to document research conducted under a specific cooperative agreement between ARS and University of Idaho. Additional details of research can be found in the report for the parent project 5354-21000-011-00D, ¿Evaluation of Advanced Potato Breeding Lines for Biotic and Abiotic Resistances and Yield¿. During the summer and fall of 2003, over 400 potato clones were evaluated in 30 trials at seven sites located across southern Idaho. These trials included evaluations of yield and adaptation, tuber quality, disease resistance, processing performance, storability, and response to agronomic inputs. In response to a need for economic efficiency and genetic resistance to major diseases and abiotic stresses, variety evaluation research remained a high priority. In 2003, the late blight resistant selection A90586-11 was released as ¿Defender¿ following 13 years of selection and evaluation. ¿Defender¿ has long shaped tubers with white skin and French fry processing quality from short-term storage. Late blight resistance for ¿Defender¿ was evaluated in all major late blight affected areas in the US and in the Toluca Valley of Mexico. The resistance appears to be stable and the level of resistance is adequate to eliminate the need for fungicides aimed at late blight control all but the most severe epiphytotics. Under normal circumstances a grower can count on saving 50 to 75 % of the cost of fungicides to control late blight. Defender also has moderate resistance to both early blight and corky ringspot. This variety is expected to give growers an additional option that will reduce the use of pesticides, fertilizers, and water, and improve economic production efficiency. Continued efforts were made to identify molecular markers to aid in selecting varieties resistant to corky ringspot. AFLP markers are being used to map the gene location. Several potentially useful markers have been identified. SSR markers are now being explored as a final step in finding a closely linked, selectable marker. This research is done cooperatively at the Aberdeen R & E Center, the UI campus in Moscow, and an infested farm site owned by Jim Blake, a cooperating farmer. An ongoing project is directed at improving the vitamin C content of the Northwest breeding germplasm base. Five populations were evaluated for vitamin C content as a first step in a recurrent selection program to detect practical upper limits and produce high content parental germplasm. This research will improve the nutritional quality of the potato crop. Research designed to improve quality measurements through the use of a viscoanalyzer was cooperatively done with Dr. Kerry Huber, food scientist at UI. In 2001-2002, viscoanalyzer measurements were evaluated against sensory culinary measurements and a high correlation was found. In 2003, the research objectives were extended to produce a multivariate model that will describe optimum quality parameters. One of the most valuable uses of this technology will be the ability to easily identify breeding clones with good processing quality. New potato varieties require unique production practices to optimize yield and quality. In 2003, research projects involving irrigation, plant population, and herbicide screening were completed at the Aberdeen R & E Center. The second year of a plant population study designed to provide data for development of a plant spacing prediction model for new varieties was completed. Information derived from these studies will be valuable to producers of new varieties and will save millions of dollars that will otherwise result from unnecessary applications of agri-chemicals and in losses in yield and tuber quality.