Heterodera carotae | Pest Rating Proposals and Final Ratings

California Pest Rating Proposal for

Heterodera carotae Jones, 1950

Pest Rating: B

PEST RATING PROFILE

Initiating Event:

None.

History & Status:

Background: Prior to the discovery of the carrot cyst nematode, “carrot-sickness” was believed to be caused by pathogenic fungi. However, in 1931, when all cyst-forming nematodes were considered strains of H. schachtii (sugarbeet cyst nematode), Triffit (1931) found that Heterodera females on carrots cultivated in UK, were atypical and smaller than H. schachtii. This led to possibly the first record of H. carotae (Mathews, 1975). In 1944, Jones (1950) found field-grown carrots infested with cyst nematodes in Chatteris, Isle of Ely, England. This discovery resulted in the report of a distinct new species, H. carotae. Since then, H. carotae has been reported as a pest of carrots in several countries of Europe, and fewer countries in Asia and North America (see: ‘Worldwide Distribution’).

Hosts: The host range is limited to Daucus spp. including, Daucus carota ssp. sativa (carrot), D. carota ssp. carota, D. pulcherrimus (Jones 1950), and several wild Umbelliferae, such as Torilis leptophylla (bristlefruit hedgeparsley), T. arvensis (spreading hedgeparsley), T. japonica (erect hedgeparsley) (Mugniéry & Bossis, 1988).

Symptoms: There are no specific above ground symptoms in plants that can be attributed to infection by carrot cyst nematode. General above ground symptoms include stunting with leaves appearing yellowish-red then turning necrotic in the older parts. In fields, poor and patchy plant growth is apparent in small, circular areas which may extend to the entire field resulting in complete loss of crop. Infested tap roots are usually smaller than those of non-infested plants with abnormal prolific growth of lateral roots giving a bearded appearance. Also, tap roots may be distorted and deformed with several growing points or digitate root apex (Greco, 1986, 1987; Mathews, 1975).

Biology: Eggs produced by Heterodera carotae females are retained in cysts and egg sacs. The first juvenile stage and first molt occur within the egg, and the infective second stage juveniles emerge during egg hatch. Hatching from cysts is usually delayed, whereas, juveniles from egg sacs hatch as soon as favorable soil temperature and soil moisture are available. Eggs from cysts hatch only under the stimulus of root exudates of carrots however, root exudates from other plant species including members of Umbelliferae, do not significantly influence hatching of eggs from cysts. Age of carrot plant affects hatching, and eggs from cysts less than 2 months old rarely hatch, but juveniles regularly emerge from mature cysts provided environmental conditions are favorable. Second stage juveniles from egg sacs hatch promptly under favorable soil moisture and soil temperature, and stimulus of exudates from host plants is not necessary since eggs from egg sacs can hatch in water under suitable environment. While egg hatch may occur at 5°C, the optimum temperature range is 15-20°C and at 25°C hatching is repressed. Emerged second stage juveniles move through the soil in search of a suitable host which, once found, they penetrate. Root penetration occurs at 5-30°C, but the nematode does not develop below 10°C. Heterodera carotae is a sedentary endoparasite. Once within the root, second stage juveniles establish a typical feeding site and undergo three more molts to develop into white, lemon-shaped females and worm-shaped males. After mating, the female produces a gelatinous matrix in which 100 or more eggs are laid. Eggs are also retained within the female’s body which forms a brown cyst, without forming an intermediate ‘yellow stage’. Females and cysts develop 26 and 36 days after carrot root invasion at 20°C (Greco, 1986, 1987; Baldwin & Mundo-OCampo, 1991).

Damage Potential: Infected carrot roots are small, deformed, and unmarketable. Yields are reduced, however quantitative losses in yield have not been reported. Severe infections may result incomplete loss of crop.

Spread: Infected nursery stock, infected plants, soil contaminated with cysts, cysts, nematode-infested irrigation water.

Worldwide Distribution: Asia: Cyprus, India; Africa: South Africa; Europe: Denmark, France, Germany, Hungary, Italy, Ireland, The Netherlands, Portugal, Poland, Russia, Serbia, Slovenia, Slovakia, Sweden, Switzerland, UK; North America: Canada, USA (Michigan) (Berney & Bird, 1992; Greco, 1986, 1987; Subbotin et al., 2010; Yu et al., 2017).

Official Control: Heterodera carotae is on the ‘Harmful Organisms Lists’ for Colombia, Ecuador, Honduras, Indonesia, and Timor-Leste (USDA-PCIT, 2017). Presently, the nematode species has a temporary ‘Q’ rating in California.

California Distribution: Heterodera carotae is not known to be present in California.

California Interceptions: None.

The risk Heterodera carotae would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Heterodera carotae may be able to establish in moderately cool and moist regions of the State wherever carrots are cultivated. Temperature requirements for egg hatch and nematode development are very specific. Optimum temperature for egg hatch is 15-20°C and is repressed at 25°C. One life cycle per season has been reported, however, with a longer growing season that would allow repeated crops under cool temperatures, as many as four cycles may occur (Greco, 1986).

Evaluate if the pest would have suitable hosts and climate to establish in California.

Score: 2

– 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.

2) Known Pest Host Range: The host range is limited to Daucus (carrot) and few wild Umbelliferae members.

Evaluate the host range of the pest.

Score: 1

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

3) Pest Dispersal Potential: One hundred or more eggs are produced in egg sacs and retained within cysts. For long and short distance dispersal the nematode species is mainly dependent on movements of cysts, cyst-infested soils, and infected planting stock.

Evaluate the natural and artificial dispersal potential of the pest.

Score: 2

– 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.

4) Economic Impact: Infestations of the carrot cyst nematode could affect carrot production resulting in crop loss and unmarketable carrots. Cysts in soil could be spread by movements of soil and irrigation water requiring changes in normal cultural practices.

Evaluate the economic impact of the pest to California using the criteria below.

Economic Impact: A, B, C, D

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.

Economic Impact Score: 3

– 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.

5) Environmental Impact: Infestations of the carrot cyst nematode could significantly affect carrot cultivations in home/urban gardening practices.

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact: E

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.

Environmental Impact Score: 2

– 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.

**Consequences of Introduction to California for Heterodera carotae: Medium (10)**

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

-Low = 5-8 points

–Medium = 9-12 points

-High = 13-15 points

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).

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 = 10.

Uncertainty:

None.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for carrot cyst nematode, Heterodera carotae, is B.

References:

Baldwin, J. G., and M. Mundo-Ocampo. 1991. Heteroderinae, cyst – and non-cyst-forming nematodes. In Manual of Agricultural Nematology Ed. W. R. Nickle, Marcel Dekker, Inc. Pp. 275-362.

Berney, M. F., and G. W. Bird. 1992. Distribution of Heterodera carotae and Meloidogyne hapla in Michigan carrot production. Journal of Nematology 24 (4S), 776-778.

Greco, N. 1986. The carrot cyst nematode. In F. Lamberti and C.E. Taylor Eds. Cyst nematodes. New York: Plenum Press. Pp.333-346.

Greco, N. 1987. Heterodera carotae: Destructive nematode of carrot. Nematology Circular No. 140, Florida Department of Agriculture and Consumer Services, Division of Plant Industry, Gainesville, FL, USA.

Jones, F. G. W. 1950. A new species of root eelworm attacking carrots. Nature 165: 81.

Mathews, H. J. P. 1975. Heterodera carotae. CIH descriptions of plant parasitic nematodes set 5, No. 61. St. Albans, UK: Commonwealth Institute of Helminthology.

Mugniéry, D. and M. Bossis. 1988. Heterodera carotae Jones, 1950. 1. Host range speed of development cycle. Revue de Nématologie 11, 307-314.

Subbotin, S. A., M. Mundo-Ocampo, and J. G. Baldwin. 2010. Systematics of cyst nematodes (Nematoda” Heteroderinae) D. J. Hunt and R. N. Perry (Series Editor). Nematology Monographs and Perspectives Volume 8B. Brill Leiden-Boston. 512 p.

USDA PCIT. 2017. USDA Phytosanitary Certificate Issuance & Tracking System. March 24, 2017, 5:49:32 PM CDT. https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.

Yu, Q., E. Ponomareva, D. Van Dyk, M. R. McDonald, F. Sun, M. Madani, et al. 2017. First report of the carrot cyst nematode (Heterodera carotae Jones) from carrot fields in Ontario, Canada. Plant Disease DOI: 10.1094/PDIS-01-17-0070-PDN. Last accessed March 9, 2017, from http://apsjournals.apsnet.org/doi/pdf/10.1094/PDIS-01-17-0070-PDN.

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

4/3/2017 – 5/18/2017

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