DIFFERENTIAL FLOWERING RESPONSES BY YOUNG DOUGLAS-FIR GRAFTS AND EQUI-SIZED SEEDLINGS TO GIBBERELLINS AND AUXIN

Flowering was significantly promoted in 2-year-old grafts of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), but only slightly increased in 4-year-old seedlings of similar physical size, by 100–200 ug of GA_4/7 applied biweekly during April-June.
Gibberellin A₉ was somewhat less effective, GA₃ was without promotive effects, and GA₅ was unique in only promoting male flowering (but only on grafts). NAA (10–20 ug) also tended to promote maleness in grafts; only 3 out of 197 seedlings examined produced pollen cones and each of these received treatments containing NAA.

The finding that increasing the level of exogenous GA_4/7 from 100 to 200 ug increased the percentage of grafts, but not seedlings, flowering argues against the possibility that the juvenile condition exists because the supply of endogenous GAs in young seedlings is inadequate for differentiation and/or development of cone buds.
As the Douglas-fir seedlings and grafts were nearly identical in height, their differential response to GA_4/7 cannot be attributed to size per se. Clearly the adult condition of the scion is maintained in vegetative propagation, and is the result of aging of the apical meristem.

Symposium on Juvenility in Woody Perennials

S. D. Ross

https://doi.org/10.17660/ActaHortic.1976.56.15