THE EFFECT OF FLURPRIMIDOL ON BUD FLUSH, SHOOT GROWTH, AND ON ENDOGENOUS GIBBERELLINS AND ABSCISIC-ACID OF DOUGLAS-FIR SEEDLINGS

For 4-month-old Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings under 17-h photoperiods in controlled environment conditions, flurprimidol (alpha-(1-methlyethyl-alpha-[4-(trifluoromethoxy)phenyl]-5-pyrim?idine-methanol) decreased incidence of second flushing from 81 to 54% and significantly reduced height growth in the second year following low-temperature treatment, in comparison to untreated controls. For seedlings under 15-h photoperiods, flurprimidol had only limited early effects, but after a period of bud dormancy, shoot growth was reduced to one-third that of the untreated controls. Under both photoperiods flurprimidol significantly depressed abscisic acid levels and gibberellin-like bioactivity. These results suggest that growth reduction in this conifer by flurprimidol may well involve inhibition of gibberellin biosynthesis.