Molecular Characterization of Cacao (Theobroma cacao) Germplasm from Jamaica Using Single Nucleotide Polymorphism (SNP) Markers

Abstract

Cacao is an economically important commodity in Jamaica. Knowledge of the genetic diversity of Jamaican cacao germplasm is essential for their conservation and management. In spite of cacao’s economic importance in Jamaica, the crop is under studied, therefore limiting sound decisions toward improving productivity. Assessment of germplasm and on-farm genetic diversity is required to assist selecting superior genotypes to propagate and distribute across the island, as well as to use them as parental clones in breeding programs. Using 94 single nucleotide polymorphism (SNP) markers, 140 Jamaican cacao samples from two germplasm collections and a farmer’s estate along with 150 reference samples were analyzed. The principal coordinate analysis demonstrated that the majority of the Jamaican cacao selections were hybrids derived from five original germplasm groups, including Criollo, Amelonado and three Upper Amazon Forastero groups. Among the Upper Amazon groups, the Bayesian clustering analysis revealed that the Parinari (PA) ancestral lineage contributed the most (29.9%) to the Jamaican cacao germplasm. The germplasm collections showed greater diversity in terms of ancestral contributions compared to the farmer’s estate. However, the genetic differentiation between the three collecting sites was small (Fst = 0.036), indicating that samples collected from the three sites were derived from a common pool of germplasm. The current study supports the historical records and clarified the ancestry of Jamaican cacao. Although the majority of the cacao genetic groups were observed in the Jamaican cacao collections, several diversity gaps were found in both germplasm collections and in the farmer’s estate, especially germplasm with disease resistance to cacao frosty pod rot that was recently found in Jamaica.