Location: Tropical Crops and Germplasm ResearchTitle: Genetic diversity of naturalized cacao (Theobroma cacao L.) in Puerto Rico
Submitted to: Tree Genetics and Genomes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/27/2016
Publication Date: 8/27/2016
Citation: Cosme-Reyes, S.M., Cuevas, H.E., Zhang, D., Oleksyk, T.K., Irish, B.M. 2016. Genetic diversity of naturalized cacao (Theobroma cacao L.) in Puerto Rico. Tree Genetics and Genomes. doi: 10.1007/s11295-016-1045-4.
Interpretive Summary: Cacao is an important agricultural crop as it supports the billion dollar chocolate industry in the United States. Genetic diversity in the crop must be conserved in order to effectively select and breed new cacao varieties that are pest resistant, more productive and of high quality chocolate. In an effort to fill gaps in diversity in the existing USDA-ARS cacao collection, a survey of naturalized cacao was conducted on the island of Puerto Rico. Genetic marker tools were used to compare and contrast the trees identified in the survey to existing trees in the collection. Many of the trees sampled belong to a unique genetic background, currently underrepresented in the collection, known as Criollo. Criollo cacao is sought for the excellent quality chocolate made from its seed. Criollo trees are thought to have been brought to Puerto Rico during Spanish colonial times. Presently, Criollo cacao is mostly found in South and Central American counties which limit access to this genetic background. Many of the identified naturalized Criollo trees on the island have been incorporated in the active collection. These trees will be evaluated for many other agriculturally important traits and made available for distribution.
Technical Abstract: Identification of genetically diverse cacao with disease resistance, high productivity and desirable organoleptic traits is vitally important to the agricultural crop’s long-term sustainability. Environmental changes, pests and diseases as well as nation’s sovereign property rights have led to a decrease in accessibility and exchange of germplasm of interest. Having been introduced during colonial times, naturalized cacao in Puerto Rico could serve as an unexplored source of genetic diversity in crop selection and improvement programs. An island-wide survey was carried out to identify naturalized trees and to determine their genetic relatedness to reference cacaos. Samples were genotyped with Expressed Sequence Tag-derived SNP markers using a Fluidigm Dynamic Array system. Principal coordinate, cluster and population structure analysis using the genotype data for both local and reference samples assigned individuals into five distinct genetic backgrounds: Criollo, Trinitario, Amelonado, Upper Amazon Forastero (UAF) and Nacional. Puerto Rican cacao fit into four (Criollo, Trinitario, Amelonado and UAF) of the five genetic backgrounds, being mainly composed of Criollo ancestry individuals. Based on historical evidence, Criollo background cacao was probably brought to Puerto Rico from Venezuela and/or Central America during colonial times. Trinitario, Amelonado and UAF genetic backgrounds are most likely products of more modern introductions. Genotyping cacao in Puerto Rico provides information on the history and possible origin of the naturalized trees on the island. In addition, the assessment has allowed the targeting of material for incorporation and long-term conservation filling gaps in the existing collection and providing new germplasm to be evaluated for agronomic performance.