Fluorescent in situ hybridization of 18S and 5S rDNA in papaya (Carica papaya l.) and wild relatives
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Papaya (Carica papaya L.) is cultivated widely as a fruit crop in the tropics. Related species as Vasconcellea cundinamarcensis and V. goudotiana are prospective sources of desirable genes. The requisite germplasm introgression will be facilitated by a better understanding of their cytogenetic relationships to papaya, but the chromosomes of Caricaceae species are very small and similar so conventional karyotyping is difficult and of limited utility. Here, we report on fluorescence in situ hybridization (FISH) of rDNA probes to create several karyological markers that enable chromosomes to be distinguished and to produce information about the genetic relationships among Caricaceae species. Based on the number and the position of rDNA sites, V. cundinamarcensis and V. goudotiana were the closest species while C. papaya was isolated from them. Both Vasconcellea species showed only one pair of 5S site whereas three pairs were found in C. papaya. On the other hand, one 18S site was observed in papaya, whereas four and five 18S sites were found in V. goudotiana and V. cundinamarcensis, respectively. It is possible that the unpaired signal of 18S probe in V. cundinamarcensis is located in a sexual chromosome, however, further studies are required to confirm this hypothesis of sex-chromosome linkage. 2008 Taylor & Francis Group, LLC.