Cross breeding of Populus and its hybrids for cold resistance

Populus tomentosa was crossed with P. tremuloidis, P. grandidentata, P. alba × P. grandidentata and P. alba × Ulmus pumila in order to maintain its rapid growth and high wood quality and improve its resistance to cold. Two methods were used to increase the germination rate from 1.5% to 41.1% and the remaining rate from 1.7% to 44.2%. Forty crossing combinations were conducted and 2 744 hybrid seedlings were obtained. MX₄ × P. grandidentata (G-1-58), MX₃ × P. tremuloidis (T-44-60), MX₂ × P. tremuloidis (1-13-87-37) and MX₂ × (P. alba × P. grandidentata) were regarded as superior combinations after analysis and selection. Thirty seedlings of these combinations and 11 triploid seedlings identified by counting their chromosomes were selected as super plants. [Supported by the Doctoral Foundation of Ministry of Education (Grant No. 200220022004) and the National “863” Project (Grant No. 2002AA241071)]