Karyotyping of the chromosomes and physical mapping of the 5S rRNA and 18S-26S rRNA gene families in five different species in Capsicum

Since clear identification of individual chromosomes in Capsicum species wa s not possible due to the gradient in sizes and similar morphology, in situ hybridization using 5S rDNA and 18S-26S rDNA probes was utilized to karyot ype the chromosomes of the five species, Capsicum annuum, C. chinense, C. f rutescens, C. baccatum, and C. pubescens. The 5S rDNA located on only one p air of chromosomes in all five species. The 5S rDNA carrying chromosome was designated as chromosome 1 by the synteny relationship with tomato. In two species, C. baccatium and C. pubescens, the 5S rDNA was physically linked with a 18S-26S rDNA locus. The number and chromosomal location of 18S-26S r DNA loci were highly variable among the species. The number of loci was as few as two in C. annuum and as many as 14 in C. baccatum. The chromosomal p ositions of the 18S-26S loci were in the telomere regions in the correspond ing chromosomes and some chromosomes showed hybridization signals in this r egion of both long and short arms. A pair of acrocentric chromosomes carryi ng the 18S-26S rDNA locus in the satellite region was found in all five spe cies. The in situ and Southern hybridization patterns of the rDNAs were sim ilar between C. annum and C. chinense. C. frutescens was similar to C. chin ense. C. baccatum and C. pubescens were speculated to be less related to th e former three Capsicum species. The variable nature of the 18S-26S rDNA lo ci in the Capsicum species might provide a good model for rDNA evolution.