Chromosome Numbers and Flow Cytometry of Strawberry Wild Relatives

摘要

The U.S. Department of Agriculture, Agricultural Research Service, National Clonal Germplasm Repository (NCGR), Corvallis, Oregon, maintains the national collection for strawberry (Fragaria L.) germplasm. The hybrid strawberry of commerce, F. ×ananassa Duchesne ex Rozier has two octoploid wild American relatives in the primary gene pool (Fragaria chiloensis (L.) Mill. subsp. chiloensis forma chiloensis and F. virginiana Miller subsp. virginiana). The secondary gene pool includes about 18 additional species native circumpolar boreal, in a polyploid series from diploid to decaploid. Chromosome numbers of root tip cells were counted for 46 strawberries in the Repository collection representing 28 taxa (species and subspecies taxa). The base chromosome number was seven. Counted genotypes included an aneuploid, fifteen diploids, 3 tetraploids, 1 hexaploid, 14 octoploids, and 2 decaploids. In addition, flow cytometry was performed. Flow cytometry reliably determined gross ploidy level. Diploid species had a range of DNA ratios from 0.22 to 0.29. Tetraploids had a DNA ratio of 0.47 to 0.50. The hexaploid DNA ratio was 0.66. That of the octoploids ranged from 0.74 to 0.82. Decaploid cytotypes, with DNA ratios of 1.0 or higher, could readily be separated from octoploids. The aneuploid F. chiloensis subsp. pacifica with 54 chromosomes had a smaller DNA ratio than other F. chiloensis having 56. Further experimentation linking the DNA ratio with the C value of these strawberry species will be performed. Propagules of these plant accessions in this study are available to researchers for breeding and genetic research.