JAPAN — In September and October 2024, researchers from the USDA Forest Service, USDA Agricultural Research Service in Beltsville and the Connecticut Agricultural Experimental Station traveled to Japan to engage with Japanese researchers and collect samples from Japanese beech (Fagus crenata) trees as part of an International Programs supported project exploring the origins of beech leaf disease.

Beech leaf disease was first discovered in Ohio in 2012 and is a major threat to American beech (Fagus grandifolia). It has now been detected in16 U.S. states and Canada. Litylenchus crenatae, an emergent plant-parasitic nematode, is being studied as the cause of BLD which deforms the tree’s leaves and buds, weakening the tree and contributing to branch dieback and tree mortality. Due to the negative consequences of BLD, this nematode is currently considered one of the top 10 most important plant-parasitic nematodes in the United States. 

The trip was a collaborative undertaking by Robert Marra from Connecticut Agricultural Experimental Station, Paulo Vieira from USDA ARS, Danielle Martin and Cameron McIntire from Forest Service Forest Health Protection, and Japanese collaborators Koichi Hasegawa from Chubu University, and Atsuhiro Iio from Shizuoka University. The purpose of the trip was to help build understanding of the populations and genetic diversity of Lc.

Samples of Japanese beech tree leaves and nuts were gathered from diverse sites across northern Japan where BLD symptoms were observed, including Mount Tsukuba, Appi Kogen Beech Station, Shirakami Forest and other sites. Japanese collaborators assisted with site selection, collection permits, graduate student support and lab space at Chubu University for observation and processing of the samples. USDA Animal and Plant Health Inspection Service staff in Tokyo assisted with permits for shipping processed samples of beechnuts to the Forest Service and processed nematode samples back to CAES in Connecticut for genetic analysis.

The collaborating researchers and graduate students exchanged knowledge with each other as they jointly observed and discussed the symptoms of BLD on Japanese beech trees, which do not appear to experience the severity nor the decline that American beech has had with BLD. The American researchers presented on BLD in American beech in a special symposium at the Japanese Nematological Society 31st annual meeting, at the Tsukuba Center for Institutes, Japan. 

By understanding more about the Lc populations in the native and invaded range, researchers will be better able to understand BLD, its spread and relationship with host trees, potentially contributing to management strategies to mitigate the impacts of BLD and strategies to prevent future introductions of the nematode to non-native regions.