Environmental Conditions After Planting Affect the Expression of Differences in Tuber Formation of In Vitro-Derived Potato Plantlets from Different Ages and Cultivars

To identify if and how the age of in vitro potato plantlets at planting affects the later tuber formation, an extensive pot experiment was performed under controlled conditions. In vitro-derived plantlets of different ages (14, 28, 42 and 56 days old at planting) and cultivars varying in maturity type (Gloria, very early; Bintje, mid-early; Elkana, late) were grown after planting for 10 weeks at photo/thermoperiods of 16 h (standard conditions) or 12 h (short-day conditions). Plants raised from older in vitro plantlets produced higher total dry weights, harvest index and tuber dry and fresh weights than plants from younger in vitro plantlets when grown under standard conditions after planting. By contrast, total and tuber dry weights were not affected by plantlet age when grown under short-day conditions. The number of tubers per plant increased with increase in in vitro plantlet age in the later cultivars and in the oldest age classes of the very early cultivar when plants were grown under standard conditions. Short-day conditions resulted in fewer, but larger tubers than standard conditions. Results support the ideas that (1) plants from older in vitro plantlets and earlier maturing cultivars are more advanced in the tuber formation process; however, this may benefit tuber yield only when plants are grown under conditions that are not strongly inducing tuberization, and (2) higher tuber numbers can be achieved by more below-ground nodes—as in older in vitro plantlets—and/or by later or less strong tuber induction—as in less inducing conditions (16-h vs. 12-h), later cultivars or younger in vitro plantlets.