Key Laboratory of Genetics and Breeding in Forest Trees and Ornamental Plants;
Ministry of Education;
Beijing Forestry University;
Beijing 100083;
P. R. China;
Department of Forestry and Environmental Resources;
North Carolina State University;
Raleigh;
NC 27695;
USA;
Present address: Shandong Academy of Forestry;
Jinan 250014;
P. R. China;