Seed potato growers seek to maximize yields of desirable sized tubers. This study examined how foliar applications of plant growth regulators influence yields of drop or single-cut seed tubers under field conditions. In 1993, paclobutrazol (PTZ; 300, 450, and 600 mg·liter–1), kinetin (KIN; 10 and 20 mg·liter–1), and methyl jasmonate (MJ; 10–7, 10–6, 10–5, and 10–4 M) were applied to `Norland' (NOR) and `Russet Burbank' (RB) potatoes. In 1994, PTZ (300 mg·liter–1), KIN (both rates), and MJ (10–7 and 10–6 M) treatments were eliminated, and GA3 at 250 mg·liter–1 or KIN at 20 mg·liter–1 was applied to some of PTZ treatments. In 1994, the cultivar Shepody (SH) also was included. Plants were treated at two growth stages; NOR (1993), RB (1993 and 1994), and SH (1994) were treated when tubers were <10 mm or <20 mm in diameter. NOR (1994) was treated at stolon initiation (no tubers) or early tuber initiation (<8 mm in diameter). PTZ had no effect on seed tuber (25–50 mm in diameter) yield in NOR in either season. PTZ increased seed tuber number (STN) in RB by 29% to 40% and in SH by 57% to 70% over the controls. KIN had no effect on STN in any cultivar. MJ had no effect on STN in NOR (1993) or in RB in either season or in SH in 1994. In 1994, the highest rate of MJ (10–4 M) increased STN in NOR by 40% over the controls. GA3 had no beneficial effect on STN when applied after PTZ. This study suggests that, under field conditions, PTZ can increase seed tuber production in RB and SH while MJ was effective in NOR potatoes.
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