Abstract
A comparative analysis of mitotic chromosomes of Theobroma cacao (cacao) and T. grandiflorum (cupuaçu) was performed aiming to identify cytological differences between the two most important species of this genus. Both species have symmetric karyotypes, with 2n = 20 metacentric chromosomes ranging in size from 2.00 to 1.19 μm (cacao) and from 2.21 to 1.15 μm (cupuaçu). The interphase nuclei of both species were of the arreticulate type, displaying up to 20 chromocentres, which were more regularly shaped in cacao than in cupuaçu. Prophase chromosomes of both species were more condensed in the proximal region, sometimes including the whole short arm. Both species exhibited only one pair of terminal heterochromatic bands, positively stained with chromomycin A 3 , which co-localized with the single 45S rDNA site. Each karyotype displayed a single 5S rDNA site in the proximal region of another chromosome pair. Heterochromatic bands were also observed on the centromeric/pericentromeric regions of all 20 chromosomes of cacao after C-banding followed by Giemsa or DAPI staining, whereas in cupuaçu they were never detected. These data suggest that the chromosomes of both species have been largely conserved and their pericentromeric chromatin is the only citologically differentiated region.
Highlights
Theobroma (Malvaceae) is a tropical genus native to South America, comprising some 22 species (Kennedy, 1995) and having T. cacao L. as its most important representative
Cacao products are widely consumed around the world but large crop plantations are restricted to Brazil, Malaysia and a few countries in West Africa
Glicenstein and Fritz (1989) reported a single satellited bivalent associated to the nucleolus in the meiosis of cacao, but this is the first report of a secondary constrictions in the mitotic chromosomes of cacao and cupuaçu
Summary
Theobroma (Malvaceae) is a tropical genus native to South America, comprising some 22 species (Kennedy, 1995) and having T. cacao L. (cacao) as its most important representative. Analyses based on conventional techniques showed that all Theobroma species investigated presented the same diploid number (2n = 20) and chromosomes with similar morphology, ranging in size between 0.5 and 2.0 mm (Carleto, 1946; Guerra, 1986; Kennedy, 1995). Four cytogenetic techniques were used: conventional staining of prophase and metaphase chromosomes, C-banding, staining with the fluorochromes chromomycin A3/4’-6-diamidino-2-phenylindole (CMA/DAPI) and fluorescent in situ hybridization (FISH).
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