California Pest Rating for
Meloidogyne floridensis Handoo et al., 2004
Pest Rating: A
PEST RATING PROFILE
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.
History & Status:
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.
Consequences of Introduction:
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.
– 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.
– 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.
Consequences of Introduction to California for Meloidogyne floridensis: 15
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.
-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.
Conclusion and Rating Justification:
Based on the evidence provided above the proposed rating for Meloidogyne floridensis is A.
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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.
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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.
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Pest Rating: A
Posted by ls