Rev 02/17/2024
Type species of the genus: Aphelenchoides kuehnei Fischer, 1894
As of 2017 there were more than 200 nominal species assigned to the genus (Esmaeli et al., 2017). Many are poorly described based on morphological and anatomical characters alone and are difficult to identify (de Jesus et al., 2016).
Species of Aphelenchoides occur in soil, decaying plant residues, moss, and on the surfaces of rocks and trees, and in associations with arthropods. Many of the species are mycophagous but a few have importance importance as ecto- and endoparasites of plants. The major plant-parasitic species include A. besseyi Christie, 1942, A. fragariae (Ritzema Bos, 1890) Christie, 1932 and A. ritzemabosi (Schwartz, 1911) Steiner & Buhrer, 1932, parasitising rice, strawberry, ornamental and other plants (Golhasan et al., 2016).
Allen provided a key to the four important species related to A. fragariae. The key is useful in that it provides gross characters for separating the four species, but Sanwal's more detailed key would be necessary for more precise diagnosis.
1. Head swollen, wider than neck, 4 lines in wing area............2
Head not swollen, 2 lines in wing area................A. fragariae.
2. Length of post-uterine branch 5 or more times body width...3
Length of post-uterine branch less than 4 times body width......A. besseyi.
3. Tail bluntly rounded, with a single ventral spine.....A. subtenuis.
Tail terminus peg-like, with 4 small mucrons........A. ritzemabosi.
[From: Allen, M.W. 1952. ]
Sanwal listed 33 species and provided a key in 1961 (Canadian J. Zool. 39: 143-148); there arearound 175 species describedas of 2018 (Aliramaji et al., 2018).
The term "foliar nematodes" is the common name of plant-parasitic forms in the genus Aphelenchoides. However, although some species of the genus are important plant pests, others are found in, and can be recovered from, soil, mosses, mushrooms and decaying organic materials (Aliramaji et al., 2018). Many of the species are fungivores or facultative funcgivores.
Species identification is difficult due to poor older descriptions and unavailable type material. Molecular data are unavailable for most species, especially those described earliest. The relatively conserved morphology andlack of qualitative diagnostic morphological features further complicates Aphelenchoides species identification. However.the recently described species usually include molecular data, which is very useful for taxonomic comparisons of morphologically close species (Mobasseri et al., 2018).
Ref: Nickle, 1970
The genus Aphelenchoides contains species that feed on plants, fungi, and insects. The plant parasitic species have a very wide host range compared to many other types of plant-pathogenic nematodes (Kohl, 2011). Three globally distributed species: A. besseyi Christie, 1942, A. fragariae (Ritzema Bos, 1891) Christie, 1932 and A. ritzemabosi (Schwartz, 1911) Steiner & Buhrer, 1932, are economically important, causing losses in a range of agricultural and horticultural crops (Duncan & Moens, 2013).
Aphelenchoides besseyi, the rice white tip nematode, is an A-rated pest in California and is reported to parasitize more than 200 plant species (Cheng et al., 2013; Duncan & Moens, 2013), with rice, strawberry and ornamental plants the most common hosts. A. besseyi is a major nematode pest in many Asian countries with yield losses in paddy rice ranging from 5.4 to 57.9% in Turkey (Tlek et al., 2014) and to 71% in China (Cheng et al., 2013; de Jesus et al., 2016).
Plant-feeding and fungal-feeding, soil-inhabiting nematodes.
Nematodes of the genus Aphelenchoides can be recovered from soil, mosses, mushrooms, decaying organic materials or, in some cases, from plant tissues. Although most species of Aphelenchoides are fungivores, around 13 species are also known as plant parasites and crop losses due to some species are well documented.
Some species endoparasitic in leaves, but also feeds ectoparasitically on leaf and flower buds in some plants.
Many species of Aphelenchoides feed on fungi. Fungal-feeding species are common in soil and generally appear to have shorter stylets (< 8 um) than plant-feeding species.
Ruess et al (2000) studied the growth of Aphelenchoides sp. populations in vitro on 17 different fungal species. Nematode populations developed on saprophytic (Agrocybe, Chaetomium) and especially on mycorrhizal fungi (Cenococcum, Hymenoscyphus, Laccaria). They speculate that grazing by nematodes may influence the establishment and maintenance of mycorrhizal associations in the field.
Mitosporic species, like Alternaria, Monocillium or Penicillium, were generally poor or non-hosts. This poor host status may be due to the release of toxic metabolites (e.g., antibiotics) and/or to morphological differences (e.g., forming of conidiophores) by the fungi.
Food preference of Aphelenchoides sp. was tested in choice chamber experiments. Nematodes showed a marked preference for particular fungal species. They changed food source with time, indicating a "mixed diet" selection. The attractiveness of a fungus was not necessarily correlated with its suitability as a host.
The genus Aphelenchoides has a wide host-range; plant-feeders usually associated with leaves and buds but most species are fungal feeders.
Video Source: J.D. Eisenback, Nemapix.
Allen, M.W. 1952. Taxonomic status of the bud and leaf nematodes related to Aphelenchoides fragariae (Ritzema Bos, 1891). Proc. Helminth. Soc. Wash., 19:108-120.
Aliramaji, F., Pourjam, E., Alvarez-Ortega, S., Afshar, F.J., Pedram, M. 2018. Description of Aphelenchoides giblindavisi n. sp. (Nematoda: Aphelenchoididae), and Proposal for a New Combination. J. Nematology 50:437-452. DOI: 10.21307/jofnem-2018-035.
Cheng, X., Xiang, Y., Xie, H., Xu, C.-L., Xie, T.-F., Zhang, C. & Li, Y. (2013). Molecular characterization and functions of fatty acid and retinoid binding protein gene (Ab-far-1) in Aphelenchoides besseyi. PLoS ONE 8, e66011.
de Jesus, D.S., Gonsalves Oliveira, C.M., Roberts, D., Blok, V., Neilson, R., Prior, T., Balbino, H.M., MacKenzie, K.M. D�Arc de Lima Oliveira, R. 2016. Morphological and molecular characterisation of Aphelenchoides besseyi and A. fujianensis (Nematoda: Aphelenchoididae) from rice and forage grass seeds in Brazil. Nematology 18:337�356.
Duncan, L.W. & Moens, M. (2013). Migratory endoparasitic nematodes. In: Perry, R.N. & Moens, M. (Eds). Plant nematology. Wallingford, UK, CABI Publishing, pp. 144-178.
Esmaeili, M. Heydari, R., Tahmoures, M. Ye, W. 2017. Aphelenchoides salixae n. sp. (Nematoda: Aphelenchoididae) isolated from Salix alba in western Iran. Nematology 19:697-707.
Golhasan, B., Ramin Heydari, Sergio Alvarez-Ortega, Mehrab Esmaeili, Pablo Castillo and Juan E. Palomares-Rius 2016. Aphelenchoides iranicus n. sp. (Nematoda: Aphelenchoididae) from West Azerbaijan province, Iran. Nematology 18:973-985.
Kohl, L. M. 2011. Foliar nematodes: A summary of biology and control with a compilation of host range. Online. Plant Health Progress doi:10.1094/PHP-2011-1129-01-RV
Mobasseri, M., E. Pourjam and M. Pedram. 2018. Morphological and molecular characterisation of Aphelenchoides primadentus n. sp. (Nematoda: Aphelenchoididae) from northern Iran .Morphological and molecular characterisation of Aphelenchoides primadentus n. sp. (Nematoda: Aphelenchoididae) from northern Iran. Nematology 20:97-109.
Nickle, W.R. 1970. A Taxonomic Review of the Genera of the Aphelenchoidea (Fuchs, 1937) Thorne, 1949 (Nematoda: Tylenchida) . J. Nematology 2:375-392.
Ruess, L., E.J. Garcia Zapata, J. Dighton. 2000. Food preferences of a fungal-feeding Aphelenchoides species. Nematology 2:223-230.
Sanwal 1961 (Canadian J. Zool. 39: 143-148).
Scheck, H.J. 2021. California Pest Rating Proposal for Aphelenchoides fragariae (Ritzema - Bos, 1891) Christie, 1932 Strawberry crimp nematode, Strawberry spring dwarf nematode, Foliar nematode CDFA, Sacramento.
Tlek, A., Ates, S.S., Akin, K., Surek, H., Kaya, R. & Kepenekci, I. (2014). Determining yield losses in rice cultivars resulting from rice white tip nematode Aphelenchoides besseyi in field condition. Pakistan Journal of Nematology 32, 149-154.