Rev 12/16/2024
Review general characteristics of the genus Meloidogyne.
Second-stage juvenile
Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:
The Columbia root-knot nematode, Meloidogyne chitwoodi, is a major pest of potatoes in the northwestern United States.
Potato-growing regions of Colorado, Idaho, Utah, Washington, and the Klamath Basin of northern California and southern Oregon are infested with the nematode. (Nyczepir et al., 1982; Pinkerton and McIntyre, 1987; Santo et al., 1980). M. chitwoodi is widespread throughout the Pacific Northwest and most western states. It is also found in Mexico, Argentina, Turkey and South Africa (Elling, 2013). Recorded from South Africa (Fourie et al., 2002).
Meloidogyne chitwoodi was first described in 1980 (Santo et al., 1980), but specimens from the Klamath Basin deposited in the nematode collection of the California Department of Food and Agriculture in the mid-1960s suggest that the nematode was previously designated as M. thamesi (R. W. Hackney and A. C. Weiner, personal communication).
B-rated pest in California Nematode Pest Rating System.
Soils of the Klamath basin of north-east California and south-east Oregon that are used for a potato cropping system are frequently infested with M. chitwoodi and Pratylenchus neglectus.
Approximately 9300 ha of "Russet Burbank" potatoes are grown in the Klamath Basin, primarily for the fresh market (mid 1990s data). Conditions become suitable for soil tillage and planting in mid-May, and the potato crop is usually harvested by early October. The nematode reproduces on both potato roots and tubers, which facilitates its spread to previously uninfested areas with seed tubers.
In potato tubers, almost all (96%) of the nematodes are found in the outermost 5.25 mm of the tuber, which corresponds to the vascular ring (Elling, 2013).
There is little evidence of yield reduction caused by the direct effect of the nematode population on potato crop growth (Griffin, 1985; Pinkerton and Santo, 1986). The major damage to potato tubers is a nematode-induced blemish which lowers or negates tuber marketability. When 10% or more of the tubers are blemished, the crop is usually unmarketable.
The nematode infects a broad range of plants, including potatoes, vegetables, wheat, corn, alfalfa, and numerous weeds. It can also parasitize several Brassica spp. (Elling, 2013).
To limit future spread of this nematode, regulatory agencies in many countries have designated M. chitwoodi as a quarantine pest, which limits trade of infested shipments and enhancesthe economic impact (Elling, 2013).
Sedentary endoparasite of roots and tubers.
Feeding site establishment and development typical of genus.
Type Host: Potato (Solanum tuberosum)
Potato, barley, wheat, alfalfa (race 2).
Ecophysiological Parameters:
Chromosone number n=18. Reproduction considered to be by facultative meiotic parthenogenesis Van der Beek and Karssen, (1997).
Nematode damage to the potato crop is caused by the second and third generation of M. chitwoodi in a given growing season.
The overwinter population penetrates roots, develops, and produces eggs about 600 degree-days (>5C) after planting (Westerdahl, Pinkerton, Ferris).
Second-stage juveniles of the second generation penetrate roots and (bulking?) (young) tubers commencing about 800 DD after planting, although very young tubers appear resistant or unattractive to the nematodes (Santo). A third generation of the nematode may be reached by mid-September, resulting in further invasion of the tubers prior to harvest.
On crops that are hosts to M. chitwoodi or P. neglectus, seasonal multiplication rates of the nematodes were log-linearly related to populations measured the previous fall. The relationship between crop yields, or nematode multiplication rates, and spring nematode population levels were weaker due to the lower precision of spring population assessments. Overwinter survival rates of both nematode species were log-linearly related to population levels measured in the fall.
The major damage to the tubers is a nematode-induced blemish which lowers or negates their marketability. Field experiments indicate little evidence of yield reduction by the direct effect of the nematode population on crop growth. The surface blemish rating of a summer-grown potato crop has a log-linear relationship with the population level of M. chitwoodi measured either the previous fall, or with lower reliability, in the spring before potato planting (Ferris et al, 1994).
Since very few second-stage juvenile in the overwintering generation can result in substantial second- and third-generation population levels, the economic threshold for the nematode measured in the spring is at or below the limit of detection. The nematode population may be best measured in the fall, at the end of the previous crop, as a basis for management decisions.
Symptoms include stunting and yellowing above-ground and small galls on roots and tubers without secondary roots emerging from them. Eggs hatch at 6°C so that invasion of roots occurs early in the growing season (Elling, 2013).
Thresholds
Only a few second-stage juveniles in the overwintering population will produce substantial second- and third-generation population levels. Thus the economic threshold for tuber blemish may be at or below the limit of detection when the M. chitwoodi population is measured in the spring. Nematode management decisions in the potato-based cropping system of the Klamath Basin can be based on the relationship between potato tuber blemish rating and population level of M. chitwoodi the previous fall as a primary criterion. Individuals are more abundant then, and there is more time available for sample processing and management decisions (Ferris, 1985). At least one composite sample of between 12 and 20 soil cores should be taken to for every 5 acres of relatively uniform edaphic conditions (Ferris et al., 1990).
The population level of M. chitwoodi the previous fall resulting in 10% blemished tubers was 133 eggs and juveniles per L soil. That population level is measurable, but our ability to detect and assess the fall population level that would result in 5% potato blemish (18 per L soil) is questionable (Ferris et al., 1990).
Nematicides
The availability and acceptability of nematicide options for nematode management are diminishing. In the Klamath Basin region of northern California and southern Oregon, much of the soil is silty clay loam with 12% organic matter content. Efficacy of fumigant nematicides on this soil has been poor or inconsistent (Westerdahl et al., 1992).
Crop Rotation
A logical strategy for the management of the Columbia root-knot nematode, and the reduction of its potential damage to potato crops in the Klamath Basin, is the use of nonhost or resistant crops in the rotation. Season length and marketing constraints have limited current rotation crops in the cropping system to alfalfa (Medicago sativa) and barley (Hordeum vulgare). Although economically questionable for the cropping system, especially in short-term rotations, both crops are used for agronomic benefits to the soil. Further, alfalfa, although a nonhost to the prevalent biotype (biotype 1) of the Columbia root-knot nematode, is a host to another root-knot nematode occurring in the area, M. hapla. Both crops are hosts of the lesion nematode, Pratylenchus neglectus, which occurs in the same fields (Griffin, 1991; Griffin and Gray, 1990; Mojtahedi and Santo, 1992; Umesh and Ferris, 1992). Sugar beets (Beta vulgaris), which are being introduced into the area, are hosts of M. chitwoodi (Ferris et al., 1993).
Alternate crops have been investigated for infested regions throughout the Pacific Northwest of the USA (Ferris et al., 1993; Griffin, 1991; Mojtahedi et al., 1991; Griffin and Asay, 1989; Santo and Ponti, 1985; Santo et al., 1988).
Host Plant Resistance, Non-hosts and Crop Rotation alternatives:
CIH 106
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