Fungi Associated With Woody Tissues of European Beech and Their Impact on Tree Health

Abstract

Filamentous fungi associated with woody tissues of European Beech (Fagus sylvatica) and isolated from diseased trees and healthy trees were examined in relation to their impact on tree health. To this end, classical culture-based isolation methods, in planta inoculations and fungal identification using ITS-barcode and morphological characters were used. Stem endophytes of healthy beech saplings collected in German forests were isolated to determine endophyte communities in woody stem tissues. Pathogenicity tests were performed on living potted beech saplings using twelve selected fungal pathogens and wood inhabiting fungi (Hypocreales, Botryosphaeriales, and Xylariales) originating mainly from European beech with symptoms of the complex disease Vitality loss, or from bark necroses, or known to be common endophytes of beech. The impact of these ascomycetous fungi with respect to tree health was discussed. The potential influences of endophytic fungi of beech and of test conditions are discussed in relation to the success of inoculation. All tested fungal strains except for Neonectria ditissima were able to establish themselves post inoculation in the beech stems and caused necroses when there was sufficient water, but at different severities. Under the experimental conditions, Botryosphaeria corticola was shown to be the most virulent tested latent pathogen against F. sylvatica. In the context of climate change and global warming, the tested Botryosphaeriaceae are able to play a primary role in the disease progress of Vitality loss of Beech. The key role of Neonectria coccinea in causing bark necroses and the loss of vitality in beech was confirmed because the tested strain induced large lesions on the beech saplings.

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

“…In our study, we observed strong enrichment of Hypoxylon fragiforme only in discolored wood areas of sample D2 and it was almost absence (detected 8 times) in nondiscolored wood areas of the same beech tree (ND2). We also detected Neonectria coccinea in the sample D2 which confirms that Hypoxylon fragiforme has the potential to co-occur with Neonectria coccinea [40].…”

“…Hypoxylon fragiforme is even classified as a latent invader within the xylem of European beech [47]. Hypoxylon fragiforme is reported to co-occur with Neonectria coccinea [40]. In our study, we observed strong enrichment of Hypoxylon fragiforme only in discolored wood areas of sample D2 and it was almost absence (detected 8 times) in nondiscolored wood areas of the same beech tree (ND2).…”

“…Neonectria coccinea is one of the most serious pathogens of beech trees, causing beech bark disease in North America and Europe [37,39]. A recent pathogenicity test also showed that Neonectria coccinea has a high potential to cause necrosis in European beech and may lead to tree mortality [40]. Furthermore, it has been hypothesized that damage caused by Neonectria coccinea will be increased under global warming scenarios, as many strains of this species show a rapid increase of mycelial growth at relatively high temperature (30 °C) [37,40].…”

“…Hypoxylon is an additional genus that was identified in discolored wood and it is generally considered either endophyte or saprotroph, but some species (i.e., Hypoxylon fragiforme) can be associated to the development of necrotic lesions on wood trunk of European beech [40]. Hypoxylon fragiforme is even classified as a latent invader within the xylem of European beech [47].…”

“…can kill lateral roots and fine roots [42], and cause beech decline without invading xylem. Furthermore, some other plant pathogenic fungi belonging to Diaporthales and Botryosphaeriales can kill twigs and branches and cause crown-dieback [23,40,54]; thus, they may not be detected in stump samples. Due to this reason, future studies should focus on all potential routes of pathogens from above (stems, branches, twigs and leaves) and below ground organs of the trees and including surrounding soils and insects.…”