American beech (Fagus grandifolia) is the target of a newly emerging disease in North America called beech leaf disease (BLD) that affects and disfigures leaves and which can lead to tree mortality. Beech leaf disease may be caused by a newly recognized subspecies of the anguinid nematode Litylenchus crenatae subsp. mccannii, but the associations of this nematode with bacterial and fungal taxa are unknown. We examined microbial communities associated with beech leaves affected by BLD in a 16-year-old American beech plantation using molecular methods. We detected L. crenatae subsp. mccannii in anywhere from 45% to 90% of leaves depending on the degree of visual BLD symptoms. Approximately 37% of asymptomatic leaves contained L. crenatae subsp. mccannii, whereas 90% of buds associated with symptomatic leaves contained L. crenatae subsp. mccannii. We found that fungal communities on leaves and buds were unaffected by BLD, but bud and leaves had significantly different fungal communities. Bacterial communities on buds also were unaffected by BLD, but bacterial communities were significantly different between symptomatic and asymptomatic leaves suggesting that the nematode could be altering the community of bacteria on the leaves. Clone libraries indicate that Wolbachia, an intracellular endosymbiont of arthropods, was found only on symptomatic leaves and buds associated with either symptomatic or asymptomatic leaves. In addition, only symptomatic leaves contained taxa in the genus Mucilaginibacter, which previous studies suggest could produce exopolysaccharides. These bacterial taxa could represent a marker for the vector of L. crenatae subsp. mccannii that enables spread between trees and a possible endosymbiont that could facilitate nematode feeding and establishment on nematode infested leaves. Our results are the first to examine changes to the leaf microbiome of this newly emerging pest and may aid identification of mechanisms associated with the spread and success of L. crenatae subsp. mccanni.

中文翻译：

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俄亥俄州山毛榉叶病的出现：探索植物微生物组以寻找原因

美国山毛榉（Fagus grandifolia）是北美一种新出现的疾病的目标，称为山毛榉叶病（BLD），它影响和毁坏叶子，并可能导致树木死亡。山毛榉叶病可能是由新发现的 Anguinid 线虫 Litylenchus crenatae subsp. 亚种引起的。mccannii，但这种线虫与细菌和真菌类群的关联尚不清楚。我们使用分子方法检查了与 16 年历史的美国山毛榉种植园中受 BLD 影响的山毛榉叶子相关的微生物群落。我们检测到 L. crenatae subsp。根据视觉 BLD 症状的程度，45% 到 90% 的叶子中都有 mccannii。大约 37% 的无症状叶片含有 L. crenatae subsp。mccannii，而 90% 与有症状叶子相关的芽含有 L. crenatae subsp。麦肯尼 我们发现叶子和芽上的真菌群落不受 BLD 的影响，但芽和叶子上的真菌群落有显着差异。芽上的细菌群落也不受 BLD 的影响，但有症状和无症状叶子之间的细菌群落有显着差异，这表明线虫可能会改变叶子上的细菌群落。克隆文库表明 Wolbachia 是节肢动物的细胞内共生体，仅在有症状的叶子和与有症状或无症状的叶子相关的芽上发现。此外，只有有症状的叶子含有粘液杆菌属的分类群，之前的研究表明它可以产生胞外多糖。这些细菌分类群可以代表 L. crenatae subsp. 载体的标记。mccannii 能够在树木和可能的内共生体之间传播，该内共生体可以促进线虫取食和在被线虫侵染的叶子上建立。我们的结果是第一个检查这种新出现的害虫叶片微生物组变化的结果，并且可能有助于识别与 L. crenatae subsp. 的传播和成功相关的机制。麦肯尼。