Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Beech forests face growing threats from both their environmental conditions and abiotic and pest biotic stressors, which are putting them at significant risk. For example, beech leaf disease (BLD), caused by a foliar nematode, has emerged as an escalating concern because of its widespread impact on American beech. In addition, European beech, a dominant tree in forests across numerous European countries, and with ornamental value in North America, is highly susceptible to BLD. This study provides evidence on how BLD affects European beech and provides additional valuable insights in the biology of this disease, which will be important for forest pathologists investigating potential methods for management of this disease.

Technical Abstract: European beech forests (Fagus sylvatica L.) are increasingly exposed to a range of environmental stressors, including the rise of plant pathogens. A concerning development is the rapid spread of beech leaf disease (BLD) in North America, prompting questions about the potential risk of this disease spreading to the native areas of F. sylvatica. As a result, there is an urgent need to better understand the relationship between the causal agent of BLD, the foliar nematode Litylenchus crenatae subsp. mccannii (Lcm), and F. sylvatica. This study explores the impact of Lcm on European beech, and aims to provide a more comprehensive assessment at the changes in bud development, leaf morphology, and alterations to the leaf epidermis. Our results demonstrate a dynamic fluctuation in nematode populations within buds, with substantial increases in nematode numbers and reproductive output, highlighting the high reproductivity of Lcm in F. sylvatica. Nematode infestations in buds lead to hypertrophy and irregular cellular patterns of the bud scales. Furthermore, histological analyses of BLD-affected leaves reveal significant alterations in leaf architecture, including an abnormal increase in the number of cell layers, particularly in the spongy mesophyll, and abnormal stomatal development. Notably, we observed irregular stomatal distributions and reduced stomatal density in symptomatic BLD leaf areas, suggesting disrupted gas exchange and reduced photosynthetic capacity of the leaf. Additionally, leaf fractures facilitate nematode dispersal into the leaf surface, potentially contributing to the spread of Lcm in natural infected forest stands. Given the impact of Lcm in beech trees, understanding how they infect their host will deliver routes to mitigate their threat to the forest.