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-pyrimidine-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 abscissic acid levels and gibberellin-like bioactivity. These results suggest that growth reduction in this conifer by flurprimidol may well involve inhibition of gibberellin biosynthesis