A r t i c l e s Theobroma cacao L. is a diploid tree fruit species (2n = 2x = 20 (ref. 1)) endemic to the South American rainforests. Cocoa was domesticated approximately 3,000 years ago 2 in Central America 3. The Criollo cocoa variety, having a nearly unique and homozygous genotype, was among the first to be cultivated 4. Criollo is now one of the two cocoa varieties providing fine flavor chocolate. However, due to its poor agronomic performance and disease susceptibility, more vigorous hybrids created with foreign (Forastero) genotypes have been introduced. These hybrids, named Trinitario, are now widely cultivated 5. Here we report the sequence of a Belizean Criollo plant 6. Consumers have shown an increased interest for high-quality chocolate, and for dark chocolate, containing a higher percentage of cocoa 7. Fine-cocoa production is nevertheless estimated to be less than 5% of the world cocoa production due to the low productivity and disease susceptibility of the traditional fine-flavor cocoa varieties. Therefore, breeding of improved Criollo varieties is important for sustainable production of fine-flavor cocoa. 3.7 million tons of cocoa are produced annually (see URLs). However, fungal, oomycete and viral diseases, as well as insect pests, are responsible for an estimated 30% of harvest losses (see URLs). Like many other tropical crops, knowledge of T. cacao genetics and genomics is limited. To accelerate progress in cocoa breeding and the understanding of its biochemistry, we sequenced and analyzed the genome
A linkage map of cacao based on codominant markers has been constructed by integrating 201 new simple sequence repeats (SSR) developed in this study with a number of isoenzymes, restriction fragment length polymorphisms (RFLP), microsatellite markers and resistance and defence gene analogs (Rgenes-RFLP) previously mapped in cacao. A genomic library enriched for (GA)(n) and (CA)(n) was constructed, and 201 new microsatellite loci were mapped on 135 individuals from the same mapping population used to establish the first reference maps. This progeny resulted from a cross between two heterozygous cacao clones: an Upper-Amazon Forastero (UPA 402) and a Trinitario (UF 676). The new map contains 465 markers (268 SSRs, 176 RFLPs, five isoenzymes and 16 Rgenes-RFLP) arranged in ten linkage groups corresponding to the haploid chromosome number of cacao. Its length is 782.8 cM, with an average interval distance between markers of 1.7 cM. The new microsatellite markers were distributed throughout all linkage groups of the map, but their distribution was not random. The length of the map established with only SSRs was 769.6 cM, representing 94.8% of the total map. The current level of genome coverage is approximately one microsatellite every 3 cM. This new reference map provides a set of useful markers that is transferable across different mapping populations and will allow the identification and comparison of the most important regions involved in the variation of the traits of interest and the development of marker-assisted selection strategies.
Background: Theobroma cacao L., is a tree originated from the tropical rainforest of South America. It is one of the major cash crops for many tropical countries. T. cacao is mainly produced on smallholdings, providing resources for 14 million farmers. Disease resistance and T. cacao quality improvement are two important challenges for all actors of cocoa and chocolate production. T. cacao is seriously affected by pests and fungal diseases, responsible for more than 40% yield losses and quality improvement, nutritional and organoleptic, is also important for consumers. An international collaboration was formed to develop an EST genomic resource database for cacao.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.