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Résumé :
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The impact of flower induction on seed cost was studied considering three models of Douglas-fir (Pseudotsuga menziesii) seed orchards corresponding to different levels of management, four flower induction treatments (none, girdling, girdling + gibberellin 4/7, girdling + gibberellin 4/7 + nitrogen fertilization) and two periods of production (20 and 30 years corresponding to 32- and 42-year life spans, respectively). Seed cost referred to seeds still on the trees before cone collection. Flower stimulation considerably reduced seed production cost regardless of the intensity of orchard management and the production period. Flower induction was found to be most cost-effective in the case of intensively managed orchards and seed costs were reduced by 33 per cent when the period of production increased from 20 to 30 years. On average, girdling, girdling + gibberellin 4/7 injection and girdling + gibberellin injection + nitrogen fertilization reduced seed production costs by 2.7, 4.6 and 5.5, respectively. Therefore, the most sophisticated and intensive treatments were the most cost-effective. The study found that it is in the interest of the seed orchard manager to use flower induction treatments since they allow the production of more seeds of higher genetic quality at a cheaper rate per seed.
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