Pratylenchus alleni | Pest Rating Proposals and Final Ratings

California Pest Rating for

Pratylenchus alleni Ferris, 1961

Pest Rating: A

PEST RATING PROFILE

Initiating Event:

The risk of infestation of Pratylenchus alleni in California is evaluated and a permanent rating is proposed.

History & Status:

Background: The root lesion nematode, Pratylenchus alleni, was first discovered in El Dorado, Illinois infesting nine varieties of soybeans cultivated in a single field (Ferris, 1961). The nematode species can seriously affect soybean production and also is associated with other agricultural crops.

Pratylenchus alleni is a migratory endoparasite that can enter plant roots, feed, reproduce and move freely within the tissue while spending its entire life cycle there. The species can also be found in soil around roots. Within the roots, feeding is confined to the root cortex. Like other Pratylenchus species, P. alleni has six life stages: egg, four juvenile stages and adults. Reproduction requires both females and males. First stage juveniles develop within the egg, followed by a first molt to the second stage juvenile that hatches from the egg. Each stage develops into the next via a molt of its cuticle (outer body covering). All juvenile and adult stages are worm-shaped (vermiform). All post-hatch stages are motile and can infect plants. Generally, root lesion nematodes have a life cycle 45-65 days, but the duration is affected by temperature and moisture. Pratylenchus alleni survives the winter in infected roots or soil as eggs, juveniles or adults. During spring, when plant growth is active, eggs hatch to commence the life cycle within roots or in rhizosphere soil. Within the root, the nematode feeds on cortical tissue causing necrosis of cortical cells, cell breakdown, and formation of cavities. Necrosis is apparent as lesions which expand as the nematodes move lengthwise within the infected roots. Some nematodes may leave the root, enter soil and re-enter the root at a different site causing a new infection.

Hosts: Soybean, vetch, chickpea, castor bean, cotton, wheat, corn, potato, tomato, Zygophyllum sp., raspberry, sunflower, chrysanthemum, marigold (Bernard & Keyserling, 1985; Castillo & Vovlas, 2007; Dickerman, 1979; Hackney & Dickerson, 1975).

Symptoms: In general, root lesion infection results in plant exhibiting symptoms of chlorosis, wilting, and stunting. Infected roots show initial symptoms of small, water-soaked lesions that soon turn brown to black. Lesions are formed along the root axis and may coalesce laterally to girdle the roots which are killed. Affected root tissue may slough off leaving a severely reduced root system. Secondary infection by fungi and bacteria may further destroy the root system by causing sloughing off of the root tissues and rot. Plant yield is reduced and in severe infections plants may be killed.

Damage Potential: Pratylenchus alleni is capable to severely reducing root growth and function thereby, causing reduction in plant growth and yield. In Canada, field-grown soybean suffered a 38 to 54 % reduction in yield due to Pratylenchus alleni (Bélair et al., 2013). In temperate regions, poor potato growth has been caused by associated P. alleni (Brodie et al., 1993).

Spread: On its own, Pratylenchus species move can move 1-2 m from an infected root. The main mode of long and short distance spread is artificial. Infected roots, bare root propagative plant materials, soil debris, run-off and irrigation water, cultivation tools, equipment and human activity that can move soils from infested to non-infested sites.

Worldwide Distribution: Asia: India, Turkey, Europe: Martinique (France), Russia; North America: USA, Canada; South America: Argentina (Castillo & Vovlas, 2007).

In the USA, Pratylenchus alleni has been reported from Arkansas, Illinois, Iowa, and Ohio (Brown et al., 1980; Ferris, 1961; Robbins et al., 1987; Williams, 1982).

Official Control: None reported.

California Distribution: Pratylenchus alleni is not known to be present in California.

California Interceptions: Pratylenchus alleni has never been detected in incoming shipments of plants and soil to California.

The risk Pratylenchus alleni 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 High (3) – Pratylenchus alleni is able to establish in cool and moist, as well as warmer regions of California, wherever its host plants are capable of growing.

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

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

Risk is Medium (2) – Of what has been reported, Pratylenchus alleni has a moderate and diverse host range that includes several economically important agricultural crops. Further studies on the host range of this species may be needed. While soybean is not a major crop produced in California, other hosts such as potato, tomato, cotton and corn are cultivated under larger acreage.

3) Pest Dispersal Potential: Evaluate the dispersal potential of the pest:

-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 Infected roots, bare root propagative plant materials, soil debris, run-off and irrigation water, cultivation tools, equipment and human activity that can move soils from infested to non-infested sites.

4) Economic Impact: Evaluate the economic impact of the pest to California using these criteria:

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) – Pratylenchus alleni infections 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.

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

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:

– 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 Pratylenchus alleni on natural environments is not known, however, the infestations of this root lesion nematode could affect cultural practices, home gardening and ornamental plantings.

Consequences of Introduction to California for Pratylenchus alleni:

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 Pratylenchus alleni 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 “Not established” (0). Pratylenchus alleni has never been detected in 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 = 13.

Uncertainty:

Pratylenchus alleni has never been detected through CDFA’s Nematode detection regulatory programs, nor has it been reported in California by other scientists. Nevertheless, surveys for this species in agricultural production and environmental sites need to be conducted to ascertain its non presence in California.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for the lesion nematode, Pratylenchus alleni, is A.

References:

Acosta, N. 1982. Influence of inoculum level and temperature on pathogenicity and population development of lesion nematodes on soybean. Nematropica 12:189-197.

Acosta, N., and R. B. Malek. 1979. Influence of temperature on population development of eight species of Pratylenchus on soybean. Journal of Nematology 11:229-232.

Bélair, G., B. Mimee, M. O. Duceppe and S. Miller. 2013. First report of the root-lesion nematode Pratylenchus alleni associated with damage on soybean in Quebec, Canada. Plant Disease 97:292. http://dx.doi.org/10.1094/PDIS-03-12-0309-PDN .

Bernard, E. C., and M. L. Keyserling. 1985. Reproduction of root-knot, lesion, spiral and soybean cyst nematodes. Plant Disease 69:103-105.

Brodie, B. B., K. Evans and J. Franco. 1993. Nematode parasites of potatoes. In: Evans, K., D. L. Trudgill and J. M. Webster (Eds). Plant parasitic nematodes in temperate agriculture. Wallingford, UK, CABI Publishing, pp. 87-132.

Brown, M. J., R. M. Riedel and R. C. Rowe. 1980. Species of Pratylenchus associated with Solanum tuberosum cv. Superior in Ohio. Journal of Nematology 12:189-192.

Castillo, P. and N. Vovlas. 2007. Pratylenchus (Nematoda: Pratylenchidae): diagnosis, biology, pathogenicity and management. Hunt, D. J., and R. N. Perry (Series Eds).Nematology monographs and perspectives

Dickerson, O. J. 1979. The effects of temperature on Pratylenchus scribneri and P. alleni populations on soybeans and tomatoes. Journal of Nematology 11:23-26.

Ferris, V. R. 1961. A new species of Pratylenchus (Nemata-Tylenchida) from roots of soybeans. Proceedings of the Helminthological Society of Washington 28:109-111.

Hackney, R. W. and O. J. Dickerson. 1975. Marigold, Castor bean, and chrysanthemum as controls of Meloidogyne incognita and Pratylenchus alleni. Journal of Nematology 7:84-90.

Robbins, R. T., R. D. Riggs and D. Von Steen. 1987. Results of annual phytoparasitic nematode surveys of Arkansas soybean fields, 1978-1986. Annals of Applied Nematology 1:50-55.

Williams, D. D. 1982. The known Pratylenchidae (Nematode) of Iowa. Iowa State Journal of Research 56:419-424.

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.