生物多样性的研究和保护是目前全世界普遍关注的问题，其中研究较多的是遗传多样性、物种多样性及生态系统多样性，遗传多样性作为生物多样性的重要组成部分，是生态系统多样性和物种多样性的基础方面。杨树是世界各国普遍种植的木本植物，研究其遗传多样性具有重要的理论和实践意义，国内外都开展了广泛研究。本文综述了杨属(Populus)植物的派、种及无性系等在表型、染色体、蛋白质及DNA水平的遗传多样性的研究进展。其表型多样性主要体现在不同水平上的种群大小、形态特征、物候期、材性以及对生物或非生物逆境的抗性等方面；在杨属植物中已发现有天然的三倍体及三倍体/非整倍体的杂交种存在；蛋白质的多态性主要集中于同工酶的研究，用于不同杨属植物的遗传差异，无性系或品种的特征、分化和遗传研究；DNA多态性是研究最多的，RFLP、RAPD、AFLP和SSR等分子标记已广泛用于杨属的遗传多样性研究中，根据不同的研究目的所选择的DNA（nDNA, cpDNA或mtDNA）也不同。并根据国内的研究现状，提出了几点建议。
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.