Cytogenetics of Manihot esculenta Crantz (cassava) and eight related species

Abstract

Thirty-nine cultivars of cassava and eight related wild species of Manihot were analyzed in this work for number, morphology and size of chromosomes, prophase condensation pattern and the structure of the interphase nucleus. In four accessions, the chromosome size was measured and in some others, the number of secondary constrictions, meiotic behavior, C-band pattern, CMA/DAPI bands, nucleoli number and the location of 5S and 18S-5.8S-28S rDNA sites were also observed. All investigated accessions showed a similar karyotype with 2n = 36, small metacentric to submetacentric chromosomes. Two pairs of terminal secondary constrictions were observed in the chromosome complement of each accession except Manihot sp. 1, which presented two proximal secondary constrictions. The prophase chromosome condensation pattern was proximal and the interphase nuclei structure was areticulate to semi-reticulate. The meiosis, investigated in seven cultivars and four wild species, was regular, displaying 18 bivalents. C-banding revealed heterochromatin in 9 or 10 chromosomes. The analysis with fluorochromes frequently showed four chromosome pairs with a single CMA+ terminal or subterminal band and a few other chromosomes with DAPI+ unstable bands. Six 45S rDNA sites were revealed by FISH, which seemed to colocalize with six CMA+ bands. Only one chromosome pair presented a 5S rDNA site. The maximum nucleoli number observed per nucleus was also six. These data suggest that all Manihot species present a very similar chromosome complement.

Heterochromatin diversity and its co-localization with 5S and 45S rDNA sites in chromosomes of four Maxillaria species (Orchidaceae)

“…The unusual feature of the Maxillaria CMA + bands was that all of them coincided with 5S or 45S rDNA. It is known that 45S rDNA sites commonly stain positively after Giemsa C-banding or after direct staining with CMA, while 5S rDNA sites are usually visualized only by in situ hybridization Vanzela et al, 2002;Carvalho and Guerra, 2002;Carvalho et al, 2005). This relationship between 5S rDNA sites and CMA + bands was most evident in M. notylioglossa, in which the largest and brightest CMA + bands co-localized with 5S rDNA sites instead of 45S rDNA sites.…”

Chromosome banding and essential oils composition of Brazilian accessions of Lippia alba (Verbenaceae)

“…A previous report showed secondary constrictions only in two pairs of chromosomes, but in the same study, the authors observed six sites for the 45S rDNA probes (Brandão et al 2007). The secondary constrictions are formed in active sites with 45S rDNA (NORs) and sites with restricted NOR activation can, but don't have to, form secondary constrictions, thus hindering the real determination of their number and position through conventional techniques (Carvalho & Guerra 2002;Panzara et al 1996;Marcon et al 2005). Four marks with AgNOR banding (Fig.…”

Sequencing wild and cultivated cassava and related species reveals extensive interspecific hybridization and genetic diversity

“…The genus Manihot belongs to the Euphorbiaceae, an angiosperm family that includes several other species with commercial importance including castor bean (Ricinus communis, 2n = 20), physic nut (Jatropha curcas, 2n = 22), and rubber tree (Hevea brasiliensis, 2n = 36), which we estimate diverged from cassava ~35 million years ago (mya) (Supplementary Note 3). The shared chromosome number of cassava and rubber tree, roughly double the chromosome count of physic nut and castor bean, suggests that the paleotetraploidy present in cassava might be shared with Hevea 28,29 . Our analysis confirms this hypothesis, as both species have thousands of homologous gene pairs that diverged approximately 10 million years before the cassava-Hevea speciation ( Fig.…”