Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2004
Publication Date: N/A
Interpretive Summary: There are severe diseases that are attacking trees from which chocolate is derived in most parts of the tropical environments where they are grown. Each of these countries have a collection of trees in a living collection, but many of the trees have been mislabelled, or given duplicate names and there is great confusion about the genetic makeup of these valuable resources. Because US dairy, nut, and confectionary industries are vitally linked to the economic production of chocolate in these tropical enviroments, we have developed a system to correctly identify the chocolate trees in the producing countries through a molecular DNA fingerprinting program. This report describes the molecular tools to do this project so that they can be accepted as a standard procedure by all cacao producers on a worldwide basis. It provides a common test that will be adopted as an international standard to identify cacao in an effort to locate plants that might be resistant to the diseases that are effecting this important tree crop.
Technical Abstract: A collaborative international program was initiated to identify and describe the genetic diversity of living germplasm collections of Theobroma cacao genotypes that are maintained in several international collections scattered throughout tropical cacao growing countries of the world. Simple Sequence Repeat (SSR) DNA analysis was identified as the most appropriate molecular tool for DNA fingerprinting of these collections during an international forum representing academic, government and industry scientists in the cacao community. Twenty-five SSR primers, which had been previously described, were evaluated as potential candidates to define an efficient, standardized, molecular fingerprinting protocol for Theobroma cacao accessions. These primers have been evaluated for reliability, widespread distribution across the cacao genome, degree of heterogeneity of alleles produced by the SSR primers in cacao and their ability to discriminate between cacao accessions. Approximately 400 cacao accessions were used to evaluate the utility of these SSR primers as international molecular standards. DNA fragments were selectively amplified by PCR using the SSR primers, labeled with fluorescent dyes, and separated by capillary electrophoresis. Based on this study, the 15 SSR primers that had the highest reproducibility and consistency within a common genotype, while allowing the differentiation of separate divergent genotypes, were selected as international molecular standards for DNA fingerprinting of T. cacao.