2008 Annual Report 1a.Objectives (from AD-416) Characterize factors that affect the quality or nutritional value of potatoes. 1b.Approach (from AD-416) Tubers from multiple genotypes will be analyzed for quality or nutritional value. Genotypes with traits useful to the potato industry such as tuber size and set or superior phytonutrients with be characterized. Factors influencing or controlling trait expression, such as molecular, developmental and environmental control will be characterized. Documents SCA with WSU. 3.Progress Report The way in which seed-tubers are handled can significantly affect physiological age and thus productive potential. Seed-tuber age is affected by time and temperature, especially during the period from vine kill to planting. The respiration rate of tubers increases with temperature, which in turn accelerates the rate of aging. One way to estimate physiological age is to track the number of degree-days (heat-units) from vine kill through storage and handling to planting. This can be calculated in degrees centigrade or Fahrenheit by subtracting a base temperature of 4 degrees C (39 degrees F) from the average tuber pulp temperature on a particular day and summing the daily values over an extended period (e.g. from vine kill through storage to planting) to arrive at the total accumulated degree-days for a particular seed lot. The number of stems per seed piece increases with increasing degree-days (age). Tuber set per hill increases with stem number, resulting in a decrease in average tuber size. At particular in-row spacing, the tuber set and final size distribution are largely dictated by the average stem number per seed piece. Hence, there is an opportunity to control tuber size distribution and potentially add value to seed, processing, and fresh market crops by managing seed-tuber age and stem numbers. Toward this goal, we have modeled these relationships for Umatilla Russet, Russet Burbank, Ranger Russet, three Norkotah selections, and Shepody. Biochemical markers of seed age for these cultivars were identified and we have further demonstrated that crop value can be enhanced substantially by manipulating age. Stem number and tuber set relationships for Premier Russet, Summit Russet, GemStar Russet, and A95109 are now being modeled. Based on our studies, seed growers are altering the way in which they manage seed at the end of the growing season and throughout storage to maximize productive and economic value to commercial growers. Progress on this project was monitored by the ADODR via phone, on-site visits, and email correspondence with Washington State University's lead researcher.