Field Guide efficacy in the identification of reallocated clonally propagated accessions of cacao (Theobroma cacao L.)

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Misidentification is a major constraint to the conservation and utilization of cacao genetic resources. One solution for rapid and accurate identification is to produce a Field Guide for each recognized cacao early generation original population. Each Field Guide in this series of compendia would be comprised of pod digital images with complementary morphological descriptors, molecular fingerprint data with kinship analyses and agronomic data useful to cacao cultivar development. This Field Guide Concept culminated in the production of the first compendium entitled, Field Guide to the ICS Clones of Trinidad. In the current study, this Field Guide was used to verify the identity of 69 trees representing a possible 15 ICS clone genotypes introduced nearly 50 years ago to Costa Rica. Phase one of this study involved identity verification of the trees in Costa Rica using the pod digital image and morphological descriptor data in the Field Guide to the ICS Clones of Trinidad. The error rate was 3.5% for misidentification in the field in Costa Rica. In the second and final phase, SSR fingerprint data were generated for each of the 69 trees and analyzed for verification to the original ICS genotype in the Field Guide. Misidentification was reduced to 0% with the addition of SSR fingerprint analyses. The 69 trees in this study clustered into two groups or sub-populations clearly differentiated by Discriminant analyses with six SSR primers. A 46% cost reduction in SSR fingerprinting of the ICS clones was realized by combining use of the pod image and morphological descriptor data in the Field Guide with genetic diversity estimates derived from these six primers. A Field Guide approach to the identification of reference genotypes for cacao germplasm is discussed.

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