Datasheets on Xiphinema americanum sensu lato, Xiphinema bricolense, Xiphinema californicum and Xiphinema rivesi are also available in Global Database.

Preferred name: Xiphinema americanum sensu stricto
Authority: Cobb
Taxonomic position: Animalia: Nematoda: Enoplea: Dorylaimida: Longidoridae
Other scientific names: Tylencholaimus americanus (Cobb) Micoletzky, Xiphinema americanum Lamberti & Bleve-Zacheo
Common names in English: American dagger nematode, tobacco ring nematode
view more common names online...
Notes on taxonomy and nomenclature EPPO Categorization: A1 list
EU Categorization: A1 Quarantine pest (Annex II A)
view more categorizations online...
EPPO Code: XIPHAA

X. americanum s.s. appears to be non-specific with regard to host plants, having been recorded from agricultural, horticultural and forest soils. The host plants of particular quarantine significance are those to and from which X. americanum s.s. transmits viruses. Brown et al. (1994) reported that X. americanum s.s. transmits cherry rasp leaf virus (CRLV) (Cheravirus), tobacco ringspot virus (TRSV) (Nepovirus) and tomato ringspot virus (ToRSV) (Nepovirus). Klos et al. (1967) reported X. americanum s.l. as a vector of peach rosette mosaic virus (PRMV) (Nepovirus); however, it is unclear whether X. americanums.s. can vector PRMV. The ability to transmit virus may also vary among different populations of the same nematode species (Griesbach & Maggenti, 1989). Brown et al. (1984) noted the broad-spectrum virus transmission capabilities of the North American populations compared with the relatively narrow specificity of transmission that exists between indigenous European viruses and their vector species. Important host plants of these viruses include Malus spp., Prunus spp. (plum, cherry and peach), Vitis spp. (Taylor & Brown, 1997). The host plant range of these viruses is wide, including woody and ornamental plants and several weed species.

Host list: Prunus persica, Rosa sp., Solanum tuberosum, Vitis vinifera, Zoysia sp.

X. americanum s.s. has been reported from North America and has not been reported in the EPPO region.

North America: Canada (Ontario, Québec), United States of America (Arkansas, California, Florida, Georgia, Illinois, Indiana, Iowa, Kansas, Louisiana, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, New York, North Carolina, North Dakota, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Virginia)

X. americanum s.s. is a migratory ectoparasite and spends its entire life cycle in the soil, moving in the moisture film covering soil particles. The individuals appear to be attracted to young growing roots where they feed by puncturing, with their stylet, several successive layers of cells and extracting cytoplasm. Females produce eggs parthenogenetically (males being rare or absent). The number of developmental stages for this species is unclear, data indicates the possibility of either 3 or 4 juvenile development stages. Alkemada and Loof (1989) reviewed the literature on X. americanum s.l. juveniles and reported that some published measurements clearly indicated four juvenile stages, while three larval developmental stages were also reported (Halbrendt & Brown, 1992; Robbins et al., 1996). The life cycle requires at least 1 year to complete. Optimum temperatures for reproduction are 20-24°C (Hunt, 1993). There is no specialized long term survival stage however, all stages have been found to survive and mature (but not multiply) in soil in the absence of a host. The nematode does not survive long periods in frozen soil, and in areas of low winter temperatures overwintering is mainly in the egg stage. Where the soil is not frozen, all stages can survive over winter.

X. americanum s.s. is an efficient vector of several viruses, with adults and juvenile stages able to transmit viruses (McGuire, 1964; Teliz et al., 1966). However, the viruses do not persist during the successive juvenile developmental stages (Bitterlin & Gonsalves, 1986; Hunt, 1993; Brown et al., 1994; Taylor & Brown, 1997). When the nematode feeds on a virus-infected plant, virus particles are extracted from the cells within the cytoplasm, and these adhere to the lining of the stylet and pharynx. The virus particles are injected into the next healthy plant on which the nematode feeds. Nematodes may transmit virus acquired up to 2 years previously (Bitterlin & Gonsalves, 1987).

An EPPO diagnostic protocol is available for Xiphinema americanum sensu lato (EPPO, 2017) as well as an IPPC Diagnostic Protocol (IPPC, 2016).

Symptoms

Plants roots attacked by X. americanum s.s., in the absence of a virus, generally exhibit no clear characteristic symptoms in the aerial parts. Symptoms are most often similar to those resulting from environmental stresses. With high population densities, a general reduction in vigour is observed and this appears in characteristic patches in the crop corresponding to the highest concentration of nematodes (Heve et al., 2015). When nematode feeding results in virus transmission the characteristic symptoms of the particular virus develop in the crop. These usually first appear in the aerial parts of the plant in the growing season after transmission to the roots has occurred. However, some host plants remain symptomless after infection and therefore may escape detection (NVWA, 2010).

Morphology

X. americanum s.s. nematodes are minute, soft-bodied, vermiform and almost transparent. They have a hard, needle-like stylet (odontostyle and odontophore) at the mouth-end of the body. General morphological characteristics of X. americanum s.s. are relatively short compared to other non X. americanum s.l. species (usually <150 μm) stylet (odontostyle + odontophore), thick cuticular lining of the pharynx, males usually absent or rare, female genital branches equally developed, uterus short and without Z-organ, presence of symbiotic bacteria surrounding the oocytes and in the intestines of juveniles, short conoid tail with rounded terminus, females without sperm present in uteri or oviduct.

Detection and inspection methods

X. americanum s.s. can be detected by extraction from soil or growing media (as is the case with most ectoparasitic plant‐parasitic nematodes). Nematode extraction techniques, such as the Flegg‐modified Cobb technique (Flegg, 1967) or Oostenbrink (Oostenbrink, 1960) or other suitable elutriation methods can be used for extraction of longidorid nematodes. Migratory endoparasites may also be present in soil residues adhered to plant roots, bulbs and tubers. Consequently, X. americanum s.s. may be found following processing of plant material using other methods such as modified Baermann processes. Detailed descriptions of extraction equipment and procedures can be found in EPPO PM 7/119 Nematode extraction (EPPO, 2013). Following extraction, nematodes are examined using high-power microscopy in order to identify the specimens.

X. americanum s.s. spends the entirety of its life cycle in the soil, feeding on roots of host plants. It can only live in moist soil where it can move at most 1 m per year, unless assisted by run-off. Bare rooted plants free from soil are not a pathway for movement. The pest is transported solely in soil associated with plants for planting, plant products (such as, soil associated with ware potatoes), bulk soil and any other goods contaminated with soil. Spread over longer distances is possible in moist soil transported with or without plants. Soil and growing media attached to (agricultural) machinery, tools and packaging materials may also constitute a pathway for movement, but such soil may dry out and consequently lead to reduced viability of the pest.

Economic impact

The importance of X. americanum s.s. is linked to its capacity to vector of the following American viruses (Taylor & Brown, 1981), which are important mainly on fruit crops: ToRSV, TRSV, CLRV and PRMV.

Both ToRSV and TRSV have wide host ranges. Reported effects of the viruses on economically important crops were performed by NVWA (2010). Adverse economic effects caused by ToRSV are principally related to fruit crops, particularly grapes and raspberries. In grapes, yield reductions between 37 and 63% were reported in vineyards in New York, USA. Fifty percent yield reductions were reported in some raspberry cultivars whilst other cultivars were unaffected. ToRSV was also implicated in apple union necrosis and decline in American apple orchards. Severe losses have also been reported on blueberry in New York and peach in Pennsylvania. The virus is known to infect species of Prunus, Ribes spp. and Rubus spp., however it was not detected in neighboring peach orchards (Sertkaya, 2010). Among the horticultural crops ToRSV has been reported to produce symptoms on leaves of pelargonium, making plants unmarketable. In Lithuania, ToRSV was detected in 4.6% of one raspberry cultivar (Stankiene et al., 2012), although impacts due to the virus infection are unknown. TRSV causes yield losses in soybean and blueberries in the USA. Serious losses were also reported in grapes in vineyards affected by a mixed infection of TRSV and ToRSV. The virus also affects cucurbits but causes only minor damage to these crops. Elsewhere, 60-80% yield losses were reported in aubergine in India and minor losses were reported in capsicum in Mexico (FERA, 2014).

After introduction into the production area, the virus associated with its vector will spread slowly since the nematodes will spread naturally 1 m at maximum per year. The virus and its vector may spread over longer distance mainly with trade of plants with soil attached but the total infested area will however increase slowly. Thus, on the short term, e.g. the first 10 years after introduction the impact is assessed to be low and only very locally impact may occur. Longer term (decades), the virus-vector combination is expected to spread further mainly by human assistance and the impact may become similar to that in the USA where both the virus and vector are present. In Europe the impact of ToRSV and/or TRSV in combination with the vector may become higher than in the USA because of the limited availability of soil fumigants in Europe. The potential impact of the viruses in combination with the vector in Europe was assessed as follows (NVWA, 2010):

• - ToRSV: high impact for several fruit crops.
  - TRSV: high impact for blueberry and probably also for grapes.
  - CLRV: low impact.
  - PRMV: low impact.

Control

Control of viruliferous nematodes in the field is problematic. Disinfection of soil can be carried out by physical (heat, steam) or chemical (nematicides) treatments. However, the efficacy of these measures is limited (it is considered that the efficacy never reaches 100%) and the nematodes that remain in the soil can still transmit viruses to the roots of the host plants (EFSA, 2018). Soil disinfection by physical treatments does not eliminate nematodes under field conditions due to the vertical distribution (depth) of the nematode which depends on availability of roots of host plants and moisture regime (EFSA, 2018). The use of nematicides is restricted in EPPO countries (e.g. EU countries) and at present, no methods are available to control nematode populations in an established orchard (NVWA, 2010).

Keeping the soil free from plants for over 2 years will significantly reduce the nematode population.

Phytosanitary risk

The main phytosanitary risk for the EPPO region is linked to the capacity of X. americanum s.s. to transmit three American viruses CRLV, TRSV and ToRSV, which are also quarantine pathogens. X. americanum s.s. may thus introduce or spread these viruses.

If the viruses were introduced or spread in the EPPO region, introduction of the vector nematodes would create an additional phytosanitary risk of more rapid spread, and more complex measures for the certification of virus-free material of fruit crops would be needed. Populations of X. americanum s.s. from outside the EPPO region, especially those from North America, could establish and spread in the EPPO region.

Natural spread of the nematode (and associated viruses) is slow and considered to be at maximum 1 m per year. The virus and its vector may spread over longer distance with trade of plants with soil attached but the total infested area will increase slowly. Thus, on the short term, e.g. the first 10 years after introduction the impact is deemed to be low (NVWA, 2010) and only very local impact may occur. On a longer term (decades), the virus-vector combination is expected to spread further mainly by human assistance and the impact may become similar to that in the USA where both the virus and vector are present (NVWA, 2010). In Europe the impact of ToRSV and TRSV in combination with the vector may become higher than in the USA because of the limited availability of soil fumigants.

There are numerous reports of TRSV and ToRSV detection in the EPPO region, however, most relate to interceptions, are under eradication and are not known to be widely distributed. CRLV is not known to be present in the EPPO region.

Klos et al., (1967) reported X. americanum s.l. species as a vector of PRMV, it is unclear whether, X. americanums.s. can vector PRMV. Should X. americanum s.s. be proven as a vector of PRMV this would result in additional risk as PRMV was detected at a low incidence in west Anatolia, Türkiye during almond nursery trees survey in 1992 and 1993 (Azerý & Çýçek, 1997).

It can be recommended that soil from non-EPPO countries where X. americanum sensu s.s. occurs should be prohibited. Plants with roots may also be prohibited or precautions should be taken to ensure that the nematodes will not be carried in the roots. The field from which the plants came should have been tested and found free from the nematodes and, if the plants were in a growing medium, that must be either inorganic or have been tested, or treated against nematodes. If this is not the case, soil or growing medium attached to the plants can be removed and after removal, the plants can be repotted in pest-free soil or growing medium before export. Plants should have then been kept under special conditions to avoid the risk of reinfestation.

Soil or growing medium can be treated to kill nematodes by heating to 60°C and maintaining at that temperature for 1 h.

The use of certified or tested plants for planting, grown under specific conditions to prevent infestation help to reduce the risk of introduction and spread of TRSV, ToRSV and CRLV and X. americanum s.s. vector nematodes. Only planting material originating from areas where these viruses and their vector have not been reported, and where surveillance is carried out to confirm the absence of the pest (Pest Free Area, Pest Free Production Site) could be declared as pest free material and could be therefore used in the EU (Jager et al., 2018). The use of certified or tested plants for planting help to reduce the risk of introducing and spreading of viruses not present or having a limited distribution in the region, and of their vector nematodes. Only planting material originating from areas where these viruses and their vector nematodes have not been reported, and where surveillance is carried out to confirm the absence of the pest (Pest Free Area, Pest Free Production Site) can be declared as pest free material.

Alkemada JM & Loof PA (1989) Observations on the ontogeny of some Xiphinema species (Nematoda: Dorylaimida). Mededelingen van de Faculteit landbouwwetenschappen. Rijksuniversiteit Gent 54(3b), 1177-1186.

Azerý T & Çýçek Y (1997) Detection of virus diseases affecting almond nursery trees in Western Anatolia (Turkey). EPPO Bulletin 27(4), 547-550.

Bitterlin MW & Gonsalves D (1987) Spatial distribution of Xiphinema rivesi and persistence of tomato ringspot virus and its vector in soil. Plant Disease 71, 408-411.

Brown DJF, Halbrendt JM, Jones AT, Vrain TC & Robbins RT (1994) Transmission of three North American nepoviruses by populations of four distinct species of the Xiphinema americanum group. Phytopathology 84, 646-649.

Cobb NA (1913) New nematode genera found inhabiting freshwater and non-brackish soils. Journal of the Washington Academy of Science 3, 432–444.

EFSA PHL Panel (2018) Jeger M, Bragard C, Caffier D, Candresse T, Chatzivassiliou E, Dehnen‐Schmutz K, Gilioli G, Grégoire JC, Miret JAJ, MacLeod A & Navarro MN. Pest categorisation of Xiphinema americanum sensu lato. EFSA Journal 16(7), 5298. https://doi.org/10.2903/j.efsa.2018.5298

EPPO (2013) EPPO Standards. Diagnostics. PM 7/119 (1) Nematode extraction. EPPO Bulletin 43, 471–495.

EPPO (2017) EPPO Standards. Diagnostics. PM 7/95 (2) Xiphinema americanum sensu lato. EPPO Bulletin 47(2), 198–210.

FERA (2014) Rapid Pest Risk Analysis for Xiphinema americanum s.l. (European populations). https://secure.fera.defra.gov.uk/

Flegg JJM (1967) Extraction of Xiphinema and Longidorus spp. from soil by a modification of Cobb’s decanting and sieving technique. Annals of Applied Biology 60, 429–437.

Griesbach JA & Maggenti AR (1989) Vector capability of Xiphinema americanum sensu lato in California. Journal of Nematology 21(4), 517.

Halbrendt JM & Brown DJ (1992) Morphometric evidence for three juvenile stages in some species of Xiphinema americanum sensu lato. Journal of Nematology 24, 305-309.

Heve WK, Crow WT & Mengistu T (2015) Xiphinema spp. - dagger nematode. Available online: https://entnemdept.ifas.ufl.edu/creatures/nematode/dagger_nematode.htm

Hunt DJ (1993) Aphelenchida, Longidoridae and Trichodoridae: Their Systematics and Bionomics. Wallingford, CABI, UK: 352 pp.

IPPC (2016) ISPM 27 Diagnostic Protocols for Regulated Pests DP 11: Xiphinema americanum sensu lato. IPPC Secretariat, FAO, Rome (IT).

Klos EJ, Fronek F, Knierim JA & Cation D (1967) Peach rosette mosaic transmission and control studies. Michigan Agricultural Experiment Station Quarterly Bulletin 49, 287-293.

Lazarova S, Oliveira CMG, Prior T, Peneva V & Kumari S (2019) An integrative approach to the study of Xiphinema brevicolle Lordello and Da Costa 1961, supports its limited distribution worldwide (Nematoda: Longidoridae). European Journal of Plant Pathology 153(2),441-464.

Mobasseri M, Hutchinson MC, Afshar FJ & Pedram M (2019) New evidence of nematode-endosymbiont bacteria coevolution based on one new and one known dagger nematode species of Xiphinema americanum-group (Nematoda, Longidoridae). PloS One 14(6), e0217506. https://doi.org/10.1371/journal.pone.0217506

NVWA (The Netherlands Food and Consumer Product Safety Authority) (2010) Pest Risk Analysis for Xiphinema americanum s.l. 77pp. https://pra.eppo.int/pra/1eb7d285-8ce3-4170-8f95-9a1b44547555

Oostenbrink M (1960) Estimating nematode populations by some selected methods. In Nematology (ed. Sasser JN & Jenkins WR), pp. 85–102. The University of North Carolina Press, Chapel Hill, NC(US).

Robbins RT, Brown DJF, Halbrendt JM & Vrain TC (1996) Compendium of juvenile stages of Xiphinema species (Nematoda: Longidoridae). Russian Journal of Nematology 4, 163-171.

Sertkaya G (2010) Tomato ringspot nepovirus (ToRSV) in wild blackberry (Rubus fruticosus L.) in Hatay province of Turkey. Julius-Kuhn-Archiv (Conference proceedings) 427, 201-203.

Stankiene J, Mazeikiene I, Gelvonauskiene D, Siksnianiene JB & Bobinas C (2012) Virological assessment of stock planting material of apple and raspberry cultivars. Zemdirbyste-Agriculture 99 (1), 93-98.

Taylor CE & Brown DJF (1997) Nematode vectors of plant viruses. CABI, Wallingford, UK, 278 pp.

Teliz D, Grogan RG & Lownsbery BF (1966) Transmission of tomato ringspot, peach yellow bud mosaic, and grape yellow vein diseases by Xiphinema americanum. Phytopathology 56, 658-663.

Vazifeh N, Niknam G, Jabbari H & Naghavi A (2019) Description of a new dagger nematode, Xiphinema barooghii n. sp. (Nematoda: Longidoridae) and additional data on the three known species of the genus from northwest of Iran. Journal of nematology 51, 1-17. https://doi.org/10.21307/jofnem-2019-007

This datasheet was prepared in 2023 by Tom Prior. His valuable contribution is gratefully acknowledged.

EPPO (2024) Xiphinema americanum sensu stricto. EPPO datasheets on pests recommended for regulation. https://gd.eppo.int (accessed 2024-12-22)

This datasheet was first published in the EPPO Bulletin in 1984 and revised in the two editions of 'Quarantine Pests for Europe' in 1992 and 1997 (as part of Xiphinema americanum), as well as in 2023. It is now maintained in an electronic format in the EPPO Global Database. The sections on 'Identity', ‘Hosts’, and 'Geographical distribution' are automatically updated from the database. For other sections, the date of last revision is indicated on the right.

CABI/EPPO (1992/1997) Quarantine Pests for Europe (1st and 2nd edition). CABI, Wallingford (GB).

EPPO (1984) Data sheet on quarantine organisms no 150: Xiphinema americanum. EPPO Bulletin 14(1), 67-71. https://doi.org/10.1111/j.1365-2338.1984.tb01984.x