Molecular Screening of Microorganisms Associated with Discolored Wood in Dead European Beech Trees Suffered from Extreme Drought Event Using Next Generation Sequencing.

Ernst-Detlef Schulze,Witoon Purahong,Benjawan Tanunchai,François Buscot,Sara Fareed Mohamed Wahdan

doi:10.3390/plants10102092

Abstract

Drought events weaken trees and make them vulnerable to attacks by diverse plant pathogens. Here, we propose a molecular method for fast screening of microorganisms associated with European beech decline after an extreme drought period (2018) in a forest of Thuringia, Germany. We used Illumina sequencing with a recent bioinformatics approach based on DADA2 to identify archaeal, bacterial, and fungal ASVs (amplicon sequence variants) based on bacterial and archaeal 16S and fungal ITS genes. We show that symptomatic beech trees are associated with both bacterial and fungal plant pathogens. Although the plant pathogen sequences were detected in both discolored and non-discolored wood areas, they were highly enriched in the discolored wood areas. We show that almost each individual tree was associated with a different combination of pathogens. Cytospora spp. and Neonectria coccinea were among the most frequently detected fungal pathogens, whereas Erwinia spp. and Pseudomonas spp. were the dominant bacterial plant pathogens. We demonstrate that bacterial plant pathogens may be of major importance in beech decline.

Highlights

Drought is a complex multivariate environmental phenomenon that is presently intensified by climate changes [1,2]
Our results suggest that plant pathogenic bacteria can potentially be an additional agent for beech decline, especially for weak beech trees suffering from drought, which may already have wounds from fungal infection or insect infestation
Our work demonstrates that European beech decline after an extreme drought event in 2018 and sampling in 2019 is associated with both bacterial and fungal plant pathogens

Summary

Introduction

Drought is a complex multivariate environmental phenomenon that is presently intensified by climate changes [1,2]. Drought events are predicted to occur with higher intensity, duration, and frequency in the future, with expected negative impacts on plant health and productivity in both agricultural and forest ecosystems [1,2,3]. The processes to identify the correct pathogens causing specific diseases on each tree species require time, from sample collection, microbial isolation, purification, characterization and re-inoculation to fulfilling Koch’s postulates. These processes are needed, they rely on culturing techniques, which are known to capture only a small part of microbial communities [7]. A full assessment of the species assembly living in trees exposed to pathogenic attacks becomes an essential first step in such analyses

Objectives

Results

Conclusion