University of Wisconsin-Madison, Botany Department/Birge Hall, 430 Lincoln Drive, Madison, WI 53706-1381, USA.
Am J Bot. 2013 May;100(5):857-66. doi: 10.3732/ajb.1200482. Epub 2013 Apr 2.
Manioc (Manihot esculenta subsp. esculenta), one of the most important tropical food crops, is commonly divided according to cyanide content into two use-categories, "sweet" and "bitter." While bitter and sweet varieties are genetically differentiated at the local scale, whether this differentiation is consistent across continents is yet unknown. •
Using eight microsatellite loci, we genotyped 522 manioc samples (135 bitter and 387 sweet) from Ecuador, French Guiana, Cameroon, Gabon, Ghana, and Vanuatu. Genetic differentiation between use-categories was assessed using double principal coordinate analyses (DPCoA) with multivariate analysis of variance (MANOVA) and Jost's measure of estimated differentiation (D(est)). Genetic structure was analyzed using Bayesian clustering analysis. •
Manioc neutral genetic diversity was high in all sampled regions. Sweet and bitter manioc landraces are differentiated in South America but not in Africa. Correspondingly, bitter and sweet manioc samples share a higher proportion of neutral alleles in Africa than in South America. We also found seven clones classified by some farmers as sweet and by others as bitter. •
Lack of differentiation in Africa is most likely due to postintroduction hybridization between bitter and sweet manioc. Inconsistent transfer from South America to Africa of ethnobotanical knowledge surrounding use-category management may contribute to increased hybridization in Africa. Investigating this issue requires more data on the variation in cyanogenesis in roots within and among manioc populations and how manioc diversity is managed on the farm.
木薯（Manihot esculenta subsp. esculenta）是最重要的热带粮食作物之一，通常根据氰化物含量分为“甜”和“苦”两种用途。虽然苦味和甜味品种在局部范围内存在遗传分化，但这种分化是否在整个大陆上一致尚不清楚。
利用 8 个微卫星位点，我们对来自厄瓜多尔、法属圭亚那、喀麦隆、加蓬、加纳和瓦努阿图的 522 个木薯样本（135 个苦味和 387 个甜味）进行了基因型分析。采用双主坐标分析（DPCoA）结合多元方差分析（MANOVA）和 Jost 估计分化测量值（D(est)）评估了用途类别的遗传分化。采用贝叶斯聚类分析进行遗传结构分析。
在所有采样地区，木薯中性遗传多样性均较高。南美地区的甜木薯和苦木薯品种存在分化，但非洲地区不存在这种分化。相应地，非洲的甜木薯和苦木薯样本共享更多的中性等位基因。我们还发现了 7 个克隆，一些农民将其归类为甜木薯，而另一些则归类为苦木薯。
非洲地区缺乏分化很可能是由于苦木薯和甜木薯引入后发生了杂交。从南美向非洲不一致地转移了与用途类别管理有关的民族植物学知识，可能导致了非洲杂交的增加。解决这个问题需要更多关于木薯根内和种间氰化物生成变异以及木薯多样性在农场管理方面的信息。
