Characterization of Naturalized Cacao Populations in Puerto Rico

Native to the headwaters of the Amazon River, cacao (Theobroma cacao L.) is an important agricultural tree crop produced in tropical regions around the world.  Its raw product, the seed or ‘beans’, is the source for the multi-billion dollar chocolate industry.  The USDA-ARS Tropical Agriculture Research Station in Mayaguez, PR maintains a diverse, replicated field cacao collection consisting of close to 200 clonally propagated accessions.  Although no large scale commercial production exists on the island today, Puerto Rico has a long history of cacao introduction and production.  Based on anecdotal information, on historical publications and data presented here, ‘old’ (>100 years) naturalized cacao trees can be found throughout the island.  In addition, and based on preliminary evidence, many of the cacao trees appeared to belong to the ‘Criollo’ genetic background with unique morphological pod features and characteristic white colored beans.  To confirm preliminary findings and in order to asses genetic relationships between naturalized trees and existing cacao in the TARS collection, a collection leaf samples from close to 160 trees from diverse regions on the island was carried out.  DNAs from collected leaves were screened with 48 EST-derived SNP markers which had been previously assessed for their allelic range and informativeness in assessing genetic diversity in cacao germplasm.  Analysis of the SNP data supported initial findings and showed that a large number of trees sampled indeed belonged to the ‘Criollo’ genetic background.  In addition, other unique genetic backgrounds including trees belonging to Upper Amazon populations, Amelonado, Trinitario and hybrids among these germplasm groups were identified.  The results revealed a high level of allelic and genotype diversity in the cacao samples collected from Puerto Rico.  Furthermore, during sample collecting trips several trees with important agronomic traits (e.g., large pods with many large seed) were located.  A subset of Criollo-background trees, as well as those with agronomic potential, are being collected and propagated to fill gaps in genetic diversity coverage in the existing TARS collection and for further evaluation.