EARLY GROWTH INVIGORATION OF JACK PINE-SEEDLINGS BY NATURAL PLANT-GROWTH REGULATORS

Survival of conifer transplants is often poor on exposed planting site s in the boreal forest. More than one-third of all conifers do not bec ome established. To enhance the competitive ability of jack pine seedl ings, seeds were treated with natural plant growth regulators (PGRs; v iz., homobrassinolide, salicylic acid, and two polyamines, spermine an d spermidine) and growth promotion was studied for 16 days. Homobrassi nolide (5 ng l(-1)), salicylic acid (100 mu g l(-1)) and spermine (10 mu g l(-1)) enhanced elongation growth and elongation rate of whole pl ant. Homobrassinolide (5 ng l(-1)) and salicylic acid (100 mu g l(-1)) stimulated root elongation by 38% and 10% respectively while spermine (1000 mu g l(-1)) increased needle growth by 14%, Homobrassinolide st imulated dry weight growth and growth rate. Homobrassinolide re corded over 20% increase in dry matter production, apportioned equally to ro ot and needles, whereas spermine enhanced total dry matter production by almost 10%, mostly by increasing needle weight. Homobrassinolide fa cilitated nearly 19% increase in growth rate while spermine recorded o nly a 7% growth promotion. Spermidine inhibited both elongation and dr y weight growth at all concentrations. Growth promotion by homobrassin olide, salicylic acid and spermine may be through an acceleration of p rocesses connected to cell elongation, cell division and C allocation and these PGRs showed most promise for the early invigoration and impr ovement of jack pine seedling growth.