PHYSICAL MAPPING OF 5S AND 45S RDNAS BY FLUORESCENT IN SITU HYBRIDIZATION IN MANGO (MANGIFERA INDICA L.)

Abstract

Mango (Mangifera indica L.) is thought to be diploid despite the many numbers of chromosomes (2n=2x=40). Although the allopolyploid nature of M. indica is reported by Mukherjee (1950), no chromosome studies are available to elucidate genome composition of mango until now. We have applied fluorescent in situ hybridization (FISH) technique using 5S and 45S ribosomal DNAs (rDNAs) as probes on the somatic metaphase chromosome of mango for the first step to elucidate genome composition of mango. The digoxigenin (DIG)-labeled 5S or 45S probe was hybridized onto the chromosomes separately, and both of them were visualized by incubation with anti-DIG-fluorescein isothiocyanate (FITC). Strong signals of 5S rDNA were observed on two chromosomes, and these two seemed to be homologous chromosomes due to their size and identical chromosomal location of 5S rDNA loci. On the other hand, six chromosomes were demonstrated to carry 45S rDNA loci. Among these six chromosomes, two chromosomes seemed to be homologous from their size and the location of rDNA loci in addition to signal intensity. But, another four chromosomes could not be identified whether or not these four form two pairs of chromosomes, since no clear images of these chromosomes were observed. In addition, multicolor FISH using 5S and 45S rDNA probes differently labeled with DIG and biotin, revealed separate localization of the two rDNA genes on different chromosomes of mango. We could distinguish eight chromosomes among forty chromosomes of mango in this study, but no evidence was obtained for a possibility of heterozygotic karyotype in mango not like in sweet orange.