Hormonal enhancement of cone production in Douglas-fir grafts and seedlings

Abstract

Gibberellic acid (GA) and naphthaleneacetic acid (NAA) were applied alone and in combination to both girdled and nongirdled branches of Douglas-fir in four seed orchards (two containing seedlings and two containing grafts). GA significantly increased seed-cone buds and cones and caused a nonsignificant increase in pollen-cone buds. Cone production was not significantly affected by girdling or the application of NAA. Trees treated with the combination of GA + NAA responded similarly to those treated with GA alone. Cone production response to GA varied according to the orchard locations, with better response in the normally more productive orchards. The percentage of trees flowering was increased by GA. Hormone treatments had no effect on seeds per cone but they significantly reduced filled seed per cone. Owing to increased cone number, however, the GA treatments greatly increased the yield of viable seed. NAA increased the percentage of seed germinating and the rate of seed germination, while GA had no effect.

Promotion of seed production in Douglas-fir grafts by girdling + gibberellin A4/7 stem injection, and effect of retreatment

“…Although some workers reported reduced seed set in cones induced by G and GA treatments (Puritch et al 1979;Longman et al 1986;Philipson 1987), this was not apparent in the present study. Whereas grafts treated in 1987 produced slightly smaller cones in 1988, presumably as a result of the G + GA treatment being somewhat phytotoxic, total and filled seed per cone were not affected.…”

Hormonal Aspects of Phase Change and Precocious Flowering

“…Occasionally GA 3 has been successful for Pinaceae family conifers (BLEYMÜLLER 1976, PHARIS andKuo 1977), although resuIts with this "poIar" GA are variabIe and not readiIy repeatabIe (CHALUPKA 1978). To date, the most effective treatment for Pinaceae species has invoIved GA4 + 7 and screening triaIs have confirmed its efficacy on 16 Pinaceae species in 5 genera (Larix, Picea, Pinus, PseudoIsuga, and Tsuga;CHALUPKA 1978, HARE 1979, LUUKKANEN and JOHANSSON 1980, PHARIS and Kuo 1977, PURITCH et al 1979, Ross and GREEN-WOOD 1979, SWEET 1979, WHEELER et al 1980. Other cultural treatments, such as nondestructive girdling, water stress, high temperature, and nitrate fertiIization can enhance the response to these Iess-poIar GA's by seed-lings of Pinaceae (CHALUPKA 1981, PHARIS 1976, POL-LARD and PORTLOCK 1981, Ross 1976.…”

Promotion of flowering in the Pinaceae by gibberellins

“…Flowering in Douglas fir normally does not occur until age 10 to 15 years, depending upon the locality and the chance timing of climatic conditions which constitute a "good cone induction year", and appreciable seed production generally does not occur before age 20 to 25 (Puritch 1972). Such reproductive behaviour is a serious obstacle to genetic improvement within the species.…”