Location: Subtropical Horticulture ResearchTitle: Parentage analysis and outcrossing patterns in cacao (Theobroma cacao L.) farms in Cameroon) Author
|Schnell ii, Raymond|
Submitted to: Heredity
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/3/2009
Publication Date: 4/15/2009
Citation: Efombagn, M., Sounigo, O., Eskes, A.B., Motamayor, J.C., Manzanares-Dauleux, J.J., Schnell Ii, R.J., Nyasse, S. 2009. Parentage analysis and outcrossing patterns in cacao (Theobroma cacao L.) farms in Cameroon. Heredity. p.1-8. Interpretive Summary: Parentage analysis for 400 farm accession was estimated using 12 molecular markers with the goal of tracking changes in population structure on the commercial cocoa farms. In the 1970s biclonal seed gardens were planted to deliver farmers seeds of superior families that demonstrated heterosis for yield and other traits. These seed gardens had 24 specific parents that consisted of Upper Amazon Forastero (UA) and Trinitario (Tr) types that were different from the traditional 'German cocoa' that had been grown on farms and that is an Amelonado type. Seed gardens were arranged to take advanatage of natural pollinations using self compatible and self incompatible parents. Of the 400 accessions analyzed 26% were found to be closely related to the traditinal Amelonado variety. Another 46% were found to be direct descendents from the 24 parental clones used in the biclonal seed gardens. This 46% could be sub-divided into accessions that were hybrids between the first generation F1 plants (21%) and selfs of the first generation hybrids (25%). The remaining 28% of the accessions resulted from uncontrolled pollination events on cacao farms. The implications for cacao breeding in Cameroon are clear, only 21% of the progenies distributed from the seed gardens corresponded to F1 hybrid combinations originally planned to be released. This research demonstrates the need for strict control of pollinations in cocoa seed gardens in Cameroon. The current situation has resulted in a higher rate of inbreeding in commercial fields and a higher rate of Phytophthora pod rot. Increasing the quality control of seed production in the seed gardens should alleviate these problems and reduce the number of seeds from farmers' selections.
Technical Abstract: The present study investigates the parentage of farm accessions in Cameroon using data from 12 microsatellite loci. Bayesian analysis suggests that 25.5% of the 400 farm accessions studies are still closely related to the traditinal Amelonado variety called 'German Cocoa' by the farmers. Another 46.3% of the farm accessions were found to be direct descendants (20.8% first generation (F1) hybrids and 25.5% selfed genotypes) from 24 parental clones used in biclonal seed gardens (BSGs) established in the 1970s in southern and western Cameroon. Furthermore, 28.3% of farm accessions appeared to descend from uncontrolled pollination events in cacao farms, which could be related to a common practice of cacao growers to use seeds collected in their own farm for new plantings. All farm accessions descending from BSG could be individually related through parentage analysis to the 24 progenitors of the BSG. Only 25% of the progenies distributed from BSG corresponded to F1 hybrids combinations originally planned to be released. Significant biparental inbreeding estimates were observed for all 'traditional' farms and for most 'F1 hybrids' farms due to presence of a high proportion of selfed accessions. Biparental inbreeding occurs when plants receive pollen from genetically related neighbors. High levels of outcrossing observed in 'mixed' farms might be explained by the admixture of traditinal varieties and BSG progeny. The implications of our finding for management of seed gardens and for further breeding using farm accessions in Cameroon are discussed.