Early growth invigoration of jack pine seedlings by natural plant growth regulators

 Survival of conifer transplants is often poor on exposed planting sites in the boreal forest. More than one-third of all conifers do not become established. To enhance the competitive ability of jack pine seedlings, seeds were treated with natural plant growth regulators (PGRs; viz., homobrassinolide, salicylic acid, and two polyamines, spermine and spermidine) and growth promotion was studied for 16 days. Homobrassinolide (5 ng l^–1), salicylic acid (100 μg l^–1) and spermine (10 μg l^–1) enhanced elongation growth and elongation rate of whole plant. Homobrassinolide (5 ng l^–1) and salicylic acid (100 μg l^–1) stimulated root elongation by 38% and 10% respectively while spermine (1000 μg l^–1) increased needle growth by 14%. Homobrassinolide stimulated dry weight growth and growth rate. Homobrassinolide recorded over 20% increase in dry matter production, apportioned equally to root and needles, whereas spermine enhanced total dry matter production by almost 10%, mostly by increasing needle weight. Homobrassinolide facilitated nearly 19% increase in growth rate while spermine recorded only a 7% growth promotion. Spermidine inhibited both elongation and dry weight growth at all concentrations. Growth promotion by homobrassinolide, salicylic acid and spermine may be through an acceleration of processes connected to cell elongation, cell division and C allocation and these PGRs showed most promise for the early invigoration and improvement of jack pine seedling growth. Received: 27 August 1997 / Accepted: 8 January 1998