Evaluation of Shoot Collection Timing and Hormonal Treatment on Seedling Rooting and Growth in Four Poplar Genomic Groups

Populus spp. is an economically valuable tree worldwide, known for its adaptability, fast growth, and versatile wood, often cultivated in short-rotation plantations. Effective propagation is crucial for rapid genetic improvement and global demand for forest products and biomass energy. This study focused on the rooting and growth of poplar cuttings, examining shoot collection timing and growth stimulant treatments across four hybrids: Populus deltoides × P. nigra (Agathe F), P. maximowiczii × P. trichocarpa (Arges), P. deltoides × P. trichocarpa (Donk), and an interspecific hybrid Populus × canadensis (F-448). The experiment used hybrid poplar cuttings collected in spring 2022 and 2023, planted in controlled climates with a randomized block design. Cuttings were soaked for 24 h in growth stimulants, namely indole-3-butyric acid, cinnamic acid, and indole-3-acetic acid. After 12 weeks, rooting percentage and seedling height were assessed. The study found that the optimal time for collecting poplar cuttings for best rooting is late winter to early spring, specifically from March to early April, with shoots collected after early April showing the lowest rooting potential. The growth stimulants significantly influenced the growth of poplar seedlings. There was a tendency for lower concentrations to increase root formation and seedling height, while higher concentrations had adverse effects. Despite variations in growth rates, a consistent growth pattern was observed across different shoot collection dates for all genomic groups.