Further studies on beech leaf disease and Litylenchus crenatae mccannii in Canada and the USA
Beech leaf disease (EPPO Alert List) is an emerging disease of beech (Fagus spp.) in North America, which can lead to tree mortality in some cases. It was first observed in 2012 in Lake County, Ohio (US) in 2012 and is currently known to occur in other US states (Connecticut, New York, Pennsylvania), as well as in Ontario in Canada. Although the possible causes of beech leaf disease are still being investigated, the presence of a foliar nematode Litylenchus crenatae mccannii has been associated with disease symptoms (see EPPO RS 2018/178, 2019/083, 2020/082, 2020/083, 2020/202).
Further studies were conducted in 2018/2019 across the range of the disease (i.e. Connecticut, New York, Ohio, Pennsylvania, and Ontario). Leaves and buds were collected in selected areas affected by beech leaf disease (with one control site without any symptomatic trees) and nematodes were extracted using a modified ‘pan method’ (i.e. plant tissues are soaked in water before extracting nematodes). Monthly collections of symptomatic and asymptomatic leaves during the growing season (May-October), and of leaves and buds between growing seasons (November–March), revealed that Litylenchus crenatae mccannii was present in all tissue types. In symptomatic leaves from Ohio and Ontario, it was also found that numbers of nematodes progressively increased over time with the greatest number of detections being made at the end of the growing season. Smaller numbers of L. crenatae mccannii were detected in asymptomatic leaves collected from diseased trees, typically at the end of the growing season. In addition, L. crenatae mccannii was found overwintering in buds and detached leaves (in the leaf litter). Other nematode species (Plectus and Aphelenchoides spp.) were detected, but infrequently and only in small numbers. The authors concluded that these results further support the involvement of L. crenatae mccannii in beech leaf disease.
Sources
Reed SE, Greifenhagen S, Yu Q, Hoke A, Burke DJ, Carta LK, Handoo ZA, Kantor MR, 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 50, e12599.