Abstract:

Conservation of biodiversity is a major issue of concern within the international community, and genetic diversity, the basis of species diversity and ecosystem diversity, is an important research area. Populus is planted widely throughout the world, and understanding its genetic diversity is critical for both theory and application. To date, the genetic diversity of Populus has been studied at different levels of organization: phenotype, chromosome, protein and DNA. 1) Phenotype diversity. Studying the morphology or phenotypic diversity of trees is the easiest and oldest method to measure genetic diversity. Phenotypic diversity is expressed in the size of the population, morphology, phenology, wood properties and tolerance to biotic or abiotic stress. 2) Chromosome polymorphism. Chromosomes are the carriers of genes, and their variation must lead to the variation of biological organisms and thus play an important role in evolution. Diversity of chromosomes includes both the number and structure variation. For Populus, the natural triploidy is found in P. tomentosa, P. bolleana, and the tri/aneuploid hybrid is found in the lager population of P. trichocarpa×P. deltoides hybrids, but chromosome structure variation is not found. 3) Protein polymorphism. Most studies focus on the isozyme. The method of isozyme e1ectrophoresis, a popular method for examining genetic diversity, is used to examine the genetic diversity of Populus and the characters or differentiation of clones or varieties. 4) DNA polymorphism. Genetic messages result from the sequencing of DNA, so analyzing DNA directly is the best method for studying genetic diversity. The DNA molecular markers, RFLP, RAPD, AFLP and SSR, have been applied to the study of Populus. Based on the objectives of a study, different types of plant DNA (nDNA, cpDNA and mtDNA) are used. Using molecular markers, the origins and evolution of Populus have been studied. This paper reviewed the progress in research on the genetic diversity of Populus. The results show that the genetic diversity in sections, populations and clones of Populus is high and related to its origins, large number of species and broad global distribution. Because genetic diversity controls evolution rates of biological adaptation and is the basis of breeding and conservation biodiversity, we suggest research in the following areas: 1) combine the study of population genetic structure and differentiation with studies of the conservation and utilization of Populus; 2) construct the gene pool of Populus; 3) develop breeds of fast-growing and stress tolerant Populus.

Key words: Populus, Phenotype, Isozyme, Chromosome, DNA, Genetic diversity