Data from: Heterozygote deficits in cyst plant parasitic nematodes: possible causes and consequences

Deviations of genotypic frequencies from Hardy-Weinberg equilibrium (HWE) expectations could reveal important aspects of the biology of populations. Deviations from HWE due to heterozygote deficits have been recorded for three plant parasitic nematode species. However, it has never been determined whether the observed deficits were due (i) to the presence of null alleles, (ii) to a high level of consanguinity and/or (iii) to a Wahlund effect. The aim of the present work was, while taking into the possible confounding effect of null alleles, to disentangle consanguinity and Wahlund effect in natural populations of those three economically important cyst nematodes using microsatellite markers: Globodera pallida, G. tabacum and Heterodera schachtii, pests of potato, tobacco and sugar-beet, respectively. The results show a consistent pattern of heterozygote deficiency in the three nematode species sampled at the spatial scale of the host plant. We demonstrate that the prevalence of null alleles is weak and that heterozygote deficits do not have a single origin. Our results suggested that it is restricted dispersal that leads to heterozygote deficits through both consanguinity and sub-structure, which effects can be linked to soil movement, cyst density, and the number of generations per year. We discuss potential implications for the durability of plant resistances that are used to protect crops against parasites in which mating between relatives occur. While consanguineous mating leads to homozygosity at all loci, including loci governing avirulence/virulence, which favors the expression of virulence when recessive, the Wahlund effect is expected to have no particular effect on the adaptation of nematodes to resistances.

基因型频率偏离哈迪-温伯格平衡（Hardy-Weinberg equilibrium, HWE）的预期值，可揭示种群生物学的诸多重要特征。已有研究记录了三种植物寄生线虫物种因杂合子缺失而偏离HWE的现象。然而，此前尚未明确观测到的杂合子缺失究竟源于以下三种因素之一：(i) 无效等位基因（null alleles）的存在；(ii) 高水平近交；抑或(iii) 瓦尔隆德效应（Wahlund effect）。
本研究旨在在考虑无效等位基因可能带来的混杂效应的前提下，利用微卫星标记（microsatellite markers）解析上述三种具有经济重要性的胞囊线虫自然种群中的近交与瓦尔隆德效应：这三种线虫分别为马铃薯金线虫（Globodera pallida）、烟草胞囊线虫（G. tabacum）以及甜菜胞囊线虫（Heterodera schachtii），它们分别危害马铃薯、烟草和甜菜作物。
研究结果显示，在以宿主植物为空间取样尺度的三种线虫种群中，均呈现出一致的杂合子缺失模式。我们证实，无效等位基因的发生频率较低，且杂合子缺失并非由单一诱因所致。研究结果表明，有限扩散通过近交与种群亚结构共同引发了杂合子缺失，该效应与土壤移动、胞囊密度以及年世代数相关。
我们还探讨了该现象对植物抗性耐久性的潜在影响：当前用于保护作物抵御寄生线虫的抗性品种，其靶标线虫类群存在近亲交配行为。近交交配会使所有位点（包括调控无毒性/毒性的位点）发生纯合化，若毒性基因为隐性，则会促进毒性性状的表达；而瓦尔隆德效应预计不会对线虫适应寄主抗性产生特殊影响。