The effects of the application of poultry litter at 0.0, 6.7, 13.4, and 20.1 tons/ha on population changes during the growing season on nematode communities were evaluated in two cotton production fields in North Carolina. Numbers of bactivorous nematodes increased at midseason in response to the rate at which litter was applied but decreased with increasing litter application rates at cotton harvest. Numbers of fungivores at cotton harvest were related positively to the rate of litter applied, and this affected a positive increase in the fungivore-to-bacterivore ratio at this sampling date. The rate at which poultry litter was applied resulted in an increase in the bacterivore to plant-parasite ratio, and this corresponded with increased cotton lint yield. Trophic diversity was increased by litter application rate at cotton harvest at one location but not at another. The plant-parasite maturity index was greater consistently at one site than at a second site where the Hoplolaimus columbus population density was above the damage threshold for cotton. The population density of H. columbus was suppressed with increasing rates of poultry litter application, but other plant-parasitic nematodes were affected marginally.
Columbia lance nematode; community structure; cotton; ecology; Gossypium hirsutum; Helicotylenchus dihystera; Hoplolaimus columbus; management; nematode; Paratrichodorus minor; poultry litter; population changes; Pratylenchus brachyurus; soil health; trophic groups
The effectiveness of selected cultural practices in managing the Columbia lance nematode, Hoplolaimus columbus, on cotton was evaluated in experiments in growers' infested fields. The effects of planting date, cotton cultivar, treatment with the growth regulator mepiquat chloride, and destruction of cotton-root systems after harvest on cotton-lint yield and population densities of H. columbus were studied. The yield of cotton cultivar Deltapine 50 was negatively related (P = 0.054) to initial population density of H. columbus whereas the yield of Deltapine 90 was not affected by preplant density of this nematode, indicating tolerance in Deltapine 90. Reproduction of this nematode did not differ on the two cultivars. Planting date and treatment with the growth regulator mepiquat chloride did not influence cotton yield in a consistent manner. Application of mepiquat chloride suppressed (P ≤ 0.05) numbers of Columbia lance nematode, although there was an interaction (P ≤ 0.05) with cultivar and year. Early vs. late destruction of cotton-root systems did not impact population densities of this nematode either year, and had no impact on the subsequent cotton crop. The nematicide fenamiphos increased (P ≤ 0.03) cotton yield when H. columbus numbers exceeded the damage threshold.
columbia lance nematode; cotton; crop loss; cropping system; cultural practices; Gossypium hirsutum; Hoplolaimus columbus; host-plant tolerance; management; nematode; planting date
Selected cotton cultivars were evaluated for resistance to the southern root-knot nematode, Meloidogyne incognita, in greenhouse and field experiments. Cotton cultivars LA 887, Auburn 634, and NemX cotton were highly resistant to three North Carolina populations of root-knot nematode in greenhouse experiments compared to susceptible cultivars. The relative susceptibility of cultivars tested in the greenhouse from most to least susceptible were Deltapine 16 > Deltapine 50 > LA 887 or NemX > Auburn 634. The yields of resistant and susceptible cotton cultivars were increased by fumigation in fields infested with root-knot nematode. Reproduction of M. incognita in field plots on NemX, Paymaster H 1560, and Stoneville LA 887 was less than on susceptible cultivars. Diminished reproduction of the nematode on resistant cultivars may reduce the need for nematode control tactics in subsequent years.
crop loss; host-plant resistance; nematode; southern root-knot nematode
The reproductive and damage potential of the reniform nematode, Rotylenchulus reniformis, on five cotton breeding lines reported as tolerant to this nematode in Texas were compared with two standard cotton cultivars, Deltapine 50 and Stoneville LA 887, in a North Carolina field naturally infested with R. reniformis. Numbers of R. reniformis in soil were suppressed at mid-season, and cotton-lint yield was increased by preplant fumigation with 1,3-dichloropropene. Population densities of R. reniformis at cotton harvest were unaffected by fumigation in 1998, but were affected in 1999. Some of the putatively tolerant breeding lines supported lower levels of R. reniformis and had higher tolerance indices to reniform nematode than the standard cultivars, but the yields of the breeding lines were significantly lower than the standard cultivars. Fumigation resulted in a 100- to 200-kg/ha increase in cotton lint yield for cultivars LA 887 and Deltapine 50.
cotton; crop loss; Gossypium hirsutum; host-plant resistance; nematode; plant disease loss; reniform nematode Rotylenchulus reniformis; tolerance
Monoxenic cultures of burrowing nematode populations extracted from banana roots from Belize, Guatemala, Honduras, and Costa Rica were established on carrot discs. Cultures of Radopholus spp. were also obtained from Florida, Puerto Rico, Dominican Republic, and Ivory Coast. The aggressiveness (defined as reproductive fitness and root necrosis) of these populations was evaluated by inoculating banana plants (Musa AAA, cv. Grande Naine) with 200 nematodes/plant. Banana plants produced by tissue culture were grown in 0.4-liter styrofoam cups, containing a 1:1 mix of a coarse and a fine sand, at ca. 27 °C and 80% RH. Banana plants were acclimated and allowed to grow for 4 weeks prior to inoculation. Plant height, fresh shoot and root weights, root necrosis, and nematode population densities were determined 8 weeks after inoculation. Burrowing-nematode populations varied in aggressiveness, and their reproductive fitness was generally related to damage reported in the field. Plant height and fresh shoot and root weight did not reflect damage caused by nematodes under our experimental conditions. Necrosis of primary roots was closely related to the reproductive fitness of the nematode populations. Variation in aggressiveness among nematode populations followed a similar trend in the two susceptible hosts tested, Grande Naine and Pisang mas. All nematode populations had a low reproductive factor (Rf ≤2.5) in the resistant host except for the Ivory Coast population which had a moderate reproductive factor (Rf ≤ 5) on Pisang Jari Buaya. This is the first report of a burrowing nematode population parasitizing this important source of resistance to R. similis.
banana; burrowing nematode; host resistance; Musa spp.; nematode; Radopholus; reproductive fitness
A survey of soybean-production areas in the Piedmont, Coastal Plain and Tidewater regions of North Carolina was conducted from 1994 to 1996. Heterodera glycines was detected in 55 of 77 fields sampled in 15 counties. The host race of H. glycines was determined for 39 of the populations collected. Of all populations collected, 4% were race 1, 40% race 2, 16% race 4, 7% race 5, and 4% race 9; the remaining 29% could not be accurately categorized. None of the populations evaluated had high levels of reproduction on the resistant cultivar Hartwig. The southern root-knot nematode Meloidogyne incognita was detected in 26% of the fields. Helicotylenchus spp. were detected in all fields sampled, Tylenchorhynchus spp. were found in 62%, Paratrichodorus spp. in 56%, and Pratylenchus spp. in 72% of fields sampled. Mesocriconema spp., Xiphinema spp., and Hoplolaimus spp. were detected in less than 20% of the fields sampled.
Distribution; Glycine max; Helicotylenchus; Heterodera glycines; Hoplolaimus columbus; Hoplolaimus galeatus; host race; Meloidogyne incognita; Mesocriconema; nematode; Paratrichodorus; populations; Pratylenchus; race; soybean; soybean cyst nematode; survey; Tylenchorhynchus; Xiphinema
Field experiments were conducted to determine peanut growth and yield responses to selected fumigant and nonfumigant nemaficide treatments in 1988 and 1989. All treatments with the fumigant 1, 3-D significantly suppressed nematode reproduction (Meloidogyne arenaria, M. hapla, and Mesocriconema ornatum) and enhanced peanut yields over the other treatments in four tests in 1988. Yield increases with the fumigant ranged from about 20% to 100% over the untreated control. Test sites in 1989 had lower nematode levels than those for 1988, and fewer positive plant and nematode responses were detected. Treatments with 1,3-D improved peanut quality but not yield in one experiment with low levels of M. hapla and M. ornatum in 1988. The 1,3-D + chloropicrin treatments at another site gave higher peanut yields than 1,3-D alone.
Arachis hypogaea; chemical control; management; Meloidogyne arenaria; Meloidogyne hapla; Mesocriconeraa ornatum; nematicides; nematode; peanut
Soybean breeding lines and reported sources of nematode resistance were evaluated in repeated greenhouse tests for resistance to North Carolina populations of the soybean cyst nematode Heterodera glycines, reniform nematode Rotylenchulus reniformis, and the root-knot nematode species Meloidogyne incognita, M. arenaria, and M. arenaria. Lines from the soybean breeding program in Missouri that had 'Hartwig' soybean as a parent were the most resistant to races 1-4 of the soybean cyst nematode and the population of reniform nematode evaluated here. Numerous cysts of an inbred soybean cyst nematode race 4 population were produced on several of these Hartwig descendants, however, and accession $92-1603 had a cyst index of 29.2%. These accessions were also susceptible to M. arenaria and M. arenaria. Soybean lines N87-539 and N91-245 from the breeding program in North Carolina had strong resistance to an inbred soybean cyst nematode race 1 population and to M. arenaria, respectively. Soybean germplasm from the Georgia breeding program demonstrated the strongest resistance to the root-knot nematode species tested. Lines from the Georgia program, including G80-1515, G83-559, G93-9106, and G93-9223, that incorporated both root-knot and soybean cyst nematode resistance had the best overall resistance to the nematode populations evaluated. Resistance reported in the soybean lines was generally upheld. In a few cases, differences in the origin and culture of the nematode populations used in this study may have led to discrepancies between reported and observed resistance.
Glycine max; Heterodera glycines; Meloidogyne arenaria; Meloidogyne incognita; Meloidogyne javanica; nematode; reniform nematode; resistance; root-knot nematode; Rotylenchulus reniformis; soybean cyst nematode
The effects of soil type and initial inoculum density (Pi) on the reproductive and damage potentials of Meloidogyne incognita and Rotylenchulus reniformis on cotton were evaluated in microplot experiments from 1991 to 1993. The equilibrium nematode population density for R. reniformis on cotton was much greater than that of M. incognita, indicating that cotton is a better host for R. reniformis than M. incognita. Reproduction of M. incognita was greater in coarse-textured soils than in fine-textured soils, whereas R. reniformis reproduction was greatest in a Portsmouth loamy sand with intermediate percentages of clay plus silt. Population densities of M. incognita were inversely related to the percentage of silt and clay, but R. reniformis was favored by moderate levels of clay plus silt (ca. 28%). Both M. incognita races 3 and 4 and R. reniformis effected suppression of seed-cotton yield in all soil types evaluated. Cotton-yield suppression was greatest in response to R. reniformis at high Pi. Cotton maturity, measured as percentage of open bolls at different dates, was affected by the presence of nematodes in all 3 years.
cotton; ecology; edaphic factor; Gossypium hirsutum; Meloidogyne incognita; nematode; plant-disease loss; reniform nematode; root-knot nematode; Rotylenchulus reniformis; soil texture; yield
Selected soybean genotypes were evaluated for resistance to North Carolina populations of the soybean cyst nematode Heterodera glycines, the root-knot nematodes Meloidogyne incognita races 3 and 4, M. arenaria races 1 and 2, M. javanica, and the reniform nematode Rotylenchulus reniformis in two greenhouse tests. Populations of cyst nematode used in the first test were cultures from field samples originally classified as races 1-5, and those used in the second test included inbred cyst lines that corresponded to races 1, 3, and 4. The original race classification of some cyst populations shifted after repeated culture on susceptible 'Lee 68' soybean. Most of the cyst-resistant soybean cultivars tested were susceptible to M. arenaria and M. javanica. Exceptionally large galls were induced by M. arenaria on roots of Asgrow 5979, Hartwig, and CNS soybean. Hartwig soybean and PI 437654 were resistant to all cultured field populations of cyst nematodes in a first greenhouse test. In the second test, cyst indices of 11.3% and 19.4% were observed on roots of PI 437654 and Hartwig, respectively, when infected with an inbred line (OP50) of H. glycines corresponding to race 4. The cyst-resistant soybean germplasm tested, including Hartwig and PI 437654, supported only low numbers of reniform nematodes. The most severe soybean root necrosis observed, however, was associated with reniform nematode infection.
Glycine max; Heterodera glycines; Meloidogyne incognita; M. arenaria; M. javanica; reniform nematode; resistance; root-knot nematode; Rotylenchulus reniformis; soybean; soybean cyst nematode
Aldicarb, ethoprop, and fenamiphos were evaluated for their efficacy in controlling various species of root-knot nematodes on flue-cured tobacco and for their residual activity, as determined through periodic sampling and bioassays of soil taken from field plots. Field experiments were conducted at five locations over 2 years with flue-cured tobacco. Soil in plots treated with nematicides were formed into high, wide beds before transplanting with 'Coker 371-Gold' or 'K 326' tobacco. Residual control of Meloidogyne spp. was greatest (P ≤ 0.05) with fenamiphos (in some cases up to 10 weeks, as measured in tomato bioassays of infested soil and root fragments). Suppression of nematode reproduction by ethoprop was short-lived, and numbers of second-stage juveniles + eggs and numbers of galls in bioassays sometimes surpassed those of untreated plots within 4 weeks after treatment. Aldicarb gave intermediate control over time as compared to the other compounds. Although nematicidal efficacy of all compounds varied with site and season, fenamiphos and aldicarb generally produced the highest yields.
chemical control; Meloidogyne arenaria; M. incognita; M. javanica; nematode management; population dynamics; root-knot nematode; nernaticide; nematode; 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.
Arachis hypogaea; infection; interaction; Meloidogyne arenaria; M. hapla; nematode; Nicotiana tabacum; peanut; reproduction potential; root-knot nematode; tobacco
A 3-year microplot study was conducted to characterize the interaction between Meloidogyne arenaria race 1 (MA1) and M. hapla (MH), as affected by the five peanut genotypes: Florigiant, NC 7, NC 6, NC Ac 18416, and NC Ac 18016. The interactive effects on infection (total parasitic forms per root unit) and reproduction potentials of each nematode species and crop damage were determined. As a single population, MA1 had greater infection capacity and caused more crop damage than did MH, but both species had similar reproduction potentials. In mixed infestations, MA1 was more competitive than MH, as reflected by incidence of infection. Infection and reproduction potentials, and crop-damage capabilities of the mixed populations were similar to those of MA1 alone. All peanut genotypes were susceptible to infection by both nematodes. NC 6 was less susceptible to damage by MA1 and the mixed populations than other genotypes. A nematode treatment x genotype interaction was detected for root infection and crop damage, but not for population density or reproduction. With high preplant nematode levels (Pi), the populations reached their peak by midseason, whereas those with low Pi peaked after midseason. Crop damage in the second and third years was correlated with Pi level.
Arachis hypogaea; competition; infection potential; interaction; Meloidogyne arenaria; M. hapla; mixed population; parasitic fitness; peanut; reproduction potential; root-knot nematode
A 3-year microplot study was initiated to characterize the population dynamics, reproduction potential, and survivorship of single or mixed populations of Meloidogyne arenaria race 1 (Ma1) and race 2 (Ma2), as affected by crop rotations of peanut 'Florigiant' and M. incognita races 1 and 3-resistant 'McNair 373' and susceptible 'Coker 371-Gold' tobacco. Infection, reproduction, and root damage by Ma2 on peanut and by Ma1 on resistant tobacco were limited in the first year. Infection, reproduction, and root-damage potentials on susceptible tobacco were similar for Ma1 and Ma2. In the mixed (1:1) population, Ma1 was dominant on peanut and Ma2 was dominant on both tobacco cultivars. Crop rotation affected the population dynamics of different nematode races. For years 2 and 3, the low numbers of Ma1 and Ma2 from a previous-year poor host increased rapidly on suitable hosts. Ma1 had greater reproduction factors ([RF] = population density at harvest/population density at preplandng) than did Ma2 and Ma1 + Ma2 in second-year peanut plots following first-year resistant tobacco, and in third-year peanut plots following second-year tobacco. In mixed infestations, Ma1 predominated over Ma2 in previous-year peanut plots, whereas Ma2 predominated over Ma1 in previous-year tobacco plots. Moderate damage on resistant tobacco was induced by Ma1 in the second year. In the third year, moderate damage on peanut was associated with 'Ma2' from previous-year peanut plots. The resistant tobacco supported sufficient reproduction of Ma1 over 2 years to effect moderate damage and yield suppression to peanut in year 3.
Arachis hypogaea; interaction; Meloidogyne arenaria; Nicotiana tabacum; parasitic fitness; peanut; population dynamics; reproduction potential; root-knot; rotation; tobacco
The effects of soil types and soil water matric pressure on the Heterodera glycines-Glycine max interaction were examined in microplots in 1988 and 1989. Reproduction of H. glycines was restricted in fine-textured soils as compared with coarse-textured ones. Final population densities of this pathogen in both years of the study were greater in nonirrigated soils than in irrigated soils. The net photosynthetic rate of soybean (per unit area of leaf) was suppressed only slightly or not at all in response to infection by H. glycines and other stresses. Relative soybean-yield suppression in response to H. glycines was not affected by water content in fine-textured soils, but slopes of the damage functions were steepest in sand, sandy loam, and muck soils at high water content (irrigated plots). Yield restriction of soybean in response to this pathogen under irrigation was equal to or greater than the yield suppression under dry conditions. Although yield potential may be elevated by irrigation when soil-water content is inadequate, supplemental irrigation cannot be used to circumvent nematode damage to soybean.
Damage function; ecology; edaphic factors; Glycine max; Heterodera glycines; irrigation; photosynthesis; soil moisture; soil texture; soil water matric pressure; soybean; soybean cyst nematode
Plant and soil nematodes significandy impact our lives. Therefore, we must understand and manage these complex organisms so that we may continue to develop and sustain our food production systems, our natural resources, our environment, and our quality of life. This publication looks specifically at soil and plant nematology. First, the societal impact of nematodes and benefits of nematology research are briefly presented. Next, the opportunities facing nematology in the next decade are outlined, as well as the resources needed to address these priorities. The safety and sustainability of U.S. food and fiber production depends on public and administrative understanding of the importance of nematodes, the drastic effects of nematodes on many agricultural and horticultural crops, and the current research priorities of nematology.
alternative management tactics; behavior; benefit to society; beneficial nematodes; biochemistry; biological control; constraints in nematology; control; crop rotation; cultural practice; ecology; education; environment; extension; diagnostics; funding; genetics; host-parasite interaction; information transfer; molecular genetics; nematicide; nematode; nematology; nematode management; nutrient cycling; pesticide; plant parasites; research goals; research priorities; resistance; resource; science of nematology; society; spread; sustainable agriculture; systematics
Two Rotylenchulus reniformis populations (North Carolina and Georgia) were compared on sweetpotato and tomato. 'Beauregard' sweetpotato and 'Better Boy' and 'Marion' tomato were excellent hosts for both R. reniformis populations. On Beauregard sweetpotato, the two populations did not differ in fecundity; however, on both tomato cultivars, the Georgia population reproduced at a higher rate than the North Carolina population (P ≤ 0.05). Meloidogyne javanica reproduction was higher (P ≤ 0.05) on Marion than on Better Boy. Neither population of reniform nematodes suppressed shoot growth of tomato or sweetpotato at any Pi (initial population density). Both populations of R. reniformis, however, restricted storage-root growth of Beauregard sweetpotato but enhanced shoot growth. When the Georgia population was evaluated in microplots with Pi levels of 0, 20,000, or 40,000 R. reniformis/500 cm³ soil, total fruit weights of Better Boy tomato were not affected. In the greenhouse, Marion tomato fresh shoot and fruit growth (weights) was suppressed by M. javanica, but Better Boy was not affected. Root necrosis increased linearly with Pi on Beauregard sweetpotato grown in the greenhouse and became more pronounced as numbers of R. reniformis increased, regardless of the population. The cultivars of tomatoes evaluated were tolerant to the two populations ofR. reniformis in a sandy soil and exhibited no root necrosis. Marion tomato was highly susceptible to M. javanica, while Better Boy was tolerant.
Ipomoea batatas; Lycopersicon esculentum; Meloidogyne javanica; nematode; reniform nematode; root-knot nematode; Rotylenchulus reniformis; sweetpotato; tomato; yield
The spatial and temporal dynamics of Meloidogyne incognita, relative to soybean shoot and root growth in field microplots, were determined at 11 sampling dates during a growing season. The population dynamics of M. incognita on soybean were dependent on initial population (Pi), soil moisture, and root spatial distribution. Final egg and juvenile population densities were greatest in plots with higher Pi. The population densities of juveniles and eggs were highest from mid- to late-season and were associated with increased soil moisture. Root spatial distributions and M. incognita numbers were closely related. Numbers of juveniles and eggs decreased with soil depth and distance from the center of the row. Greater numbers of juveniles and eggs were found in the upper 30 cm in the row center, and in the upper 15 cm at 10 and 20 cm from the center of the row. There were no consistent differences in root weights between nematode-infected and uninfected plants at any depth or distance from the center of the row. The optimum time for determining the relationship between Pi and soybean shoot growth was from late mid-season (September) to final harvest (14 November). The relationship between Pi and seed yield for the final harvest was best described by a quadratic model: yield (g) = 71.4 + 1.1(log₁₀[Pi + 1]) - 2.3(log₁₀[Pi + 1])², (R² = 0.99, P = 0.03).
Glycine max; Meloidogyne incognita; nematode; population dynamics; root-knot nematode; soybean; yield loss
Differential sensitivity of Meloidogyne arenaria, M. hapla, M. incognita, M. javanica, and Heterodera glycines races 1 and 5 to the nonfumigant nematicides aldicarb, ethoprop, and fenamiphos was evaluated using a 48-hour root-penetration bioassay. Generally, H. glycines was more tolerant of the nematicides, especially ethoprop, than were the Meloidogyne species. Among Meloidogyne species, M. incognita was most sensitive to aldicarb and fenamiphos, but its reaction to ethoprop was similar to the other three Meloidogyne species.
aldicarb; differential sensitivity; ethoprop; fenamiphos; Glycine max; Heterodera glycines; juvenile; Meloidogyne arenaria; Meloidogyne hapla; Meloidogyne incognita; Meloidogyne javanica; nematicide; nematode penetration; root-knot nematode; soybean; soybean cyst nematode
The rates of soybean root penetration by freshly hatched second-stage juveniles (J2) of Meloidogyne arenaria, M. hapla, M. incognita, M. javanica, and Heterodera glycines races 1 and 5 were examined over a period of 1 to 240 hours. Heterodera glycines entered roots more quickly than Meloidogyne spp. Penetration by most nematodes was accomplished within 48 hours. The increases in penetration after 48 hours were insufficient to warrant further assessments. Penetration of J2 into roots of soybean seedfings in a styrofoam container was as good or better than in a clay pot. Thus, rapid and accurate root-penetration assessments can be made at 48 hours after inoculation.
Glycine max; Heterodera glycines; infection; Meloidogyne arenaria; M. hapla; M. incognita; M. javanica; nematode; penetration; root; soybean
Three field experiments were established in a loamy sand soil in the Coastal Plain of North Carolina to determine downward movement of aldicarb and fenamiphos with a nematode bioassay. Penetration of bioassay plant roots by Meloidogyne incognita was measured at 1, 3, 7, 14, 21, and 28 days after treatment in the greenhouse as a means of determining nematicide effectiveness. Chemical movement was similar in planted and fallow soil. Nematicidal activity was greater in soil collected from the 0 to 10 cm depth than from the 10 to 20 cm depth. Fenamiphos suppressed host penetration by the nematode more than aldicarb under the high rainfall (19 cm) and low soil temperatures that occurred soon after application in the spring. During the summer, which had 13 cm precipitation and warmer soil temperatures, both chemicals performed equally well at the 0 to 10 cm depth. At the lower soil level (10 to 20 cm), aldicarb limited nematode penetration of host roots more quickly than fenamiphos. Both of these chemicals moved readily in the sandy soil in concentrations sufficient to control M. incognita. Although some variability was encountered in similar experiments, nematodes such as M. incognita have considerable potential as biomonitors of nematicide movement in soil.
aldicarb; chemical movement; fenamiphos; Glycine max; Meloidogyne incognita; nematicide; nematode; root-knot nematode; soybean
The soybean cultivars 'Braxton' and 'Kirby' were less susceptible to both races 1 and 2 of Meloidogyne arenaria than 'Centennial' and 'Young', which were highly susceptible. Soybean seed yields of resistant cultivars were greater (P = 0.05) than susceptible cultivars. Reproduction of M. arenaria races 1 and 2 was significantly lower on less susceptible cultivars compared to highly susceptible cultivars. Root galling, caused by M. arenaria, was 5-10 times greater on Centennial and Young than on less susceptible cultivars Kirby and Braxton. Resistance was independent of the host race of M. arenaria used in this study. Populations of M. arenaria that are highly pathogenic to soybean should be used in screening for soybean resistance rather than specific host races.
Glycine max; Meloidogyne arenaria; nematode; resistance; root-knot nematode; soybean
Survival of biotypes of Heterodera glycines was studied in microplots and in the field. The field population was subjected to various cropping sequences. Viability of eggs overwintered in microplots was determined each spring by percentage hatch, percentage of hatched eggs penetrating roots, and numbers of females developing on Peking and PI 88788 soybeans. Eggs from the field were collected in the spring and fall and assayed for ability to develop on Peking and PI 88788. Hatch of isolates overwintered in the microplots averaged 13% in May 1989 and 19% in 1990. No differences in hatch were detected among the isolates in 1989. Numbers of juveniles penetrating susceptible roots averaged less than 20% of the hatched eggs each year. An isolate of a biotype parasitic on susceptible soybeans and the resistant soybean PI 88788 penetrated roots more successfully than other biotypes. A second isolate from North Carolina, parasitic on susceptible soybeans, PI 88788, and the resistant soybean Peking experienced selection against development on Peking during two winters. Only 17 % of the expected numbers of females developed on Peking from this isolate. In the microplot experiment, parasitism of PI 88788 and Peking had a selective disadvantage (selection coefficient) of s = 0.29 and 0.62 over all isolates, respectively. In the field experiment, the relative numbers of cysts on Peking and PI 88788 increased between the spring and fall on soybean, then decreased over the winter and under corn. Selection coefficients against parasitism of PI 88788 and Peking averaged 0,19 and 0.3 in the field population. In neither experiment did juveniles lose their ability to parasitize susceptible soybeans.
fitness; genetics; Heterodera glycines; nematode; race; selection; soybean cyst nematode; survival
The host-parasite relationships of asparagus and Meloidogyne spp. were examined under greenhouse and microplot conditions. Meloidogyne species and races differed greatly in their ability to reproduce on asparagus seedlings. Meloidogyne hapla generally failed to reproduce, and M. javanica, M. arenaria race 1, and M. incognita race 3 reproduced poorly, with a reproduction factor (Rf = final population/initial population) usually < 1.0. Only M. arenaria race 2 and M. incognita races 1 and 4 reproduced consistently on all asparagus cultivars tested (Rf typically 1-11). No effect of M. incognita race 4 on host growth was detected. Meloidogyne arenaria race 2 and M. incognita race 1 had slight negative effects (5-10%) on plant and root growth.
asparagus; Asparagus officinalis; damage potential; Meloidogyne spp.; nematode; population dynamics; resistance; root-knot nematode; tolerance
The reproductive potential and damage functions for Meloidogyne hapla and M. arenaria race 1 on Virginia-type peanuts (Arachis hypogaea cv. Florigiant) were determined over 2 years in microplot experiments in North Carolina. Peanut yield suppression and damage to pods as a result of galling were greatest in response to M. arenaria (P = 0.01). Damage functions for the two species were adequately described by the quadratic models: yield (g/plot) = 398 - 17.1 (log₁₀[Pi + 1]) - 17.0(log₁₀[Pi + 1])²; (R² = 0.83, P = 0.0001) for M. arenaria; and yield = 388 - 10.2(log₁₀[Pi + 1]) - 7.5(log₁₀[Pi + 1])², (R² = 0.30, P = 0.0001) for M. hapla. Both species caused galling on pods, but this was more severe in response to M. arenaria. Reproduction of M. arenaria race 1 was greater than M. hapla on peanut, which accounts in part for the more severe pod galling. Peanut was an excellent host for both M. arenaria race 1 and for M. hapla, but reproduction by M. hapla was more variable.
Arachis hypogaea; damage function; Meloidogyne arenaria; Meloidogyne hapla; nematode; peanut; reproductive potential; root-knot nematode