Longidorus elongatus: Needle nematode

California Pest Rating for

Longidorus elongatus (de Man, 1876) Micoletzky, 1922

(Needle nematode)

Pest Rating: B

PEST RATING PROFILE

Initiating Event:

The CDFA’s latest record of detection of Longidorus elongatus was in 2013 during a statewide survey for plant parasitic nematodes associated with golf course turf and citrus orchards. The nematode species was detected in turf (Poa sp.) samples from a golf course in Marin County, California. Prior to this find, L. elongatus was last detected in California only few times during the early 60s to late 70s. The current temporary Q-rating of the nematode species is reassessed here and a permanent rating is proposed.

History & Status:

Background: Longidorus elongatus is an obligate ectoparasite of host plants and feeds at or just behind root tips causing a characteristic swelling or galling of the tips as well as a general stunting of the root system. Longidorus elongatus has four juvenile stages and most likely produces one generation a year especially under field conditions however, there is a two- to four-fold increase on favored hosts. The nematode species is found in cool soils that may vary from peat to sandy loams, although the species appears to prefer coarse, well-drained soils. Adults may live for several years, and the time to complete its life cycle is dependent on soil temperature. At 20 ºC a generation takes 19 weeks with a twenty-fold increase in population on wild (Woodland) strawberry, and at 30 ºC the life cycle is completed in 9 weeks. Males are rare and reproduction is usually by parthenogenesis, except where males are common, in which case bisexual reproduction occurs.

Damage Potential: Severe damage to certain crops has been caused by the direct feeding of the nematode. However, the major economic impact caused by this nematode is due to its ability to vector plant viruses. Longidorus elongatus transmits the Scottish strains of raspberry ringspot virus (RRV), tomato black ring virus (TBRV). Strawberry roots are damaged both by the direct feeding of the nematode as well as transmitted RRV and TBRV. Raspberry, although a poor host to the nematode, is readily infected by both viruses transmitted by the nematode resulting in severe crop loss. Longidorus elongatus and Trichodorus spp. (stubby root nematode) and viruses are involved in ‘Docking Disorder” of sugarbeet. The virus is carried on the inner surface of the guiding sheath of the nematode’s stylet. The nematode species also transmits spoon leaf virus to red currants, certain raspberry varieties and weeds.

Hosts: The species can feed on over 60 plant species comprising of a wide variety of herbaceous annual and perennial crops and weeds. Direct feeding by the nematode alone has caused severe crop damage to strawberry, sugarbeet, rye grass, potato, cereals (millets, wheat and barley), carrots and peppermint. In the USA, there are reports of severe damage caused to carrots, rye grass and peppermint.

Transmission: The nematode species is able to spread over short and long distances when transported in infested soils accompanying plant stock, farm machinery, runoff and splash contaminated irrigation water, human and animal activity and soil contaminated clothing.

Worldwide Distribution: Longidorus elongatus occurs in a wide range of soils, especially, sandy and sandy loam soils, and has been found mainly in temperate regions. Worldwide distribution of the species include, Asia: India, Kazakhstan, Pakistan, Tajikstan, Turkey, Uzbekistan, Vietnam; Africa: South Africa; North America: Canada, USA; Europe: Austria, Belgium, Bulgaria, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Latvia, Moldova, Netherlands, Norway, Poland, Portugal, Romania, Russian Federation, Slovakia, Spain, Sweden, Switzerland, United Kingdom, Ukraine; Oceania: New Zealand (CABI, 2014; EPPO, 2014).

In the USA, Longidorus elongatus has been found in Arkansas, Oregon and California (CABI 2014; EPPO, 2014; CDFA Nematode detection records – ‘Initiating event’). Robbins and Brown (1991) noted that the accuracy of early reports of L. elongatus from Alabama, Florida, Idaho, Illinois, Michigan, New Jersey, New Mexico, Pennsylvania, Rhode Island, South Carolina, Texas, and Tennessee listed by Norton et al., (1984), was doubtful due to the wide morphometric variation in range values for L. elongatus that may refer to other Longidorus species.

Official Control: Longidorus elongatus is on the Harmful Organism lists of the following countries: Canada, Chile, Costa Rica, Ecuador, Honduras, Indonesia, and Taiwan (PCIT, 2015).

California Distribution: CDFA’s Nematode detection records indicate that Longidorus elongatus was detected 34-40 years ago in two commercial sites: 1 in Borrego, San Diego County on Grape in 1962, and the other in Yountville, Napa County on Pear in 1977. Also it was discovered on 3 private properties: San Leandro, Alameda County in 1962; Santa Barbara, Santa Barbara County in 1976; San Francisco, Harding Park Golf course, San Francisco County in 1979. The nematode species was not detected in California until 2013 in Marin County during a statewide golf course survey.

California Interceptions: Since 1979, there has only been a single detection of Longidorus elongatus associated with an unknown houseplant that was intercepted at the Alturas Border Protection Station.

The risk Longidorus elongatus would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.
– Medium (2) may be able to establish in a larger but limited part of California.
– High (3) likely to establish a widespread distribution in California.

Risk is Medium (2) – Longidorus elongatus is able to establish in cool and moist regions of California.

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.
– Medium (2) has a moderate host range.
– High (3) has a wide host range.

Risk is High (3) – Longidorus elongatus has a very wide host range which includes herbaceous annual and perennial crops, turf grass, and weeds.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.
– Medium (2) has either high reproductive or dispersal potential.
– High (3) has both high reproduction and dispersal potential.

Risk is High (3) – The nematode’s life cycle and increase is dependent on soil temperature and plant host. Long and short distance spread is mainly through infested soils accompanying plant stock, farm machinery, runoff and splash contaminated irrigation water, human and animal activity and soil contaminated clothing.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield.
B. The pest could lower crop value (includes increasing crop production costs).
C. The pest could trigger the loss of markets (includes quarantines).
D. The pest could negatively change normal cultural practices.
E. The pest can vector, or is vectored, by another pestiferous organism.
F. The organism is injurious or poisonous to agriculturally important animals.
G. The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts.
– Medium (2) causes 2 of these impacts.
– High (3) causes 3 or more of these impacts.

Risk is High (3) – Infestations of Longidorus elongatus could result in lowered crop yield and value, loss in market, and change in cultural practices to mitigate risk of spread to non-infested sites. The main economic damage is due to the ability of L. elongatus to vector Raspberry ringspot virus and Tomato black ring virus.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.
B. The pest could directly affect threatened or endangered species.
C. The pest could impact threatened or endangered species by disrupting critical habitats.
D. The pest could trigger additional official or private treatment programs.
E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.
– Medium (2) causes one of the above to occur.
– High (3) causes two or more of the above to occur.

Risk is Medium (2) – The impact of Longidorus elongatus on natural environments is not known, however, the infestations of the pest could affect cultural practices, home gardening and ornamental plantings.

Consequences of Introduction to California for Longidorus elongatus:

Add up the total score and include it here. (Score)

-Low = 5-8 points
-Medium = 9-12 points
-High = 13-15 points

Total points obtained on evaluation of consequences of introduction of Longidorus elongatus to California = (13).

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

-Not established (0) Pest never detected in California, or known only from incursions.
-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).
-Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.
-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is Medium (-2). Including the earlier detections of Longidorus elongatus, the species has been detected in northern and southern cool coastal and sub coastal counties of California.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score: Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 11

Uncertainty:

While Longidorus elongatus has not been detected in California’s agricultural production sites for the past 34 years, as determined through CDFA’s different nematode detection programs and special surveys, there is always the possibility that this species may be detected in future targeted surveys thereby increasing its distribution. Such detections may alter the proposed rating of L. elongatus.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for the needle nematode, Longidorus elongatus, is B.

References:

CABI. 2014. Longidorus elongatus full datasheet report. Crop Protection Compendium. www.cabi.org/cpc/ .

EPPO. 2014. Longidorus elongatus (LONGEL). European and Mediterranean Plant Protection Organization PQR database. http://www.eppo.int/DATABASES/pqr/pqr.htm .

Norton, D. C., P. Donald, J. Kimpinski, R. F. Meyers, G. R. Noel, E. M. Noffsinger, R. T. Robbins, D. C. Schmitt, C. Sosa-Moss, and T. C. VRAIN. (1984). Distribution of plant-parasitic nematodes in North America. Society of Nematologists, Hyattsville, Maryland, 1-19.

PCIT. 2015. USDA Phytosanitary Certificate Issuance & Tracking System. https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp .

Robbins, R. T. and D. J. F. Brown. 1991. Comments on the taxonomy, occurrence and distribution of Longidoridae (Nematoda) in North America. Nematologica 37:395-419.

Responsible Party:

Dr. John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.