INFLUENCING SEED TUBER YIELD OF RANGER RUSSET AND SHEPODY POTATOES WITH GIBBERELLIC-ACID

Freshly-cut seed pieces of the potato cultivars Ranger Russet and Shep ody were dipped in 0, 0.5, 1 or 2 mg/l Gibberellic Acid (GA3) prior to planting. GA3 treatments increased stem and tuber numbers per hill of both cultivars and shifted tuber size profile toward the production o f more seed-sized (up to 226 g) tubers and fewer large (greater than 3 40 g) tubers. The effect of GA3 on reducing average tuber size was sim ilar for the two cultivars. Total tuber yields were not affected. A 2 mg GA3/l seed piece dip decreased the yield of US#1 tubers in Ranger R usset primarily due to a significant increase in yield of tubers less than 226 g. Also, yields of culls were greater after a 1 mg GA3/l seed piece treatment, suggesting Ranger Russet is sensitive to this concen tration of GA3. One and 2 mg GA3/l seed piece dips to Shepody increase d yields of tubers less than 113 g by 93 % and reduced the yield of tu bers greater than 340 g by 25% to 50%. GA3 at 1 to 2 mg/l may be usefu l in the production of seed potatoes with the cultivar Shepody which t ends to produce many large tubers.