Abstract
To increase the genetic diversity sources of resistance to witches' broom disease, 59 cacao trees of commercial plantations of the State of Bahia, Brazil, were selected and cloned. The diversity of these clones was evaluated with RAPD markers. Their pedigree was investigated by comparison to traditional resistance sources used as parents for most hybrid mixtures cultivated in the State. One hundred and six RAPD bands were obtained, 85.8% of which were polymorphic. Genetic distances among the clones varied from 0.04 to 0.41. The MDS plot showed large genetic variability among clones. Analyses based on rare markers inherent to Scavina-6 and Scavina-12 clones, which represent important resistance sources, showed a close relationship of these sources to most accessions. However, some accessions did not present any of the rare Scavina markers, suggesting potentially different alleles, which could contribute to broaden the gene pool of breeding programs for resistance to witches' broom.
Highlights
Witches’ broom, a cacao disease caused by Crinipellis perniciosa (Stahel) Singer, has caused serious economic, social, and ecological losses in Bahia, Brazil, since its arrival in 1989 (Pereira et al 1989)
This study aims at an evaluation of the genetic diversity among VB selections by RAPD molecular markers and of the origin of VB selections based on their relationship with traditional resistance sources
The resistance and genetic diversity among these selected clones can be explained by the history of the breeding program carried out at the CEPEC
Summary
Witches’ broom, a cacao disease caused by Crinipellis perniciosa (Stahel) Singer, has caused serious economic, social, and ecological losses in Bahia, Brazil, since its arrival in 1989 (Pereira et al 1989). The identification of genotypes with high yield and resistance to witches’ broom is the first step in the breeding program. Two sibling plants, called Scavina-6 and Scavina-12 (Baker and Holliday 1957) were originally selected as immune to witches’ broom. These sources of resistance, together with others like IMC, Cruzeiro do Sul, and RB have been widely used in several breeding programs including the one carried out by the CEPEC - Cacao Research Center. Many cacao trees used on farms come from crosses involving these sources, recommended for planting since the 1960s
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