Promotion of Flowering in the Pinaceae by Gibberellins

Abstract

GibberelUns (GAs) were effective in promoting flowering in sexually mature (45-year-old scions) grafts of loblolly pine (Pinus taeda L.). Seed-cone production was increased 12-fold in fieldgrown, grafted ramets by bi-weekly, May-September applications of 500 ^g per branch of GA^,,. Gibberellin A3 was equally effective at 500 fig but not at 100 fig per branch, while GA5 was ineffective at either concentration. A second study using potted, less-sexually mature (8-to 10-year-old scions) grafts gave a reduced level of seed cones in response to GAs. However, even on these younger grafts GA4/7 was a significant promotive treatment, GA3 being considerably less effective. Branch girdling, tested as an adjunct treatment, was ineffective. It is now apparent that exogenous applications of GA4/7 are effective on a number of Pinaceae species, and their use to promote earlier and more abundant flowering in breeding orchards of grafted ramets for at least two species, loblolly pine and Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] is practical.

Lateral Female Strobili Production in a Japanese Red Pine (Pinus densifloraSieb. et Zucc.) Clone by Exogenous Cytokinin Application

“…With other species of Pinaceae such as Pinus banksiana (Cecich, 1981(Cecich, , 1983, P. sylvestris (Chalupka, 1984(Chalupka, , 1987, P. elliottii, P. palustris (Hare, 1984), P. radiata (Ross et al, 1984), P. taeda (Greenwood, 1982;Ross and Greenwood, 1979) and P. caribaea (Harrison and Slee, 1991), GA4 or GA4n application showed positive effects on strobili formation. These GA application methods cannot be compared directly with the present BAP application method, since the experiments differed in the tree species used, their size and age.…”

“…Hashizume (1985) has described that GA application was less effective in young than in aged, over five or six years, seedlings and graftings. Also according to Ross and Greenwood (1979), "certain degree of sexual maturity" is needed before Pseudotsuga menziesii seedlings will respond to GA treatment. BAP induced lateral female strobili even in fouryear-old seedlings of Japanese red pine (unpublished data), suggesting that the effect is independent of age.…”

Promotion of Lateral Female Strobili Production inPinus densifloraby Cytokinin Application at a Specific Stage

“…Many researchers report that the optimum period for effective GA application to promote flowering of Pinaceae species ranged from March to July or, at the latest, to September (Cecich, 1981(Cecich, , 1983Greenwood, 1982;Harrison and Slee, 1991;Hashizume, 1985;Kanekawa and Katsuta, 1982;Luukkanen and Johansson, 1980;Ross and Pharis, 1976;Ross and Greenwood, 1979;Ross et aL, 1981;Ross, 1983;Ross et al, 1984;Tompsett and Fletcher, 1979). According to Pharis et aL (1987), GA's of a less-polar nature play a direct morphogenic role in the promotion of flowering in conifers.…”

The biology and management of coniferous forest seeds: Genetic perspectives

“…Pohtion mechanisms (Owens and Blake 1985), cone induction in natural stands (Pmtch 1972) and seed orchards (Ross and Greenwood 1979), seed production from natural populations (Eis and Craigdallie 1983) and seed orchards (Schmidtling 1983), seed germination, maturity, and dormancy (Edwards 1980), have been studied. These facets have contributed sigmficantly to understanding the various components of tree reproductive systems.…”