Relationship between ploidy level and genome size in strawberries

Abstract

This study investigated the pattern of variation in nuclear DNA content at different ploidy levels in Fragaria (Strawberry, Rosaceae) using flow cytometry based on mean fluorescent intensity (MFI) reflected by propidium-iodide-stained nuclei. On average, MFI values were 237 for diploids F. vesca, F. viridis, and F. nubicola, 416.5 for tetraploid F. orientalis, 621.5 for hexaploid F. moschata, and 798 for octoploids F. × ananassa, F. virginiana, and F. chiloensis. Within diploids MFI ranged from 225.9 in F. vesca ssp. vesca to 255.4 in F. nubicola, and within octoploids varied from 766 in F. × ananassa to 808 in F. virginiana. The nuclear DNA variation was significant among diploid species (N = 21, P < 0.008), but not across octoploid species (N = 17, P>0.386). MFI values were also variable among different genotypes of a given species though not significant. The values of mean basic genome DNA (MFI divided by ploidy level) were 118.5, 104, 103.5, and 99.8, respectively, for diploids, tetraploid, hexaploid, and octoploid species. This indicates that relative genomic size decreases by increasing ploidy level, and that there is no direct proportional relationship between DNA content and ploidy levels in Fragaria, supporting the idea of genome downsizing during polyploidization in plants.