Rotylenchulus reniformis (Reniform Nematode)

California Pest Rating for

Rotylenchulus reniformis Linford & Oliveira, 1940

(Reniform Nematode)

Pest Rating: A

PEST RATING PROFILE

Initiating Event:

For the past several decades, CDFA Nematologists have detected the invasive reniform nematode, Rotylenchulus reniformis, mainly in imported nursery plants. For example, in 2012, the reniform nematode was detected in three separate shipments of 1,288 Beaucarnea sp. and 44 Beaucarnea recurvata and 174 Dracaena marginata plants from Florida destined to Orange County, one shipment of 24 Euphorbia sp. and 12 Dracaena marginata plants also from Florida destined to San Mateo County, and 250 Yucca elephantipes destined to San Diego County. While in 2013, 90 reniform nematode-infected Sansevieria sp. plants were intercepted in shipments from Florida to San Mateo County, and in 2015, 45 reniform nematode-infected Dracaena reflexa plants in shipments from Florida to San Diego County. Detection of this nematode species resulted in subsequent action taken to prevent its introduction and establishment in California. The pest rating proposal is used here to test the validity of the current rating of an already considered high-risk nematode pest.

History & Status:

Background: The reniform nematode, in its adult female stage, is an obligate sedentary semi-endoparasite of plant roots. All juvenile stages, immature females, mature males and eggs are found within rhizosphere soils of host plants. The species is bisexual and reproduces through cross fertilization and parthenogenesis, completely a life cycle from egg to egg in about 24-29 days on okra (17-23 days on cotton). Males do not feed. Soon after the final molt the vermiform, immature adult female becomes infective and seeks to penetrate host roots. After infecting the roots the young females become oriented perpendicularly to the longitudinal axis of the roots with usually only the anterior part of the body embedded within the root tissue. In cotton and other crops, Feeding occurs on tissue of the cortex, phloem and pericycle. Nurse cells are formed near the pericycle with hypertrophy of pericycle and endodermis cells. Epidermal and cortical cells are destroyed resulting in slight browning and necrosis of surrounding tissue. About one week after root penetration, the immature female body enlarges and matures to form the typical kidney shape and secretes a gelatinous matrix that encases her body on the surface of the root. It is within this matrix that the female lays 75-120 eggs per day. The nematode is capable of surviving in air-dried soil for extended periods of time: 7 months at 20-25C, for 6 months in dry soil, and has been reported to survive 29 months in the absence of the host. Two races have been reported in India, differentiated by reactions on cowpea, castor and cotton. Reproduction and development of the reniform nematode are favored by fine textured soils with a relatively high content of silt and/or clay.

The Reniform Nematode has been found to attack over 140 species of more than 115 plant genera in 46 families. Some of the economically important host plants are banana, cabbage, cantaloupe, citrus, kale, lettuce, mango, okra, pigeon pea, pineapple, sugarcane, cotton, corn, onion, beans, potato, carrot, plum, pear, cowpea, soybean, tobacco, eggplant, and tomato. Several ornamental foliage plants also are hosts. In California, potential damage and crop loss of cotton, grapes, citrus, tomato, and ornamentals would be of major concern. Yield loss in cotton up to 60% was reported in infested fields of Louisiana and Mississippi, also in tomato.

The nematode is readily transported over long distances in plant roots and associated soil, as well as spread over short distances in contaminated, run-off irrigation water, infested plant roots and soil. Therefore, imported nursery plants and farm -destined crops are potential pathways of entry.

Worldwide Distribution: The reniform nematode is widely distributed in many tropical and subtropical regions of the world. It has been reported in most of Africa, the Caribbean, Japan, the Middle East, South Pacific, Central America, Italy, Spain, Mexico, China and the Far East. Within the USA it is established in Alabama, Arkansas, Florida, Georgia, Hawaii, Louisiana, Mississippi, North Carolina, South Carolina and Texas.

Official Control: In 2012, the reniform nematode is included on a list of harmful organism under official control in Argentina, Bermuda, Chile, French Polynesia, Republic of Korea and Turkey. Within the USA it is under official control in the states of Arizona and California.

California Distribution: Reniform nematode is not established in California. In 1967, the nematode was detected in 13 residential properties in San Bernardino County. The infestation was traced to yuccas brought into California from Harlingen, Texas, and plant in the subdivision. In December, 1978, the nematode was officially declared eradicated after subsequent herbicide and fumigation (DBCP) trials of the infested areas.

California Interceptions: Over the past several decades, reniform nematode has been frequently detected in incoming quarantine shipments of nursery and household plants at nurseries and border stations.

The risk reniform nematode 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). Rotylenchulus reniformis is likely to establish a widespread distribution in California especially in fine textured soils, and mainly wherever its host is able to grow.

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 High (3). Rotylenchulus reniformis has a wide host range.

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). Rotylenchulus reniformis has both high reproduction and dispersal potential.

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 by other states or countries)

D. The pest could negatively change normal production 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). The establishment of Rotylenchulus reniformis in California could result in the lowered crop yield and value, increased crop production costs, loss of markets, imposition of domestic and international quarantines against California export plant commodities, and alteration of normal cultural practices, including application of irrigation water, to inhibit spread of the pathogen to non-infested sites. Cotton, grape, tomato, citrus and ornamental are the main industries that would be affected, additionally several other crops of lesser production are also at risk.

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. Significantly impacting 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 High (3). The establishment of Rotylenchulus reniformis in California could adversely impact the environment by destroying natural communities, critical habitats, significantly affect residential gardening and cultural practices thereby requiring additional official or private treatment programs. Given its wide host range several, agricultural and environmental communities are at definite risk of being impacted. These can include habitats of minor and major animal communities.

Consequences of Introduction to California for Common Name: Score

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 to California = 15 (High).

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: Rotylenchulus reniformis is not established in California (0). The nematode species has never been detected within California. Eradicative actions taken subsequent to the detection of the nematode species in imported nursery and household plant shipments, vigilant screening of plant materials grown in California soils and inspected for plant parasitic nematodes through CDFA’s phytosanitary certification programs, and all published studies to date on plant parasitic nematodes in California have never resulted in the detection of R. reniformis.

Final Score:

Final Score: Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 15 (High).

Uncertainty:

The damage potential and crop loss information on several hosts of this nematode species are yet to be determined. Nevertheless, based on the nematode’s biology, diverse host range, and favorable climatic conditions that (historically have) allowed the pest to establish within California (and then be eradicated), more information gained on crop damage and losses can only further confirm the reniform nematode as a pest of major economic importance within several regions of California.

Conclusion and Rating Justification:

Based on the evidence presented above, reniform nematode is definitely a pest of high risk to agricultural and environmental communities of California. The current given “A” pest rating of Rotylenchulus reniformis is duly justified and is herein, proposed to remain unchanged.

References:

Birchfield, W., and W. J. Martin. 1967. Reniform nematode survival in air-dried soil. Phytopathology 57:804.

Chitambar, J. J. 1997. A brief review of the reniform nematode, Rotylenchulus reniformis. California Plant Pest & Damage Report, California Department of Food and Agricultural 16:71-73.

Dasgupta, D. R., and A. R. Seshadri. 1971. Races of the reniform nematode Rotylenchulus reniformis Linford and Oliviera, 1940. Indian Journal of Nematology 1:21-24.

Ferris, H., K. M. Jetter, I. A. Zasada, J. J. Chitambar, R. C. Venette, K. M. Klonsky, and J. Ole Becker. 2003. Risk Assessment of plant parasitic nematodes. In Exotic Pests and Diseases Biology and Economics for Biosecurity, D. A. Summer Editor. Iowa State Press. 265 p.

Jatala, P. 1991. Reniform and false root-knot nematodes, Rotylenchulus and Nacobbus spp. In Manual of Agricultural Nematology, edited by W. R. Nickle, Marcel Dekker, Inc., 1035p.

Koenning, S. R., S. A. Walters, and K. R. Barker. 1996. “Impact of soil texture on the reproductive and damage potentials of Rotylenchulus reniformis and Meloidogyne incognita on Cotton. Journal of Nematology, 28:527-536.

Robinson, A. F., C. M. Heald, S. L. Flanagan, W. H. Thames and J. Amador. 1987. Geographical distribution of Rotylenchulus reniformis, Meloidogyne incognita, and Tylenchulus semipenetrans in the lower Rio Grande valley as related to soil texture and land use. Annals of Applied Nematology 1:20-25.

Responsible Party:

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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