Location: Subtropical Horticulture ResearchTitle: Mapping of quantitative trait loci for butter content and hardness in cocoa beans (Theobroma cacao L.)) Author
|De Souza Filho, G.|
|De Barros, E.|
|Schnell Ii, Raymond|
Submitted to: Plant Molecular Biology Reporter
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2008
Publication Date: 12/2/2008
Citation: Araujo, I.S., De Souza Filho, G.A., Faleiro, F.G., Queiroz, V.T., Moreira, M.A., De Barros, E.G., Guimaraes, C.T., Machado, R.C., Pires, J.L., Lopes, U.V., Schnell Ii, R.J. 2008. Mapping of quantitative trait loci for butter content and hardness in cocoa beans (Theobroma cacao L.). Plant Molecular Biology Reporter. DOI 10.1007/s11105-008-0069-9 Interpretive Summary: Butter produced from cocoa beans has unique chemical characteristics. It is an important raw material for the chocolate, pharmaceutical, and cosmetic industries. Cocoa butter is the fatty component of the cocoa bean and constitutes about 45% of the whole bean. Cocoa butter quality is a consequence of the proportion of unsaturated fatty acids and this is associated with its melting point. One goal of cocoa breeding programs is to increase the butter fat content of the beans and to mainipulate the proportion of unsaturated fatty acids to better control the melting point of the butter. The majority of economic traits in crop plants are controlled by many genes and are quantitatively inherited. Using molecular genetic linkage maps, regions of the chromosome that control these traits can be identified and these are called Quantitative trait Loci (QTL). A number of linkage maps have been produced for cocoa including a map made from selfing a single offspring from a cross of ICS1 x SCA6. Evaluating 82 progeny in this population for fat content and proportion of unsaturated fatty acids (butter hardness) three QTL for these characteristics would be identified. One QTL was discovered on linkage group (LG) 9 for butter fat content and two QTL were discovered for butter hardness on LG7 and LG9. These QTL will be useful in cacao breeding for increasing the butter fat content and in manipulating the butter hardness.
Technical Abstract: Cocoa butter is an important raw material for the chocolate, pharmaceutical, and cosmetic industries. The butter content and quality in cocoa beans are genetically controlled characteristics, and affect its commercial values and industrial applicability. In the present work, an F2 population derived from the cross between the ICS-1 and Scavina-6 cocoa clones was used for molecular mapping. A linkage map was constructed based on amplified fragment length polymorphism, random amplified polymorphic DNA, and simple sequence repeat markers, resulting in a total of 271 markers, distributed in 14 linkage groups (LGs). Phenotyping of butter content was performed after ether exteraction and butter hardness was determined by sweeping differential calorimetry. One quantitative trait locus (QTL) was mapped at linkage group 9 (LG9) and two QTLs for butter hardness were identified at linkage groups 9 and 7 (LG9 and LG7). The two QTLs mapped at the LG9 explained 51.0% and 28.8% of the phenotypic variation for butter content and hardness, respectively. These QTLs were concentrated at the same map region, suggesting a close genetic linkage or pleiotropic effect. The QTLs identified may be useful in further marker-assisted selection breeding programs aimed at cocoa butter quality improvement.