Karyotype variation in cultivars and spontaneous cocoa mutants (Theobroma cacao L.).

Four mutant cocoa accessions with morphological changes and a cultivar sample were karyomorphologically characterized. Slides were prepared by enzymatic digestion of the root meristem and squashed in 45% acetic acid, followed by 2% Giemsa staining. The chromosome number of 2n = 20 was seen in all accessions. The karyotype formula for Cacau Comum and Cacau Rui was 2n = 20m. Submetacentric chromosomes were observed in Cacau Pucala and Cacau Jaca, both with 2n = 18m + 2sm, but the karyotype formula for Cacau Sem Vidro was 2n = 16m + 4sm. Satellites were located on the long arm of the 1st and 2nd chromosome pairs of Cacau Comum, whereas Cacau Pucala had satellites on the 6th chromosome pair. Greater karyotypic variation in Cacau Sem Vidro was found, whose 1st and 2nd chromosome pairs had satellites on the long arm and 6th and 10th pairs had satellites on the short arm. Analysis revealed a lower average chromosome length in Cacau Comum (1.53 ± 0.026 µm) and a higher length in Cacau Sem Vidro (2.26 ± 0.038 µm). ANOVA revealed significant difference (P < 0.01) for the average chromosome length and the length of chromosome pairs within and between accessions. The average chromosome lengths of mutants of Cacau Rui and Cacau Jaca were not statistically different by the Tukey test at 5% probability. The karyotypic diversity observed in this study is not necessarily associated with the changing character of the accessions analyzed, but may reflect the genetic variation observed in Theobroma cacao.

Single nucleotide polymorphisms from Theobroma cacao expressed sequence tags associated with witches' broom disease in cacao.

In order to increase the efficiency of cacao tree resistance to witches' broom disease, which is caused by Moniliophthora perniciosa (Tricholomataceae), we looked for molecular markers that could help in the selection of resistant cacao genotypes. Among the different markers useful for developing marker-assisted selection, single nucleotide polymorphisms (SNPs) constitute the most common type of sequence difference between alleles and can be easily detected by in silico analysis from expressed sequence tag libraries. We report the first detection and analysis of SNPs from cacao-M. perniciosa interaction expressed sequence tags, using bioinformatics. Selection based on analysis of these SNPs should be useful for developing cacao varieties resistant to this devastating disease.