Submitted to: Genetic Resources and Crop Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 28, 2006
Publication Date: June 1, 2007
Citation: Johnson, E.S., Mora, A., Schnell Ii, R.J. 2007. Field guide efficacy in the identification of reallocated clonally propagated accessions of cacao (theobroma cacao l.). Genetic Resources and Crop Evolution. 54:1301-1313.
Interpretive Summary: Cacao is the raw material for the production of chocolate and the chocolate industry is one of the main consumers of US grown dairy, nuts, oils and sugar products. The misidentification of cacao germplasm is reported to be as high as 40% especially in frequently exchanged materials. A Field Guide was made for the identification of a specific group of tree clones from Trinidad. This guide contains agronomic traits, molecular fingerprint and digital images of the mature fruit and was used to correct misidentified trees. This guide will be useful to germplasm curators, cacao researchers, plant breeders and cacao farmers.
Misidentification of germplasm presents a major constraint to cacao cultivar development. Misidentification of parents has impeded resolution of the genetic basis for agronomic traits as mixtures of genotypes produce inconsistent results and conflicting genetic estimates resulting in slow progress in cacao breeding programs. The Field Guide Concept, a combination of current technologies such as digital imaging and molecular fingerprinting with statistical analyses and the traditional morphological descriptors, was used to verify the genotypes of cacao clones introduced nearly 50 years ago to the Republic of Costa Rica from the Republic of Trinidad and Tobago. A total of 69 trees representing a possible 15ICS clone genotypes were studied. All trees identified in the field in Costa Rica, as 'Off-type', or not the reference ICS clone in the Field Guide, were later corroborated by SSR fingerprint analyses. The error rate was 3.5% for misidentification in the field in Costa Rica based solely on pod digital image and morphological descriptors. This was reduced to 0% once SSR fingerprint analyses were applied. A 46% cost reduction in cacao SSR fingerprint analyses could be realized by separating SSR primers into sets and using statistical analyses and genetic diversity measures in combination with pod digital images and complementary morphological descriptors. The use of the Field Guide Concept in the designation of Reference genotypes and contribution to the resolution of the misidentification of cacao germplasm is discussed.