Genetic diversity and population structure of diploid and polyploid species of isoetes in east asia based on amplified fragment length polymorphism markers

Isoetes L. is critically endangered in areas of East Asia, including Taiwan, Japan, and South Korea. The genetic diversity and the population structure of six Isoetes species from East Asia were evaluated by using amplified fragment length polymorphism (AFLP). Three AFLP-selective primer combinations generated a total 923 amplification products, of which 919 (99.6%) were polymorphic. The levels of genetic diversity of two diploid species (I. taiwanensis [percentage of polymorphic loci (PPL) = 33.1%-38.3%] and I. asiatica [PPL = 49.0%]) are higher than those of polyploid species (tetraploid: I. jejuensis [PPL = 9.3%-29.3%] and I. hallasanensis [PPL = 22.3%]; hexaploid: I. coreana [PPL = 1.6%-20.6%] and I. japonica [PPL = 5.6%-20.5%]). Higher genetic differentiation was detected for populations of I. coreana (0B = 0.730) than for the diploid species I. taiwanensis (0B = 0.074). In addition, analysis of molecular variance showed that a large proportion (79.8%) of genetic differentiation existed among population of I. coreana. However, 93.2% of the total genetic variation was attributed to differentiation within populations of I. taiwanensis. A neighbor-joining dendrogram resulted in three clusters, one for I. asiatica, one for I. japonica, and one for the rest of the species, subdivided into two: (1) I. taiwanensis/I. jejuensis and (2) I. coreana/I. hallasanensis. Furthermore, individuals from each population of I. coreana and I. jejuensis were clustered into population-specific subclusters. The probable causes of the current pattern of genetic variation and population structure are discussed, and suggestions on the future protection of Isoetes species are also given. © 2009 by The University of Chicago. All rights reserved.