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OSU Nematode Testing Service - Plant-Parasitic Nematodes on Central Oregon Crops

BIOLOGY, HOST RANGES, AND DAMAGE LEVELS OF ROOT-PARASITIC NEMATODES ON SELECTED CENTRAL OREGON CROPS

March 1999: Version 3
plant-parasitic nematodes 

Contents of this Survey:

Damage Levels: an introduction

Gall ratings
Reproductive factor (Rf)
Plants inoculated/plants infected

Biology of Nematode Genera

Criconemella
Heterodera
Longidorus
and Xiphinema
Meloidogyne
Paratylenchus
Pratylenchus
Trichodorus
and Paratrichodorus

Host ranges and damage levels by host common name

Bean
Bentgrasses
Bluegrasses
Carrot
Chinese cabbage
Dill
Garlic
Onion
Parsley
Peppermint
Radish
Rutabaga
Ryegrasses
Spearmint
Sugarbeet
Turnip cultivars

Literature Cited

DAMAGE LEVELS: AN INTRODUCTION

How many plant-parasitic nematodes will damage a particular plant species? This is the most frequently asked question of the Nematode Testing Service at Oregon State University. This literature survey is an attempt to answer that question for crops grown in central Oregon. Non-quantitative host range information is also included to facilitate control through crop rotation: if remaining volunteers are host to a plant-parasitic nematode, the nematode population can be maintained in the volunteers even if the crop itself is not a host.

Most information listed below is from replicated studies or systematic surveys. Studies conducted in pots are indicated. Study conditions may deviate from local Oregon conditions in soil type, climate, moisture, and other factors. Cultivars often vary in susceptibility to parasitic nematode damage and in the number of nematodes they will support.

Numbers of most plant-parasitic nematodes vary seasonally. In many of these studies, the season at which samples were taken is not indicated. In some, however, nematode numbers are designated as initial or as final levels.

These studies report levels at which damage has occurred rather than predict damage that will occur. Therefore, these data are presented only as statements of nematode levels at which damage occured.

If a particular crop is not included in the list, no information has been found for that crop. If a nematode species of concern is not listed under a particular crop, no information has been found on the species for that crop. A lack of information does not necessarily imply a lack of damage.

Nematode damage numbers in this survey are expressed in this survey as nematodes/100 grams (g) soil or number of nematodes/100 cubic centimeters (cm3 or cc) soil. Numbers/100 g soil may be multiplied by 20 to give the number of nematodes/2000 g soil (traditionally designated by the OSU Nematode Testing Lab as one "quart").

Nematode numbers from the OSU Nematology Lab are reported as number/100 g and are corrected for soil moisture. Nematode numbers/100 cm3 soil can provide a rough estimate of numbers/100 g soil corrected for dry weight but should be divided by the soil bulk density for accuracy. Bulk densities of clay, clay loam, and silt loam surface soils range from about 1.0 to 1.6 g/cm3, and those of sands and sandy loams range from about 1.2 to 1.8 g/cm3 (Buckman and Brady 1969). However, the bulk density of the sample actually processed is dependent upon packing density during measurement. Since bulk densities are not frequently reported in studies in which nematode numbers are expressed on a volume basis, accurate conversion of numbers/100 cm3 to numbers/100 grams soil is not usually possible. Nevertheless, since the variation associated with bulk density conversions is generally less than the variation associated with field sampling, numbers/100 cm3 soil provide an acceptable approximation of numbers/100 g soil for making management decisions.

HOST DESIGNATIONS BASED ON GALL RATINGS

These designations apply only to Meloidogyne. A rating of "1" = no galls (resistant); "2" = 1 to 10 galls; "3" = 11 to 100 galls; "4" = more than 100 galls (susceptibile) (LaMondia 1995, LaMondia 1996).

HOST DESIGNATIONS BASED ON REPRODUCTIVE FACTOR

(Rf). Rf = final population/initial population. An Rf of over 10 indicates an excellent host; an Rf of 1 to 10 indicates a good host; an Rf of about 1 indicates a maintenance host; and an Rf of between 1 and 0 indicates a poor host or nonhost (Ferris et al. 1993).

HOST DESIGNATIONS BASED ON NUMBER OF PLANTS INFECTED COMPARED TO NUMBER OF PLANTS INOCULATED

This is expressed as a fraction. If 10 plants were inoculated and 5 were infected, then 5/10 inoculated plants were infected (Faulkner and McElroy 1964).

BIOLOGY OF NEMATODE GENERA

CRICONEMELLA

Criconemella, the ring nematodes, are migratory root ectoparasites. Plump, stubby bodies, coarsely and strongly annulated ("ringed") cuticles, and long, heavy stylets render them distinctive even under the dissecting microscope. Adults of C. xenoplax are about 0.4 mm long. The life cycle of Criconemella is typical of all migratory root ectoparasites considered in this survey. They spend their entire lives in the soil outside the root, using their pointed, hollow stylets to puncture cells and suck out cell liquids. Females lay eggs in the soil. The first of four molts occurs inside the egg, and the nematodes hatch as second stage juveniles (J2). The juveniles enlarge during the next two molts. Sex organs do not appear until after the fourth and final molt to adulthood. Males are necessary for reproduction in some species but not in others. Females lay eggs, and the cycle begins again.

HETERODERA

Members of this genus are known as the cyst nematodes, sedentary endoparasites named for the plump, exposed mature female. J2 and adult females are about 0.5 mm long, and males reach about 1.0 mm. Second stage juveniles hatch from eggs and enter new host roots near the tips, destroying cells in their paths by piercing cells and sucking out cell liquids. They establish a permanent feeding site of several cells with partially dissolved walls. Both males and females fatten at first, but during subsequent molts, the male becomes thin and motile; it leaves the root as an adult and mates with a female. The female continues to fatten in this, her permanent home, achieving nearly spherical plumpness by adulthood following the fourth molt. Cortical cells are destroyed, and the root cracks to accomodate the flourishing female, exposing all but her anterior end, which is still feeding. Eggs may remain alive packed inside the female for several years, protected by her cuticle, which becomes leathery after death. J2 become active in response to root exudates. Life cycles take about 3 to 4 weeks. Most cyst nematode species have narrow host ranges.

LONGIDORUS AND XIPHINEMA

The life histories of these two migratory ectoparasic genera, the needle and dagger nematodes, respectively, resemble that of Criconemella, but their anatomy is different. Their long stylets enable them to feed on deep tissues, and they may even penetrate the stele. This feeding causes necrosis, shrivelling, and stunting of young roots and reduction of above-ground growth as well as root galls in some cases. Both genera can vector viruses. Members of both Longidorus and Xiphinema are larger than other plant parasites, sometimes exceeding 5 mm. They are barely visible to the unaided eye when floating in clear water, but they are not visible when in soil. Longidorus has been recovered from central Oregon only rarely, and so it may not be a problem in this region. Longidorus sylphus is a synonym of L. elongatus. 

MELOIDOGYNE

The sedentary endoparasitic root-knot nematodes (Meloidogyne spp.) hatch from eggs and enter roots as second stage juveniles (J2), select a feeding site of three to eight cells, and swell in their chosen site as they progress through two more juvenile stages towards adulthood. While piercing root cells and sucking out cell liquids, they introduce hormone-like substances into cells, causing the formation of a rich feeding site containing multiple nuclei and excess proteins. The resulting swellings are called galls or knots. Males regain their slender profiles and leave the root at adulthood, but the fattened adult females remain inside, exuding eggs into the soil within a gelatinous matrix. First stage juvenile nematodes (J1) develop within the eggs, undergo their first molt to J2, hatch, and migrate through soil before entering host plant roots. Adult females are about 0.7 mm long, J2 are about 0.4 mm long, and males are 1-2 mm long. Roots inhabited by root-knot nematodes often have visible galls and may exhibit excessive branching. Parasitized plants may be weak and stunted, and root systems may be deformed. However, galling is not essential for nematode feeding, and gall development may be inconspicuous or absent on some hosts.

PARATYLENCHUS

The life cycle of the migratory ectoparasitic pin nematodes resembles that of Criconemella. Adults are about 0.4 mm long. Paratylenchus in our area cannot be identified to species because they belong to one or more undescribed species. Thus, damage levels by nematode species cannot be listed. Paratylenchus is not considered damaging on most crops except in high numbers, usually 500/100 g soil or more.

PRATYLENCHUS

The migratory endoparasitic root-lesion nematodes (Pratylenchus spp.) create holes in root cells and crawl inside. They move longitudinally through the cortex, piercing, sucking, and leaving behind a trail of eggs and toxic metabolites. Eggs deposited in both roots and soil hatch, and the life cycle continues through four molts to sexual maturity and reproduction. Root cell death results in brown longitudinal root lesions, which begin on one side but may eventually encircle a root and thereby girdle it. The overall effect is a weak, shallow root system with extensive dead areas. Pratylenchus spp. are disseminated by transportation of soil or plant parts and by surface or irrigation water (Evans et al. 1993). Adults are about 0.5 mm long. 

TRICHODORUS AND PARATRICHODORUS

These two genera, the stubby-root nematodes, are separatable only by microscopically discernible characteristics. Adults are about 0.7 mm long. They have slender, curved stylets and fairly fat, blunt-ended bodies. Species included in this survey are limited to those detected on Oregon agricultural crops or those in nearby states and provinces: P. allius, P. minor (formerly T. christei), P. teres, Trichodorus aequalis, and T. obscurus. Only P. allius has been positively identified by the OSU Nematode Testing Lab. The life cycle of this migratory ectoparasite resembles that of Criconemella. The nematodes feed mostly at root tips but also along the sides of young, succulent roots. Root tip growth is slowed or stopped, resulting in a generally stunted root system or in short, stubby roots. Like Xiphinema and Longidorus, stubby-root nematodes can vector plant viruses.

HOST RANGES AND DAMAGE LEVELS LISTED ALPHABETICALLY BY HOST COMMON NAME

BEAN, BUSH (Phaseolus vulgaris var. humuli)

Heterodera humulii: Cyst formation, but poor host (Stone and Rowe 1977). H. humuli multiplied 11 times over 5 months (Stone and Rowe 1977).

BEAN, COMMON (Phaseolus vulgaris)

Xiphimena americanum: Associated with a commercial crop in California (Siddiqui et al. 1973).

BEAN, FABA, BROAD, OR FIELD (Vicia faba)

Heterodera gottingiana: Host (Stone and Course 1974)
Meloidogyne hapla: In pots, lightly susceptible (Gaskin and Crittenden 1956).
Paratrichodorus allius: Host (Norton et al. 1984).
Pratylenchus neglectus: Host in California (Siddiqui et al 1973).

BEAN, GREEN OR SNAP (Phaseolus vulgaris)

Meloidogyne chitwoodi: Apollo is a suitable host (Rf = 94.4) for Race 2 (alfalfa race) (Mojtahedi et al. 1988b). In pots, Blue Mountain was a suitable host for Race 2 (alfalfa race) (Mojtahedi et al. 1988b). Cv. Apollo in pots: moderate reproduction, moderate host (O'Bannon et al. 1984). Xiphimena bakeri: On Blue Lake in pots, 123/100 cm3 resulted in light damage and -49 % population increase (i.e., decrease) after 12 weeks (McElroy 1972).

BEAN, LIMA (Phaseolus lunatus)

Heterodera schachtii: Host in California (Siddiqui et al. 1973)
Pratylenchus thornei: Host in California (Siddiqui et al. 1973).
Xiphimena americanum: Associated with commercial crops in California (Siddiqui et al. 1973).

BEAN, NAVY (Phaseolus vulgaris)

Pratylenchus penetrans: Initial populations of 50 to 300 (but not 25)/100 cm3 soil significantly reduced yield and shoot and root weight on Sanilac, Seafarer, and Tuscola but not on Saginaw, Gratiot, and Kentwood (Elliott and Bird 1985).
Pratylenchus thornei: Host in California (Siddiqui et al. 1973). Bean, red kidney (Phaseolus vulgaris)
Pratylenchus neglectus: Large cavities surrounded by suberin are formed in the cortex and result in stunting and decline of the plant (Townshend and Anderson 1976).

BEAN, SCARLET RUNNER (Phaseolus coccineus)

Meloidogyne hapla: In pots, moderately susceptible (Gaskin and Crittenden 1956).

BENTGRASS, ASTORIA (Agrostis canina)

Meloidogyne naasi: Host for 4 US and 1 English population (Michell et al. 1973a).
Xiphimena americanum: In pots, 169 days after inoculation with 72/100 g soil, the final population was 8/100 g soil (Miller 1980). Bentgrass, creeping; Redtop (Agrostis stolonifera = A. palustris)
Meloidogyne hapla: In pots, not susceptible, and none of 23 inoculated plants were infected (Faulkner and McElroy 1964).
Meloidogyne naasi: Host for 4 US and 1 English population of redtop (Michell et al. 1973a). 67/100 ml soil in pots significantly reduced top growth and in root weight after 10 but not 6 months (Sikora et al. 1972). 24/100 ml soil in pots resulted in densities of 84 to 1763/g root after 8 months; all but one of 5 races caused significant reduction in top weights but usually not root weights (Michell et al. 1973b). Causes severe damage (Franklin 1973). "Toronto C-15" is a host for 3 US but not California and English populations (Michell et al. 1973a). Penncress and Seaside are hosts (Radewald et al. 1966, Radewald et al. 1970).
Pratylenchus penetrans: In pots, inhibited top growth only when co-inoculated with Meloidogyne naasi. A. palustris is a poor host for P. penetrans (Sikora 1972).

BENTGRASS, COLONIAL (Agrostis tenuis = A. capillaris)

Meloidogyne naasi: Highland is a host (Radewald et al. 1970).

BENTGRASS, UNSPECIFIED (Agrostis spp.)

Heterodera avenae: Host; can maintain populations between cereal crops (Williams and Siddiqi 1972)
Longidorus elongatus: Associated (Norton et al. 1984).
Pratylenchus thornei: Host in Mexico (Fortuner 1977). 

BLUEGRASS, KENTUCKY (Poa pratensis)

Criconemella xenoplax: In pots, after 90 days, reproductive factor was 0.71 times initial population of 250/100 cm3 soil (Zehr et al. 1986).
Meloidogyne chitwoodi: In pots, trace reproduction: very poor host (O'Bannon et al. 1984).
Meloidogyne naasi: Filking is a host for 4 US and 1 English population (Michell et al. 1973a). Kentucky, Merion, Newport, and Park are hosts (Radewald et al. 1970).
Pratylenchus penetrans: Experimentally infected with P. penetrans (Jensen 1953).

BLUEGRASS, ROUGH (Poa trivialis)

Meloidogyne naasi: Host for 4 US and 1 English population (Michell et al. 1973a). Host (Radewald et al. 1970).
Heterodera avenae: Host; can maintain populations between cereal crops (Williams and Siddiqi 1972)

BLUEGRASS, UNSPECIFIED (Poa spp.)

Heterodera avenae: Host; can maintain populations between cereal crops (Williams and Siddiqi 1972)

CARROT (Daucus carota)

Longidorus elongatus: Severely damaged (Hooper 1973).
Meloidogyne chitwoodi: Suitable hosts for Race 1 (non-alfalfa race): Imperator Six Pak II (Rf = 17.9), Pak More (Rf = 14.4), Six Pak (Rf = 12.3), Imperator 58 (Rf = 11.6), Top Pak (Rf = 2.2), Nantes Amsterdam Minicor (Rf = 10.6), Red Cored Chantenay (Rf = 4.4), Hybrid Orlando Cold (Rf = 10.5), Hybrid Chancellor (Rf = 6.4), Hybrid Golden State (Rf = 4.7), Hybrid A Plus (Rf = 2.1) (Santo et al. 1988). Suitable hosts for Race 1: In pots, Red-cored Chantenay (Rf = 4.4) and Imperator 58 (Rf = 11.6) (Mojtahedi et al. 1988b). Moderate hosts for Race 1: Imperator Gold Pak (Rf = 1.3) and Imperator Trophy (Rf = 1.2) (Santo et al. 1988). Moderate host for Race 1: In pots, Gold Pak (Rf = 1.3) (Mojtahedi et al. 1988b). Poor host for Race 1: Imperator Charger (Rf = 0.4) (Santo et al. 1988). Poor hosts for Race 2 (alfalfa race): Imperator Six Pak II (Rf = 0.8), Pak More (Rf = 0.2), and Six Pak (Rf = 0.8) (Santo et al. 1988). Poor host for Race 2: In pots, Imperator 58 (Rf = < 0.1) (Mojtahedi et al. 1988b). Non-hosts for Race 2 : Imperator 58 (Rf = 0.01), Top Pak (Rf = 0), Gold Pak (Rf = 0), Trophy (Rf = 0), Charger (Rf = 0.01); Nantes Amsterdam Minicor (Rf = 0.01) Half-Long Nantes (Rf = 0); Red Cored Chantenay (Rf = 0), Hybrid Chancellor (Rf = 0), Golden State (Rf = 0.02), and A Plus (Rf = 0) (Santo et al. 1988). Non-host for Race 2: Gold Pak (Rf = 0) (Mojtahedi et al. 1988b). Rf of race 1 and race 2 isolates from Oregon, Washington, and Idaho on Red Cored Chantenay vary from < 0.01 to 10.7 (Mojtahedi et al. 1988b). Host status for unspecified races: In pots, Gold Pak: moderate reproduction, moderate host; Half Long: light reproduction, poor host; Imperator: trace reproduction: very poor host (O'Bannon et al. 1984).
Meloidogyne hapla: Economic threshold in Canada is 9/100 cm3 soil, but since deformity renders roots unmarketable, a zero tolerance threshold may be reasonable (Potter and Olthof 1993). Economic threshold is 9/100 cm3 soil (Vrain 1982). Imperator Six Pak II, Pak More, Six Pak, Imperator 58, Top Pak, Gold Pak, Trophy, and Charger; Nantes Amsterdam Minicor and Half-Long Nantes, Red Cored Chantenay, and Hybrid Orlando Gold, Chancellor, Golden State, and A Plus are all good hosts (Santo et al. 1988). In organic soil, yield was reduced by 50% when percent infection of indicator plants increased from 5.1 to 93.2 (Wilson 1957, cited in Wong and Mai 1973). 58% of Spartan Premium grown in soil with 5 J2 and an unknown number of eggs/100 cm3 were suitable for fresh market, compared to 97% those of grown in nematode-free soil (Slinger and Bird 1978.) In organic soil field microplots, marketable storage root weight was decreased 36% by 20 eggs/100 cm3 soil, 59% by 40 eggs, 75% by 80 eggs, 92% by 160 eggs, and 89% by 240 eggs. In pots, root and leaf weight and storage root length were significantly reduced at all inoculum levels, and percentage of forked roots was significantly increased to 57 and 59% at 160 and 240/100 cm3 soil (Vrain 1982). In pots, Red Cored Chantenay was a suitable host (Rf = 54.9) (Mojtahedi et al. 1988b). In pots, Chantenay Red Cored was severely susceptible, and 12/12 inoculated plants were infected (Faulkner and McEvoy 1964).
Pratylenchus spp.: Threshold range is 30 to 180/100 g soil at planting, with moderate damage at about 100/100 g (Potter and Olthof 1993). Pratylenchus crenatus: Taproots are branched and reduced; side roots have lesions and dead tips; above-ground parts are thin and chlorotic (Potter and Olthof 1993).
Pratylenchus neglectus: Host in California (Siddiqui et al 1973). Pratylenchus penetrans: Recorded (Kleynhans 1996).
Pratylenchus thornei: Reproduced on carrot disk cultures: Rf 5.1 after 25 days, 3619 after 100 days (Castillo et al. 1995).
Xiphimena americanum: Host in urban areas in California (Siddiqui et al. 1973). 

CHINESE CABBAGE (Brassica rapa ssp. pekinensis)

Meloidogyne hapla: In pots, cv. Rhubarb moderately susceptible; 2/2 plants infected (Faulkner and McElroy 1964). In pots, Wong Bok and Chihli were lightly susceptibile (Gaskin and Crittenden 1956). See also turnip and stubble turnip, which are different subspecies of Brassica rapa.

DILL (Anethum graveolens)

Meloidogyne hapla In pots, Mammoth Long Island was moderately susceptible, and 4/15 inoculated plants were infected (Faulkner and McEvoy 1964). In pots, Long Island Mammoth was severely susceptible (Gaskin and Crittenden 1956).
Pratylenchus penetrans: In pots, initial populations of 45/100 g soil resulted in 110-220/g root, 30% height reduction, and moderately severe necrosis after three weeks (Miller 1978). 

GARLIC (Allium sativum)

Heterodera schachtii: Host in California (Siddiqui et al. 1973)
Meloidogyne hapla: In pot trials, garlic was not infected (Raski 1957). Pratylenchus neglectus: Host in California (Siddiqui et al 1973). Pratylenchus thornei Found in plants that were weeds in California nurseries (Siddiqui et al. 1973).
Xiphimena americanum: Host in commercial crops and nursery in California (Siddiqui et al. 1973).

ONION (Allium cepa)

Criconemella xenoplax: Associated with roots (Kleynhans et al. 1996). Meloidogyne chitwoodi: Non-hosts for Race 2 (alfalfa race): Carmen, Cima, Granada, Magnum, Rocket, Snow White, Vega, Walla Walla Sweet, and Yula (Rf = 0.0 to 0.07) (Mojtahedi et al. 1988b). Poor hosts for Race 2: In pots,Snow White, Walla Walla Sweet (Rf = 0.2) (Mojtahedi et al. 1988b). Non-hosts for Race 1 (non-alfalfa race): Carmen, Cima, Granada, Magnum, Rocket, Vega, Yula. In pots, and Snow White and Walla Walla Sweet were non-hosts for race 1 (non-alfalfa race) (Mojtahedi et al. 1988b). In pots, cv. Rocket: trace reproduction, very poor host; cv. Walla Walla Sweet: light reproduction, poor host (O'Bannon et al. 1984).
Meloidogyne hapla: Threshold is 200 J2/100 g soil (Barker and Olthof 1976; Potter and Olthof 1993). In microplots, marketable yields of Canada No 1 Copper Gem bulbs 5 cm and larger were reduced 31% by 200/100 g soil, 72% by 600/100 g soil, and 64% by 1800/100 g soil. A progressive decrease in the number of marketable bulbs and an increase in numbers of unmarketable culls was correlated with these reductions (Olthof and Potter 1972). In organic soil, yield was reduced by 23% when percent infection of indicator plants increased from 5.1 to 93.2 (Wilson 1957, cited in Wong and Mai 1973). Extrapolation indicated that economic loss (5% or more of marketable yield) would occur at preplant density of 100/100 g soil (Olthof and Potter 1971). In pots, South Port White Globe was slightly susceptible, and 25/46 inoculated plants were infected. White Bunching was not susceptible, and 0/52 inoculated plants were infected (Faulkner and McEvoy 1964). Southport White Globe was infected (Raski 1957). Meloidogyne naasi. Damages onion seedlings (Franklin 1973). Sweet Spanish is a host (Radewald et al. 1970).
Pratylenchus neglectus: Host in California (Siddiqui et al 1973). Pratylenchus penetrans: At 7-13o C, < 100/g root caused significant root weight reduction, but > 400 were required to produce injury at 16-25o C (Ferris 1970). Losses in marketable yields ranged from 14% at 67/100 g soil to 71% at 1800/100 g soil (Olthof and Potter 1973). Threshold is 100/100 g soil (Barker et al. 1976; Potter and Olthof 1993).
Pratylenchus neglectus: Host in California (Siddiqui et al 1973) and Egypt (Fortuner 1977).
Pratylenchus thornei: Host in California (Siddiqui et al 1973) and Egypt (Fortuner 1977).
Paratrichodorus allius: Stockton Yellow Globe and Sweet Spanish are hosts (Norton et al. 1984).
Xiphimena americanum: Host in California (Siddiqui et al. 1973).

PARSLEY (Petroselinum crispum)

Meloidogyne hapla: In pots, Champion Moss Curled was moderately susceptible, and 4/4 inoculated plants were infected (Faulkner and McElroy 1964).

PEPPERMINT (Mentha piperita)

Criconemella xenoplax: Mean populations peaked in August or September in the Willamette Valley, Oregon (Merrifield and Ingham 1996).
Longidorus elongatus: In pot studies, growth was reduced by 6/100 g soil (Ingham and Merrifield 1996). Severely damaged (Hooper 1973). Host (Norton et al. 1984).
Meloidogyne chitwoodi: Todd's and Black in pots: trace reproduction, very poor host (O'Bannon et al 1984).
Meloidogyne hapla: In pots, severely susceptible, and 10/10 inoculated plants were infected (Faulkner and McElroy 1964). In pots, growth was reduced by 5 to 15/100 g soil. Shoot weights were reduced by 23% after four months by a single egg mass (300 eggs). Root weight was increased, but roots were shorter, thicker, and brittle. These effects increased slightly with greater inoculum densities (Eshtiaghi 1975, cited in Ingham and Merrifield 1996).
Pratylenchus neglectus: Reduces growth of peppermint in Washington. Small numbers (up to a final population of 7,462/plant) increased dry weight of the plants by 17-25% over that of uninfected plants. When the population exceeded 14,000/plant, the dry weight was 21% below that of the control plants (Townshend and Anderson 1976). Associated with reduced growth of peppermint (Kleynhans et al. 1996). Associated with mint in Washington (Norton et al. 1984) Recovered from mint soil and roots in Oregon; widespread (Merrifield 1998).
Pratylenchus penetrans: One lb. of oil is lost for each 322/g root or 83/100 g soil recovered in March (Ingham and Merrifield 1996).
Pratylenchus thornei: Found in an irrigated Columbia Basin, OR mint field previously in wheat (W. T. Cobb, pers. comm., 1987). Associated in Washington (Norton et al. 1984).

RADISH (Raphanus sativus)

Heterodera schachtii: Crop plants in California were hosts (Siddiqui et al. 1973) Host (Franklin 1972).
Meloidogyne hapla: In pots, Round Blade was lightly susceptible, and 3/3 inoculated plants were infected (Faulkner and McElroy 1964). In pots, of 21 cultivars, Buccaneer and Scarlet were severely susceptible, and all others were moderately susceptible (Gaskin and Crittenden 1956).
Pratylenchus penetrans: In pots, initial populations of 45/100 g soil resulted in 300-600/g root, 57% height reduction, and very severe necrosis after three weeks (Miller 1978).

RADISH, OILSEED (Raphanus sativus)

Meloidogyne chitwoodi: In pots, cultivar 1 is a maintenance host (Rf = 2.58); cultivars 2, 3, 4, 5, 6, Nemex, Siletta Nova, Siletena, and Pegletta are poor hosts (Rf = 0.0 to 0.6) for race 1 (Ferris et al. 1993).

REDTOP See Bentgrass, creeping
RUTABAGA (Brassica rapa ssp. napobrassica)

Pratylenchus neglectus: Recovered from soil in which turnips and rutabagas had been grown (Merrifield 1998). 

RYEGRASS, ITALIAN (Lolium multiflorum)

Meloidogyne naasi: Host for 4 US and 1 English population (Michell et al. 1973a).
Pratylenchus neglectus: L. multiflorum is a host in California (Norton et al. 1984).
Pratylenchus penetrans: In pots, initial inoculum increased 50% (McDonald and Mai 1963).

RYEGRASS, PERENNIAL (Lolium perenne)

Criconemella xenoplax: Did not suppress C. xenoplax when grown in association with peach trees (Whittington and Zehr 1992). In pots, after 90 days, reproductive factor was 2.17 times initial population of 250/100 cm3 soil: host (Zehr et al. 1986).
Heterodera avenae: Host; can maintain populations between cereal crops (Williams and Siddiqi 1972)
Longidorus elongatus: Severely damaged (Hooper 1973). Induces galls (Griffiths and Robertson 1984).
Meloidogyne hapla: In pots, not susceptible, and 0/3 inoculated plants were infected (Faulkner and McElroy 1964).
Meloidogyne naasi: Host for 4 US and 1 English population (Michell et al. 1973a). Host (Franklin 1965, Radewald et al. 1970). Aldicarb applied at spring sowing of perennial ryegrass on field plots with 3800 J2/100 cm3 soil increased first year yields by 22%.(Cook and Yeates 1993). In pots, 200 J2/ml soil reduced yields by 51% after 3 months, but 60/ml had no effect in the field (Cook and Yeates 1993).
Pratylenchus penetrans: In pots, initial inoculum increased 37% (McDonald and Mai 1963).

RYEGRASS, UNSPECIFIED (Lolium spp.)

Pratylenchus penetrans: In pots, initial populations of 33/100 g soil resulted in Spearmint, Scotch (Mentha cardiaca) 50/ g root and little necrosis on Oregon ryegrass after 3 months (Miller 1978).
Meloidogyne chitwoodi: In pots, trace reproduction: very poor host (O'Bannon et al. 1984). In pots, Scotch spearmint is a is a non-host for Race 2 (alfalfa race) (Mojtahedi et al. 1988b).
Meloidogyne hapla: In pots, moderately susceptible, and 10/10 inoculated plants were infected (Faulkner and McElroy 1964). 

SPEARMINT, NATIVE (Mentha spicata)

Longidorus elongatus: Host (Norton et al. 1984).
Meloidogyne hapla: In pots, moderately susceptible, and 10/10 inoculated plants were infected (Faulkner and McElroy 1964).

SUGARBEET (Beta vulgaris)

Criconemella xenoplax: In pots, Rf = 0 after 3 months (Seshadri 1964). Heterodera schachtii: Preferred over several weeds (Bendixen et al. 1979) Longidorus elongatus: Has been severely damaged in England. L. elongatus is responsible for "docking disorder," a fangy, distorted root system causing considerable crop loss (Hooper 1973).
Meloidogyne chitwoodi: In pots, poor host (Rf = 0.4) for Race 1 (non-alfalfa race) (Mojtahedi et al. 1988b). In pots, maintenance host for race 1 (Ferris et al. 1993). U & I Hybrid No. 9: in pots, moderate reproduction: moderate host (O'Bannon et al. 1984) Tolerance limit is 280 J2 and/or eggs/100 cm3 soil. Reproduction of M. hapla was greater than that of M. chitwoodi at most inoculum levels (Griffin et al. 1982). In pots, Rf of 0.8 on Idahybrid 9 from inoculation of approximately 200/100 cm3 soil (Santo et al. 1980). Meloidogyne hapla: Threshold is less than 100 J2/100 cm3 soil (Barker and Olthof 1976). Threshold is 60 eggs + 280 juveniles/100 cm3 soil (Cooke 1993). Tolerance limit is 60 J2 and/or eggs/100 cm3 soil. Reproduction of M. hapla was greater than that of M. chitwoodi at most inoculum levels (Griffin et al. 1982). 100 J2/100 ml reduced shoot but not root weight in sandy loam and did not affect plant growth in silt loam, supporting the observation that Meloidogyne spp. damage sugarbeets more in coarse-textured soils (Santo and Bolander 1979). In pots, fresh weight of total plants inoculated with 1250 M. hapla J2/100 cm3 soil was 84% less than that of noninoculated controls. Dry weight of infested roots was 20% of weight of noninoculated controls (Inserra et al. 1984). In pots, cv. 22H was severely susceptible, and 28/28 inoculated plants were infected (Faulkner and McElroy 1964). In pots, Rf of 0,1 on Idahybrid from inoculation of approximately 200/100 cm3 soil (Santo et al. 1980).
Meloidogyne naasi: U. S. 75 is a host for four US and one English population (Michell et al. 1973a). Damaging populations have been recorded from Belgium and France, but elsewhere in northern Europe and the US, infestations have caused relatively little damage (Cooke 1993). Sugar beet.may be severely damaged in young stages but is a poor host because many attacked roots die (Franklin 1973). U.S. 75 is a good host (Golden and Taylor 1967). Host (Franklin 1965, Radewald et al. 1970). Pratylenchus crenatus: Host (Norton et al. 1984).
Pratylenchus neglectus: Host in California (Siddiqui et al 1973). Pratylenchus penetrans: Host in California (Siddiqui et al 1973). Pratylenchus thornei: Host in California (Siddiqui et al 1973). Associated in Utah (Norton et al. 1984). Turnip (Brassica rapa ssp rapifera)
Pratylenchus neglectus: Recovered from soil in which turnips and rutabagas had been grown (Merrifield 1998).
Xiphimena bakeri: On Aberdeen Yellow in pots, 123/100 cm3 resulted in light damage and -3 % population increase (i.e., decrease) after 12 weeks (McElroy 1972). 

TURNIP, STUBBLE (Brassica rapa)

Meloidogyne chitwoodi: In pots, cvs. Alander, Endiviana, Gelria, Ponda, Samson, Voillenda, and Weseler: moderate reproduction: moderate hosts (O'Bannon et al. 1984).

TURNIP, STUBBLE X CHINESE CABBAGE (Brassica rapa)

Meloidogyne chitwoodi: In pots, light reproduction on cv. Appin (poor host) and moderate reproduction on cf. Daisy (moderate host) (O'Bannon et al. 1984).

TURNIP OR CHINESE CABBAGE (Brassica rapa - unspecified cultivar)

Paratrichodorus allius: Host (Norton et al. 1984).

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