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Nacobbus aberrans (Thorne, 1935) Thorne & Allen, 1944
Sugarbeet False Root-knot Nematode
Nacobbus serendipiticus bolivianus
N. aberrans is considered synonymous with N. batatiformis (Gerald Thorne called Sher a fool in correspondence over the taxonomy). However, there is considerable disagreement regarding the taxonomy of N. aberrans (Sher, 1970; Baldwin & Cap, 1992) and some consider N. aberrans sensu lato to include N. batatiformis, N. serendipiticus and N. aberrans sensu stricto.
Molecular, morphological and host range studies suggest that N. aberrans is a species complex with at least three groupings. A North/South American group includes populations from Mexico, Argentina and Ecuador; and two South American groups that include one from Argentina and another from Bolivia and Peru. The latter has been characterised as the original N. serendipiticus bolivianus of Lordello, Zamith and Boock, 1961 now elevated to species status as N. bolivianus.
|DNA sequences suggest three groupings of the Nacobbus
aberrans species complex: i) North/South American group of
populations from Mexico, Argentina and Ecuador; South American group
of by populations from Argentina; and Nacobbus bolivianus
represented by populations from Peru and Bolivia. Overlap of
circles represents shared DNA sequences.
Diagram from Manzanilla-López et al. (2010).
saccate (0.8 to 1.4 mm long and 0.2 to 0.45 mm wide);
Mature females; whole nematode (left), posterior (upper right), anterior
(Photographs by IgnacioCid del PradoVera)
Vermiform and of the same body length as females.
Nebraska, Wyoming, Utah, Colorado, Montana, South Dakota, Kansas in USA.
Also occurs in England, the Netherlands, South America, and Mexico.
Distribution of Nacobbus aberrans in Mexico, 2005
(Cid del Prado et al., 2005)
A-rated pests in California.
Nacobbus aberrans is economically important in temperate
and subtropical latitudes of North and South America. The host range,
which includes at least 84 plant species. Many common weeds are good hosts.
Populations can be separated into bean, potato and sugarbeet groups. The
populations of each group have distinct host preferences.
Reported yield losses reported average 65% for potato in the Andean region of Latin America, 55% and 36% for tomato and bean in Mexico, respectively, and 10-20% for sugarbeet in the United States (Nebraska).
Ref. Manzanilla-Lopez et al. (2002).
| All juveniles are
migratory endoparasites and
penetrate plant root tips and/or axial roots. Juvenile penetration
induces slight swellings on sugarbeet and tomato roots at their axis and
tips. However, potato roots invaded by juveniles exhibit lesions
with discolored tissues. On sugarbeets, the swellings may extend
over a large portion of the root axis.
Mature females penetrate roots, become swollen and sedentary, cause formation of root galls and enlarged cells.
The feeding site is a multinucleate syncytium formed by cell wall breakdown.
Nacobbus aberrans populations, which parasitize sugarbeet in the western US do not parasitize potato. Similarly, populations in Mexico do not parasitize potato. However, many South American populations infect both potato and sugarbeet.
Potatoes, sugarbeets, beans, peppers, crucifers, Solanaceae, e.g., tomato, but not Poaceae (grasses).
Nacobbus aberrans has a wide host range; important commercial crops affected in South America and the United States are potato and sugarbeet, respectively.
Bean, pepper, and tomato are among the most important hosts of this nematode in South America and Mexico.
Infests plants of the families Apiaceae, Brassicaceae, Cactaceae, Chenopodiaceae, Cucurbitaceae, Fabaceae, Solanaceae and Zygophyllaceae. It is found on important food crops, such as cabbage, carrot, cucumber, lettuce, mustard, pea, potato, sugarbeet and tomato (Canto, 1992).
The known host range of N. aberrans includes: Austrian winter pea (Pisum sativum var. arvense), sweetpotato (Ipomoea batatas), beet (Beta vulgaris), broccoli, Brussel sprouts, cabbage, collard and kohlrabi (Brassica oleracea), carrot (Daucus carota), cucumber (Cucumis sativus), egg plant (Solanum melogena), grain amaranth (Amaranthus sp.), (Brassica oleracea), lettuce (Lactuca sativa), mashua (Tropaeolum tuberosum), ornamental gourd (Cucurbita pepo), pepper (Capsicum annuum and C. baccatum), potato (Solanum tuberosum), prickly pear (Opuntia sp.), pumpkin (Cucurbita maxima), spinach (Spinacia oleracea), sugarbeet (Beta vulgaris), tobacco (Nicotiana tabacum), tomato (Solanum lycopersicum), turnip (Brassica rapa).
Other hosts may be common weeds, including black mustard (Brassica nigra), chickweed (Stellaria media), corn spurry (Spergula arvensis), fat hen (Chenopodium album), fireweed (Datura ferox), ground cherry (Physalis), London rocket (Sysimbrium irio), kochia (Kochia scoparia), lambsquarter (Chenopodium album), nightshade (Solanum nigrum), oregano (Origanum vulgare), puncture vine (Tribulus terrestris), purslane (Portulaca oleracea), quinoa (Chenopodium quinoa), saltwort (Salsola kali), and shadescale (Atriplex confertifolia) (Brodie, et al., 1993; CAB International, 2001; Canto, 1992; Society of Nematologists).
For an extensive list of host plant species and their susceptibility, copy the name
select Nemabase and paste the name in the Genus and species box
Eggs are deposited in a gelatinous matrix; some may be retained in the posterior part of the body. This is different from N. dorsalis in which the eggs are reatined in the body.
The first molt occurs within the egg; the J2 stage is infective and penetrates host roots. Subsequent motls occur in either roots or soil. The immature female moves to the root cortex and gall formation occurs as the nematode feeds. The posterior of the female extends towards the outside of the root and eggs are deposited in a matrix. Males may be entangled in the matrix suggesting that copulation occurs after the feeding site is established and females have started to swell.
Life cycle is approximately 48 days at 25 C.
Most favorable conditions for N. aberrans development include sand to sandy-loam soils, temperature range between 15 and 23°C and 5 and 19% soil moisture (Cruz et al., 1987).
In Mexico, N. aberrans J3 and J4 survive under field conditions without a host for one year. The J3 and J4 stages, possibly in an anhydrobiotic state, are the primary inoculum infecting susceptible hosts the next year. Survival of J3 and J4 increases if they are in root fragments. Eggs and J2 do not survive without a host or under adverse conditions.
(Cid del Prado et al, 2005; Stone and Burrows, 1985).
The degree of yield losses caused by this nematode depends primarily on soil population densities.
In western Nebraska, complete destruction of sugarbeet seedlings has been observed in heavily infested fields.
[Ref: Inserra, et al. (1985).]
|Galled tomato root, Mexico
(photograph by Cid del Prado)
|Nacobbus aberrans in
greenhouse-grown tomatoes, Texcoco Edo. Mexico
(photograph by Cid del Prado)
Exclusion: The ability of South American populations to adapt to many hosts and to diverse conditions increases the risk of their establishment in new locations. Exclusion efforts on a national and regional basis are important.
Fumigants (e.g., Telone II) are most effective.
Non-fumigants, such as Aldicarb, oxamyl, and phenamiphos also look promising.
Host Plant Resistance
|Tests in Mexico:|
In chili pepper:
Of 90 varieties and lines of Capsicum spp., all were susceptible. Only Capsicum pendulum = C. baccatum was considered tolerant.
All varieties (wild, criollas, hybrid) tested in the greenhouse (60) and in the field (81) were susceptible to N. aberrans.
Only four varieties were resistant.
For a list of plant species or cultivars (if any) reported to be immune or to have some level of resistance to this nematode species, copy the name
select Nemabase Resistance Search and paste the name in the Genus and species box
Baldwin, J.H. and Cap, G.B. 1992. Systematics of Nacobbus, the false root-knot nematode. In: Gommers, F.J. and Maas, P.W.Th. (Eds). Nematology from molecule to ecosystem. Europeann Soc. Nematologists. Dundee.
Inserra, Griffin & Anderson, (1985). The False Root-Knot Nematode Nacobbus aberrans.
Stone, A.R. and P.R. Burrows. 1985. Nacobbus aberrans. CIH 119.
Manzanilla-López, R. H., M. A. Costilla, M. Doucet, J. Franco, R. N. Inserra,
P. S. Lehman, I. Cid del Prado-Vera, R. M. Souza, and K. Evans. 2002. The genus
Thorne & Allen, 1944 (Nematoda:Pratylenchidae):Systematics, distribution, biology and management. Nematropica 32:149-227.
Manzanilla-López R.H. 2010. Speciation within Nacobbus: consilience or controversy? Nematology 12:321-334.
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