Affiliation:
1. The Holden Arboretum, Kirtland, Ohio, USA
2. The United States Forest Service, Forest Health Protection, Morgantown, West Virginia, USA
Abstract
ABSTRACT
Beech leaf disease (BLD) is a newly emerging disease in North America that affects American beech (
Fagus grandifolia
). It is increasingly recognized that BLD is caused by a subspecies of the anguinid nematode
Litylenchus crenatae
subsp.
mccannii
(hereafter
L. crenatae
)
,
which is likely native to East Asia. How nematode infestation of leaves affects the leaf microbiome and whether changes in the microbiome could contribute to BLD symptoms remain uncertain. In this study, we examined bacterial and fungal communities associated with the leaves of
F. grandifolia
across nine sites in Ohio and Pennsylvania that were either symptomatic or asymptomatic for BLD and used qPCR to measure relative nematode infestation levels. We found significantly higher levels of infestation at sites visibly symptomatic for BLD. Low levels of nematode infestation were also observed at asymptomatic sites, which suggests that nematodes can be present without visible symptoms evident. Bacterial and fungal communities were significantly affected by sampling site and symptomology, but only fungal communities were affected by nematode presence alone. We found many significant indicators of both bacteria and fungi related to symptoms of BLD, with taxa generally occurring in both asymptomatic and symptomatic leaves, suggesting that microbes are not responsible for BLD but could act as opportunistic pathogens. Of particular interest was the fungal genus
Erysiphe,
which is common in the
Fagaceae
and is reported to overwinter in buds—a strategy consistent with
L. crenatae
. The specific role microbes play in opportunistic infection of leaves affected by
L. crenatae
will require additional study.
IMPORTANCE
Beech leaf disease (BLD) is an emerging threat to American beech (
Fagus grandifolia
) and has spread quickly throughout the northeastern United States and into southern Canada. This disease leads to disfigurement of leaves and is marked by characteristic dark, interveinal banding, followed by leaf curling and drop in more advanced stages. BLD tends to especially affect understory leaves, which can lead to substantial thinning of the forest understory where
F. grandifolia
is a dominant tree species. Understanding the cause of BLD is necessary to employ management strategies that protect
F. grandifolia
and the forests where it is a foundation tree species. Current research has confirmed that the foliar nematode
Litylenchus crenatae
subsp.
mccannii
is required for BLD, but whether other organisms are involved is currently unknown. Here, we present a study that investigated leaf-associated fungi and bacteria of
F. grandifolia
to understand more about how microorganisms may contribute to BLD.
Funder
U.S. Department of Agriculture
Publisher
American Society for Microbiology