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

Freshly-cut seed pieces of the potato cultivars Ranger Russet and Shepody 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 of more seed-sized (up to 226 g) tubers and fewer large (greater than 340 g) tubers. The effect of GA3 on reducing average tuber size was similar 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 Russet 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 concentration of GA3. One and 2 mg GA3/l seed piece dips to Shepody increased yields of tubers less than 113 g by 93 % and reduced the yield of tubers greater than 340 g by 25% to 50%. GA3 at 1 to 2 mg/l may be useful in the production of seed potatoes with the cultivar Shepody which tends to produce many large tubers.