Physical mapping of 45S rDNA by fluorescent in situ hybridization in persimmon (Diospyros kaki) and its wild relatives

In an attempt to elucidate speciation and genome composition of hexaploid cultivated species of Diospyros kaki, fluorescent in situ hybridization (FISH) using an rDNA probe was performed on somatic chromosome spreads of D.kaki and nine wild species including both diploid and polyploid species. There appeared to be geographical variability in the number of rDNA sites in diploid species of Diospyros. More rDNA sites were observed in the species from Southern part of Africa (six or eight sites in D. lycioides, D. glabura, D. simii ) than those from Asian species (two or four sites in D. ehretioides, ,D. morrisiana, D. oldhami and D. lotus). Three polyploid species tested, tetraploid D. rhombifolia, and hexaploid D. kaki and D. virginiana, had eight rDNA sites. In terms of the number and location of rDNA sites and DAPI staining patterns, chromosomes of D. lotus, an Asian diploid, most resembled D. kaki among the species tested. Phylogenetic relationships between D. kaki and the nine species tested and the genome composition of D. kaki are discussed based on the number and chromosomal distribution of 45S rDNA.