Use of Molecular, Morphological and Agronomic Parameters to Maximize Conservation of Genetic Diversity in Cacao.

USE OF MOLECULAR, MORPHOLOGICAL AND AGRONOMIC PARAMETERS TO MAXIMIZE CONSERVATION OF GENETIC DIVERSITY IN CACAO

A.M Arciniegas¹, E.S Johnson² and W. Phillips-Mora¹

¹Tropical Agricultural Research and Higher Education Center (CATIE), P.O Box 7170 CATIE, Turrialba, Costa Rica;  ²USDA-ARS, Plant Science Institute, Sustainable Perennial Crops Lab, 10300 Baltimore Ave, Beltsville, MD 20705

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ABSTRACT

In cacao (Theobroma cacao L.) fifteen simple sequence repeat (SSR) loci are used for routine fingerprinting. In 2000, the 15 SSR loci profile of the 712 accessions maintained in the cacao collection at CATIE showed that 21% (152 accessions) shared 40 unique genotypes. All accessions sharing a common 15-SSR-loci fingerprint or genotype were grouped to form a synonymous set and as such targeted for reduction of genetic redundancy. However, germplasm curators have difficulty taking the decision to eliminate healthy cacao trees from collections solely based on a molecular fingerprint.

Five synonymous sets comprised of 52 accessions and represented by 290 trees in the CATIE collection were characterized using a set of morphological descriptors, agronomic metrics and ten additional SSR loci. Each tree representing an accession was evaluated using 13 flower and fruit descriptors, pod and seed indexes, and the reaction to frosty pod (Moniliophthora roreri) and black pod (Phytophthora palmivora) diseases was determined by artificial inoculation methods.

The results of morphological descriptor characterization showed that 5% of the trees were off-type when compared to the morphological traits of their respective reference tree or that used for SSR fingerprinting in 2000. This was corroborated by the additional 10 SSR loci used in this study which further separated the five synonymous sets into seven and generated unique fingerprints for seven accessions. Further two new sources of resistance to frosty pod disease were discovered in the accessions ARF-5 and RIM-15 Type A. The results of this study strongly support the combined use of molecular, morphological descriptor and agronomic traits in the characterization of cacao germplasm to maximize utilization and conservation of genetic diversity in this species.

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[1] E-mails: aleal@catie.ac.cr and wphillips@catie.ac.cr

² elizabeth.johnson@ARS.USDA.GOV