California Pest Rating for
Pratylenchus neglectus (Rensch, 1924) Filipjev & Schuurmans-Stekhoven, 1941
Pest Rating: C
PEST RATING PROFILE
During the 1950-60s, several species of plant parasitic nematodes were given a ‘D’ rating as they were regarded as parasites, predators or organisms of little or no economic importance that did not require State enforced regulatory action. However, these nematode species were inaccurately assigned a D rating as most, if not all, are plant parasitic and therefore, capable of damaging plant production and causing significant economic losses especially at the county and local residential/grower level. Furthermore, the detection of plant parasitic nematodes in nursery stock is an indication of contamination in violation of the State’s standard of pest cleanliness required for nurseries. Pratylenchus neglectus was originally rated D and its risk of infestation and permanent rating are re-assessed here.
History & Status:
Background: The California meadow nematode, Pratylenchus neglectus (synonym P. minyus) is an obligate migratory endoparasite that first feeds externally then enters plant roots, feeds, reproduces and moves 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. neglectus has six life stages: egg, four juvenile stages and adults. Reproduction is by parthenogenesis (without fertilization). 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 in P. neglectus, the life cycle can take as few as 28 days on tobacco with greater reproduction at 38°C than at higher and lower temperatures (Townshend & Anderson, 1976). Pratylenchus neglectus survives the winter in infected roots or soil as eggs, juveniles or adults. It can survive at 2°C but not at sub-zero temperatures. During spring, when plant growth is active, eggs hatch, nematodes are attracted to the plant roots and begin to feed and continue their 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: Pratylenchus neglectus is primarily a parasite of grasses, but its diverse range of hosts include, fruit trees, pistachio, pear, apple, maize, potato, wheat, cereals, rapeseed, legumes, alfalfa, red clover, tobacco, peppermint, soybean, turf and pasture grasses, sugarcane, strawberry, carrots, cabbage (CABI, 2014; Castillo & Vovlas, 2007; Townshend & Anderson, 1976).
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 neglectus is capable to reducing root growth and function thereby, causing reduction in plant growth and yield of its associated host plants. It can cause significant losses in tobacco and peppermint production. In the Pacific Northwest of the United States, P. neglectus has been reported to reduce wheat yields individually or in mixed populations with a different root lesion nematode species, P. thornei (Smiley, et al., 2014).
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: Pratylenchus neglectus has been reported worldwide in Asia: India, Iran, Japan, Oman, Pakistan, Turkey, Africa: Algeria, Tunisia, Morocco, South Africa; Australia: Western Australia, Tasmania; Europe: Bulgaria, Croatia, Estonia, France, Germany, Italy, Poland, Portugal, Russia, Slovakia, Slovenia, Spain, Yugoslavia; North America: USA, Canada, Mexico; South America: Argentina (CABI, 2014; Castillo & Vovlas, 2007; Townshend & Anderson, 1976).
In the USA, Pratylenchus neglectus has been reported in California, and several other states including, Idaho, Iowa, Montana, New York, Ohio, Oregon, Washington, and the Pacific Northwest United States (CABI, 2014; Castillo & Vovlas, 2007; Hafez et al., 2010; Smiley et al., 2004).
Official Control: Currently, Pratylenchus neglectus is rated ‘D’ by CDFA. Canada, Ecuador and Peru include the species on their Harmful Organism Lists (PCIT, 2015).
California Distribution: Pratylenchus neglectus is widely distributed in California. In statewide surveys for plant parasitic nematodes in California’s agricultural crop production site conducted by CDFA during 2005-2009, P. neglectus was found in almost every county.
California Interceptions: Pratylenchus neglectus has been detected in several incoming shipments of plants and soil to California.
The risk Pratylenchus neglectus 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 neglectus is able to establish throughout the State.
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 Medium (2) – Pratylenchus neglectus is primarily a parasite of grasses, but its diverse range of hosts are grown throughout the State and include, fruit trees, pistachio, pear, corn, potato, wheat, cereals, rapeseed, legumes, alfalfa, red clover, tobacco, peppermint, soybean, turf and pasture grasses, sugarcane, strawberry, carrots.
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) –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 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 Low (1) – At the local residential/grower level, Pratylenchus neglectus infections could result in lowered crop yield.
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 Pratylenchus neglectus on natural environments is most likely not significant as the species is already widespread without causing apparent detriment to ecological balances and processes, however, the infestations of this root lesion nematode could affect home/urban gardening.
Consequences of Introduction to California for Pratylenchus neglectus:
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 neglectus to California = (11).
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 High (-3). Pratylenchus neglectus is widely spread in several contiguous and non-contiguous climate and host regions throughout the state.
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 = 8
Conclusion and Rating Justification:
Based on the evidence provided above the proposed rating for the lesion nematode, Pratylenchus neglectus, is C.
CABI. 2014. Pratylenchus neglectus (nematode, California meadow) basic datasheet. http://www.cabi.org/cpc/datasheet/43899
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
Smiley, R.W., K. Merrifield, L. M. Patterson, R. G. Whittaker, J. A. Gourlie, and S. A. Easley. 2004. Nematodes in dryland field crops in the semiarid Pacific Northwest United States. Journal of Nematology, 36:54-68.
Smiley, R. W., J. A. Gourlie, G. Yan., and K. E. L. Rhinhart. 2014. Resistance and tolerance of Landrace wheat in fields infested with Pratylenchus neglectus and P. thornei. Plant Disease, 98:797-805.
Townshend, J. L. and R. V. Anderson. 1976. Pratylenchus neglectus [=P. minyus]. C.I.H. Descriptions of Plant-parasitic Nematodes, Set 6, No. 82.
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.
Comment Period: CLOSED
The 45-day comment period opened on Tuesday, January 5, 2016 and closed on February 19, 2016.
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Consequences of Introduction: 1. Climate/Host Interaction: [Your comment that relates to “Climate/Host Interaction” here.]
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Pest Rating: C
Posted by ls