The evolution of CMA bands in Citrus and related genera Ana Emília Barros e Silva & André Marques & Karla G. B. dos Santos & Marcelo Guerra Received: 4 January 2010 / Revised: 25 March 2010 / Accepted: 8 April 2010 / Published online: 21 May 2010 # Springer Science+Business Media B.V. 2010 Abstract Most species of Citrus and related genera display a similar karyotype with 2n =18 and a variable number of terminal heterochromatic blocks positively stained with chromomycin A 3 (CMA + bands). Some of these blocks are 45S rDNA sites, whereas others may correspond to the main GC-rich satellite DNA found in several Citrus species. In the present work, the distribution of the 45S rDNA and the main satellite DNA isolated from C. sinensis (CsSat) were investigated by in situ hybridization in seven species of Citrus, two species of closely related genera (Fortunella obovata and Poncirus trifoliata) and four species of the subfamily Aurantioideae, which were less related to Citrus (Atalantia mono- phylla, Murraya paniculata, Severinia buxifolia, and Triphasia trifolia). In Citrus, Fortunella, and Ponci- rus, most CMA + bands colocalized only with CsSat sites, whereas others colocalized only with rDNA sites. However, some of these species displayed a few CMA + bands that colocalized with sites of both probes and other CMA + bands that did not colocalized with any of the probes. On the other hand, in the four species less related to Citrus, no CsSat signal was found on chromosomes. On Southern blot, the CsSat probe hybridized with genomic DNA from Citrus, Fortunella, and Poncirus at high stringency only, while under the less stringent conditions, it also hybridized with distantly related species. Therefore, CsSat sequen- ces are the principal component of the heterochromatic blocks of Citrus, Poncirus, and Fortunella, whereas CsSat-like sequences seem to be widespread in the subfamily Aurantioideae. These data further suggest that the variable number of terminal CMA + bands observed on chromosomes of Citrus and related genera are probably the consequence of amplification or reduction in the number of CsSat-like sequences distributed on chromosome termini, paralleled by mutation and homogenization events, as proposed by the library hypothesis. Keywords Citrus . CMA + bands . Fortunella . Poncirus . rDNA . satellite DNA Abbreviations CMA Chromomycin A 3 DAPI 4′,6-diamidino-2-phenylindole FISH Fluorescence in situ hybridization FITC Fluorescein isothiocyanate CsSat Citrus sinensis satellite DNA PCR Polymerase chain reaction Chromosome Research (2010) 18:503–514 DOI 10.1007/s10577-010-9130-2 Responsible Editor: Pat Heslop - Harrison. A. E. Barros e Silva : A. Marques : K. G. B. dos Santos : M. Guerra (*) Laboratory of Plant Cytogenetics, Department of Botany, Federal University of Pernambuco, 50.670-420 Recife, PE, Brazil e-mail: msfguerra@hotmail.com