Mycobiota associated with vascular wilt of poplar

In 2017, the 560-ha area of hybrid poplar plantation in northern Poland showed symptoms of tree decline. Leaves appeared smaller, yellow-brown, and were shed prematurely. Twigs and smaller branches died without distinct cankers. Trunks decayed from the base. Phloem and xylem showed brown necrosis. Ten per cent of trees died 1-2 months after the first appearance of symptoms. None of these symptoms was typical for known poplar diseases.<b> </b>Mycobiota was analysed with Illumina sequencing. A total of 69 467 and 70 218 OTUs were obtained from the soil and wood. Blastocladiomycota and Chytridiomycota occurred only in soil, with very low frequencies (0.005% and 0.008%). Two taxa of Glomeromycota with frequency 0.001% occurred in wood. In soil and wood, frequencies of Zygomycota were 3.631% and 0.006%, of<i> </i>Ascomycota 45.299% and 68.697%, and of Basidiomycota 4.119% and 2.076%. At least 400 taxa of fungi were present. Identifiable Zygomycota, Ascomycota, and Basidiomycota were represented by at least 18, 263 and 81 taxa, respectively. Many fungi were common to soil and wood, but 160 taxa occurred only in soil and 73 only in wood. Root pathogens included species of Oomycota. Vascular and parenchymal pathogens included species of Ascomycota and of Basidiomycota.<b> </b>The initial endophytic character of fungi is emphasized. Soil and possibly planting material may be the sources of pathogen inoculum, and climate warming is likely to be a predisposing factor<b>.</b> Water deficit may increase tree susceptibility

2017年，波兰北部一片560公顷的杂交杨树人工林出现林木衰退症状：叶片变小、呈黄棕色且提前脱落；细枝与小枝枯死，无明显溃疡症状；树干从基部开始腐朽；韧皮部（phloem）与木质部（xylem）出现棕色坏死现象。症状首次出现后的1~2个月内，已有10%的树木死亡。上述症状均不符合已知杨树病害的典型特征。
本研究采用Illumina测序对真菌群落（Mycobiota）进行分析，从土壤与木材样本中分别获得69467与70218个操作分类单元（Operational Taxonomic Unit，简称OTU）。芽枝霉门（Blastocladiomycota）与壶菌门（Chytridiomycota）仅在土壤中检出，占比极低（分别为0.005%与0.008%）；2个球囊霉门（Glomeromycota）类群仅存在于木材样本中，占比为0.001%。在土壤与木材样本中，结合菌门（Zygomycota）的占比分别为3.631%与0.006%，子囊菌门（Ascomycota）为45.299%与68.697%，担子菌门（Basidiomycota）为4.119%与2.076%。本研究共检出至少400个真菌类群，其中可鉴定的结合菌门、子囊菌门与担子菌门分别包含至少18、263与81个类群。多数真菌类群在土壤与木材中均有分布，但160个类群仅存在于土壤，73个类群仅存在于木材。
病原菌类群方面，卵菌门（Oomycota）物种为根部病原菌；子囊菌门与担子菌门物种则为维管束与薄壁组织病原菌。
本研究着重强调了真菌的初始内生特性。土壤及潜在的种植材料可能为病原菌接种体的来源，气候变暖或为病害发生的易感诱因，而水分亏缺则会提升树木的感病性。