Foliar Nematode Aphelenchoides spp. (Nematoda: Aphelenchida: Aphelenchoididae)

There are nematodes of several genera that feed on plant stems and foliage, including Aphelenchoides, Bursaphelenchus, Anguina, Ditylenchus and Litylenchus. Herein, we apply the common name “foliar nematode” specifically to plant-feeding nematodes in the genus Aphelechoides, specifically Aphelenchoides besseyi, Aphelenchoides fragariae, and Aphelenchoides ritzemabosi. While most members of Aphelenchoides are fungivorous (feed on fungi), these three species have populations that are facultative plant-parasites that can feed on live plant tissue. Ten other species of Aphelenchoides also are recognized as facultative plant-parasites, but these are not as commonly encountered or as economically significant as the aforementioned species. Unlike most plant-parasitic nematodes, foliar nematodes can infest the aerial portions of plants rather than dwelling strictly in soil and plant roots. Damage from their feeding can reduce yield in food crops and ruin the appearance of ornamentals.https://edis.ifas.ufl.edu/in1279

Identification and Characterization of a Fatty Acid- and Retinoid-Binding Protein Gene (Ar-far-1) from the Chrysanthemum Foliar Nematode, Aphelenchoides ritzemabosi

The chrysanthemum foliar nematode (CFN), Aphelenchoides ritzemabosi, is a migratory, plant-parasitic nematode that is widely distributed and infects the aboveground parts of many plants. The fatty acid- and retinoid-binding proteins (FAR) are nematode-specific proteins that are involved in the development, reproduction, and infection of nematodes and are secreted into the tissues to disrupt the plant defense reaction. In this study, we obtained the full-length sequence of the FAR gene (Ar-far-1) from CFN, which is 727 bp and includes a 546 bp ORF that encodes 181 amino acids. Ar-FAR-1 from CFN has the highest sequence similarity to Ab-FAR-1 from A. besseyi, and they are located within the same branch of the phylogenetic tree. Fluorescence-based ligand-binding analysis confirmed that recombinant Ar-FAR-1 was bound to fatty acids and retinol. Ar-far-1 mRNA was expressed in the muscle layer, intestine, female genital system, and egg of CFN, and more highly expressed in females than in males among the four developmental stages of CFN. We demonstrated that the reproduction number and infection capacity of CFN decreased significantly when Ar-far-1 was effectively silenced by in vitro RNAi. Ar-far-1 plays an important role in the development, reproduction, infectivity, and pathogenesis of CFN and may be used as an effective target gene for the control of CFN. The results provide meaningful data about the parasitic and pathogenic genes of CFN to study the interaction mechanism between plant-parasitic nematodes and hosts.

First Report of the Foliar Nematode Aphelenchoides ritzemabosi Infecting Chrysanthemum in Iran

During a nematode survey on cut flowers in the Pakdasht Region, Tehran Province, Iran, a species of foliar nematode belonging to the genus Aphelenchoides Fischer was detected in leaves of 10- to 11-month-old, greenhouse-grown (26 to 28°C) chrysanthemum (Dendranthema grandiflorum Kitam., cv. Puja) plants. Chrysanthemum leaves appeared discolored and slightly deformed. Diseased plants comprised approximately 40% of all plants in the greenhouse and occurred in scattered clumps along irrigation paths. Spots and blackish brown, irregular, necrotic areas occupied 5 to 50% of the leaf surface. Symptomatic tissue contained females, males, juveniles, and embryonated eggs of the nematode. All life stages of the nematode were detected in the mesophyll of younger and older infected leaves. The nematode population was extracted and quantified from symptomatic samples of 5 g of leaf tissues by modified Baermann funnel extraction and from 250 g of soil with a modification of the sugar centrifugal flotation method (1), counted, and identified. Morphological observations showed four incisures in the lateral field, excretory pore posterior to nerve ring, ovary single with oocytes in multiple rows, post-vulval uterine sac extending more than one-half of the vulva-anus distance, often containing sperm, tail elongate-conoid bearing a terminal peg with 2 to 4 minute processes. Males common (40% of females) posteriorly curved through 180° upon relaxation, tail conoid bearing a terminal peg with 2 to 3 processes. Measurements of 14 females and 11 males (body length = 987 ± 48 μm, a = 49.2 ± 4.4, b = 12.3 ± 1.1, c = 20.6 ± 2.8, V = 71 ± 1.7, T = 49 ± 2.3, stylet length = 12.6 ± 0.6 μm, tail length = 47.9 ± 5.2 μm; position of vulva = 70.8 ± 1.7%; spicules length = 22.8 ± 1.4 μm) conformed to the description of the chrysanthemum foliar nematode Aphelenchoides ritzemabosi (Schwartz) Steiner & Buhrer, (2). Voucher specimens have been deposited in the University of California Davis Collection. An average of 1,064 A. ritzemabosi per gram were found in the leaves of chrysanthemum, while only 48 nematodes were detected in the soil. To our knowledge, this is the first report of A. ritzemabosi infecting chrysanthemum plants in Iran. References: (1) W. A. Coolen. Page 317 in: Root-Knot Nematodes (Meloidogyne Species) Systematics, Biology, and Control. F. Lamberti and C. E. Taylor, eds., Academic Press, New York, 1979. (2) N. Vovlas et al. Nematology 7:301, 2005.

Identification and histopathology of the foliar nematode Aphelenchoides ritzemabosi (Nematoda: Aphelenchoididae) on basil in Italy

The foliar nematode species Aphelenchoides ritzemabosi is reported attacking sweet basil in glasshouses in the province of Imperia, northwest Italy. The nematode colonised and reproduced within the leaf, petiole and stem tissues. The epidermis and mesophyll were invaded by the nematode which caused internerval discoloration and necrosis and collapse of the palisade and spongy parenchyma. All nematode developmental stages, including eggs, were observed in the leaf tissues. Morphology and morphometrics of A. ritzemabosi from chlorotic and necrotic leaf tissues are presented. Possible control measures, which are complicated by the short life cycle of the nematode, the broad host range, and the short productive cycle of basil, are also discussed, together with the risk of an erroneous field diagnosis caused by difficulty in differentiating the symptoms of basil downy mildew and basil black spot from those of the foliar nematode.

Aphelenchoides ritzemabosi. [Distribution map].

A new distribution map is provided for Aphelenchoides ritzemabosi (Schwartz) Steiner & Buhrer Nematoda: Aphelenchida: Aphelenchoididae Hosts: Mainly Chrysanthemum x morifolium, also strawberry (Fragaria x ananassa[Fragaria ananassa]), Dahlia and other plants. Information is given on the geographical distribution in EUROPE, Bulgaria, Denmark, Germany, Hungary, Ireland, Italy, Mainland Italy, Latvia, Netherlands, Poland, Portugal, Madeira, Russia, Southern Russia, Western Siberia, Spain, Canary Islands, Mainland Spain, Switzerland, UK, Ukraine, Yugoslavia (Fed. Rep.), ASIA, China, Guizhou, India, Himachal Pradesh, Jammu and Kashmir, Japan, Honshu, Kazakhstan, Korea Republic, Uzbekistan, AFRICA, Mauritius, South Africa, NORTH AMERICA, Mexico, USA, California, Colorado, Florida, Wyoming, SOUTH AMERICA, Brazil, Bahia, Sao Paulo, Chile, Venezuela, OCEANIA, Fiji, New Zealand.