Effect of Pot Size and Timing of Plant Growth Regulator Treatments on Growth and Tuber Yield in Greenhouse-Grown Norland and Russet Burbank Potatoes

Abstract

The effects of pot size, timing of the applica- tion of paclobutrazol (PTZ) and gibberellic acid (GA3), and the counteractive effect of these two compounds on growth and tuber yield of greenhouse-grown Norland and Russet Burbank potatoes were investigated. Plants were grown either in 1.5-liter pots (15 cm deep) or 3.0- liter pots (18 cm deep) and received a foliar application of either 1.5 mM PTZ or 9◊1 0 ˛3 mM GA3 at early or late stolon initiation. Some plants that had been foliar treated with 1.5 mM PTZ at early stolon initiation were foliar treated wit h9◊1 0 ˛3 mM GA3 at late stolon initiation. PTZ reduced haulm length in both cultivars significantly, particularly when the treatment was applied at early sto- lon initiation, but the late treatment reduced haulm length only when growing in 3.0-liter pots. Irrespective of the timing of treatment, GA 3 increased haulm length in Nor- land growing in both pot sizes, but the treatment in- creased haulm length in Russet Burbank only when ap- plied at late stolon initiation. GA 3 applied after PTZ did not overcome the growth-inhibiting effect of the PTZ treatment. The PTZ treatment effectively increased us- able tuber number/plant (UTN) in Norland, but PTZ had no effect on UTN in Russet Burbank. PTZ reduced us- able tuber weight/plant (UTW) only in Norland growing in 1.5-liter pots. By contrast, GA3 increased UTN only when treated at late stolon initiation of 1.5-liter pot- grown Norland, whereas the same treatment was effec- tive when applied only at early stolon initiation for Rus- set Burbank. For Norland, the increase in UTN by early applied PTZ was reduced by the subsequent application of GA 3 . The use of 3.0-liter pots for minituber produc- tion in both Norland and Russet Burbank appears to have no advantage over growing in 1.5-liter pots, particularly when PTZ or GA3 is used to enhance tuberization.