Taxonomy identification of principal foliar nematode species (Aphelenchoides and Litylenchus)

Authors: Handoo, Zafar; KANTOR, MIHAIL - Oak Ridge National Laboratory; Carta, Lynn

Submitted to: Plants
Publication Type: Review Article
Publication Acceptance Date: 11/2/2020
Publication Date: 11/4/2020
Citation: Handoo, Z.A., Kantor, M.A., Carta, L.K. 2020. Taxonomy identification of principal foliar nematode species (Aphelenchoides and Litylenchus). Plants. 9(1490):1-31. https://doi.org/10.3390/plants9111490.
DOI: https://doi.org/10.3390/plants9111490

Interpretive Summary: Plant-parasitic nematodes are microscopic worms that cause an estimated ten billion dollars of crop losses each year in the United States and 100 billion dollars globally. Foliar nematodes are the most economically important groups of plant-parasitic nematodes that damage the above ground parts of plants such as leaves of many kinds of plants worldwide. In this article, ARS scientists from Beltsville, Maryland, review major species of foliar nematodes, including a relatively new genus Litylenchus described in 2011. Species included in the Litylenchus are important emerging foliar pathogens parasitizing trees and bushes especially beech trees in the United States of America. Diagnostic, morphological and brief molecular features for distinguishing these species around the world are provided, as well as a detailed historical background, updated systematic position, list of valid species and synonyms, and an amended diagnosis of Aphelenchoides, with brief information on various techniques for species identification, are discussed. The general techniques for killing, fixing, processing, mounting, and scanning electron microscopy are presented, together with descriptions of diagnostic characters, conclusions and prospects in foliar nematode taxonomy and diagnostics. This report will serve as a useful guide to researchers and diagnosticians identifying important foliar nematodes including recent emerging nematodes species on beech trees in the United States of America.

Technical Abstract: Nematodes are Earth’s most numerous multicellular animals and include species that feed on bacteria, fungi, plants, insects, and animals. Foliar nematodes are mostly pathogens of ornamental crops in greenhouses, nurseries, forest trees and field crops. Nematode identification has traditionally relied on morphological and anatomical characters using light microscopy and, in some cases, scanning electron microscopy (SEM). This review article focuses on morphometrical and brief molecular details and key characteristics of some of the most widely distributed and economically important foliar nematodes that can aid in their identification. Aphelenchoides genus includes some of the most widely distributed nematodes which can cause crop damages and losses to agricultural, horticultural and forestry crops. Morphological details of the most common species of Aphelenchoides (A. besseyi, A. bicaudatus, A. fragariae, A. ritzemabosi) are given with brief molecular details including distribution, identification, conclusion and future directions, as well as an updated list of the nominal species with its synonyms. Litylenchus is a relatively new genus described in 2011 and includes two species and one subspecies. Species included in the Litylenchus are important emerging foliar pathogens parasitizing trees and bushes especially beech trees in the United States of America. Brief morphological details of all Litylenchus species are provided.