Duputié Anne, David Patrice, Debain Chantal, McKey Doyle
Centre d'Ecologie Fonctionnelle et Evolutive, UMR 5175 CNRS, 1919 Route de Mende, 34293 Montpellier cedex 5, France.
Mol Ecol. 2007 Jul;16(14):3025-38. doi: 10.1111/j.1365-294X.2007.03340.x.
Because domestication rarely leads to speciation, domesticated populations often hybridize with wild relatives when they occur in close proximity. Little work has focused on this question in clonally propagated crops. If selection on the capacity for sexual reproduction has been relaxed, these crops would not be expected to hybridize with their wild relatives as frequently as seed-propagated crops. Cassava is one of the most important clonally propagated plants in tropical agriculture. Gene flow between cassava and wild relatives has often been postulated, but never demonstrated in nature. We studied a population of a wild Manihot sp. in French Guiana, which was recently in contact with domesticated cassava, and characterized phenotypes (10 morphological traits) and genotypes (six microsatellite loci) of individuals in a transect parallel to the direction of hypothesized gene flow. Wild and domesticated populations were strongly differentiated at microsatellite loci. We identified many hybrids forming a continuum between these two populations, and phenotypic variation was strongly correlated with the degree of hybridization as determined by molecular markers. Analysis of linkage disequilibrium and of the diversity of hybrid pedigrees showed that hybridization has gone on for at least three generations and that no strong barrier prevents admixture of the populations. Hybrids were more heterozygous than either wild or domesticated individuals, and phenotypic comparisons suggested heterosis in vegetative traits. Our results also suggest that this situation is not uncommon, at least in French Guiana, and demonstrate the need for integrated management of wild and domesticated populations even in clonally propagated crops.
由于驯化很少导致物种形成，所以驯化种群在与野生近缘种近距离共存时，常常会与其杂交。对于无性繁殖作物，很少有研究关注这一问题。如果对有性繁殖能力的选择已经放松，那么预计这些作物与野生近缘种杂交的频率不会像种子繁殖作物那样高。木薯是热带农业中最重要的无性繁殖植物之一。木薯与其野生近缘种之间的基因流动一直被推测存在，但从未在自然环境中得到证实。我们研究了法属圭亚那的一个野生木薯种群，该种群最近与驯化木薯有接触，并对沿着假定基因流动方向的一个样带中的个体的表型（10个形态特征）和基因型（6个微卫星位点）进行了表征。野生种群和驯化种群在微卫星位点上有显著差异。我们识别出许多杂种，它们在这两个种群之间形成了一个连续体，并且表型变异与分子标记所确定的杂交程度密切相关。对连锁不平衡和杂交谱系多样性的分析表明，杂交已经持续了至少三代，并且没有强大的障碍阻止种群的混合。杂种比野生个体或驯化个体具有更多的杂合性，表型比较表明营养性状存在杂种优势。我们的研究结果还表明，至少在法属圭亚那，这种情况并不罕见，并且证明即使对于无性繁殖作物，也需要对野生种群和驯化种群进行综合管理。
