The plant family Brassicaceae includes some of the most studied hosts of plant microbiomes, improving our knowledge of microbial diversity, community assembly rules, and effects on host performance. Compared to bacteria, eukaryotes in the microbiome of Brassicaceae remain understudied, especially under field conditions. Here, we assessed the impact of host identity and age on the assembly of fungal and oomycete root communities, using DNA metabarcoding of roots and associated soil of three annual co-habiting Brassicaceae collected at two growth stages from a site untouched for a long time. Our results showed that communities of root-associated fungi are more diverse and structured across factors than those of oomycetes. In both cases, plant identity and growth stage had little influence on the community structure of fungi and oomycetes, whereas soil/root compartment had a strong effect by filtering, resulting in a reduction of the number of microorganisms in roots as compared to the surrounding soil. The enrichment in roots with respect to soil of specific fungi and oomycetes, such as members of the Helotiales or the Peronosporales, suggests a specialization towards the asymptomatic colonization of plant tissues that could be relevant to host fitness and health.

十字花科植物科包括一些研究最深​​入的植物微生物群宿主，提高了我们对微生物多样性，群落组装规则和对宿主性能的影响的知识。与细菌相比，十字花科微生物组中的真核生物仍处于研究不足状态，尤其是在田间条件下。在这里，我们使用了三个长期共生的十字花科植物的根和相关土壤的DNA元条形码，从两个地方长期未接触的生长阶段，评估了宿主身份和年龄对真菌和卵菌根群落组装的影响。我们的研究结果表明，与卵菌相比，与根相关的真菌群落具有更多的多样性和结构性。在这两种情况下，植物的身份和生长阶段对真菌和卵菌的群落结构几乎没有影响，而土壤/根部隔室通过过滤具有很强的作用，与周围的土壤相比，根部中的微生物数量减少了。特定真菌和卵菌纲（例如Helotiales或Peronosporales的成员）在土壤中根部的富集表明，植物的无症状定殖专门化可能与宿主的健康和健康有关。