FLOWERING RESPONSE OF DAY-NEUTRAL AND SHORT-DAY CULTIVARS OF NICOTIANA-TABACUM-L INTERACTIONS AMONG ROOTS, GENOTYPE, LEAF ONTOGENIC POSITION AND GROWTH-CONDITIONS

The interaction between roots and leaves as a function of the capacity of differently positioned leaves to induce flowering of four cultivars of Nicotiana tabacum, L. was assessed under long- and short-day growth conditions with three types of manipulations: 1) repeated rooting of the shoot tip, 2) removal of apical leaves, and 3) removal of basal leaves. Repeated rooting of the shoot tip increased the number of nodes produced by all cultivars; however, a substantial extension of vegetative growth was only caused by rerooting in conditions where apical leaves exhibited little or no inductive capacity. The simplest and most consistent interpretation of these data is that floral initiation in tobacco results from an interaction of inputs from the leaves and the roots and that the root influence can be overridden by a strong leaf signal.