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Cultivated strawberry (Fragaria×ananassa) originated from four diploid ancestors: F. vesca, F. viridis, F. iinumae and F. nipponica. Among them, F. vesca is the dominant subgenome for cultivated strawberry. It is not well understood how differences in gene expression between diploid and octoploid strawberry contribute to differences during fruit development. In this study, we used comprehensive transcriptomic analyses of F. vesca and F.×ananassa to investigate gene expression at the different stages of fruit development. In total, we obtained 3 508 (turning stage) and 3 958 (red stage) differentially expressed genes with pairwise comparisons between diploid and octoploid. The genes involved in flavonoid biosynthesis were almost upregulated in the turning stages of octoploid, and we also discovered a ripe fruit-specific module associated with several flavonoid biosynthetic genes, including FveMYB10, FveMYB9/11, and FveRAP, using weighted gene coexpression network analysis (WGCNA). Furthermore, we identified the species-specific regulated networks in the octoploid and diploid fruit. Notably, we found that the WAK and F-box genes were enriched in the octoploid and diploid fruits, respectively. This study elucidates new findings on flavonoid biosynthesis and fruit size of strawberry with important implications for future molecular breeding in cultivated strawberry.