Beech leaf disease symptoms caused by newly recognized nematode subspecies Litylenchus crenatae mccannii (Anguinata) described from Fagus grandifolia in North America

Abstract

Symptoms of beech leaf disease (BLD), first reported in Ohio in 2012, include interveinal greening, thickening and often chlorosis in leaves, canopy thinning and mortality. Nematodes from diseased leaves of American beech (Fagus grandifolia) sent by the Ohio Department of Agriculture to the USDA, Beltsville, MD in autumn 2017were identified as the first recorded North American population of Litylenchus crenatae (Nematology, 21, 2019, 5), originally described from Japan. This and other populations from Ohio, Pennsylvania and the neighbouring province of Ontario, Canada showed some differences in morphometric averages among females compared to the Japanese population. Ribosomal DNA marker sequences were nearly identical to the population from Japan. A sequence for the COI marker was also generated, although it was not available from the Japanese population. The nematode was not encountered in Fagus crenata (its host in Japan) living among nematode-infested Fagus grandifolia in the Holden Arboretum, nor has L. crenatae been reported in American beech in Japan. The morphological and host range differences in North American populations are nomenclaturally distinguished as L. crenatae mccannii ssp. n. from the population in Japan. Low-temperature scanning electron microscopy (LT-SEM) demonstrated five lip annules and a highly flexible cuticle. Females, juveniles and eggs were imaged within buds with a Hirox Digital microscope and an LT-SEM. Nematodes swarmed to the tips of freshly cut beech buds, but explants could not be maintained. Inoculation of fresh nematodes from infested leaves or buds to buds or leaves ofF. grandifolia seedlings resulted in BLD leaf symptoms. Injuring dormant buds prior to nematode application, in fall or spring, promoted the most reliable symptom expression. The biogeography and physiology of anguinid nematode leaf galling, and potential co-factors and transmission are discussed. K E Y W O R D S Anguinidae, digital and scanning electron microscopy, foliar nematode, host range, molecular identification, morphometrics, new continent detection, new subspecies, symptom transmission, taxonomy 2 of 15 | CARTA eT Al.

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

“…Number of locations where the nematode, Litylenchus crenatae ssp. mccannii (Carta et al., 2020), was detected in Canadian and US counties in the Great Lakes Region and along the Atlantic coast as well as the known range of beech leaf disease (BLD) as of October 1, 2019. BLD US county distribution in part from Martin, Volk, Macy, and Pognacik (2019).…”

“…(a) Mean number of Litylenchus crenatae ssp. mccannii (Carta et al., 2020) nematodes per leaf sample (± SE ) and (b) frequency of their detection from asymptomatic and symptomatic leaves between June and October 2018 from three locations with easily detectable beech leaf disease in southwestern Ontario ( n = 1–2 trees per site June through August and 5 trees per site in September and October)…”

“…Total number of Litylenchus crenatae ssp. mccannii (Carta et al., 2020) per gram leaf tissue collected from F. grandifolia Ehrh. tree, ID No.…”

“…Parasitism of American beech leaves and buds by the nematode, Litylenchus crenatae ssp. mccannii (Carta et al., 2020) is known to result in BLD (Carta et al., 2020). The mechanisms resulting in disease development and whether other organisms, such as the bacteria Mucilaginbacter , are needed for symptoms to develop are being investigated (Burke et al., 2020).…”

“…(2019) observed adult male and female L. crenatae in beech leaf mesophyll tissue, and Carta et al. (2020) observed female, juvenile and eggs of L. crenatae ssp. mccannii in buds of beech.…”