Beech leaf disease symptoms caused by newly recognized nematode subspecies Litylenchus crenatae mccannii (Anguinata) described from Fagus grandifolia in North America

Authors: Carta, Lynn; Handoo, Zafar; Li, Shiguang; KANTOR, MIHAIL - Oak Ridge National Laboratory; Bauchan, Gary; MCCANN, DAVID - Ohio Department Of Agriculture; GABRIEL, COLETTE - Ohio Department Of Agriculture; YU, QING - Agri Food - Canada; REED, SHARON - Forest Service - Canada; KOCH, JENNIFER - Ohio Department Of Agriculture; MARTIN, DANIELLE - Forest Service (FS); BURKE, DAVID - Holden Arboretum

Submitted to: Forest Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2019
Publication Date: 2/27/2020
Citation: Carta, L.K., Handoo, Z.A., Li, S., Kantor, M., Bauchan, G.R., Mccann, D., Gabriel, C.K., Yu, Q., Reed, S., Koch, J., Martin, D., Burke, D.J. 2020. Beech leaf disease symptoms caused by newly recognized nematode subspecies Litylenchus crenatae mccannii (Anguinata) described from Fagus grandifolia in North America. Forest Pathology. 50(2):e12580. https://doi.org/10.1111/efp.12580.
DOI: https://doi.org/10.1111/efp.12580

Interpretive Summary: A new disease of American beech trees, a major component of many deciduous forest areas in eastern North America, was discovered near Cleveland, Ohio, in 2012. Beech leaf disease (BLD) caused dark green and sometimes yellow stripes in leaves and could kill mature trees within seven years of detection; however, its cause was not known. Therefore researchers from the USDA Agricultural Research Service, Forest Service, Ohio Department of Agriculture, Holden Arboretum, Ontario Forest Research Institute Ministry of Natural Resources and Forestry and Agriculture Canada worked together to determine the cause of this destructive tree disease by identifying microorganisms that were present in or on the diseased leaves and whether or not they could cause the same symptoms. During this work, a microscopic, parasitic roundworm or nematode was discovered in diseased leaf tissue. With microscopic images and DNA markers researchers established that the nematode is closely related to a nematode population on Japanese beech trees (F. crenata) in Japan where the disease associated with the nematode is not lethal. Methods for inoculating the nematode to buds of seedlings in the greenhouse are given and successful transmission of symptoms through buds but not leaves by the nematode are also demonstrated. To date, Japanese beech trees at the Holden Arboretum do not appear to have been infested by the new nematode subspecies in North America. These results are significant because the disease is spreading primarily eastward and identification of agents of transmission of the nematode are needed to stop its progression. This information will be used by foresters, ecologists, geneticists and plant pathologists developing methods for integrated control of BLD.

Technical Abstract: Symptoms of beech leaf disease (BLD), first reported in Ohio in 2012, include interveinal greening, thickening and often chlorosis in leaves, canopy thinning and mortality. Nematodes from diseased leaves of American beech (Fagus grandifolia) sent by the Ohio Department of Agriculture to the USDA, Beltsville, MD in autumn 2017 were identified as the first recorded North American population of Litylenchus crenatae Kanzaki,et al., 2019, originally described from Japan. This and other populations from Ohio, Pennsylvania and the neighboring province of Ontario, Canada showed some differences in morphometric averages among females compared to the Japanese population. Ribosomal DNA marker sequences were nearly identical to the population from Japan. A sequence for the COI marker was also generated, although it was not available from the Japanese population. The nematode was not encountered in Fagus crenata (its host in Japan) living among nematode-infested Fagus grandifolia in the Holden Arboretum, nor has L. crenatae been reported in American or European beech in Japan. The morphological and host range differences in North American populations are nomenclaturally distinguished as L. crenatae mccanii ssp. n., after the plant pathologist who first observed the nematodes in BLD affected leaves. Low Temperature Scanning Electron Microscopy (LT-SEM) demonstrated five lip annules and a highly flexible cuticle. Females, juveniles and eggs were imaged within buds with a Hirox Digital microscope and an LT-SEM. Nematodes swarmed to the tips of freshly cut beech buds, but explants could not be maintained. Inoculation of fresh nematodes from infested leaves or buds to buds or leaves of F. grandifolia seedlings resulted in BLD leaf symptoms. Injuring dormant buds prior to nematode application, in fall or spring, promoted the most reliable symptom expression. The biogeography and physiology of anguinid nematode leaf galling, and potential co-factors and transmission are discussed.