Manipulating stem number, tuber set, and yield relationships for northern- and southern-grown potato seed lots

The ability to predict tuber set and size development for a particular lot of seed potatoes (Solanum tuberosum L) would facilitate the development of techniques for optimizing tuber grade. Toward this goal, stem number, tuber set, yield, and grade relationships were manipulated and modeled for northern- (Alberta, Canada) and southern-grown (Montana and Washington) Ranger Russet and Russet Burbank seed potatoes. Seed-tubers with a range in apical dominance were produced by varying the temperature (aging) at the beginning of a 200-d storage period. Seed source affected stem numbers, tuber set, and size, with southern seed producing more but smaller tubers than northern seed; however, seed source had no effect on total and U.S. No. I tuber yields. Tuber set and size distributions were highly correlated with stem numbers, the latter increasing substantially when storage degree days were held constant but temperature was increased. Changes in tuber size distribution with increasing stems occurred with relatively little effect on total, U.S. No. 1, and marketable tuber yields. Therefore, in long growing season area like the Columbia Basin, adding heat units to seed at the beginning of storage effectively alters tuber size distribution. The differential behavior of these seed sources, along with the ability to predict tuber set and size from mainstem numbers, provides an opportunity to adjust agronomic practices to optimize yield for specific markets.