FLORAL INDUCTION IN WOODY ANGIOSPERMS

The long juvenile period of trees is a severe impediment to study of r eproductive biology and genetic inheritance, and is a serious constrai nt for traditional breeding programs. Very little effort has been dire cted toward the development of practical methods for inducing early fl owering in most woody angiosperms, particularly members of the genus P opulus. This review is intended to stimulate interest in, and provide direction for, future research in this area. An emphasis is placed on techniques that can be applied easily and inexpensively. Inductive tre atments discussed include: phytohormones (gibberellins, cytokinins, ab scisic acid, ethylene and auxin); growth retardants (paclobutrazol, un iconazole, daminozide, chlormequat and cimecthacarb); physical constra ints (girdling, root restriction and shoot training); cultural conditi ons (photoperiod, mineral nutrition, moisture stress and temperature); and grafting. Recent reports on stimulation of flowering by genetic t ransformation with floral homeotic genes are also described. Several r esearch avenues which appear promising are proposed for near-term stud y.