PHOTOPERIOD, TEMPERATURE, GIBBERELLIN, AND AN ANTIGIBBERELLIN AFFECT TUBERIZATION OF POTATO STEM SEGMENTS IN-VITRO

'Katahdin' potato plants were grown under conditions that did not indu ce tuberization (noninducing conditions) and the foliage was sprayed w ith either a growth retardant (BAS-111) at 1000 mg.L-1 or distilled wa ter. Other plants, grown under tuber-inducing conditions, received a f oliar spray of gibberellic acid (GA(3)) at 100 mg.L-1 or distilled wat er, After 1 week, treatments were repeated. Two-node stem segments wer e excised from the apical, subapical, medial, and basal sections of ea ch plant 72 hours after the second foliar treatment, disinfested, and inserted into flasks containing 50 mL of Murashige and Skoog medium (2 % sucrose). After 3 weeks in a darkened incubator adjusted to 24 degre es C, tuberization response was evaluated. Orthogonal contrasts reveal ed significant differences between induced and noninduced controls for tuber number, diameter, and fresh mass. BAS-111 reduced rhizome lengt h and increased tuber number, diameter, and fresh mass. GA(3) increase d rhizome length, but reduced tuber number, diameter, and fresh mass. Node location influenced tuber development, as basal explants produced significantly more and larger tubers, as well as longer rhizomes, tha n did apical explants, and subapical segments produced more and larger tubers than did apical segments. There were no significant difference s between medial and basal nodal segments with respect to tuber number or tuber/rhizome size. Chemical names used: oxy-5,5-dimethyl-3-(1,2,4 -triazol-1-yl)-hexan-5-ol (BAS-111); oxy-1-methyl-8-methylenegibb-3-en e-1,10-carboxylic acid 1->4 lactone (GA(3)).