| The Fragaria genus belongs to the family Rosaceae,and is comprised of one cultivated species,F.x ananassa,and 23 wild species,including 12 diploid species,5 tetraploid species,1 hexaploid species,3 octoploid species and 2 decaploid species.Understanding the genetic relationships between wild Fragaria species and the origin of polyploid species will provide an important theoretical basis for the protection and rational use of wild Fragaria resources,which is of great significance to Fragaria breeding.However,with the exception of the F.x ananassa and its two parents of F.chiloensis and F.virginiana,the origins and genomic properties(auto or allopolyploid)of other polyploid Fragaria species are still unclear.Chromosome karyotyping analysis is very useful in determining species relationships and origin of polyploid species.The identification of individual chromosome is the foundation for developing a karyotype.However,for Fragaria species,it is almost impossible to definitive identification of the individual chromosomes by traditional karyotype.Because the chromosomes of the Fragaria genus are small,and the shape of the chromosomes are similar,the number of chromosomes in polyploid species is large.The chromosome specific oligonucleotide(oligo)library is an effective marker for chromosome identification.In this study,we used the synthetic oligonucleotide library corresponding to 6 chromosomes of F.vesca to identify individual chromosome of 13 Fragaria species with different ploidy,and constructed the FISH-based molecular cytogenetic karyotypes for these Fragaria species.The results of the karyotyping analysis showed that:1.These Fragaria species have a very similar karyotype,so karyotype analysis based on chromosome morphological characteristics is difficult to distinguish between various diploid species,and provides no effective information for the origin of polyploid species.However,there are differences in the signal intensity of oligonucleotide probes among the homologous chromosomes of several polyploid species,which provides important information for the origin of these polyploid species.2.It is determined that the tetraploid F.orientalis and F.tibetica are allotetraploids.The F.orientalis may be a hybrid of a diploid species and a hexaploid F.moschata.The F.tibetica may be a hybrid of a diploid unreduced gamete with a normal gamete from a tetraploid specie,or be obtained from the cross of two diploid unreduced gametes.3.According to the signal intensity of oligonucleotide probes between homologous chromosomes,the chromosomes of pentaploid specie cannot be distinguished,but according to chromosomes morphology and rDNA distribution,the chromosomes can be divided into 3 groups,2 groups of chromosomes are paired,and 1 group is single chromosome,and the single chromosome should be derived from a diploid.So it is speculated that the natural pentaploid in China is a hybrid of a tetraploid unreduced gamete and a diploid normal gamete.4.It is determined that the hexaploid F.moschata is an allohexaploid,and the six homologous chromosomes can be clearly divided into 3 pairs according to the signal intensity of the oligonucleotide probes.The signals intensity on two chromosomes in each pair are similiar,it is proved that there are 3 parental genome donors of hexaploid F.moschata.5.In the octoploid species of F.chiloensis and F.virginiana,the eight homologous chromosomes can be divided into 4 pairs according to the difference in the signal intensity of the oligonucleotide probes,which proves that there are 4 parental genome donors for octoploids,and one of the ancestors was the diploid F.vesca. |
