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

Abstract

A foliar nematode, Litylenchus crenatae ssp. mccannii, is associated with beech leaf disease (BLD) symptoms. Information about the types of tissues parasitized and how nematode populations fluctuate in these tissues over time is needed to improve surveys as well as understand the nematodes role in BLD. During this study, the nematode was detected throughout the known range of BLD by researchers at both Canadian and US institutions using a modified pan method to extract nematodes. Monthly collections of symptomatic and asymptomatic leaves during the growing season (May–October), and leaves and buds between growing seasons (November–March), revealed that nematodes were 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 nematodes were detected in asymptomatic leaves from BLD‐infected trees, typically at the end of the growing season. The nematode was detected overwintering in buds and detached leaves. The discovery of small numbers of nematodes in detached leaves at one location before BLD was detected indicates that nematodes may have been present before disease symptoms were expressed. Other nematodes, Plectus and Aphelenchoides spp., were infrequently detected in small numbers. Our findings support the involvement of the nematode in BLD and indicate that symptoms develop only when certain requirements, such as infection of buds, are met. We also found that the nematode can be reliably detected in buds and leaves using the modified pan extraction method.

Cellular insights of beech leaf disease reveal abnormal ectopic cell division of symptomatic interveinal leaf areas

“…Beech leaf disease begins within the bud because the leaves are already symptomatic when they break through the bud in early spring [ 4 , 20 ]. Therefore, we quantified the nematode population dynamics within the buds at the beginning of the autumn, when senescent leaves fall, and the buds become the only leaf related structure until the following season.…”

A combined approach for early in-field detection of beech leaf disease using near-infrared spectroscopy and machine learning

“…Given this information, it is possible that lignin levels are higher in the local-naïve beech samples and serving as a barrier to LCM/pathogen infection, which could be responsible for the changes in the spectral profile compared to pre-symptomatic samples. While the exact BLD disease cycle has not been clearly defined, studies show that LCM overwinters in American beech buds as well as attached and detached leaves; live nematodes are found in leaves throughout the growing season with the greatest numbers found in late summer/early fall (Carta et al, 2020;Reed et al, 2020). Since BLD symptoms are present at bud break and do not progress throughout the season (Fearer et al, 2022), this suggests that LCM causes symptoms prior to bud break, which Carta et al (2020) confirmed in their study, and LCM migration into the leaf occurs sometime before September (Reed et al, 2020).…”

“…While the exact BLD disease cycle has not been clearly defined, studies show that LCM overwinters in American beech buds as well as attached and detached leaves; live nematodes are found in leaves throughout the growing season with the greatest numbers found in late summer/early fall (Carta et al, 2020;Reed et al, 2020). Since BLD symptoms are present at bud break and do not progress throughout the season (Fearer et al, 2022), this suggests that LCM causes symptoms prior to bud break, which Carta et al (2020) confirmed in their study, and LCM migration into the leaf occurs sometime before September (Reed et al, 2020). Therefore, it is possible that higher lignin levels in local-naïve leaves are preventing LCM/pathogen infection prior to bud break.…”

Rapid assessment of beech leaf disease in Fagus sylvatica buds

“…Under highly severe levels of nematode infection, leaves become leathery and crinkled. As the disease progresses in the following years, there is a significant reduction in bud and leaf survival leading to a substantial decrease in the tree canopy, eventually resulting in tree mortality (Burke et al., 2020; Reed et al., 2020). Although this distinct interveinal leaf banding is a hallmark of BLD, it is only observed at advanced nematode infection stages, making early detection challenging.…”