Tuesday, December 27, 2016

Differentiation of the amazonian chocolate tree (theobroma cacao L)

Cacao is cultivated in the humid tropics and is a major source of currency for small farmers as well as the main cash crop of several West African countries. Its fruits (pods) contain the seeds (beans) that are later processed by the multi-billion-dollar chocolate industry. Average yields are about 300 kg per hectare but 3,000 kg/ha are often reported from field trials. Genetic improvement of cacao through breeding has focused on increasing yield and disease resistance. To increase yield, breeders have capitalized on heterosis that occurs in crosses between trees from different genetic groups.
Cacao native tree

Traditionally, two main genetic groups, “Criollo” and “Forastero”, have been defined within cacao based on morphological traits and geographical origins. A third group, “Trinitario”, has been recognized and consists of “Criollo”דForastero” hybrids. In parallel, botanists described two subspecies: cacao and sphaeorocarpum, corresponding to “Criollo” and “Forastero”, which, according to some authors, evolved in Central and South America, respectively. For other authors, “Criollo” and “Trinitario” should be considered as traditional cultivars rather than genetic groups. Two other traditional cultivars have been described: Nacional and Amelonado. Nonetheless, a sound classification of Theobroma cacao L. populations, based on genetic data, is lacking for the breeding and management of its genetic resources.

Diferent types of cacao in Perú

The Amazon basin contains some of the most biologically diverse tree communities ever encountered; tree species richness may attain three hundred species in one-hectare plots. In cacao, flowers are hermaphrodites. However, it is an outcrossing species due to the action of self-incompatibility mechanisms in wild individuals, while the cultivated ones are generally self-compatible. Other Amazonian species of importance such as Theobroma grandiflorum show similar mating systems.

At the end, we can find a new classification of cacao germplasm into 10 major clusters, or groups: Marañon, Curaray, Criollo, Iquitos, Nanay, Contamana, Amelonado, Purús, Nacional and Guiana. This new classification reflects more accurately the genetic diversity now available for breeders, rather than the traditional classification as Criollo, Forastero or Trinitario. We encourage the establishment of new mating schemes in the search of heterotic combinations based on the high degree of population differentiation reported. Furthermore, we propose that germplasm curators and geneticists should use this new classification in their endeavor to conserve, manage and exploit the cacao genetic resources. Read more in Geographic and Genetic Population Differentiation of the Amazonian Chocolate Tree (Theobroma cacao L)

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