Foliar nematode, Litylenchus crenatae ssp. mccannii, population dynamics in leaves and buds of beech leaf disease-affected trees in Canada and the US

Authors: REED, SHARON - Forest Service - Canada; GREIFENHAGEN, SYLVIA - Forest Service - Canada; YU, QING - Agri Food - Canada; BURKE, DAVID - Holden Arboretum; Carta, Lynn; Handoo, Zafar; KANTOR, MIHAIL - Orise Fellow; KOCH, JENNIFER - Forest Service (FS)

Submitted to: Forest Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/23/2020
Publication Date: 5/20/2020
Citation: Reed, S., Greifenhagen, S., Yu, Q., Burke, D., Carta, L.K., Handoo, Z.A., Kantor, M., Koch, J. 2020. Foliar nematode, Litylenchus crenatae ssp. mccannii, population dynamics in leaves and buds of beech leaf disease affected trees in Canada and the US. Forest Pathology. https://doi.org/10.1111/efp.12599.
DOI: https://doi.org/10.1111/efp.12599

Interpretive Summary: Beech trees (primarily American beech, Fagus grandifolia) are an important component within Northeastern and Appalachian deciduous forests in North America. An urgent problem is beech leaf disease (BLD) associated with a foliar microscopic, parasitic roundworm (nematode) called Litylenchus crenatae mccannii that probably originated in Asia. The disease and nematode appears to have spread from the US and Canada near Lake Erie when it was first detected in 2013, eastward to Connecticut and Long Island, NY in 2019. It can be lethal to trees within seven years of detection. Confirming disease symptoms and associated nematodes within leaves and buds of beech trees at specific localities are critical facts needed to design effective management strategies. Therefore researchers from the Ontario Forest Research Institute Ministry of Natural Resources and Forestry, Agriculture Canada, USDA Agricultural Research Service, USDA Forest Service, and the Holden Arboretum, Kirtland, OH cooperated to map the disease spread and describe where and when different life stages of nematodes occur. This is important because visualizing the nature and pattern of disease occurrence assists in developing strategies to stop or manage disease progression. This information will be used by foresters, ecologists, plant pathologists and regulators developing methods for integrated control of BLD.

Technical Abstract: A new subspecies of parasitic nematode, Litylenchus crenatae ssp. mccannii, has been associated with beech leaf disease (BLD) symptoms in North America. Little is known about the distributions or life histories of Litylenchus nematodes. Here, we report that Litylenchus crenatae ssp. mccannii has been detected throughout the range of BLD in North America using traditional extraction techniques. Monthly collections of symptomatic and asymptomatic leaves during the growing season and leaves and buds between growing seasons revealed the nematode was present in all tissue types. Progressively larger numbers of nematodes were detected in symptomatic leaves from Ohio and Ontario with the greatest detections at the end of the growing season. Smaller numbers of the nematode were detected in asymptomatic leaves from BLD infected trees, typically at the end of the growing season. The nematode was detected overwintering in detached beech leaves and buds. The discovery of small numbers of nematodes in detached leaves at one location prior to the detection of BLD indicates that the nematode is present prior to disease development. No L. crenatae ssp. mccannii nematodes were extracted from samples taken from study locations outside of the known BLD range. Other nematodes, Plectus and Aphelenchoides spp., were infrequently detected in small numbers. Our findings support the involvement of the nematode in BLD and indicates that symptom development is dependent on certain requirements. In addition, the nematode can be reliably detected in buds and leaves using traditional extraction.