Although recent genetic studies suggest that octoploid cultivated strawberry, Fragaria ×ananassa Duch., is highly diploidized, there have been no reports that directly and clearly described the behavior of four allelic pairs. In this study, we demonstrated the disomic inheritance of four allelic pairs in F. ×ananassa by using two highly polymorphic simple sequence repeat markers. By genotyping the offspring of ‘Summer-princess’ (containing eight distinct alleles of marker FxaHGA02P13) × ‘Dekoruju’ (containing another four distinct alleles for this marker), four allelic pairs could be identified in ‘Summer-princess’. In a similar way, four allelic pairs could be identified for cultivar Ohishi-shikinari and marker EMFvi136. The results of this study provide direct evidence that at least part of the octoploid strawberry genome is fully diploidized and that the genome composition hypothesis AAA′A′BBB′B′ is possible as suggested by other recent genetic studies.
Masanori Honjo, Susumu Yui and Miyuki Kunihisa
Masanori Honjo, Sono Kataoka, Susumu Yui, Masami Morishita, Miyuki Kunihisa, Takayoshi Yano, Megumi Hamano and Hiromichi Yamazaki
We analyzed sequence variation in chloroplast DNA (cpDNA) to investigate the origin of the cultivated strawberry, Fragaria ×ananassa. From analysis of two noncoding regions, trnL–trnF and trnR–rrn5, we found three haplotypes (V, C, and X) in F. ×ananassa. Haplotype V corresponded to the haplotype of F. virginiana and was possessed by cultivars bred over a wide geographic range, including North America, Europe, and Japan. Almost all the North American cultivars analyzed in this study possessed haplotype V, suggesting a founder effect. Haplotype C corresponded to the haplotype of F. chiloensis and was detected mainly in Japanese cultivars. Haplotype X was found in only two English cultivars. This haplotype was positioned as intermediate between haplotypes V and C in a median-joining network and was considered to be representative of the process of differentiation between F. virginiana and F. chiloensis. Results of controlled crosses indicate that cpDNA haplotypes of F. ×ananassa are maternally inherited. These results verify that F. ×ananassa is an interspecific hybrid between F. virginiana and F. chiloensis and indicate that traditional cultivars of F. ×ananassa have been derived from at least three maternal lineages. We demonstrate that the cpDNA variation detected in this study can be used to verify parentage and for extending hypotheses about June yellows, a leaf variegation disorder in strawberry.