Efombagn M I B, Sounigo O, Eskes A B, Motamayor J C, Manzanares-Dauleux M J, Schnell R, Nyassé S
Institute of Agricultural Research for Development, Yaoundé, Cameroon.
Heredity (Edinb). 2009 Jul;103(1):46-53. doi: 10.1038/hdy.2009.30. Epub 2009 Apr 1.
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 studied is still closely related to the traditional 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 descent 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 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 traditional varieties and BSG progenies. The implications of our finding for management of seed gardens and for further breeding using farm accessions in Cameroon are discussed.
本研究利用12个微卫星位点的数据，对喀麦隆农场种质的亲本来源进行了调查。贝叶斯分析表明，在所研究的400份农场种质中，有25.5%仍然与农民称为“德国可可”的传统阿梅洛纳多品种密切相关。另外46.3%的农场种质被发现是20世纪70年代在喀麦隆南部和西部建立的双克隆种子园（BSG）中使用的24个亲本无性系的直接后代（20.8%为第一代（F1）杂种，25.5%为自交基因型）。此外，28.3%的农场种质似乎源自可可农场中不受控制的授粉事件，这可能与可可种植者使用自己农场收集的种子进行新种植的普遍做法有关。通过亲缘关系分析，所有源自BSG的农场种质都可以与BSG的24个亲本单独关联。从BSG分发的后代中只有25%对应于最初计划发布的F1杂种组合。由于存在高比例的自交种质，在所有“传统”农场和大多数“F1杂种”农场中都观察到了显著的双亲近亲繁殖估计值。当植物从基因相关的邻居那里接受花粉时，就会发生双亲近亲繁殖。在“混合”农场中观察到的高异交水平可能是由传统品种和BSG后代的混合所解释的。本文讨论了我们的研究结果对喀麦隆种子园管理以及利用农场种质进行进一步育种的意义。
