Mycobiota Associated with the Vascular Wilt of Poplar

Abstract

In 2017, a 560-ha area of hybrid poplar plantation in northern Poland showed symptoms of tree decline. The leaves appeared smaller, yellow-brown, and were shed prematurely. Twigs and smaller branches died without distinct cankers. Trunks decayed from the base. The phloem and xylem showed brown necrosis. Ten percent of the trees died 1–2 months after the first appearance of the symptoms. None of these symptoms were typical for known poplar diseases. The trees’ mycobiota were analysed using Illumina sequencing. A total of 69 467 and 70 218 operational taxonomic units (OTUs) were obtained from the soil and wood. Blastocladiomycota and Chytridiomycota occurred only in the soil, with very low frequencies (0.005% and 0.008%). Two taxa of Glomeromycota, with frequencies of 0.001%, occurred in the wood. In the soil and wood, the frequencies of Zygomycota were 3.631% and 0.006%, the frequencies of Ascomycota were 45.299% and 68.697%, and the frequencies of Basidiomycota were 4.119% and 2.076%. At least 400 taxa of fungi were present. The identifiable Zygomycota, Ascomycota, and Basidiomycota were represented by at least 18, 263 and 81 taxa, respectively. Many fungi were common to the soil and wood, but 160 taxa occurred only in soil and 73 occurred only in wood. The root pathogens included species of Oomycota. The vascular and parenchymal pathogens included species of Ascomycota and of Basidiomycota. The initial endophytic character of the fungi is emphasized. Soil, and possibly planting material, may be the sources of the pathogen inoculum, and climate warming is likely to be a predisposing factor. A water deficit may increase the trees’ susceptibility. The epidemiology of poplar vascular wilt reminds grapevine trunk diseases (GTD), including esca, black foot disease and Petri disease.

Bacteria associated with vascular wilt of poplar

“…Many bacteria detected were possibly the initial endophytes in a variety of tissues in trees that were, so far, healthy. They probably do not participate in the initial development of disease but become pathogenic later, after development of disease started by fungi (Kwaśna et al 2021). They need favorable conditions, including lower temperature and higher humidity of soil from where they spread to plants.…”

“…Poplar's susceptibility to phytopathogens is the main obstacle to its exploitation (reviewed in Newcombe 1996). The most serious fungal pathogens include vascular and parenchymal colonizers (Kwaśna et al 2021).…”

“…None of the observed symptoms was typical for known poplar diseases. The possible contribution of vascular and parenchymal fungal pathogens has been suggested (Kwaśna et al 2021).…”

Lifestyle-specific responses ofTrichodermaspp. in mycoparasitic confrontations and implications for biocontrol ofPopulusxcanescens

“…Populus spp. are naturally found in complex symbiotic interactions with beneficial microbes such as ectomycorrhizal fungi (ECM) (Karliński et al, 2010; Kwaśna et al, 2021; Luo et al, 2009; Plett & Martin, 2012; Schnitzler et al, 2010). However, monocultures of poplar hybrids in large-scale short rotation coppices (SRC) are also often susceptible to a wide range of soil-born and foliar fungal pathogens such as Armillaria root rot, Melampsora leaf rust, or leaf spot caused by Alternaria alternata (Hacquard et al, 2011; Ostry et al, 2014).…”

Defense mechanisms promoting tolerance to aggressive Phytophthora species in hybrid poplar

“…In line with the trade-off theory, rapid growth is correlated with lower defense mechanisms and a relatively short lifespan, at least compared with long-lived trees ( Piovesan and Biondi, 2021 ). Poplars are hosts to a plethora of microbes and opportunistic pathogens ( Biselli et al., 2022 ), and poplar’s susceptibility to phytopathogens is the main obstacle to its mass cultivation and exploitation ( Isebrands and Richardson, 2014 ; Li et al., 2019 ; Ji et al., 2020 ; Kwaśna et al., 2021 ).…”