Nematodes are microscopic, eel-like roundworms. The most troublesome species in the garden are those that live and feed within plant roots most of their lives and those that live freely in the soil and feed on plant roots.
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Posted by ka
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Posted by ka
Heather J. Scheck, CDFA Primary Plant Pathologist/Nematologist. 204 West Oak Ave, Lompoc, CA
93463. 805-736-8050. plant.health[@]cdfa.ca.gov.
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Posted by ka
Heather J. Scheck, CDFA Primary Plant Pathologist/Nematologist. 204 West Oak Ave, Lompoc, CA
93463. 805-736-8050. plant.health[@]cdfa.ca.gov.
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Posted by ka
Heather J. Scheck, CDFA Primary Plant Pathologist/Nematologist. 204 West Oak Ave, Lompoc, CA
93463. 805-736-8050. plant.health[@]cdfa.ca.gov.
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Posted by ka
Heather J. Scheck, CDFA Primary Plant Pathologist/Nematologist. 204 West Oak Ave, Lompoc, CA
93463. 805-736-8050. plant.health[@]cdfa.ca.gov.
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Posted by ka
None. The current rating and status of Ditylenchus dipsaci in California are re-evaluated.
Background: During the 1920s, the stem and bulb nematode was one of the earliest nematodes known to affect garlic and narcissus production in California where it continues to be a major pest of garlic, onion and alfalfa (Siddiqui, 1973). In alfalfa, damage is most severe in moist, cool weather in cooler, sprinkler-irrigated inland valley and foggy coastal areas of California, and the nematode may be found as far south in the Central Valley as Madera County (Westerdahl, 2007). Ditylenchus dipsaci, the stem and bulb nematode, is one of the most devastating plant parasitic nematodes on a wide range of plants and is distributed worldwide especially in temperate regions. It is a migratory endoparasitic nematode that feeds and inhabits mostly aerial parts of host plants (stems, leaves, inflorescence, seeds) but also invades below ground modified parts (bulbs, tubers, stolons, rhizomes and rarely roots). Ditylenchus dipsaci has been documented in early reports as a complex containing several species (Sturhan and Brzeski, 1991). However, D. dipsaci sensu stricto can now be distinguished from other related species by host plant range, chromosome number, morphometric values and gene sequences (Subbotin et al., 2005).
Disease cycle: D. dipsaci completes a life cycle from egg to egg in about 21 days at 59°F and a female lays 200-500 eggs within garlic and onion tissue, and egg development occurs between 59 and 70°F (Becker and Westerdahl, 2018). Several generations can occur over one growing season. Under favorable moisture and temperature conditions, preadults become active, swim in films of water in soil or on wet plant surfaces, and attack a germinating seed or seedling entering near the root cap or within the seed. Nematodes remain intercellular and feed on parenchymatous tissue causing cell division and enlargement. In young plants, the nematodes enter leaves through stomata or directly through the epidermis in leaf bases – resulting in cell enlargement, disappearance of chloroplasts, and increase in intercellular spaces. As bulbs enlarge, the nematodes move down the leaves intercellularly or on the surface of leaves and re-entering at the outer sheaths of the stem or neck to infect the outer scales of bulbs. Middle lamellae of cells and cells break down forming large cavities and stems lose their rigidity and collapse. Nematodes continue to feed through the parenchymatous outer scales. The macerated tissue has a white mealy texture but soon turn brown due to secondary invasion. In early stages the nematodes remain within individual scales causing complete or incomplete rings of frosty white or brown tissue. Later, the nematodes infect more scales even after harvest and in storage usually resulting in totally infecting a bulb. When heavily infected bulbs decay, preadults exit and accumulate about the basal plates of dried bulbs as cottony masses called “nematodes wool” and can survive there for years (Agrios, 2005; Westerdahl and Becker, 2018). Survival: The pre-adults or fourth stage larvae can survive freezing or extreme dry conditions in anhydrous state for long periods in plant tissue, stems, leaves, bulbs, seeds or in soil (Agrios, 2005).
Dispersal and spread: Infested plant material including bulbs, stems, leaves, and seeds; infested soil, contaminated cultivation tools and equipment, contaminated irrigation and splash water.
Hosts: There are more than 500 plant species in over 40 angiosperm families that are known to be hosts of D. dipsaci. Many of the biological races of D. dipsaci have limited host ranges (EPPO, 2008). In California, D. dipsaci is an important nematode pest particularly of onion, garlic, and alfalfa.
Symptoms: Emergence of infected onion seedlings is retarded, with reduced stands, appearing pale green to yellow, twisted and arched and collapsed. Most infected seedlings die within three or more weeks. Developing plants exhibit stunting, light yellow or brown spots, swellings (spikkles) and open lesions, swollen and deformed stems, thickened, curled, distorted leaves, collapse of leaves and premature drying and defoliation; and bloated tissue with a spongy appearance, leaf tips often exhibit a gray to brown dieback. Older plants may also die before harvest.
Bulb tissue begins softening at the neck and gradually proceeds downwards. Young bulbs are soft, swollen and malformed, and exhibit a coarse-textured tissue beneath the outer scale. Bulb scales appear pale gray, soft, and loose. Bulb tissue underneath the loose outer scales is soft, puffy, mealy and frosty in appearance. Affected scales appear as discolored rings in cross sections of infected bulbs, and as irregular, discolored lines in longitudinal sections. Individual cloves or, in severe cases, larger areas of the bulb become affected. Bulbs may split, become malformed, or produce sprouts and double bulbs. Under dry conditions bulbs become desiccated, light in weight, odorless, and split at the base. Basal plate and roots of severely infested bulbs may also appear to a have a dry rot and can be easily separated from the bulbs, mimicking symptoms of Fusarium basal plate rot. Under moist conditions, secondary invaders set in and bulbs rots and decay. In storage, bulbs decay (EPPO, 2008).
Carrots and sugar beet: The plant is most affected at 2-4 cm below and above ground level. Early symptoms include straddled (collapsed on both sides) leaves, multi-bud plant crowns and light discoloration of taproot tops (EPPO, 2008).
Alfalfa: Nematodes enter bud tissue and developing buds. Infected stems are enlarged, discolored – later may turn black as nematode numbers increase, swollen nodes, shortened internodes (stunted). Infected plants have fewer shoots, and deformed buds. White or pale flags (destruction of chloroplasts) are formed as nematodes move to leaf tissue (EPPO, 2008).
Seeds: Small seed generally show no symptoms of infestation, but the skin of larger seeds, (Phaseolus vulgaris, Vicia faba), may be shrunken with discolored spots (EPPO, 2008).
Damage Potential: If not controlled, the stem and bulb nematode has the potential to affect host crop production by reducing yield and quality, increasing costs of nematode-free production, and management options. The seedborne capability of D. dipsaci would impact international trade of host seed and planting stock, if the latter were found infested with the nematode. However, California’s Seed Certification Program that ensures the use of clean, nematode-free seeds, has provided California garlic growers a strong preventive measure against the stem and bulb nematode.
Worldwide Distribution: Asia: Armenia, Azerbaijan, China, Republic of Georgia, India, Iran, Iraq, Israel, Japan, Jordan, Kazakhstan, Republic of Korea, Kyrgyzstan, Oman, Pakistan, Syria, Taiwan, Turkey, Uzbekistan, Yemen; Africa: Algeria, Kenya, Morocco, Nigeria, Réunion, South Africa, Tunisia; Europe: Albania, Austria, Belarus, Belgium, Bosnia-Hercegovina, Bulgaria, Croatia, Cyprus, Czech Republic, Czechoslovakia (former), Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Macedonia, Malta, Moldova, Netherlands, Norway, Poland, Portugal, Romania, Russian Federation, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, United Kingdom, Ukraine, Yugoslavia; North America: Canada, Mexico, USA; Central America and Caribbean: Costa Rica, Dominican Republic, Haiti; South America: Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Paraguay, Peru, Uruguay, Venezuela; Oceania: Australia, New Zealand (CABI, 2018).
In the USA it has been reported from several states including: Alabama, Arizona, California, Colorado, Hawaii, Idaho, Michigan, Minnesota, Montana, Nevada, New Hampshire, New York, North Carolina, Ohio, Oregon, South Dakota, Utah, Virginia, Washington, Wyoming (CABI, 2018).
Official Control: Currently, D. dipsaci is on the ‘Harmful Organism Lists’ for 50 countries including: Algeria, Antigua and Barbuda, Bangladesh, Brazil, Canada, Chile, China, Cook Islands, Costa Rica, Cuba, Egypt, El Salvador, European Union, French Polynesia, Georgia, Grenada, Guatemala, Holy See (Vatican City State), Honduras, India, Indonesia, Israel, Jordan, Lebanon, Madagascar, Mexico, Monaco, Morocco, Namibia, New Caledonia, New Zealand, Nicaragua, Norway, Panama, Paraguay, San Marino, Serbia, South Africa, Sri Lanka, Taiwan, United Republic of Tanzania, Thailand, Timor-Leste, Tunisia, Turkey, Uganda, United Arab Emirates, Uruguay, Viet Nam, and Yemen (USDA PCIT, 2018).
California Distribution: Ditylenchus dipsaci is widely distributed in California.
California Interceptions: None.
The risk Ditylenchus dipsaci would pose to California is evaluated below.
1) Climate/Host Interaction: Ditylenchus dipsaci is already widespread within California. The state provides suitable hosts and climate for the establishment and spread of dipsaci to uninfected sites.
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: Ditylenchus dipsaci has a very wide host range comprising more than 500 plant species in over 40 angiosperm families. The species also has several biological races which have limited host ranges. In California, dipsaci is an important nematode pest particularly of onion, garlic, and alfalfa.
Evaluate the host range of the pest. Score: 3
– 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: The nematode is dispersed artificially mainly through Infested plant material including bulbs, stems, leaves, and seeds; infested soil, contaminated cultivation tools and equipment, contaminated irrigation and splash water. The ability to survive anhydrously over adverse environmental conditions particularly within plant seed and infested planting stock enables dipsaci for long distance movement over extends periods of time.
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.
Economic Impact: If left unmanaged, the stem and bulb nematode has the potential to affect host crop production by reducing yield and quality, changing normal cultural practices including supply of irrigation water to field grown crops, and increasing costs of nematode-free production. The seedborne capability of dipsaci would impact international trade of host seed and planting stock, if the latter were found infested with the nematode. However, California’s Seed Certification Program that ensures the use of clean, nematode-free seeds, has provided California garlic growers a strong preventive measure against the stem and bulb nematode, and the use of resistant varieties is regarded the most effective control of D. dipsaci in alfalfa.
Evaluate the economic impact of the pest to California using the criteria below.
Economic Impact: A, B, C, D, G
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: Ditylenchus dipsaci has not been reported to have significant environmental impact in California. Home gardening and ornamental plantings are usually protected against the nematode through use of nematode-free planting materials.
Evaluate the environmental impact of the pest on California using the criteria below.
Environment Impact: None
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.
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 = 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.
Evaluation is in California.
Score: (-3)
-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.
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
None.
Based on the evidence provided above the proposed rating for Ditylenchus dipsaci is C.
Agrios, G. N. 2005. Plant Pathology (Fifth Edition). Elsevier Academic Press, USA. 922 p.
Becker, J. O. and Westerdahl, B. B. 2018. Onion and garlic nematodes. UCIPM Statewide Integrated Pest Management Program, University of California Agriculture and Natural Resources. (Updated 2/07). http://ipm.ucanr.edu/PMG/r584200111.html
CABI. 2018. Ditylenchus dipsaci full datasheet. Crop Protection Compendium. https://www.cabi.org/cpc/datasheet/19287
EPPO. 2008. Ditylenchus destructor and Ditylenchus dipsaci Diagnostics. European and Mediterranean Plant Protection Organization. OEPP/EPPO Bulletin 38: 363-373.
Siddiqui, I. A., Sher, S. A., and French, A. M. 1973. Distribution of plant parasitic nematodes in California. State of California Department of Food and Agriculture, Division of Plant Industry, 324 p.
Sturhan, D., and Brzeski, M. W. 1991. Stem and bulb nematodes, Ditylenchus spp. In: Manual of Agricultural Nematology Ed. Nickle, W. R., pp.423–464. Marcel Dekker, Inc., New York (US).
Subbotin, S. A., Madani, M. Krall, E., Sturhan, D., and Moens, M. 2005. Molecular diagnostics, taxonomy, and phylogeny of the stem nematode Ditylenchus dipsaci species complex based on the sequences of the internal transcribed spacer-rDNA. Phytopathology 95: 1308-1315.
USDA PCIT. 2018. USDA Phytosanitary Certificate Issuance & Tracking System. Retrieved July 26, 2018, 1:20:45 pm CDT. https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.
Westerdahl, B. B. 2007. Parasitic nematodes in alfalfa. In Irrigated Alfalfa Management for Mediterranean and Desert Zones. University of California Division of Agriculture and Natural Resources Publication 8297 Chapter 11.
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.
8/2/18 – 9/16/18
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Posted by ls
On March 8 and 29, and April 19, 2018, unidentified root knot nematode female and juvenile specimens and galled Prunus sp. roots were sent by A. Westpahl, University of California, Parlier, CA, to S. A. Subbotin, Nematology Lab, CDFA, for identification of the nematode species. After several molecular tests, S. A. Subbotin determined the identity of the species as M. floridensis – a root knot nematode species not known to be present in California and quarantine actionable. The root samples had been collected from an almond orchard in Merced County. Consequently, the field was visited by J. Chitambar, CDFA, S. A. Subbotin, A. Westpahl, and D. Doll, UC Cooperative Extension Merced County. Official root and rhizosphere soil samples from apparently stunted and non-stunted 2-3-year-old almond scion on Hansen and non-stunted 8-9-year-old Nemaguard rootstock plantings, were collected from an estimated 3-acres of the infested orchard by J. Chitambar and S. A. Subbotin. The samples were processed for nematode diagnosis at the CDFA Nematology Lab in Sacramento. On July 18, 2018, S. A. Subbotin identified the root knot nematode species, M. floridensis, in galled roots and associated rhizosphere soil samples collected from the stunted plants as well as the older plantings. The risk of infestation of M. floridensis in California is assessed and a permanent rating is herein proposed.
Background: Meloidogyne floridensis was first detected in 1966 in Gainesville, Florida, as an unnamed root knot nematode species parasitizing M. incognita and M. javanica – root knot nematode-resistant Nemaguard and Okinawa peach rootstocks (Sharpe et al., 1969) and later Nemared peach rootstock (Sherman et al., 1991). At that time, the unnamed species was referred to as the ‘Nemaguard type root knot nematode’, ‘a new nematode’ and a ‘biotype of root knot nematode’ (Sharpe et al., 1969; Sherman et al., 1981; Young and Sherman, 1977). Then in 1982, this nematode was characterized as race 3 of M. incognita (Sherman & Lyrene, 1983), however, subsequent morphological, molecular and host range studies proved this species to differ from M. incognita race 3 and other species (Nyczepir et al., 1998), and in 2004, Handoo et al. described it as a new species, M. floridensis and proposed the common name, ‘peach root knot nematode’.
The peach root knot nematode is one of the most important root knot nematode species because it can overcome resistance in plants by reproducing in high-value crops carrying genes for resistance against the main Meloidogyne spp., thereby causing substantial reduction in crop growth and yields. In 2005, M. floridensis was reported for the first time in field-grown tomato in Florida (Church, 2005).
Since its original detection, M. floridensis has only been reported in Florida, infecting different crops, peaches, and weed species in 12 counties (Brito et al., 2015). During 2015 to 2017, and in support of a survey conducted in Florida, Subbotin molecularly identified M. floridensis in nematode samples collected from nine peach orchards in six counties. These results added four new counties to the previously reported 12 counties, thereby indicating an increased distribution of the peach root knot nematode to 16 counties over a relatively short duration (S. A. Subbotin, Senior Plant Nematologist, CDFA: personal communication). The recent 2018 detection marks its first official and limited detection within California and outside the State of Florida. An earlier incident occurred in 2011 when M. floridensis was detected in a tomato soil and root sample submitted to, and diagnosed by a nematologist at the University of California, Davis. The sample had originated from a commercial tomato field in Kern County. However, on further investigation by CDFA, the crop had been destroyed by the grower and the field was left fallow without any vegetation before being planted to a non-host. Consequently, and after repeated sampling of the field, CDFA did not find any plant parasitic nematodes and the presence of M. floridensis was not substantiated nor has it ever been reported in California.
Development and life cycle: Meloidogyne floridensis is a root knot nematode species with a life cycle and feeding behavior similar to other root knot nematode species. It is an obligate, sedentary endoparasite that feeds within host plant roots. Adult females embedded in host roots produce eggs within a mass either on the surface of, or within roots. The first stage juvenile develops within the egg and molts to develop into the second stage. The second-stage juveniles (J2) are the infective stage that hatch from eggs, migrate in rhizosphere soil to host roots, re-infest the roots or are attracted to other nearby host roots which are then penetrated. Within roots, J2 establish a specialized feeding site or giant plant cells that are formed at the head end of the nematode in response to its feeding. The second stage juveniles become sedentary while feeding at the specialized site, increase in size and undergo two more molts and non-feeding stages before developing into mature adult females or males and completing the life cycle. Reproduction is by mitotic parthenogenesis. Generally, the life cycle for root knot nematodes may take about 30 days at 25-28°C and longer at lower temperatures.
Dispersal and spread: Infected roots, bare root propagative material, infested soils, root debris, and irrigation water.
Hosts: Meloidogyne floridensis infects peach (Prunus persica) as well as other agricultural and ornamental crops and weeds.
Agricultural crops include: basil (Ocimum basilicum cv. Genovese), common bean (Phaseolus vulgaris), corn (Zea mays cvs. Dixie 18 and Mp 710), crimson clover (Trifolium incarnatum), cucumber (Cucumis sativus), dill (Anethum graveolens), eggplant (Solanum melongena), gourd (Cucurbita pepo), green bean (Phaseolus vulgaris cvs. Fortex and Heavyweight II), lima bean (Phaseolus lunatus cv. Big Mama), mustard (Brassica juncea cv. Florida Broadleaf), pepper (Capsicum annuum cvs. California Wonder, Charleston Bell), snapbean (Phaseolus sp.), squash (Cucurbita moschata cv. Yellow Crookneck), sugar beet (Beta vulgaris cvs. Alota, Bobcat, Mandella and Trinita), tobacco (Nicotiana tabacum cv. NC 95), tomato (Solanum lycopersicon cvs. Florida 47, Rutgers, Solar Set, and tomato hybrid Crista), vetch (Vicia sativa), and watermelon (Citrullus lanatus) (Brito et al., 2008, 2010; Cetintas et al., 2007; Church, 2005; Esmenjaud, 2009; Mendes and Dickson, 2010a, 2010b; Kokalis-Burelle and Nyczepir, 2004; Stanley et al., 2006; 2009).
Ornamental plant hosts include: calendula (Calendula officinalis cv. Oktoberfest), dracaena (Dracaena sp.), hibiscus (Hibiscus sp.), impatiens (Impatiens wallerana), snapdragon (Phaseolus sp.), and verbena (Verbena rigida) (Brito et al., 2010; Mendes and Dickson, 2010b; Kokalis-Burelle and Nyczepir, 2004).
Weed hosts (under greenhouse conditions) include: amaranth (Amaranthus spinosus); American pokeweed (Phytolacca americana), barnyard grass (Echinochloa muricata), cyprusvine (Ipomoea quamoclit), dichondra (Dichondra repens), English watercress (Nasturtium officinale), molinillo (Leonotis nepetaefolia), morning glory (Ipomoea triloba and I. violacea), rape (Brassica napus), redroot pigweed (Amaranthus retroflexus), spurge nettle (Cnidoscolus stimulosus), velvet leaf (Abutilon theophrasti), wild mustard (Brassica kaber), wild cucumber (Cucumis anguria), and zebrina (Zebrina pendula) (Kaur et al., 2007, Stanley et al., 2006).
Symptoms: Symptoms in plants induced by M. floridensis are similar to those induced by other economically important root knot nematode species. Above ground symptoms include stunting, yellowing of leaves, wilting of plants, and canopy dieback. Field symptoms of affected plants may appear in patches, depending on the nematode population density. Below ground, swellings and galls are produced in young and major roots of infested plants. Root galls can harbor second to fourth stage juveniles, swollen adult females, and egg masses containing variable numbers of eggs. Second stage juveniles are the motile infective stage and can be found in roots and rhizosphere soil (Brito et al., 2015).
Damage Potential: Meloidogyne floridensis can break resistance in peach and other crops that are reported to be resistant to root knot nematodes namely tomato hybrid cv. Crista and corn cv. Mp 710 (Stanley et al., 2009). Peach rootstocks ‘Nemaguard, ‘Okinawa’, ‘Nemared’, and ‘Guardian’ with resistance to the southern root knot nematode, M. incognita, the Javanese root knot nematode, M. javanica, and the northern root knot nematode, M. hapla, are susceptible to the peach root knot nematode, M. floridensis (Brito et al., 2015; Sherman and Lyrene, 1983). Small numbers of M. floridensis have been found infecting root knot nematode resistant ‘Flordaguard in Florida’s commercial orchards (Brito and Stanley, 2011). Handoo et al., (2004) confirmed previous reports that none of the Amygdalus subgenus (grouping of peach and almond) of the genus Prunus provided suitable resistance to M. floridensis. In California, the introduction, establishment, and spread of M. floridensis is of concern as ninety percent of the peach industry in the state is planted on Nemaguard rootstock (Westerdahl and Duncan, 2015). Productions on hybrid rootstocks with parentage susceptible to M. floridensis such as Hansen 536 (almond – ‘Nemaguard’ hybrid rootstock) detected in California, are also threatened by the nematode (see ‘Initiating Event’). Furthermore, reproduction of M. floridensis on resistant peach cultivars and other host crops would challenge implementation of management strategies in infested regions especially with increased use of root knot resistance with the absence or restricted use of nematicides (Brito et al., 2015).
Worldwide Distribution: Since its original detection, M. floridensis has only been reported from Florida. The species has only recently been detected in an almond orchard in California (see ‘Initiating Event’).
Official Control: Presently, Meloidogyne floridensis is on the ‘Harmful Organism List’ for the Republic of Korea (USDA PCIT, 2018).
California Distribution: Merced County (limited distribution).
California Interceptions: There are no records of the detection of Meloidogyne floridensis in incoming shipments of plants and soil to California.
The risk Meloidogyne floridensis would pose to California is evaluated below.
1) Climate/Host Interaction: California has suitable climate and hosts for the introduction, establishment and spread of floridensis. Already the detection of this species within a limited region of the State proves it ability to infest and establish in high-value crop production sites as for almond and peach. If left unchecked, other major crops, such as tomato, may also be affected.
Evaluate if the pest would have suitable hosts and climate to establish in California. Score: 3
– 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: Meloidogyne floridensis has a wide and diverse host range that includes peach, almond, several agricultural crops, ornamentals, and weed hosts.
Evaluate the host range of the pest.
Score: 3
– 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: Meloidogyne floridensis has high reproduction. A single female floridensis may produce several hundreds to over one thousand eggs in an egg mass, similar to other Meloidogyne species. Dispersal is mainly passive through the movement of infected roots, planting stock, infested soils and irrigation water. The potential for spread is high.
Evaluate the natural and artificial dispersal potential of the pest.
Score: 3
– 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: floridensis is able to break resistance in important crops carrying genes of resistance to the main Meloidogyne spp. thereby causing substantial reduction in crop yields, crop value, loss of markets, including the likely imposition of quarantines by other states and countries against California. Peach rootstocks ‘Nemaguard, ‘Okinawa’, ‘Nemared’, and ‘Guardian’ with resistance to the root knot nematode species widely distributed in California, are susceptible to M. floridensis. In California, the introduction, establishment, and spread of M. floridensis is of concern as ninety percent of the peach industry in the state is planted on Nemaguard rootstock. Productions on hybrid rootstocks with parentage susceptible to M. floridensis such as Hansen 536 (almond – ‘Nemaguard’ hybrid rootstock) are also threatened by the nematode. Reproduction of M. floridensis on resistant peach cultivars and other host crops would challenge implementation of management strategies in infested regions especially with increased use of root knot resistance with the absence or restricted use of nematicides.
Evaluate the economic impact of the pest to California using the criteria below.
Economic Impact: A, B, C, D, G
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: Several ornamental plants are hosts of the peach root knot nematode. Home gardening and ornamental plantings may also be impacted and trigger additional official or private treatment programs.
Evaluate the environmental impact of the pest on California using the criteria below.
Environment Impact: D, 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: 3
– 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.
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
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.
Evaluation is Low (-1). Presently, M. floridensis has only been detected within a limited region of an almond orchard in Merced County.
Score: -1
-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.
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 = 14
The presence and true distribution of M. floridensis in California is not known. It is possible that the nematodes species may have entered the State undetected prior to 2005. This is largely because prior to 2005 Meloidogyne spp. were not always identified by the CDFA Nematology Laboratory to species level, when detected in samples that originated outside and within California. However, since 2005, M. floridensis has never been detected in regulatory samples generated through CDFA’s nematode control and phytosanitary certification programs or through statewide nematode surveys of host plants grown in agricultural production sites and nurseries in California. Also, except for one unsubstantiated record, M. floridensis has not been reported from California by other researchers/nematologists. The status of M. floridensis in non-cultivated and residential environments is not known. Those environments, as well as infested weed hosts, may serve as sources of inoculum for infestations of cultivated production sites. Identification to species level through DNA analysis is now essential for accurate identification of this species.
Based on the evidence provided above the proposed rating for Meloidogyne floridensis is A.
Brito, JA, Kaur, R, Cetintas, R, Stanley, JD, Mendes, ML, McAvoy, EJ, Powers, TO, and Dickson, DW. 2008. Identification and isozyme characterization of Meloidogyne spp. infecting horticultural and agronomic crops and weed plants in Florida. Nematology 10: 757-766.
Brito, JA, Kaur, R, Cetintas, R, Stanley, JD, Mendes, ML, Powers, TO, and Dickson, DW. 2010. Meloidogyne spp. infecting ornamental plants in Florida. Nematropica 40: 87-103.
Brito, JA, and Stanley, JD. 2011. Nematology Section in Dixon, W. and Andson, P. (Eds.). Tri-ology, FDACS/DPI, Vol. 50. Number 1.
Cetintas, R, Kaur, R, Brito, JA, Mendes, ML, Nyczepir, AP, and Dickson, DW. 2007. Pathogenicity and reproductive potential of Meloidogyne mayaguensis and M. floridensis compare with three common Meloidogyne spp. Nematropica 37: 21-31.
Church, GT. 2005. First report of the root-knot nematode Meloidogyne floridensis on tomato (Lycopersicon esculentum) in Florida. Plant Disease 89: 527.
Esmenjaud, D. 2009. Resistance to root knot nematodes in Prunus: Characterization of sources, marker-assisted selection and cloning strategy for the Ma gene from myrobalan plum. Acta Horticulturae 814: 707-714.
Handoo, ZA, Nyczepir, AP, Esmenjaud, D, Vander Beek, JG, Castagnone-Sereno, P, Carta, LK, Skantar, AM, and Higgins, JA. 2004. Morphological, molecular, and differential-host characterization of Meloidogyne floridensis n. sp. (Nematoda: Meloidogynidae), a root-knot nematode parasitizing peach in Florida. Journal of Nematology 36: 20-35
Kaur, R, Brito, JA, and Rich, JR. 2007. Host suitability of selected weed species to five Meloidogyne species. Nematropica 37: 107-120.
Kokalis-Burelle, N., and Nyczepir, AP. 2004. Host range studies for Meloidogyne floridensis. Journal of Nematology 36: 328
Mendes, ML, and Dickson, DW. 2010a. Reproduction of root-knot nematodes on four sugarbeat cultivars. Journal of Nematology 42: 258.
Mendes, ML, and Dickson, DW. 2010b. Suitability of some annual crops to three species of root-knot nematodes. Nematropica 40: 142.
Nyczepir, AP, Esmenjaud, D, and Eisenback, JD. 1998. Pathogenicity of Meloidogyne sp. (FL-isolate) on Prunus in the southeastern United States and France. Journal of Nematology 30: 509.
Sharp, RH, Hesse, CO, Lownsbery, BA, Perry, VG, and Hansen, CJ. 1969. Breeding peaches for root knot nematode resistance. Journal of the American Society for Horticultural Science 94: 209-212.
Sherman, WB, and Lyrene, PM. 1983. Improvement of peach rootstock resistant to root-knot nematodes. Proceedings of the Florida State Horticultural Society 96: 207-208.
Sherman, WB, Lyrene, PM, and Sharpe, RH. 1991. Flordaguard peach rootstock. HortScience 26: 427-428.
Sherman, WB, Lyrene, PM, and Hansche, PE. 1981. Breeding peach rootstocks resistant to root knot nematodes. HortScience 16: 523-524.
Stanley, JD, Kokalis-Burelle, N, and Dickson, DW. 2006. Host status of Meloidogyne floridensis on selected weeds and cover crops common to Florida. Nematropica 36:148 (Abstr.)
Stanley, JD, Brito, JA, Kokalis-Burelle, N, Frank, JH, and Dickson, DW. 2009. Biological evaluation and comparison of four Florida isolates of Meloidogyne floridensis. Nematropica 39: 255-271.
USDA PCIT. 2018. USDA Phytosanitary Certificate Issuance & Tracking System. Retrieved July 19, 2018, 1:47:12 pm CDT. https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp.
Westerdahl, BB, and Duncan, RA. Peach nematodes. UCIPM Pest Management Guidelines: Peach. UC ANR Publication 3454. http://ipm.ucanr.edu/PMG/r602200111.html
Young, MJ, and Sherman, WB. 1977. Evaluation of peach rootstocks for root knot and nematode resistance. Proceedings of the Florida State Horticultural Society 90:241-242.
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.
7/27/18 – 9/10/18
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Consequences of Introduction: 1. Climate/Host Interaction: [Your comment that relates to “Climate/Host Interaction” here.]
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Posted by ls
None.
Background: Anguina funesta is a plant parasitic nematode that induces formation of galls in developing seeds of annual rye grass (Lolium rigidium), Festuca and Vulpia species. Commonly known as a seed gall nematode, A. funesta is not only an agricultural pest of economic significance in its own right, but is considered more important because it is a vector of the toxigenic actinomycete bacterium, Rathyibacter toxicus that causes Rathayibacter poisoning most commonly known as annual ryegrass toxicity (ARGT) disease (Murray et al., 2014; Riley & Barbetti, 2008). This bacterium is also vectored by other Anguina species, namely, A. agrostis, A. tritici, A. australis, and A. paludicola, and is a USDA APHIS Select Agent (Murray et al., 2014). It is also noteworthy that Anguina funesta and other Anguina species are vectors of the fungus, Dilophospora alopecuri which inhibits gall formation and bacterial colonization thereby providing biological control of both nematode and bacterium. Rathyibacter toxicus and Dilophospora alopecuri are transported to the plant host by adhering to the external cuticular surface of A. funesta.
The first record of ARGT was in Southern Australia in 1956, and caused considerable crop and animal losses. Since then, ARGT and A. funesta spread to Western Australia, South Africa in 1981, and Japan in 1997, most likely with the importation of contaminated ryegrass seed and hay from Australia (Meng et al., 2012). Both nematode and bacterial pathogen now continue to be an economic problem in northern cropping regions of Western Australia. They generally follow a pattern of increase, impact, and then decline. The decline appears to be associated with the build-up of Dilophosphora alopecuri and alterations in land management practices that had supported high host densities protected through to seed set (Subbotin & Riley, 2012).
In the USA, Anguina funesta has only been reported from Oregon having been detected in annual ryegrass seed lots in 2010. Rathayibacter toxicus was not found in Oregon (ODA, 2011; Meng et al., 2012). To date, the nematode and bacterial species have not been reported from any other US states outside of Oregon. Anguina funesta has not been detected in California, nor was it found in turf and pasture seed samples analyzed at CDFA in 2012. During that year, the CDFA Nematology Laboratory did not detect seed gall nematodes in seed samples of perennial ryegrass, tall fescue, and annual bluegrass received from various sources in Oregon, California, and Arizona and maintained in storage at the CDFA Seed Laboratory.
Hosts: The principal host of A. funesta is annual ryegrass (Lolium rigidum). It also induces galls in Festuca and Vulpia species. Only L. rigidum and V. myuros are natural hosts of the nematode pathogen (Subbotin & Riley, 2012).
Symptoms: Ryegrass plants do not show any visible symptoms of infection until inflorescence appears. Nematode galls in annual ryegrass are difficult detect in the field as galls are covered by lemma and paleas. However, once the latter are removed the galls are shrunken, fusiform, smaller than normal seed, and purplish. On the other hand, the bacterial pathogen, R. toxicus may remain within a nematode gall or ooze out and partly or completely cover a gall with yellow bacterial slime which turns orange once it dries. Also, while infected plants do not exhibit apparent symptoms, some entire seed heads may be twisted and malformed and covered with yellow slime. However, the absence of slime (gummosis) does not necessarily indicate that a field is free of the bacterium (Murray et al., 2014; Putnam, 2011).
Disease cycle: Mature seed galls induced in the plant by the nematode contain anhydrobiotic second stage juveniles (J2) which form its survival and dispersal stage. These juveniles overwinter in seed galls on the soil surface and can survive in dry state for many years. Under moist conditions, the nematodes rehydrate, become active, and emerge from degrading galls onto the soil surface. If the soil surface dries out, then the juveniles again become anhydrobiotic until another period of rehydration. In moist soil surfaces, active juveniles seek and invade host seedlings and feed on the growing point (meristem tissue) of tillers where they accumulate until ovaries initiate development. Then they invade ovaries of inflorescence and transform developing seed into seed galls. J2 feed within galls, and develop through two further juveniles stages into adults. A gall may be infested with a few to 20 male and female nematodes. Sexual reproduction is necessary for formation of successive generations and occurs within the galls resulting in several hundred eggs per gall. J2s hatch from the eggs within galls. Freshly-hatched J2s cannot survive desiccation, however, as infested plants mature and senesce, J2s also mature into their anhydrobiotic survival stage. Galls are harvested and replanted along with healthy seed. During harvest, galls fall to the ground and remain there until the nematodes regain activity under moist spring conditions, thus completing the cycle. Toxigenic Rathyibacter toxicus bacteria in soil adhere to the external cuticular surface of Anguina J2s and are carried into the host plant’s inflorescence and nematode galls where thy proliferate and colonize these structures. As the plant matures, bacteria produce glycolipid toxins known as corynetoxins that when consumed, cause neurological disorders, toxicosis, and fatality in animals. When galls fall to the ground at harvest, bacteria reenter the soil (Riley & Barbetti, 2008; Subbotin & Riley, 2012).
Spread: The nematode and bacteria can be spread commonly in galls intermixed with non-cleaned or poorly cleaned grass seed lots. They can be dispersed by wind and in hay. Other means of spread include infested soil/gall contaminated machinery, vehicles, humans and animals or run-off water.
Damage Potential: While Anguina funesta will reduce healthy seed set in host plants, it must be noted that galled florets are likely to be removed with regular seed cleaning procedures. However, there is the possibility for A. funesta galls to be accidently overlooked during cleaning procedures because they are concealed by lemma and palea coverings. In which case, the likelihood of introduction to non-infested regions is increased. The nematode species is considered a “High-Risk” species by USDA and the Society of Nematologists (SON, not dated), mainly due to its ability to vector the toxigenic bacterium which is a USDA APHIS Select Agent. The threat of introduction, spread and establishment of the bacterium is very high due to the presence of susceptible grasses and the occurrence of Anguina species in the USA including California. Pasture, rangeland, private and commercial lawns and turf gardens cultivated to annual ryegrass and fescue grasses are potentially susceptible to the nematode and bacterium. Livestock deaths and production losses to annual ryegrass toxicity (ARGT) disease are caused by corynetoxins produced by R. toxicus and vectored by A. funesta. Most valuable susceptible livestock include cattle, sheep and horses. Domestic and international trade are likely to be negatively impacted.
Worldwide Distribution: North America: USA (Oregon); Oceania: Australia;
Official Control: Presently, Anguina funesta is on the ‘Harmful Organism List’ for Lolium spp. and L. temulentus seeds intended for export to Chile, while Anguina spp. is on the ‘Harmful Organism List’ for Australia, Namibia, Nauru, and South Africa (USDA-PCIT, 2017). The USDA APHIS originally added the Anguina spp.-vectored bacterial pathogen, Rathayibacter toxicus to the Select Agent List in 2008, relisted it in 2012 and continues to date.
California Distribution: Anguina funesta has not been reported from California.
California Interceptions: None reported.
The risk Anguina funesta would pose to California is evaluated below.
1) Climate/Host Interaction: If allowed introduction, Anguina funesta is likely to establish a widespread distribution wherever annual ryegrass and fescue grass are able to grow throughout California. The grasses are commonly grown in commercial, private, and agricultural environments within the State.
Evaluate if the pest would have suitable hosts and climate to establish in California.
Score: 3
– 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 annual ryegrass (Lolium rigidum) and fescue grasses (Festuca spp. and Vulpia). Only L. rigidum and V. myuros are natural hosts of the nematode pathogen.
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: The nematode is spread over short and long distances mainly through artificial means. The primary means of spread is through galls intermixed with non-cleaned or poorly cleaned grass seed lots. They can also be spread by wind and in hay. Other means of spread include infested soil/gall contaminated machinery, vehicles, humans and animals or run-off water. The nematodes have high reproductive potential and are capable of surviving in dry state within seeds for many years, thus enhancing spread over long durations.
Evaluate the natural and artificial dispersal potential of the pest.
Score: 3
– 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: Anguina funesta infestations resulting in seed galls, could potentially lower crop yield, increase costs of crop production, trigger loss of markets including establishment of quarantines, and change normal cultural practices. Furthermore, the nematode species is a vector of bacterial pathogen, Rathayibacter toxicus that causes Rathayibacter poisoning or annual ryegrass toxicity (ARGT) disease resulting in death of agricultural livestock. Therefore, a high rating is given to this category.
Evaluate the economic impact of the pest to California using the criteria below.
Economic Impact: A, B, C, D, E, F.
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: Anguina funesta may significantly affect residential and commercial turf gardens. Annual ryegrass may also be used in agricultural and other environments as a cover crop to prevent soil erosion, improve soil structure and drainage, suppress weeds, and improve organic content of soil. Infestation of the nematode species could impact these environments and consequently trigger additional official or private treatment programs. A ‘High’ rating is given to this category.
Evaluate the environmental impact of the pest on California using the criteria below.
Environmental Impact: D, 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: 3
– 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.
Add up the total score and include it here.
-Low = 5-8 points
-Medium = 9-12 points
–High = 13-15 points
Total points obtained on evaluation of consequences of introduction of Anguina funesta 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.
Evaluation is ‘Not established in California’.
Score: 0
–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.
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
None.
Based on the evidence provided above the proposed rating for the seed gall nematode, Anguina funesta is A.
Alderman S. C. et al. 2003. Use of a seed scarifier for detection and enumeration of galls of Anguina and Rathayibacter species in Orchard grass seed. Plant Disease 87:320-323.
Kessell, D. 2010. Annual ryegrass toxicity – current situation. Department of Agriculture and Food, Government of Western Australia, Note: 417.
Murray, T. D., I. Agarkova, S. Alderman, J. Allen, R. Bulluck, J. Chitambar, C. Divan, I. Riley, B. Schroeder, A. Sechler, and S. Subbotin. 2014. Recovery Plan for Rathayibacter Poisoning caused by Rathayibacter toxicus (syn. Clavibacter toxicus) National Plant Disease Recovery System, a cooperative project of The American Phytopathological Society and The United States Department of Agriculture, posted at http://www.ars.usda.gov/research/npdrs. Updated March 2015.
ODA. 2011. 2011 Plant Health Section Annual Report Commodity Inspection Division. State of Oregon Department of Agriculture.
Price, P. C., Fisher, J. M. and Kerr, A. 1979. On Anguina funesta n. sp. and its association with Corynebacterium sp., in infecting Lolium rigidium. Nematologica 25:76-85.
Putnam M. L. 2011. Rathyibacter toxicus, select agent. Oregon State University Plant Clinic, Corvallis, Oregon (Poster).
Riley, I. T. and Barbetti, M. J. 2008. Australian anguinids: their agricultural impact and control. Australasian Plant Pathology 37:289-297.
Riley, I. T. and McKay, A. C. 1990. Specificity of the adhesion of some plant pathogenic microorganisms to the cuticle of nematodes in the genus Anguina (Nematoda: Anguinidae). Nematologica 36:90-103.
SON. (Not dated). Anguina funesta Pest Information. Exotic Nematode Plant Pests of Agricultural and Environmental significance to the United States. The Society of Nematologists. http://nematode.unl.edu/pest55.htm
Subbotin, S. A. et al. 2003. Evolution of the gall-forming plant parasitic nematodes (Tylenchida: Anguinidae) and their relationships with hosts as inferred from Internal Transcribed Spacer sequences of nuclear ribosomal DNA. Molecular Phylogenetics and Evolution 30:226-235.
Subbotin, S. A. and I. T. Riley. Stem and gall forming nematodes. In Practical Plant Nematology. Eds. Manzanilla-Lopez R., and M. Marban-Mendoza. Biblioteca Básica de Agricultura, Grupo Mundi-Prensa, Mexico. 521-577 pp.
USDA PCIT. 2017. USDA Phytosanitary Certificate Issuance & Tracking System. May 24, 2017, 11:51:23 am CDT. https://pcit.aphis.usda.gov/PExD/faces/ReportHarmOrgs.jsp
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
6/5/2017 – 7/20/2017
♦ Comments should refer to the appropriate California Pest Rating Proposal Form subsection(s) being commented on, as shown below.
Example Comment:
Consequences of Introduction: 1. Climate/Host Interaction: [Your comment that relates to “Climate/Host Interaction” here.]
♦ Posted comments will not be able to be viewed immediately.
♦ Comments may not be posted if they:
Contain inappropriate language which is not germane to the pest rating proposal;
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♦ Comments may be edited prior to posting to ensure they are entirely germane.
♦ Posted comments shall be those which have been approved in content and posted to the website to be viewed, not just submitted.
Posted by ls
None.
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.
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.
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).
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.
None.
Based on the evidence provided above the proposed rating for carrot cyst nematode, Heterodera carotae, is B.
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.
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
4/3/2017 – 5/18/2017
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