In vitro tuberization of potato clones from different maturity groups.

In vitro tuberization on shoot cultures of early, mid-season, late and very late potatoes was compared. Shoots were grown at 12, 16, or 20 h photoperiods; tuberization was then induced at 0, 8 or 16 h light. In the dark, shoots from early plants initially grown at 16 h consistently set tubers earlier than the other types, whereas the very late line tuberized later and produced significantly fewer tubers. Tuber setting of mid-season plants could not be distinguished from the late type. Tuberization of the very late line was significantly hastened by shortening the photoperiod from 20 h to 12 h during the shoot growth period. Light during tuber induction delayed tuberization. This system may be useful to screen callus-derived plants for maturity, and may also be suitable for in vitro study of the photoperiodic control of tuberization.