Location: Subtropical Horticulture ResearchTitle: Recurrent selection of cocoa populations in Cote d'Ivoire: comparative genetic diversity between the first and second cycles Author
|Schnell Ii, Raymond|
Submitted to: Plant Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/28/2008
Publication Date: 7/1/2009
Citation: Pokou, N.D., N'Goran, J.A., Lachenaud, P., Eskes, A.B., Motamayor, J.C., Schnell Ii, R.J., Kolesnikova-Allen, M., Clement, D., Sangare, A. 2009. Recurrent selection of cocoa populations in Cote d'Ivoire: comparative genetic diversity between the first and second cycles. Plant Breeding. 128: 514-520. Interpretive Summary: The cocoa tree (Theobroma cacao L.) is native to the Amazonian forests. The trees are sub-divided into three large morphological groups: Criollo, Forastero and Trinitario. The Trinitario group is derived from crosses of Criollo and Forrastero (Upper Amazon, Amelonado types) while the Forastero group is further subdivided into Upper Amazon (UA) and Lower Amazon (LA) types. Cocoa genetic improvement programmes in West Africa have been based on the development of hybrid varieties with yield as the main selection criterion. In Cote d'Ivoire single pair crosses of UA x LA (Amelonado) types have been the primary varieties released to farmers. The increasing incidence of Phytophthora pod rot (Ppr) has required increasing the genetic diversity in the varieties and applying new methods of breeding. A reciprocal recurrent selection (RRS) technique has been applied since 1990 to simultaneously increase yield and Ppr resistance along with other desirable traits such as self compatibility. In this research two cycles of RRS have been completed and microsatellite markers were then used to estimate the change in genetic diversity over cycles. In the first cycle two populations were produced UA0 and LA+T0. Progeny from inter population crosses were evaluated and parents selected for cycle two. The second cycle parental populations, named UA1 and LA+T1 consisted of trees selected in the first cycle crosses. All four populations were evaluated using 12 microsatellite molecular markers and genetic diversity analysis performed. The results indicated that the genetic diversity of the two groups UA and LA+T was not greatly reduced after the first RS cycle. The genetic diversity parameters of the UA group were unchanged, whereas the observed and expected heterozygosity of the LA+T group decreased slightly. The results indicated the RRS should be successful in simultaneously increasing yield and disease resistance without loss of genetic diversity in advanced cycles of selection.
Technical Abstract: In Cote d'Ivore, the cocoa breeding programme has been based on the creation of hybrids between different genetic groups. From 1990 onward, a reciprocal recurrent selection programme has been set up with the purpose of improving simultaneously the characteristics of the two main genetic groups: Upper Amazon Forastero (UA) and a mixture of Lower Amazon Forastero (LA) and Trinitario (T). Based on data obtained from 12 microsatellite primers, the genetic diversity and genetic distances of the parental populations used in the first and second selection cycles are presented. The results revealed that the diversity of the populations UA0 and UA1 on the one hand and (LA+T)0 and (LA+T)1 on the other is similar. The genetic distances were small between the parental populations used for the first and second cycles. Genetic diversity was greater in the UA group than in the LA+T group. The number of rare and private alleles was reduced for both genetic groups, as well as the number of the frequent alleles in the LA+T group.