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Pest Description
IDENTITY: Scientific name: Nacobbus aberrans
(Thorne, 1935) Thorne & Allen, 1944
 Common name: False root-knot nematode or potato rosary nematode

NOTES ON TAXONOMY AND BIOLOGY:  Nacobbus aberrans vermiform females resemble lesion nematodes (Pratylenchus) with respect to the flattened head and the posterior vulva position, and the burrowing nematodes (Radopholus sp.) with respect to the position of the esophageal glands that overlap the intestine dorsally. As the reproductive system matures, their vermiform body becomes swollen and saccate, similar to root-knot nematodes. Swollen females are usually spindle-shaped. This species has peculiar parasitic habits. The vermiform stages are migratory endoparasites. Like lesion nematodes, they cause cavities and lesions inside root tissues. In contrast, the mature females are sedentary and obese causing root galls and specialized feeding sites as do root-knot nematodes. Vermiform stages develop an extended survival strategy and overwinter in lenticels under the skin of stored or marketed potato tubers (Costilla, 1985; Inserra, et al., 1985).

Information sheet on: Potato pathotype of Nacobbus aberrans

GEOGRAPHICAL DISTRIBUTION:  The false root-knot nematode is endemic to the Americas. It occurs in Argentina, Bolivia, Chile, Ecuador, Mexico and USA. Reports of this nematode in countries outside the Americas deal with detection of this pest in potato shipments or with populations maintained in quarantine greenhouses (CAB International, 2001; Lehman, 1985; Stone and Burrows, 1985)).  Populations with different host preference have evolved in various geographicals areas. Based on different host preference, N. aberrans populations can be separated into three main groups 1) the sugarbeet group infecting sugarbeet, but not potato. Populations of this group occurs in Argentina and USA. (Nebraska and Pacific Northwest); 2) the potato group, which damages potato and also sugarbeet, but not chili pepper. Populations of this group do not occur in the USA and are common in the highland Andean regions of Argentina, Bolivia, Chile, and Peru, and Mexico; 3) the bean group, which damages bean, but not potato and sugarbeet. Populations of this group occurs in Mexico (Inserra et al., 1985; Manzanilla et al., 2002).

HOSTS: The false root-knot nematode reproduces on the following agronomic and vegetable crops, Austrian winter pea (Pisum sativum var. arvense), batata (Ipomea batata), beetroot (Beta vulgaris), black mustard (Brassica nigra), broccoli, Brussel sprouts, cabbage and collard (Brassica oleracea), carrot (Daucus carota), cucumber (Cucumis sativus), egg plant (Solanum melogena), fat hen (Chenopodium album), grain amaranth (Amaranthus sp.), kohlrabi (Brassica oleracea), lettuce (Lactuca sativa), mashua (Tropaeolum tuberosum),  ornamental gourd (Cucurbita pepo), pepper (Capsicum annuum and C. baccatum), potato (Solanum tuberosum) pumpkin (Cucurbita maxima), spinach (Spinacia oleracea),  sugarbeet (Beta  vulgaris), tobacco (Nicotiana tabacum), tomato (Lycopersicon esculentum), turnip (Brassica rapa), and ulluco (Ullucus tuberosum). Other plants include chickweed (Stellaria media), corn spurry (Spergula arvensis), fireweed (Datura ferox), ground cherry (Physalis), London rocket (Sysimbrium irio), kochia (Kochia scoparia), lambsquarter (Chenopodium album), nightshade (Solanum nigrum), oregano (Origanum vulgare), prickly pear (Opuntia sp.), 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).

CROP LOSSES: Estimated losses as high as 65% on potato and 36% on bean are reported in South America and in Mexico, in fields infested with populations belonging to the potato and bean groups, respectively (Manzanilla et al., 2002; Otazú et al., 1985).

MEANS OF MOVEMENT AND DISPERSAL: The false root-knot nematode is spread through soil debris, poorly sanitized bare root propagative plant material and edible roots or tubers.

RATING: (H) Nacobbus aberrans occurs in the Pacific Northwest of the United States, however there is no evidence that N. aberrans populations able to parasitize potato are present in the country. Taking into consideration the wide distribution of these populations in South America and Mexico and the increased chance of their introduction in the US due to the increase of the exchange of agricultural commodities between US and Latin America, a high priority is given for a complete pest risk assessment.

    Brodie, B.B., K. Evans, and J. Franco. 1993. Nematode parsites of potatoes. Pp.87-132 in K. Evans, D. L. Trudgill, and J. M. Webster eds. Plant parasitic nematodes in temperate agriculture. Wallingford, U K: CAB International.
    CAB International. 2001. Nacobbus aberransin Crop protection compendium, global module, 3rd edition. Wallingford, U K: CAB International.
    Canto M. 1992. Life cycle and pathogenicity of Nacobbus aberrans (Thorne, 1935) Thorne & Allen, 1944. Pp 113-127 in F. Gommers and P. W. Th. Maas eds. Nematology from molecule to ecosystem. Wildervank, The Netherlands: Dekker and Huisman.
    Costilla, M. 1985. El falso nematodo del nudo Nacobbus aberrans (Thorne, 1935) Thorne & Allen, 1944 y su relación con el cultivo de la papa en el Noroeste Argentino. Revista Internacional y Agrícola de Tucumán 62:79-97.
    Inserra, R. N., G. D.GRIFFIN and J. L. Anderson. 1985. The false root-knot nematode, Nacobbus aberrans. Research bulletin 510, Utah Agriculture Experiment Station, Logan Utah, USA.
    Lehman, P. S. 1985. Nacobbus, the false root-knot nematode. Nematology Circular No. 119. Florida Department of Agriculture and Consumer Services, Division of Plant Industry, Gainesville, FL, USA.
    Manzanilla, R., M. A. Costilla, M. Doucet, J. Franco, R. N. Inserra, P.S. Lehman, I. Cid Del Prado, R. Souza, and K, Evans. 2002. Nacobbus species: Systematic, distribution, biology and management. Nematropica (in preparation).
    Otazu, V. R. Hoopes, G. Caero, and I. Huayta. 1985. El rosario de la papa causado po Nacobbus aberrans (Thorne, 1935) Thorne & Allen 1944. Su efecto en el rendimiento y algunos aspectos que inciden en su propación y prevalencia en Bolivia. Fitopatología 20:65-70.