Interrelationships of Meloidogyne Species with Flue-cured Tobacco

Microplot and field experiments were conducted to determine relationships of population densities of Meloidogyne spp. to performance of flue-cured tobacco. A 3-yr microplot study of these interactions involved varying initial nematode numbers (P_i).and use of ethoprop to re-establish ranges of nematode densities. Field experiments included various nematicides at different locations. Regression analyses of microplot data from a loamy sand showed that cured-leaf yield losses on ''Coker 319'' for each 10-fold increase in P_i were as follows: M. javanica and M. arenaria—-13-19%; M. incognita—5-10%; M. hapla—3.4-5%; and 3% for M. incognita on resistant ''Speight G-28'' tobacco. A P_i of 750 eggs and larvae/500 cm³ of soil of all species except M. hapla caused a significant yield loss; only large numbers of M. hapla effected a loss. M. arenaria was the most tolerant species to ethoprop. Root-gall indices for microplot and most field-nematicide tests also were correlated negatively with yield. Relationships of P_i(s) and necrosis indices to yield were best characterized by linear regression models, whereas midseason numbers of eggs plus larvae (P_m) and sometimes gall indices vs. yield were better characterized by quadratic models. The relation of field P_m and yield was also adequately described by the Seinhorst model. Degrees of root galling, root necrosis, yield losses, and basic rates of reproduction on tobacco generally increased from M. hapla to M. incognita to M. arenaria to M. javanica.     

Evaluation of Paecilomyces lilacinus as a Biocontrol Agent of Meloidogyne javanica on Tobacco

The efficacy of the nematode parasite Paecilomyces lilacinus, alone and in combination with phenamiphos and ethoprop, for controlling the root-knot nematode Meloidogyne javanica on tobacco and the ability of this fungus to colonize in soil under field conditions were evaluated for 2 years in microplots. Combinations and individual treatments of the fungus grown on autoclaved wheat seed, M. javanica eggs (76,000 per plot), and nematicides were applied to specified microplots at the time of transplanting tobacco the first year. Vetch was planted as a winter cover crop, and the fungus and nematicides were applied again the second year to specified plots at transplanting time. The fungus did not control the nematode in either year of these experiments. The average root-gall index (0 = no visible galls and 5 = > 100 galls per root system) ranged from 2.7 to 3.9 the first year and from 4.3 to 5.0 the second in nematode-infested plots treated with nematicides. Plants with M. javanica alone or in combination with P. lilacinus had galling indices of 5.0 both years; the latter produced lower yields than all other treatments during both years of the study. Nevertheless, the average soil population densities of P. lilacinus remained high, ranging from 1.2 to 1.3 × 106 propagules/g soil 1 week after the initial inoculation and from 1.6 to 2.3 × 104 propagules/g soil at harvest the second year. At harvest the second year the density of fungal propagules was greatest at the depth of inoculation, 15 cm, and rapidly decreased below this level.     

Reducing Meloidogyne incognita Injury to Cucumber in a Tomato-Cucumber Double-Cropping System

The effects of a root-knot nematode-resistant tomato cultivar and application of the nematicide ethoprop on root-knot nematode injury to cucumber were compared in a tomato-cucumber double-cropping system. A root-knot nematode-resistant tomato cultivar, Celebrity, and a susceptible cultivar, Heatwave, were grown in rotation with cucumber in 1995 and 1996. Celebrity suppressed populations of Meloidogyne incognita in the soil and resulted in a low root-gall rating on the subsequent cucumber crop. Nematode population densities were significantly lower at the termination of the cucumber crop in plots following Celebrity than in plots following Heatwave. Premium and marketable yields of cucumbers were higher in plots following Celebrity than in plots following Heatwave. Application of ethoprop through drip irrigation at 4.6 kg a.i./ha reduced root galling on the cucumber crop but had no effect on the nematode population density in the soil at crop termination. Ethoprop did not affect cucumber yield. These results indicate that planting a resistant tomato cultivar in a tomato-cucumber double-cropping system is more effective than applying ethoprop for managing M. incognita.     

Yield Response and Injury Levels of Meloidogyne incognita and M. javanica on the Susceptible Tobacco 'McNair 944'

The effects of Meloidogyne incognita and M. javanica on a susceptible tobacco (Nicotiana tabacum L.) cv. McNair 944 were investigated in field microplots during 1978 and 1979. Three initial inoculum levels—4, 16, and 64 nematode eggs and/or second-stage larvae per 100 cm³ of soil—were used for each nematode species. Data obtained from the experiments included plant yield and the amount of reproduction of the two nematode species. At comparative inoculum levels, M. javanica was more aggressive than M. incognita on tobacco and caused approximately twofold more yield suppression than M. incognita. The calculated initial population of M. incognita, derived from the average for 2 yr, which produced a 7% suppression in plant yield was four eggs and/or second-stage larvae per 100 cm³ of soil; whereas less than one M. javanica egg and/or second-stage larvae per 100 cm³ of soil was needed to achieve similar suppression. Nematode reproduction varied in the 1978 and 1979 tests, but similar trends were observed. Early season M. javanica populations were greater than those of M. incognita, but late season populations of M. incognita were twice anti three times those of M. javanica.     

Identification of Sources of Resistance to Four Species of Root-knot Nematodes in Tobacco

Resistance to the southern root-knot nematode, Meloidogyne incognita races 1 and 3, has been identified, incorporated, and deployed into commercial cultivars of tobacco, Nicotiana tabacum. Cultivars with resistance to other economically important root-knot nematode species attacking tobacco, M. arenaria, M. hapla, M. javanica, and other host-specific races of M. incognita, are not available in the United States. Twenty-eight tobacco genotypes of diverse origin and two standard cultivars, NC 2326 (susceptible) and Speight G 28 (resistant to M. incognita races 1 and 3), were screened for resistance to eight root-knot nematode populations of North Carolina origin. Based on root gall indices at 8 to 12 weeks after inoculation, all genotypes except NC 2326 and Okinawa were resistant to M. arenaria race 1, and races 1 and 3 of M. incognita. Except for slight root galling, genotypes resistant to M. arenaria race 1 responded similarly to races 1 and 3 of M. incognita. All genotypes except NC 2326, Okinawa, and Speight G 28 showed resistance to M. javanica. Okinawa, while supporting lower reproduction of M. javanica than NC 2326, was rated as moderately susceptible. Tobacco breeding lines 81-R-617A, 81-RL- 2K, SA 1213, SA 1214, SA 1223, and SA 1224 were resistant to M. arenaria race 2, and thus may be used as sources of resistance to this pathogen. No resistance to M. hapla and only moderate resistance to races 2 and 4 of M. incognita were found in any of the tobacco genotypes. Under natural field infestations of M. arenaria race 2, nematode development on resistant tobacco breeding lines 81-RL-2K, SA 1214, and SA 1215 was similar to a susceptible cultivar with some nematicide treatments; however, quantity and quality of yield were inferior compared to K 326 plus nematicides.     

Control of Heterodera carotae,Ditylenchus dipsaci,and Meloidogyne javanica with Fumigant and Nonfumigant Nematicides

Five field trials were conducted in Italy in 1983 and 1984 to test the efficacy of isazofos and benfuracarb in controlling Heterodera carotae on carrot, Ditylenchus dipsaci on onion, and Meloidogyne javanica on tomato. Methyl isothiocyanate (MIT) was tested against H. carotae and M. javanica. Single (10 kg a.i./ha) and split (5 + 5 kg a.i./ha) applications of isazofos gave yield increases of carrot and onion similar to those obtained with DD (300 liters/ha) and aldicarb (10 kg a.i./ha). Population densities of H. carotae in carrot roots at harvest and of M. javanica in tomato roots 2 months after transplanting were also suppressed by isazofos. Benfuracarb (10 kg a.i./ha increased onion yields in a field infested with D. dipsaci, but it was not effective against H. carotae or M. javanica. The efficacy of MIT at 400 and 600 liters/ha was similar to that of MIT + DD (Di-Trapex) at 300 liters/ha. Both nematicides inhibited hatch of H. carotae eggs and decreased the soil population density of M. javanica.     

Control of Meloidogyne javanica by Formulations of Inula viscosa Leaf Extracts

Inula viscosa is a perennial plant that is widely distributed in Mediterranean countries. Formulations of I. viscosa extracts were tested for their effectiveness in control of Meloidogyne javanica in laboratory, growth chamber, microplot, and field experiments. Oily pastes were obtained by extraction of dry leaves with a mixture of acetone and n-hexane or n-hexane alone, followed by evaporation of the solvents. Emulsifiable concentrate formulations of the pastes killed M. javanica juveniles in sand at a concentration of 0.01% (paste, w/w) or greater and reduced the galling index of cucumber seedlings as well as the galling index and numbers of nematode eggs on tomato plants in growth chamber experiments. In microplot experiments, the hexane-extract formulation at 26 g paste/m² reduced nematode infection on tomato plants in one of two experiments. In a field experiment, a reduction of 40% in root galling index by one of two formulations was observed on lettuce plants. The plant extracts have potential as a natural nematicide, although the formulations need improvement.     

Damage Functions for Three Meloidogyne Species on Arachis hypogaea in Texas

The yield response of Florunner peanut to different initial population (Pi) densities of Meloidogyne arenaria, M. javanica, and an undescribed Meloidogyne species (isolate 93-13a) was determined in microplots in 1995 and 1996. Seven Pi''s (0, 0.5, 1, 5, 10, 50, and 100 eggs and J2/500 cm³ soil) were used for each Meloidogyne species in both years. The three species reproduced abundantly on Florunner in both years. In 1995, mean reproduction differed among the three species; mean Rf values were 10,253 for isolate 93-13, 4,256 for M. arenaria, and 513 for M. javanica. In 1996, the reproduction of M. arenaria (mean Rf = 7,820) and isolate 93-13a (mean Rf = 7,506) were similar, and both had greater reproduction on peanut than did M. javanica (mean Rf = 2,325). All three nematode species caused root and pod galling, and a positive relationship was observed between Pi and the percentage of pods galled. Meloidogyne arenaria caused a higher percentage of pod galling than did M. javanica or isolate 93-13a. A negative linear relationship between log₁₀ (Pi + 1) and pod yield was observed for all three nematode species each year. The yield response slopes were similar except for that of M. javanica, which was less negative than that of isolate 93-13a in 1995, and less negative than that of M. arenaria and isolate 93-13a in 1996.     

Suppression of Meloidogyne incognita and M. javanica by Pasteuria penetrans in Field Soil

The role of Pasteuria penetrans in suppressing numbers of root-knot nematodes was investigated in a 7-year monocuhure of tobacco in a field naturally infested with a mixed population of Meloidogyne incognita race 1 and M. javanica. The suppressiveness of the soil was tested using four treatments: autoclaving (AC), microwaving (MW), air drying (DR), and untreated. The treated soil bioassays consisted of tobacco cv. Northrup King 326 (resistant to M. incognita but susceptible to M. javanica) and cv. Coker 371 Gold (susceptible to M. incognita and M. javanica) in pots inoculated with 0 or 2,000 second-stage juveniles of M. incognita race 1. Endospores of P. penetrans were killed by AC but were only slightly affected by MW, whereas most fungal propagules were destroyed or inhibited in both treatments. Root galls, egg masses, and numbers of eggs were fewer on Coker 371 Gold in MW, DR, and untreated soil than in AC-treated soil. There were fewer egg masses than root galls on both tobacco cultivars in MW, DR, and untreated soil than in the AC treatment. Because both Meloidogyne spp. were suppressed in MW soil (with few fungi present) as well as in DR and untreated soil, the reduction in root galling, as well as numbers of egg masses and eggs appeared to have resulted from infection of both nematode species by P. penetrans.     

Effects of Etomopathiogenic Nematodes on Meloidogyne javanica on Tomatoes and Soybeans

Two Hawaiian isolates of Steinernema feltiae MG-14 and Heterohabditis indica MG-13, a French isolate of S. feltiae SN, and a Texan isolate of S. riobrave TX were tested for their efficacy against the root-knot nematode, Meloidogyne javanica, in the laboratory and greenhouse. Experiments were conducted to investigate the effects of treatment application time and dose on M. javanica penetration in soybean, and egg production and plant development in tomato. Two experiments conducted to assess the effects of entomopathogenic nematode application time on M. javanica penetration demonstrated that a single application of 10⁴ S. feltiae MG-14 or SN infective juveniles per 100 cm³ of sterile soil, together with 500 (MG-14) or 1,500 (SN) second-stage juveniles of M. javanica, reduced root penetration 3 days after M. javanica inoculation compared to that of a water treatment. Entomopathogenic nematode infective juveniles applied to assess the effects on M. javanica egg production did not demonstrate a significant reduction compared to that of the water control treatment. There was no dose response effect by Steinernema spp. On M. javanica root penetration or egg production. Steinernema spp. did not affect the growth or development of M. javanica-infected plants, but H. indica MG-13-treated plants had lower biomass than untreated plants infected with M. javanica. Infective juveniles of S. riobrave TX, S. feltiae SN, and MG-14 but not those of H. indica MG-13 were found inside root cortical tissues of M. javanica-infected plants. Entomopathogenic nematode antagonism to M. javanica on soybean or tomato was insufficient in the present study to provide a consistent level of nematode suppression at the concentrations of infective juveniles applied.     

Plant Sources of Chinese Herbal Remedies: Laboratory Efficacy,Suppression of Meloidogyne javanica in Soil,and Phytotoxicity Assays

Extracts of Chinese herbal medicines from plants representing 13 families were tested for their ability to suppress plant-parasitic nematodes. Effective concentration (EC₅₀ and EC₉₀) levels for 18 of the extracts were determined in laboratory assays with Meloidogyne javanica juveniles and all stages of Pratylenchus vulnus. Efficacy of 17 extracts was tested against M. javanica in soil. Generally, EC₅₀ and EC₉₀ values determined in the laboratory were useful indicators for application rates in the soil. Extracts tested from plants in the Liliaceae reduced galling of tomato by M. javanica and were not phytotoxic. Similarly, isothiocyanate-yielding plants in the Brassicaceae suppressed root galling without phytotoxicity. Other plant extracts, including those from Azadirachta indica, Nerium oleander, and Hedera helix, suppressed root galling but were phytotoxic at the higher concentrations tested. Many of these plant sources have been tested elsewhere. Inconsistency in results across studies points to the need for identification of active components and for determination of concentration levels of these components when plant residues or extracts are applied to soil.     

Infection,Reproduction Potential,and Root Galling by Root-knot Nematode Species and Concomitant Populations on Peanut and Tobacco

Single populations of Meloidogyne arenaria races 1 (MA1) and 2 (MA2) and M. hapla (MH), and mixed populations of MA1 + MA2 and MA1 + MH with four inoculum levels of eggs were tested on peanut cv. ''Florigiant'' and M. incognita-resistant tobacco cv. ''McNair 373'' in a greenhouse experiment. Root infection, female development, and reproduction of MA2 on peanut and MA1 on resistant tobacco were limited at 2 and 6 weeks. MA1, MH, and MA1 + MH on peanut had similar root infection (total parasitic forms per root unit) at both 2 and 6 weeks, and similar female development and reproduction potentials at 6 weeks. MA2 tended to depress root infection, female development, and reproduction of MA1 on peanut. MH had little effect on MA1 on this crop. On tobacco, MA2 population had greater incidence of root infection than did MH at 2 weeks. The two nematode species had similar development in roots at 6 weeks. All of these processes were restricted when either MA2 or MH was present together with MA1. As initial inoculum level of parasitically fit populations increased, relative infection ratio on both peanut and tobacco, and reproduction factor on peanut decreased. Populations that had high infection incidence and reproduction rates induced greater root galling than did other populations. Root galling was suppressed in the presence of antagonistic response between nematode populations.     

Comparative Studies on Root Invasion,Root Galling,and Fecundity of Three Meloidogyne spp. on a Susceptible Tobacco Cultivar

Root invasion, root galling, and fecundity of Meloidogyne javanica, M. arenaria, and M. incognita on tobacco was compared in greenhouse and controlled environment experiments. Significantly more M. javanica than M. arenaria or M. incognita larvae were found in tobacco roots at 2, 4, and 6 d after inoculation. Eight days after inoculation there were significantly more M. arenaria and M. javanica than M. incognita larvae. Ten days after inoculation no significant differences were found among the three Meloidogyne species inside the roots. Galls induced by a single larva or several larvae of M. javanica were significantly larger than galls induced by M. incognita: M. arenaria galls were intermediate in size. Only slight differences in numbers of egg masses or numbers of eggs produced by the three Meloidogyne species were observed up to 35 d after inoculation.     

Susceptibility of Several Common Subtropical Weeds to Meloidogyne arenaria,M. incognita,and M. javanica

Experiments were conducted in the greenhouse to assess root galling and egg production of three root-knot nematode species, Meloidogyne arenaria, M. incognita, and M. javanica, on several weeds common to Florida agricultural land. Weeds evaluated were Amaranthus retroflexus (redroot pigweed), Cyperus esculentus (yellow nutsedge), Eleusine indica (goosegrass), Portulaca oleracea (common purslane), and Solanum americanum (American black nightshade). Additionally, although it is recommended as a cover crop in southern regions of the U.S., Aeschynomene americana (American jointvetch) was evaluated as a weed following the detection of root galling in a heavy volunteer infestation of an experimental field in southeastern Florida. Weeds were propagated from seed and inoculated with 1000 nematode eggs when plants reached the two true-leaf stage. Tomato (Solanum lycopersicum ‘Rutgers’) was included as a positive control. Aeschynomene americana and P. oleracea roots supported the highest number of juveniles (J₂) and had the highest number of eggs/g of root for all three species of Meloidogyne tested. However, though P. oleracea supported very high root levels of the three nematode species tested, its fleshy roots did not exhibit severe gall symptoms. Low levels of apparent galling, combined with high egg production, increase the potential for P. oleracea to support populations of these three species of root-knot nematodes to a degree that may not be appropriately recognized. This research quantifies the impact of P. oleracea as a host for M. arenaria, M. incognita, and M. javanica compared to several other important weeds commonly found in Florida agricultural production, and the potential for A. americana to serve as an important weed host of the three species of root-knot nematode tested in southern regions of Florida.     

Host-Parasite Relationship of Meloidogyne chitwoodi on Potato

The soil fumigant 1,3-dichloropropene gave good to excellent control of the Columbia root-knot nematode, Meloidogyne chitwoodi, on potato, Solanum tuberosum L. Nonfumigant nematicides (aldicarb, fensulfothion, carbofuran, ethoprop, and phenamiphos) were less effective in controlling M. chitwoodi, since the nematode affects tuber quality more than quantity. Soil temperature during the growing season affected parasitism of M. chitwoodi on potato more than did the initial nematode population. There were positive linear correlations between degree-days and infected and galled tubers (r = 0.92), degree-days and nematode generations (r = 1.00), and infected and galled tubers and nematode generations (r = 0.91). Differences in degree-days and resultant nematode reproduction caused great variability in infection and galling of potato tubers during four growing seasons: 89% for 1979, 0% for 1980, 13% for 1981, and 18% for 1982, giving positive linear correlation (r = 0.99) between final nematode soil population (Pf) and percentage of infected and galled tubers. Corresponding increases in the soil populations of second-stage juveniles (J2) during the growing season were 9,700% in 1979, 170% in 1980,552% in 1981, and 326% in 1982. There was a negative linear correlation (r = -0.87) between initial soil J2 populations (Pi) and the degree of parasitism (infection and galling) of potato tubers, Pi being of secondary importance to degree-days.     

Varietal Response and Estimates of Heritability of Resistance to Meloidogyne javanica in Carrots

With methods developed in this study, varietal responses to M. javanica were evaluated and heritability of resistance of two promising carrot cultivars was estimated. More egg masses were found on root systems inoculated with eggs added to the soil in three holes in 250 cm³ cups than by mixing the inoculum with soil in the cups. A resistant breeding line, CNPH 1437, was discriminated from susceptible cultivar Nova Kuroda with inoculum levels higher than 2,000 eggs per cup. Greenhouse and field results suggested that cultivars Nantes Superior and Shin Kuroda were susceptible, Kuronan was somewhat tolerant, and Brasilia and Tropical were resistant to M. javanica. Nantes Superior or Shin Kuroda yielded less in carbofuran-treated soil (3 kg a.i./ha) than Kuronan, Brasilia, and Tropical did in nontreated soil. However, incorporation of the nematicide greatly increased yields of Kuronan (32%), Brasilia (62%), and Tropical (91%). Primary root galling at the seedling stage was an adequate parameter for resistance evaluation. Estimated heritability were 0.48 ± 0.07 for primary root galling and 0.35 ± 0.08 for egg mass production in Brasilia, and 0.16 ± 0.11 for primary root galling and 0.31 ± 0.09 for egg mass production in Kuronan.     

Comparison of Reproduction by Meloidogyne graminicola and M. incognita on Trifolium Species

The reproductive potential of Meloidogyne graminicola was compared with that of M. incognita on Trifolium species in greenhouse studies. Twenty-five Trifolium plant introductions, cultivars, or populations representing 23 species were evaluated for nematode reproduction and root galling 45 days after inoculation with 3,000 eggs of M. graminicola or M. incognita. Root galling and egg production by the two root-knot nematode species was similar on most of the Trifolium species. In a separate study, the effect of initial population densities (Pi) of M. graminicola and M. incognita on the growth of white clover (T. repens) was determined. Reproductive and pathogenic capabilities of M. graminicola and M. incognita on Trifolium spp. were similar. Pi levels of both root-knot nematode species as low as 125 eggs per 10-cm-d pots severely galled white clover plants after 90 days. Meloidogyne graminicola has the potential to be a major pest of Trifolium species in the southeastern United States.     

Variability among Populations of Meloidogyne arenaria

Variability in reproduction and pathogenicity of 12 populations of Meloidogyne arenaria race 1 was evaluated on Florunner peanut, Centennial soybean, Rutgers tomato, G70, K326, and Mc944 tobacco, and Carolina Cayenne, Mississippi Nemaheart, and Santanka pepper. Differences among M. arenaria populations in rates of egg production 45 days after inoculation were observed for all cultivars except Santanka pepper. Differences among populations in dry top weights or fresh root weights were recorded on all cultivars. Numbers of nematode eggs produced on Florunner peanut varied from 3,419 to 11,593/g fresh root weight. On resistant tobacco cultivars (G70 and K326), one nematode population produced high numbers of eggs (12,042 and 6,499/g fresh root weight on G70 and K326, respectively), whereas the other populations produced low numbers of eggs (less than 500 eggs/g fresh root weight on both cultivars). Two variant M. arenaria race 1 populations were identified by factor analysis of reproductive rates on all nine cultivars. Differences m reproduction and pathogenicity observed among populations would affect the design of sustainable management systems for M. arenaria.     

Suitability of Zucchini and Cucumber Genotypes to Populations of Meloidogyne arenaria,M. incognita,and M. javanica

The host suitability of five zucchini and three cucumber genotypes to Meloidogyne incognita (MiPM26) and M. javanica (Mj05) was determined in pot experiments in a greenhouse. The number of egg masses (EM) did not differ among the genotypes of zucchini or cucumber, but the eggs/plant and reproduction factor (Rf) did slightly. M. incognita MiPM26 showed lower EM, eggs/plant, and Rf than M. javanica Mj05. Examination of the zucchini galls for nematode postinfection development revealed unsuitable conditions for M. incognita MiPM26 as only 22% of the females produced EM compared to 95% of the M. javanica females. As far as cucumber was concerned, 86% of the M. incognita and 99% of the M. javanica females produced EM, respectively. In a second type of experiments, several populations of M. arenaria, M. incognita, and M. javanica were tested on zucchini cv. Amalthee and cucumber cv. Dasher II to assess the parasitic variation among species and populations of Meloidogyne. A greater parasitic variation was observed in zucchini than cucumber. Zucchini responded as a poor host for M. incognita MiPM26, MiAL09, and MiAL48, but as a good host for MiAL10 and MiAL15. Intraspecific variation was not observed among the M. javanica or M. arenaria populations. Cucumber was a good host for all the tested populations. Overall, both cucurbits were suitable hosts for Meloidogyne but zucchini was a poorer host than the cucumber.     

Carbon Partitioning in Soybean Infected with Meloidogyne incognita and M. javanica

Seven-day-old seedlings of two cultivars (Cristalina and UFV ITM1) of Glycine max were inoculated with 0, 3,000, 9,000, or 27,000 eggs of Meloidogyne incognita race 3 or M. javanica and maintained in a greenhouse. Thirty days later, plants were exposed to ¹⁴CO₂ for 4 hours. Twenty hours after ¹⁴CO₂ exposure, the root fresh weight, leaf dry weight, nematode eggs per gram of root, total and specific radioactivity of carbohydrates in roots, and root carbohydrate content were evaluated. Meloidogyne javanica produced more eggs than M. incognita on both varieties. A general increase in root weight and a decrease in leaf weight with increased inoculum levels were observed. Gall tissue appeared to account for most of the root mass increase in seedlings infected with M. javanica. For both nematodes there was an increase of total radioactivity in the root system with increased levels of nematodes, and this was positively related to the number of eggs per gram fresh weight and to the root fresh weight, but negatively related to leaf dry weight. In most cases, specific radioactivities of sucrose and reducing sugars were also increased with increased inoculum levels. Highest specific radioactivities were observed with reducing sugars. Although significant changes were not observed in endogenous levels of carbohydrates, sucrose content was higher than reducing sugars. The data show that nematodes are strong metabolic sinks and significantly change the carbon distribution pattern in infected soybean plants. Carbon partitioning in plants infected with nematodes may vary with the nematode genotype.