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United States Department of Agriculture

Agricultural Research Service

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Research Project: Genetics of Self-Incompatibility in Theobroma Cacao

Location: Subtropical Horticulture Research

Project Number: 6038-21000-023-10
Project Type: Specific Cooperative Agreement

Start Date: Aug 19, 2013
End Date: Sep 18, 2014

Objective:
The primary goals of this project are to identify the genes responsible for the regulation of self-incompatibility in cacao and to develop SNP markers that could be used for selecting self-compatible cultivars.

Approach:
Cacao production is plagued by very serious losses globally from insects and pests. However, yield reduction in new cultivars selected for insect and disease resistance could be due to self-incompatibility (SI). Genes associated with the process of SI in cacao have not been identified yet; the discovery of molecular markers associated with alleles that are involved in SI will be useful for selecting self-compatible cultivars with higher yields. To attain these goals, one hundred and fifty cacao clones are being sequenced at Stanford University, and of these, 117 clones are currently planted at the International Cacao Genebank in Trinidad (ICG,T). In addition, these clones belong to the ten genetic groups and their self-incompatibility status needs to be studied and correlated with genomic data so that candidate genes or markers associated with self-incompatibility could be ascertained and validated. Furthermore, this research project also presents an opportunity to investigate the relationship between self-incompatibility and yield components in a genetically variable cacao collection. Therefore, this study aims at better understanding the genetics of self-incompatibility of selected cacao genotypes, as well as characterizing self-compatibility and yield evaluation of these clones. Uniform pollination data are crucial for obtaining precision in the results of marker association studies. If we do not have uniform phenotypic pollination data, to use together with the sequence data from two cacao genomes, our marker association project results will lack the necessary precision to accomplish the primary goal of the cacao breeding program which is the development of high yielding cacao cultivars utilizing the new molecular genetic tools to increase the efficiency of the selection process. Phenotypic self-incompatibility data will be collected from over 300 trees that will be subjected to the necessary agronomic practices to induce flowering and fruit set six weeks prior to the initiation of the study. Two trees will be selected per clone, with 25 pollinations being done per tree. Unopened flower buds will be isolated/covered the day before pollination. The pollinated flowers will then be observed for flower retention over time, aiming to identify the level of self-compatibility/self-incompatibility. The number of flowers retained at 3, 6, 9, 12, 15, 18, and 21 days after pollination will be recorded. The exercise would therefore include the pollination of approximately 8,000 flowers/season and continual evaluation of flowers after pollination. The accessions will also be studied during the two crop seasons for a number of yield and yield components such as: tree girth at 1 m, number of flower cushions within 1m, number of productive cushions, number of pods per tree, pod size, pod wall thickness, pod cavity size, bean number, and average bean mass.

Last Modified: 10/31/2014
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