Abstract
Jack pine (Pinusbanksiana Lamb.), in a 3-year-old orchard established with accelerated-growth seedlings, were sprayed with gibberellin A4/7 (GA4/7) in an Aromox–ethanol solution during the 1981 growing season. Seven treatment periods were evaluated: the entire growing season, shoot elongation, bud development, early (first half) and late (second half) shoot elongation, and early and late bud development. Three concentrations of GA4/7 (200, 400, and 600 mg•L−1) were applied in all combinations with treatment periods. Three treatments increased female flowering: 400 and 600 mg•L−1 GA4/7 sprayed the entire growing season and 600 mg•L−1 sprayed during bud development. The number of pollen clusters was increased by spraying 400 and 600 mg•L−1 GA4/7 during any treatment period except early shoot elongation and late bud development or during shoot elongation (400 mg•L−1 only). The 200 mg•L−1 GA4/7 increased pollen clusters only if sprayed during early bud development or the entire growing season. The percentage of trees bearing pollen increased with all concentrations of GA4/7. The 1982 shoot growth of trees sprayed in 1981 during shoot elongation or the entire growing season (all GA4/7 levels pooled) was significantly less than control-tree growth or that of trees in the other treatment periods. The best treatment for increasing both male and female strobili was 600 mg•L−1 GA4/7 sprayed during bud development.
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