Location: National Clonal Germplasm RepositoryTitle: Karyotype Analysis in Wild Diploid, Tetraploid, and Hexaploid Strawberries, Fragaria (Rosaceae)) Author
Submitted to: Cytologia
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/4/2009
Publication Date: 3/20/2010
Citation: Nathewet, P., Yanagi, T., Hummer, K.E., Iwatsubo, Y., Sone, K. 2010. Karyotype Analysis in Octoploid and Decaploid Wild Strawberries Fragaria (Rosaceae). Cytologia. 74(3)355-364. Interpretive Summary: The strawberry has a base set of 7 chromosomes. There are about 20 wild species in the world. Some of them have the normal 2 sets, but there others have 4, 6, 8 or 10 sets of chromosomes. Few reports have been made describing the chromosome structure of strawberries. The objective of this research was to determine the shape and type of chromosomes for strawberry species with 2, 4, and 6 sets of chromosomes. We looked at strawberry root tip cells when the chromosomes were all lined up in the center before the cell divides. It is the easiest time to see the chromosomes. We looked at 17 accessions. From our data we could also evaluate the species relationships to consider their family history. The counts of the chromosomes were as expected : 14, 28, and 42. The species with 2 sets of chromosomes were similar to each other in shape and form; the species with 4 sets of chromosomes had somewhat different in form. Our analysis showed that species with 2 sets of chromosomes were in a different group than those with 4 sets, excepte for the Tibetan species. This species had 4 sets of chromosomes although it grouped with the 2-set species. The musk strawberry that has 6 sets of chromosomes clustered with the species having 4 sets of chromosomes. This kind of information is of interest to strawberry breeders who are developing strawberries with more flavor.
Technical Abstract: The Strawberry, genus Fragaria (Rosaceae) has a basic chromosome count of x = 7, and is comprised of 20 wild species having an euploid series from diploid (2n = 2x = 14) through decaploid (2n = 10x = 70). Few karyotypes of species in this genus have been reported. The objective of this research was to determine the chromosomal morphology and karyotype analysis of wild diploid, tetraploid and hexaploid Fragaria species. Somatic chromosome imates of 20 genotypes of diploids, tetraploids, and hexaploids, were taken at the metaphase stage of mitosis under a light microscope. Karyotype analysis was performed in 17 accessions. The phylogenetic relationships between species were constructed using cluster analysis based on karyotypic similarity. Somatic chromosome numbers of wild diploid, tetraploid and hexaploid species were 2n = 2x = 14, 2n = 4x = 28 and 2n = 6x = 42. Chromosome morphology in wild diploid species had greater uniformity than that in the tetraploid species. Results of the cluster analysis showed that the diploid and tetraploid species reside in separate clades,with one exception. Fragaria tibetica, a tetraploid, clustered with the diploid species clade. The hexaploid, F. moschata, clustered with the tetraploid species clade.