Abstract: 【Objective】The studies of genetic diversity of Nicotiana tabacum accessions and relationships among them are essential for the utilization of them.【Method】Inter-simple sequence repeat (ISSR) amplification analysis was used to determine the degree of intra- and inter-specific genetic variation in the genus Nicotiana,91 cultivars (Nicotiana tabacum L.) and five wild Nicotiana species were analyzed. 【Result】1)using eighteen primers screened from 90 ISSR primers,a total of 314 DNA fragments were amplified,of which 299 (PPB= 95.20%) were polymorphic,It showed that ISSR technique was capable of detecting more polymorphic than other makers; 2)The genetic similarity among 96 accessions ranged from 0.28 to 0.97.The genetic similarity coefficients between 5 wild species and cultivar was 0.28~0.58, average value was 0.42, while among cultivars was 0.62~0.98, average value was 0.78. The analysis indicated that a greater amount of genetic polymorphism exists among species of Nicotiana than among cultivars,and the genetic basis was comparatively narrow among the cultivars, except only a few of different varieties; 3) Cluster analysis by unweighted pair group method of arithmetic means（UPGMA）suggested that the 5 wild species were genetically different from the other 91 cultivars at the level of D=0.48,exhibited high levels of interspecific genetic variation.4) The cluster analysis only to 91 accessions of cultivar indicated that three small clusters and one big cluster was found at the level of D=0.40.The big cluster was consist of many different groups. Some groups were consist of cultivars that were primarily based upon the same geographic origin or manufactuing quality trait,maybe all these cultivars has similar genotype;Morever,some groups were consist of cultivars that had different geographic origin or manufactuing quality trait,that because there was close relationship among these cultivars;A few other groups were consist of only one cultivar,it showed that these cultivars has a genetic base different from other cultivars.In a word,the marker of ISSR was useful in revealing the genetic diversity and relationship among tobacco germplasm resourse.【Conclusion】This research providing a scientific basis for broadening the gene resources of cultivar through germplasm innovation and tobacco breeding,as well as construction of DNA fingerprint of core germplasm and molecular genetic linkage map of tabacco.

Key words: Tobacco, Germplasm resourse, Genetic diversity, ISSR, Genetic relationships