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)

Tuesday, December 13, 2016

The genome sequence of the most widely cultivated cacao type

The cacao tree (Theobroma cacao L.) is a neotropical species native to Amazonian lowland rainforests and is now grown in more than 50 countries throughout the humid tropics. T. cacao is a member of the Malvaceae family, and its beans (seeds), harvested from pods (fruits), are used for the chocolate, confectionery, and cosmetic industries. Cacao production is essential to the livelihoods of 40 to 50 million people worldwide, including the smallholder farmers who cultivate the crop, who number more than 5 million. Cacao-growing regions are also largely centered in important biodiversity hotspots and in proximity to 13 of the world's most biologically diverse regions.

Recent molecular analyses have permitted cacao germplasm classification into 10 major clusters or groups: Amelonado, Contamana, Criollo, Curaray, Guiana, Iquitos, Maraňón, Nanay, Nacional, and Purús. Compared with traditional cacao classification schemes, this new system more accurately reflects the genetic diversity available to breeders.

Because of its high yield and disease resistance, the most ubiquitous clone in large cacao plantations in Latin America is CCN 51. It is also the optimal parent in many breeding programs, owing to its favorable combining ability for yield. Unfortunately, it has a rather undesirable flavor profile because of its high acidity and astringency, and also because it lacks desirable floral aromas.

CCN 51 tree

On the other hand, the genome sequence of a Criollo genotype was recently reported. Although this cacao type is genetically distinct, it is a poor representative of the cacao types cultivated worldwide. In an effort to enhance the accuracy and speed of traditional cacao breeding, is sequenced the genome of Matina, a self-compatible and highly homozygous genotype that is more representative of the cacao cultivated worldwide. In conclusion, the theobroma cacao is divided in many group which they will have many characteristics, from the color, flavor, and size of the fruit; all this will depend on the type of plant, genotype that has or type of soil on which it was cultivated. However, cacao will be one of the organic products most bought in the world, for its different uses.

Saturday, December 3, 2016

Genetic Diversity of Theobroma cacaon

Cocoa or cacao (Theobroma cacao) is native to the South American rainforest, but it is thought to have been domesticated in southern Mexico and the northern Central American region. The hypothesized centre of genetic diversity is located in the upper Amazonian region. It is also well known that the Peruvian Amazon harbours a large number of diverse cocoa populations. 

During the past several decades, several expeditions have been made and a substantial amount of germplasm, from both wild populations and cultivated accessions, has been collected from this region. Today, a fraction of these accessions are maintained as ex-situ collections in various countries.

The first organized cocoa germplasm collecting expedition in the Peruvian Amazon started in 1937–1938. And the collecting sites included Rio Nanay, Rio Morona, Rio Marañón and their tributaries. This led to the establishment of the germplasm collection in Iquitos, Peru known as the ‘Pound Collection’, named after the collector F. J. Pound. Many commercial clones, now called ‘International clones’, have their origin in this collection.

Organic cacao native in Peru

Pound's expeditions were aimed at searching for genotypes resistant to witches' broom disease, caused by the fungus Crinipellis perniciosa, and this germplasm has therefore been widely used in breeding programmes as a source of resistance to witches' broom disease.

The hypothesis that the Peruvian Amazon hosts a high level of genetic diversity, and the diversity has a spatial structure in the native habitat of cocoa. The introduction of breeding progenies in the rehabilitation programme is changing the cocoa germplasm spectrum in this region. Identifying the patterns of distribution of intraspecific genetic variation can provide data concerning the temporal and special dynamics of this economically important crop, which has not been previously studied in depth at the population level. The spatial structure of cocoa diversity recorded here highlights the need for additional collecting and conservation measures for natural and semi-natural cocoa populations in the Peruvian Amazon. Read more Genetic Diversity and Structure of Managed and Semi-natural Populations of Cocoa (Theobroma cacao) in the Huallaga and Ucayali Valleys of Peru