Effects of the nematode Litylenchus crenatae subsp. mccannii and beech leaf disease on leaf fungal and bacterial communities on Fagus grandifolia (American beech)

Beech leaf disease (BLD) is a newly emerging disease in North America that affects American beech (Fagus grandifolia). It is increasingly recognized that BLD is caused by a subspecies of the anguinid nematode Litylenchus crenatae subsp. mccannii (hereafter L. crenatae), which is likely native to East Asia. How nematode infestation of leaves affects the leaf microbiome and whether changes in the microbiome could contribute to BLD symptoms remain uncertain. In this study, we examined bacterial and fungal communities associated with the leaves of F. grandifolia across nine sites in Ohio and Pennsylvania that were either symptomatic or asymptomatic for BLD and used qPCR to measure relative nematode infestation levels. We found significantly higher levels of infestation at sites visibly symptomatic for BLD. Low levels of nematode infestation were also observed at asymptomatic sites, which suggests that nematodes can be present without visible symptoms evident. Bacterial and fungal communities were significantly affected by sampling site and symptomology, but only fungal communities were affected by nematode presence alone. We found many significant indicators of both bacteria and fungi related to symptoms of BLD, with taxa generally occurring in both asymptomatic and symptomatic leaves, suggesting that microbes are not responsible for BLD but could act as opportunistic pathogens. Of particular interest was the fungal genus Erysiphe, which is common in the Fagaceae and is reported to overwinter in buds-a strategy consistent with L. crenatae. The specific role microbes play in opportunistic infection of leaves affected by L. crenatae will require additional study.

IMPORTANCE

Beech leaf disease (BLD) is an emerging threat to American beech (Fagus grandifolia) and has spread quickly throughout the northeastern United States and into southern Canada. This disease leads to disfigurement of leaves and is marked by characteristic dark, interveinal banding, followed by leaf curling and drop in more advanced stages. BLD tends to especially affect understory leaves, which can lead to substantial thinning of the forest understory where F. grandifolia is a dominant tree species. Understanding the cause of BLD is necessary to employ management strategies that protect F. grandifolia and the forests where it is a foundation tree species. Current research has confirmed that the foliar nematode Litylenchus crenatae subsp. mccannii is required for BLD, but whether other organisms are involved is currently unknown. Here, we present a study that investigated leaf-associated fungi and bacteria of F. grandifolia to understand more about how microorganisms may contribute to BLD.

Description of Nothotylenchus savadkoohensis n. sp. (Rhabditida, Anguinidae) from Iran based on morphological and molecular data

Nothotylenchus savadkoohensis n. sp. was recovered from rotten wood samples of an unidentified forest tree in the Mazandaran province and described herein. It is mainly characterized by an elongated conoid tail ending in a sharply pointed tip and four lines in the lateral field. Females of the new species have 379-662 μm long bodies with 5.8-6.9 μm long stylets ending in fine posteriorly sloping knobs, the metacorpus not valvate, the pharyngeal bulb slightly overlapping the intestine, and the vulva at 76.5-84.0% of body length. Males are also common and have 13.0-14.5 μm long spicules and bursa cloacal. By having an elongated conoid tail and four lines in the lateral field, the new species comes close to four known species, namely N. acris, N. acutus, N. antricolus, and N. truncatus. The morphological differences between the new species and the abovementioned species are discussed. The new species was sequenced for its D2-D3 segment of LSU and ITS rDNA regions. In the LSU phylogenetic tree, the currently available LSU sequences of the genus Nothotylenchus occupied distant placements from each other and the LSU sequence of the new species formed clade with a sequence assigned to Neotylenchus sp. In ITS phylogeny, the newly generated sequence of the new species formed a clade with a clade that includes sequences of Ditylenchus sp. and Neomisticius platypi and N. variabilis.

Development of Primers Specific for Detection of Litylenchus crenatae, the Causal Agent of Beech Leaf Disease, in Plant Tissue

Beech leaf disease (BLD), an emerging threat to American beech (Fagus grandifolia) in the northern United States and Canada, was recently confirmed to be caused by the nematode Litylenchus crenatae subsp. mccannii (hereafter L. crenatae). Consequently, there is a need for a rapid, sensitive, and accurate method for detecting L. crenatae for both diagnostic as well as control purposes. This research developed a new set of DNA primers that specifically amplify L. crenatae and allow for accurate detection of the nematode in plant tissue. These primers have also been used in quantitative PCR (qPCR) to determine relative differences in gene copy number between samples. This primer set provides an improved, effective tool for monitoring and detecting L. crenatae in temperate tree leaf tissue which is necessary to understand the spread of this emerging forest pest and to develop management strategies.

Morphological and Molecular Characterization of Nothotylenchus medians and N. similis (Nematoda: Anguinidae) from Southern Alberta, Canada

The nematode family, Anguinidae, is a diverse group of polyphagous nematodes, generally known as fungal feeders or parasites of aerial plant parts. Here, we present the morphological and molecular characterization of adult females of two Nothotylenchus species, N. medians and N. similis, along with host association and geographical distribution data of the genus. Both species are recorded as new reports from Canada and designated as reference populations for future studies. Morphological or morphometrical variation was not observed in the Canadian population of N. medians and N. similis, in comparison with the original description. Phylogenetic analyses based on 18S and D2–D3 of 28S genes placed both species within Anguinidae. Since the biology of the genus Nothotylenchus has not been rigorously characterized, the habitat and distribution information presented in this study will shed some light on the ecology of these nematodes. Notably, the detection of N. medians and N. similis in our nematode inventory survey indicates that considerable Nothotylenchus diversity is hidden in these soils. Consequently, increased surveys and more in-depth research are needed to explore the full diversity of anguinids inhabiting these cultivated areas.

Molecular and morphological characterization of Paurodontella composticola n. sp. (Nematoda: Hexatylina, Sphaerulariidae) from Iran

A new species of the genus Paurodontella, P. composticola n. sp., collected from Nazar Abad City, Alborz Province, Iran, is described and illustrated. The new species has a body length of 803-1053 μ m (females n = 10) and 620 and 739 μ m (males n = 2). The cuticle is weakly annulated with four lateral lines. Cephalic region is annulated and continuous with body contour. The stylet is 8.0 to 9.0 μ m long with asymmetrical knobs. Esophageal basal bulb is present with a small posterior extension projecting into the intestine. Excretory pore is situated at the level of esophageal basal bulb region. Post-uterine sac is 5 to 8 μ m long and uterus is without diverticulum. Tails of both sexes are similar, short and sub-cylindrical. Males have 24 to 25 μ m long bursa leptoderan and spicules 24 or 25 µm long. A non-branching oviduct is present to form a uterine diverticulum; the new species is closely related to five known species of the genus, namely P. asymmetrica, P. balochistanica, P. densa, P. iranica and P. niger. It most closely resembles P. iranica, but differs from it morphologically by a shorter stem-like extension projecting into lumen of intestine and male with sub-cylindrical tail vs conoid. In addition to morphological comparisons, the molecular phylogenetic analyses based on 733 bp of the partial sequence of 28S D2/D3 expansion segments of the large subunit rDNA gene (LSU) revealed this as a new species.

A new species of the genus Paurodontella, P. composticola n. sp., collected from Nazar Abad City, Alborz Province, Iran, is described and illustrated. The new species has a body length of 803–1053 μ m (females n = 10) and 620 and 739 μ m (males n = 2). The cuticle is weakly annulated with four lateral lines. Cephalic region is annulated and continuous with body contour. The stylet is 8.0 to 9.0 μ m long with asymmetrical knobs. Esophageal basal bulb is present with a small posterior extension projecting into the intestine. Excretory pore is situated at the level of esophageal basal bulb region. Post-uterine sac is 5 to 8 μ m long and uterus is without diverticulum. Tails of both sexes are similar, short and sub-cylindrical. Males have 24 to 25 μ m long bursa leptoderan and spicules 24 or 25 µm long. A non-branching oviduct is present to form a uterine diverticulum; the new species is closely related to five known species of the genus, namely P. asymmetrica, P. balochistanica, P. densa, P. iranica and P. niger. It most closely resembles P. iranica, but differs from it morphologically by a shorter stem-like extension projecting into lumen of intestine and male with sub-cylindrical tail vs conoid. In addition to morphological comparisons, the molecular phylogenetic analyses based on 733 bp of the partial sequence of 28S D2/D3 expansion segments of the large subunit rDNA gene (LSU) revealed this as a new species.

Molecular and morphological characterization of Paurodontoides siddiqii n. sp. (Nematoda: Hexatylina, Sphaerulariidae) associated with bark samples of Pinus eldarica from western Iran

A new species of Paurodontoides, P. siddiqii n. sp., is described and illustrated based on its morphological, morphometric, and molecular characters. The new species is characterized by a female 550-729 μm long, lip region continuous with body contour, stylet length 7.0-8.0 μm long or c. 1.0-1.2 times the lip region diameter, lateral fields with four smooth incisures, excretory pore at 85-125 μm from anterior end located at the base of the pharyngeal bulb or posterior to it, basal pharyngeal bulb with a short posterior extension projecting into the intestine, monodelphic-prodelphic reproductive system with prominent 19-22 μm long post-uterine sac, and elongate conoid tail with a filiform terminus. The new species is compared with two known species of the genus. It differs from the type species of the genus, P. linfordi, by having slightly shorter stylet, lateral field with smooth incisures, different position of the excretory pore, and absence of male. Compared to P. latus, the new species has a shorter body, shorter stylet, different position of the excretory pore, female tail shape and absence of male. The new species was also compared with close species of the genus Paurodontus because of lateral field marked with four lines, asymmetrical stylet knobs and absence of male. Molecular phylogenetic studies of the new species using partial sequences of 18S rDNA revealed that it forms a clade with a species of the genus Ficotylus. In phylogenetic analyses using partial sequences of the 28S rDNA D2-D3 domain, the new species formed a monophyletic group with a species of the genus Veleshkinema and Sphaerularia spp. (Sphaerulariinae).

Nothotylenchus andrassy n. sp. (Nematoda: Anguinidae) from Northern Iran

Nothotylenchus andrassy n. sp. is described and illustrated from moss ( Sphagnum sp.) based on morphology and molecular analyses. Morphologically, this new species is characterized by a medium body size, six incisures in the lateral fields, and a delicate stylet (8-9 µm long) with clearly defined knobs. Pharynx with fusiform, valveless, non-muscular and sometimes indistinct median bulb. Basal pharyngeal bulb elongated and offset from the intestine; a long post-vulval uterine sac (55% of vulva to anus distance); and elongate, conical tail with pointed tip. Nothotylenchus andrassy n. sp. is morphologically similar to five known species of the genus, namely Nothotylenchus geraerti , Nothotylenchus medians , Nothotylenchus affinis , Nothotylenchus buckleyi , and Nothotylenchus persicus . The results of molecular analysis of rRNA gene sequences, including the D2-D3 expansion region of 28S rRNA, internal transcribed spacer (ITS) rRNA and partial 18S rRNA gene are provide for the new species.