Plantard O, Porte C
UMR INRA-ENSAR 'BiO3P', Domaine de la Motte, BP 35327, 35653 Le Rheu cedex, France.
Mol Ecol. 2004 Jan;13(1):33-41. doi: 10.1046/j.1365-294x.2003.02023.x.
The sugar beet cyst nematode Heterodera schachtii is a soil-dwelling phytoparasitic nematode that feeds on beet roots. It is an important pest in most sugar beet growing areas, and better knowledge of its genetic variability is an important step to preserve the durability of resistant sugar beet varieties. The population genetic structure of this species in northern France was studied using five microsatellite markers. A hierarchical sampling design was used to investigate spatial structuring at the scale of the region, the field and the plant. Multilocus genotypes were obtained for single individual second-stage larvae, using only one individual per cyst in order to avoid the analysis of closely allied individuals (larvae from the same cyst share at least the same mother). A consistent trend of heterozygote deficit at all loci was observed at all spatial scales. Heterozygote deficit at the level of individual plants argues against its generation through a Wahlund effect. Inbreeding could be due to very limited active dispersal of larvae in the soil, favouring mating between siblings, such as larvae emerging from the same cyst. Such behaviour could have important consequences for the evolution of virulence in increasing the production of homozygous virulent individuals. Moreover, an analysis of molecular variance (amova) reveals that only 1.6% of the genetic variability is observed among regions, 3.7% among fields of the same region and 94.6% within fields. The very low level of genetic differentiation among fields is also indicated by low values of FST (</= 0.105) even for fields 150 km apart. We suggest that long-distance gene flows occur due to passive transport of cysts by human activities, water or wind. As such mechanisms of gene flow would involve cysts and not larvae, the strong signals of inbreeding observed at the local scale should not be disrupted. To our knowledge, this study constitutes the first investigation of the genetic structure of a phytoparasitic nematode based on neutral codominant genetic markers scored in single individuals.
甜菜孢囊线虫（Heterodera schachtii）是一种生活在土壤中的植物寄生线虫，以甜菜根为食。它是大多数甜菜种植区的重要害虫，更好地了解其遗传变异性是保持抗性甜菜品种持久性的重要一步。利用五个微卫星标记研究了该物种在法国北部的群体遗传结构。采用分层抽样设计来研究区域、田间和植株尺度上的空间结构。针对单个第二阶段幼虫获得多位点基因型，每个孢囊仅使用一个个体，以避免分析亲缘关系密切的个体（来自同一孢囊的幼虫至少共享同一个母体）。在所有空间尺度上，在所有位点都观察到杂合子缺失的一致趋势。单个植株水平上的杂合子缺失表明其并非由瓦伦德效应产生。近亲繁殖可能是由于幼虫在土壤中的主动扩散非常有限，有利于同胞之间交配，例如从同一孢囊孵化出的幼虫。这种行为可能对毒力进化产生重要影响，因为它会增加纯合有毒个体的产生。此外，分子方差分析（AMOVA）表明，仅1.6%的遗传变异存在于不同区域之间，3.7%存在于同一区域的不同田间，94.6%存在于田间内部。即使是相距150公里的田间，FST值也很低（≤0.105），这也表明田间之间的遗传分化水平非常低。我们认为，由于人类活动、水或风对孢囊的被动运输，会发生远距离基因流动。由于这种基因流动机制涉及孢囊而非幼虫，在局部尺度上观察到的强烈近亲繁殖信号不应被破坏。据我们所知，本研究是首次基于对单个个体进行评分的中性共显性遗传标记对植物寄生线虫的遗传结构进行调查。
