Karyotype diversity and the origin of grapefruit

Abstract

Grapefruit is a group of citrus of recent origin, probably resulting from a cross between pummelo and sweet-orange. Aiming to investigate this putative origin and the genetic variability among grapefruit cultivars, the karyotype of six grapefruits, two pummelos, and one tangelo cultivar (grapefruit x tangerine) were analyzed using sequential CMA/DAPI double staining and FISH with rDNA probes. The karyotypes of grapefruit 'Duncan' and 'Foster' differ from those of 'Flame', 'Henderson', 'Marsh' and 'Rio Red'. The former have two chromosomes with a single CMA(+) band in both terminal regions (C type chromosome) and six chromosomes with only one CMA(+) terminal band (D type), whereas the latter have three C and five D type chromosomes. All accessions investigated exhibited two chromosomes with 5S rDNA but a variable number of 45S rDNA. The two former grapefruits displayed four 45S rDNA sites, whereas the remaining grapefruit cultivars had five. The two pummelos showed identical karyotypes, homozygous for CMA(+) bands and their four rDNA sites. From each pummelo chromosome pair one chromosome seems to be present in grapefruit karyotypes. The different grapefruit karyotypes might result from independent crosses between pummelos of different karyotypic constitution and sweet-oranges. The chromosome markers found in the tangelo 'Orlando' and the position of their two 45S rDNA confirm the grapefruit 'Duncan' and the tangerine 'Dancy' as their parents.

Identification of Parental Chromosomes in Sexual Intergeneric Hybrid Progenies between Citrus Cultivar ‘Nanpu’ Tangor and Citropsis schweinfurthii in the Subfamily Aurantioideae

“…5), some centromeric regions of 'Nanpu' tangor showed small green signals by C. schweinfurthii genomic probe. Matsuyama et al (1996Matsuyama et al ( , 1999 and Moraes et al (2007) reported rDNA sites and a large number of simple sequence repeats in the telomeric and centromeric regions of Citrus. Moraes et al (2007) also revealed that type A chromosomes of some grapefruits (C. paradise Macfad.)…”

Intraspecific polymorphism of ribosomal DNA loci number and morphology in Brachypodium pinnatum and Brachypodium sylvaticum

“…A complementary approach that can be used for karyotype characterization is double fluorescent banding with DAPI and CMA fluorochromes, which discriminates between ATand GC-rich DNA regions. FISH experiments combined with CMA/DAPI staining facilitated effective identification of homologous chromosomes in uniform karyotypes of Citrus paradisi [11], Lilium [12] and Pinus [13]. rDNA sequences are widely used as chromosomal landmarks in cytogenetic studies.…”

Physical Mapping of the 5S Ribosomal RNA Gene in Citreae of Aurantioideae Species using Fluorescence in situ Hybridization

“…Detection of ribosomal RNA gene (rDNA) sites using FISH offers essential information on phylogenic relationships and on the evolution of given species (Fukui et al, 1994). In citrus, the number and location of rDNA sites in various accessions have been detected (Brasileiro-Vidal et al, 2007;Carvalho et al, 2005;Matsuyama et al, 1996;Miranda et al, 1997a;Morares et al, 2007aMorares et al, , 2007bOllitrault et al, 2000;Pedrosa et al, 2000;Roose et al, 1998). However, these results were limited to the genus Citrus to Poncirus and Fortunella, two very closely related genera.…”

“…Several studies have demonstrated the relationship between chromosomal regions containing rDNA sites and heterochromatic regions stained by CMA (Brasileiro-Vidal et al, 2007;Carvalho et al, 2005;Matsuyama et al, 1996;Miranda et al, 1997a;Morares et al, 2007aMorares et al, , 2007bPedrosa et al, 2000). These combined analyses have been more informative than any single analysis of just rDNA sites or CMA staining alone.…”