The presence and distribution of nematode Litylenchus crenatae ssp. mccannii, the causative agent of beech leaf disease, in forest stands across Ohio

Abstract

Fagus grandifolia is an important forest tree species in North America that has been afflicted with beech leaf disease (BLD) since 2012. BLD can lead to substantial canopy thinning and eventual tree mortality. Current evidence suggest that Litylenchus crenatae ssp. mccannii (hereafter LCM) is the causative agent of BLD. However, the etiology of this disease is poorly understood. In this study, we conducted multi-year monitoring to examine the presence of LCM and BLD symptoms across Ohio, including both symptomatic and asymptomatic forest stands. We collected buds each spring before leaf-out and used molecular methods to detect the presence of LCM. Symptomatic sites had a high proportion of buds colonized by LCM across all sampling years. Detection of LCM DNA in asymptomatic forest stands was largely inconsistent across years; however, its presence overall was a significant predictor of BLD symptoms developing in the county surrounding our sampling site in the following years. LCM DNA was also detected on both Acer sp. and Quercus sp. buds, but detection frequency was low. We found significant correlations between the proportion of buds infested with LCM and the forest basal area consisting of F. grandifolia, suggesting it is the host for this nematode. Our results indicate that LCM is more widespread than BLD symptoms might suggest and can be present in forests containing a greater occurrence of F. grandifolia even when the trees are asymptomatic.