Eastern White Pine Flowering in Response to Spray Application of Gibberellin A4/7 or Procone™
Eastern white pine (Pinus strobus L.) is an important forestry species in the northeastern and midwestern United States and in eastern Canada. Induction of early and reliable flowering and cone production will shorten the breeding cycle and aid in the development of genetically improved white pine. The objective of this study was to determine if a foliar spray application of gibberellin A4/7 (GA4/7) or ProCone™ would induce both male and female strobili on young grafted eastern white pine selected for white pine blister rust resistance. Trees were sprayed (500 mg L-1) weekly in 1998 during the period of rapid shoot elongation (mid-May through July), for a total of 11 applications. Flowering data were collected June 15, 1999. Twenty-five out of 53 genotypes produced male strobili. For all genotypes studied, the total number of male strobili clusters per tree (and the mean number ± SE of pollen-cones per cluster) produced with GA4/7, ProCone™, or untreated controls were: 643 (7.1 ± 0.3); 574 (7.9 ± 0.3); and 79 (8.3 ± 0.8), respectively. Twenty out of 53 genotypes produced female strobili. For all genotypes studied, the total number of female strobili per tree (and the mean number ± SE of female strobili per shoot) produced with GA4/7, ProCone™, or untreated controls were: 87 (1.1 ± 0.1); 130 (1.3 ± 0.1); and 33 (0.6 ± 0.1), respectively. Eleven genotypes produced both male and female strobili. Control trees that flowered may have been the result of spray drift. The results indicate that a foliar spray application of GA4/7 or ProCone™ at 500 mg L-1 will induce both male and female strobili, but not on all selected genotypes of eastern white pine.
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