Planting date of soybean, Glycine max, influenced winter survival of Pratylenchus brachyurus in microplots at two locations in North Carolina. Delayed planting resulted in a linear decrease (P = 0.05) in the numbers of P. brachyurus at soybean harvest. Effects of planting date on nematode numbers persisted over winter, indicating that survival in the absence of a host is density independent. Compared with winter fallow, winter wheat, Triticum aestivum, reduced winter survival of P. brachyurus. Subsequent soybean yields were suppressed by the overwintering population of this nematode at one location but not at another.
Glycine max; Triticum aestivum; lesion nematode; cropping systems; cover crops; population dynamics; damage threshold; survival
Three Xenorhabdus nematophilus subspecies influenced Steinernema glaseri growth profiles and growth rates, but this was not necessarily because of different bacterial growth rates. Virulence of dauer nematodes in larval Galleria mellonella varied with the number of dauers retaining bacteria and the bacterial subspecies. Virulence was least for dauers grown on X. nematophilus subsp. bovienii because of the lack of retained bacteria. Virulence was subsequently restored by culturing these nematodes on X. nematophilus subsp. poinari.
Steinernema glaseri; Xenorhabdus nematophilus; Galleria mellonella; dauer juveniles; bacterial retention; virulence
Electron micrographs of serial sections show that the male sexual apparatus of Scutellonema brachyurum includes two morphologically identical spicules. Each is composed of a swollen tubular head, crescentic shaft, and leaf-like blade with membranous velum expanded from the central trunk. The spicules are concave and grooved on the ventral side and convex on the dorsal side near the trunk. The trunk is continuous with the shaft and head. Nerve tissue occupies the core of the spicule and includes a dendritic process which gains access to the exterior via a small pore on the lateral side of the spicule tip. Three protractor and two retractor muscles are associated with each spicule. A sensory accessory piece connects with the tip of the gubernaculum and protrudes from the lower side of the opening of the spicular pouch; it protracts and retracts with the muscularized gubernaculum. The gubernaculum varies from bow-shaped in the distal part to boat-shaped in the mid region. A sac exits beneath the accessory piece as a buffer for its movement. A cuticular guiding bar originating from the dorsal wall of the spicular pouch has a tongue. The ventral surface of the tongue is sclerotized to separate the two spicules. It is mobile by muscles of the protractor gubernaculi, retractor gubernaculi, and seductor gubernaculi.
accessory piece; bar tongue; capitulum; gubernaculum; guiding bar; sensory organ; spicule
Few soybean cyst nematodes (SCN), Heterodera glycines, of a diverse gene pool developed into females on soybeans PI 89772 or PI 209332. Nematodes surviving the selection pressure were then inbred for nine generations by single cyst transfers on the same selecting soybean line. These nematodes appeared to tolerate concurrent selection and inbreeding. Effects of selection-inbreeding, selection only, and secondary selection were evaluated by relative ability to produce cysts on 11 soybean lines. The genetic differences of PI 89772 (also Peking and Pickett 71) and PI 209332 were reaffirmed. The random effects of inbreeding indicated that Ilsoy and Williams may have genes for resistance different from those in PI 89772 or PI 209332. Egg inoculum obtained from soil resulted in very few cysts in some tests. Fresh egg inoculum (from cysts on 27-30-day-old plants) generally resulted in more cysts and more consistent results. Concurrent with the change in inoculum, there was a large increase in relative numbers of cysts on several soybean lines but no change on other lines; the true cause of this large interaction is unknown. Secondary selection of two inbreds was effective and suppressed cyst numbers on the line on which one inbred was selected initially. These results are consistent with the allelism linkage of some SCN genes reported previously.
soybeans; cyst nematodes; resistance; genes; frequencies
The impact of Glomus fasciculatum on Meloidogyne hapla associated with Allium cepa was evaluated in two experiments. Nematode density was not different in mycorrhizal and nonmycorrhizal plants 10 weeks after the joint inoculation of M. hapla and G. fasciculatum. Differences in the age structure of M. hapla populations reared on mycorrhizal and nonmycorrhizat plants were noted. G. fasciculatum enhanced leaf and bulb growth of A. cepa in the absence of M. hapla, but did not affect plant weight when nematodes were present. Survival and reproduction of M. hapla were not affected by G. fasciculatum or phosphorus (P). The estimated time required for inoculated second-stage juveniles (J2) to mature to the adult stage was 1,000 degree hours (base = 9 C) greater in mycorrhizal than in nonmycorrhizal plants supplemented with P. Although the infectivity of J2 was not measured directly, colonization of A. cepa by G. fasciculatum appeared to alter the ability of M. hapla to penetrate roots.
mycorrhizae; onion; nematode development; interaction
The occurrence ofchlamydospores of Glomus fasciculatum (Gf) within cysts of the soybean cyst nematode, Heterodera glycines, and the effects of vesicular-arbuscular mycorrhizae on nematode population dynamics and soybean (Glycine max) plant growth were investigated. Chlamydospores occupied 1-24% of cysts recovered from field soil samples. Hyphae of Missouri isolate Gfl penetrated the female nematode cuticle shortly after she ruptured the root epidermis. Convoluted hyphae filled infected eggs, and sporogenesis occurred within infected eggs. G. microcarpum, G. mosseae, and two isolates of Gf were inoculated with H. glycines on plants of 'Essex' soybeans. Each of the two Gf isolates infected about 1% of the nematode eggs in experimental pot cuhures. The Gfl isolate decreased the number of first-generation adult females 26%, compared with the nonmycorrhizal control. The total numbers of first-generation plus second-generation adult females were similar for both Gf isolates and 29-41% greater than the nonmycorrhizal control. Soybean plants with Gf and H. glycines produced more biomass than did nonmycorrhizal plants with nematodes, but only Gfl delayed leaf senescence.
soybean cyst nematode; vesicular-arbuscular mycorrhiza; Glycine max; biocontrol
The tethered-nematode technique was adapted for use with second-stage juveniles of Meloidogyne incognita. The data demonstrate that M. incognita exhibits the same patterns of behavior as adults of the free-living nematode, Caenorhabditis elegans. The principal differences are that M. incognita is slower and less regular in its behavior than C. elegans. The frequency of normal waves is about 0.2 Hz; that of reversal waves is about 0.06 Hz. Reversal bouts last about 1 minute. In response to a change in NaCl concentration, M. incognita modulates the probability of initiating a reversal bout in the same manner as C. elegans except that it responds more slowly and is repelled instead of attracted.
chemotaxis; NaCl; root-knot nematode; nematode movement; nematode response
Seven populations, representing cytological race A (triploid, 3n = 51-56) and the two host races (infective and noninfective on peanut) of Meloidogyne arenaria were studied with light microscopy (LM) and scanning electron microscopy (SEM). Characteristics of root-knot nematodes, recently recommended as useful taxonomic traits, were reexamined among these populations, and their variability both within and between populations was ascertained. We found that stylet morphology of females and head and stylet morphologies of males and second-stage juveniles were the most reliable characters for identification. The two host races of M. arenaria could not be distinguished morphologically. Two of the populations could be separated consistently from the remainder but were not sufficiently divergent to be considered new species. These two variant populations were similar; neither produced males in culture, and they differed from the typical populations in female perineal patterns (LM) as well as in cephalic structure (SEM) and tail shape (LM) of second-stage juveniles. In morphometric studies, most characters of the variant populations differed significantly from those of the typical M. arenaria.
root-knot nematodes; cytological races; host races; morphometrics; taxonomy; scanning electron microscopy; light microscopy
Subcellular granules from the second-stage (preparasitic) juveniles of root-knot nematode Meloidogyne incognita were isolated by isopycnic centrifugation on Percoll. The granules had an apparent density of 1.13 g/cm³. The relative specific activity of acid phosphatase in the granule extract was 8.4. Acid phosphatase activity was also detected histochemically in the subventral gland granules. Electron microscopy and malate dehydrogenase activity indicated that contamination of granules by mitochondria was negligible. Electrophoresis of the granule extract in the presence of sodium dodecyl sulfate showed 15-20 major protein bands.
esophageal gland; giant cell; acid phosphatase; secretory granule; root-knot nematode
Planting date was used as a variable to determine the effects of time and different environmental conditions on the population dynamics and damage potential of Pratylenchus brachyurus on soybean at two locations in North Carolina. An initial population slightly less than the damage threshold (275 nematodes/500 cm³ soil) was used to minimize the influence of host damage on this nematode's population dynamics and to gain greater precision in characterizing factors which influence the damage potential of P. brachyurus to soybean. Equivalent nematode numbers generally resulted in greater yield suppression of soybean in early plantings. Early planting of soybean also resulted in greater (P = 0.01) population densities of P. brachyurus at midseason which often persisted until soybean harvest. Length of time for reproduction and intraspecific competition occurring when soybeans were stunted by the nematode were the most important factors influencing the population dynamics of P. brachyurus.
Glycine max; lesion nematode; control; yield suppression; microplots; ecology
The sting nematode, Belonolaimus longicaudatus, was associated with poor growth of citrus in a central Florida nursery. Foliage of trees was sparse and chlorotic. Affected rootstocks included Changsha and Cleopatra mandarin orange; Flying Dragon, Rubidoux, and Jacobsen trifoliate orange; Macrophylla and Milam lemon; Palestine sweet lime; sour orange; and the hybrids - Carrizo, Morton, and Rusk citrange and Swingle citrumelo. Root symptoms included apical swelling, development of swollen terminals containing 3-5 apical meristems and hyperplastic tissue, coarse roots, and a reduction in the number of fibrous roots. Population densities as high as 392 sting nematodes per liter soil were detected, with 80% of the population occurring in the top 30 cm of soil; however, nematodes were detected to 107 cm deep. Although an ectoparasite, the nematode was closely associated with citrus root systems and was transported with bare root nursery stock. Disinfestation was accomplished by hot water treatment (49 C for 5 minutes).
rootstocks; histopathology; population densities; vertical distribution; eradication
A 2-year field study evaluated the influence of subsoiling and nematicide application, alone and in combination, on the growth and yield of field corn in a sandy soil in north-central Florida. The field had a 25-30-cm-deep tillage pan (plowpan) and was infested with Belonolaimus longicaudatus, Hoplolaimus galeatus, Trichodorus christei, and Pratylenchus spp. Subsoiling increased corn yield both years, and the residual effect of subsoiling in the first year increased yields in the second year. Preplant application of DD injected in-row increased yields and reduced nematode populations. At-planting applications of DD injected in-row and carbofuran in-furrow or in a band were less effective than subsoiling in increasing yields and reducing nematode numbers. Interactions between subsoiling and nematicide treatments occurred in the second year.
Belonolaimus longicaudatus (sting); Hoplolaimus galeatus (lance); Pratylenchus spp. (lesion); Trichodorus christei (stubby-root); carbofuran; chemical control; DD; tillage pan
Self-thinning in alfalfa, a dynamic process involving the progressive elimination of the weakest plants, was enhanced by Meloidogyne hapla. Alfalfa stand densities decreased exponentially with time and were reduced 62% (P = 0.05) in the presence of M. hapla. As stand densities decreased over time, mean plant weights increased at a rate 2.59 times faster in the absence of M. hapla. In a stepwise multiple regression analysis, 65% of the total variation in yield could be explained by changes in stand density and 85% by average weight of individual stems. Alfalfa yields were suppressed (P = 0.05) by M. hapla, with suppression generally increasing with time and as the nematode population density increased. Yield suppression was attributable primarily to the decline in plant numbers and to suppression in individual plant weights.
self-thinning; plant competition; plant survival; yield determinant; root-knot nematode; Medicago sativa; growth suppression
Pathogenicity and reproduction of single and combined populations of Meloidogyne arenaria and M. incognita on a susceptible soybean (Glycine max cv. Davis) were investigated. Significant galling and egg mass production were observed on roots of greenhouse-grown soybean inoculated with M. arenaria and M. incognita, in combination and individually. M. arenaria produced more galls and egg masses than M. incognita, whereas in combined inoculation with both nematode species, gall and egg production was intermediate. In growth chamber tests, inoculations with M. arenaria and M. incognita, singly or in combination, produced more galls and egg masses at 30 C than at 25 C. At 25 C, M. arenaria alone produced significantly more galls and egg masses than the combined M. arenaria plus M. incognita, while M. incognita produced the fewest. At 30 C, numbers of egg masses produced by M. arenaria did not differ significantly from combined M. arenaria and M. incognita. In temperature tank tests, M. incognita produced more galls and egg masses at 28 C than at 24 C soil temperature. In contrast, numbers of galls, egg masses, and eggs of M. arenaria were slightly higher at 24 C than at 28 C. Combined inoculum of both nematode species produced greater numbers of galls at 24 C than at 28 C.
Glycine max; interaction; concomitant; root-knot nematode; soil temperature; inoculum density; ecology
Invasion of tomato (Lycopersicon esculentum L.) roots by combined and sequential inoculations of Meloidogyne hapla and a tomato population of Heterodera schachtii was affected more by soil temperature than by nematode competition. Maximum invasion of tomato roots, by M. hapla and H. schachtii occurred at 30 and 26 C, respectively. Female development and nematode reproduction (eggs per plant) of M. hapla was adversely affected by H. schachtii in combined inoculations of the two nematode species. Inhibition of M. hapla development and reproduction on tomato roots from combined nematode inoculations was more pronounced as soil temperature was increased over a range of 18-30 C and with prior inoculation of tomato with H. schachtii. M. hapla minimally affected H. schachtii female development, but there was significant reduction in the buildup of H. schachtii when M. hapla inoculation preceded that of H. schachtii by 20 days.
northern root-knot nematode; sugarbeet cyst nematode; invasion; soil temperature; populations; inoculum density; development; reproduction; Lycopersicon esculentum
Two-dimensional polyacrylamide gel electrophoretic protein patterns of H. glycines from southern Indiana (Posey County) and northern Indiana (Pulaski County) were largely similar, but many differences existed. The pattern of the Posey isolate was similar to patterns from isolates collected in other areas of the United States. Unique dense protein spots in the pattern of an isolate from Hokkaido, Japan, distinguished it from patterns of six U.S. isolates.
soybean cyst nematode; two-dimensional gel electrophoresis; soybean
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.
Columbia root-knot nematode; Solanum tuberosum; soil temperature; reproduction; generations; degree-days; chemicals; population densities; control
Ultrastructural study of the body wall of preparasitic, parasitic, and postparasitic stages of Romanomermis culicivorax showed that the cuticle of all three stages was permeable to lanthanum. The cuticle of the parasitic stage was the thinnest and showed the greatest permeability. Lanthanum accumulated on the apical surfaces of the hypodermal cells but was not found intracellularly. The negative staining characteristics of lanthanum enhanced the detection of numerous smooth septate junctions in the hypodermis of the parasitic stage.
Culex pipiens; hypodermis; mermithid ultrastructure; nematode ultrastructure; septate junctions
Root diffusate from soybean plants caused greater hatching of Heterodera glycines eggs during vegetative growth of the host, but the activity declined with plant senescence. Chelation of the root diffusate with ethylenediamine tetraacetic acid (EDTA) significantly increased hatching activity for H. glycines eggs. Diffusate from leafless plants caused little hatching, whereas treatment of intact plants with the growth regulators gibberellin and kinetin had no effect on the hatching activity of root diffusate. Treating H. glycines eggs with zinc chloride and root diffusate reduced egg hatching from zinc chloride alone. Levels of zinc in the root diffusate were insufficient to induce egg hatch, based on analysis by atomic absorption spectrophotometry. The enzymatic activity of leucine aminopeptidase in H. glycines eggs was not altered by treatment with chelated or nonchelated root diffusate.
Glycine max; soybean; Nematoda; root diffusate; chelation; zinc chloride; hatching factor; plant growth regulators
Scanning electron microscopy (SEM) of second-stage juveniles (J2), males, and females of Meloidodera floridensis, M. charis, M. belli, and Verutus volvingentis reveals detailed characteristics of the head region, lateral field, phasmid, body striae, vulva, and perineal region. In M. charis and M. belli the en face pattern conforms to a basic pattern in which the labial disc is surrounded by six lips (sectors) of the first head annulation. In J2 the head has additional annulations, whereas in males annulation is replaced by longitudinal blocks. Conversely, J2 and males of M. floridensis and V. volvingentis each have a unique derived face pattern with fusion of various lip components and with head annulation. All six lips of females of M. charis and M. belli are fused, whereas females of M. floridensis and V. volvingentis have distinct lateral lips. Lateral fields vary among species, with only slight differences at the anterior and posterior ends of the lateral lines and in the spatial relation of the lines to phasmid openings. Phasmid openings are present in adults of Meloidodera spp., but were not observed in adults of V. volvingentis; in this respect, the female perineal pattern of Verutus is different from Meloidodera spp, The very large vulva (± 48 μm long) of V. volvingentis is in sharp contrast to the minute vulva (± 6 μm long) in a population of M. charis from San Bernardino. Morphological characters revealed by SEM will be most informative when investigated throughout Heteroderidae and incorporated with additional characters for a phylogenetic analysis of the family.
en face patterns; perineal pattern; phasmids; phylogeny; SEM; systematics; vulva
Winter survival dynamics of Meloidogyne incognita and M. arenaria were studied at nine sites in Texas for 2 years. Population survival from October until April was variable among sites, ranging from 0.1% to 33%. A negative correlation (r = -0.86, P = 0.01) was observed between initial population, densities in October and survival percentage until the following April. Total population (eggs + J2) and population of eggs declined continuously during the survival period. Populations of juveniles (J2) increased initially, then declined. The total populations were 82% eggs in October; hatch of these eggs was believed responsible for the observed increase in the population density of J2. Viable eggs were recovered from the soil until March. Eggs are as important as J2 in winter survival of M. incognita and M. arenaria in Texas. Survival data were analyzed by a simple mathematical model.
root-knot nematodes; modeling; population dynamics; egg viability
Nematode and disease problems of irrigated, double-cropped soybean and corn, and zinc deficiency of corn were investigated. Ethylene dibromide, phenamiphos, and aldicarb were equally effective for controlling nematodes and increasing yields of corn planted minimum-till and soybean planted in a moldboard plow prepared seedbed. The residual effects on yields of nematicides applied to the preceeding crop occurred during 3 years for soybean and 1 year for corn. Fusarium wilt symptoms of soybean that developed during 2 years of the study were less severe in all nematicide-treated plots than in control plots. Typical zinc deficiency symptoms on 30-day-old corn plants were observed during 1 year of the study in certain plots. Symptoms were not evident on plants grown on plots treated with ethylene dibromide, and only occasional plants had symptoms on plots treated with phenamiphos and aldicarb. The amount of yield response directly related to nematode control could not be determined because of the apparent interaction of nematodes on the expression of Fusarium wilt of soybean. Our study strongly indicates that the expression of Fusarium wilt of soybean and zinc deficiency in corn are influenced by nematodes and that nematicides will reduce their severity.
Glycine max; Zea mays; Meloidogyne incognita; Paratrichodorus christiei; Belonolaimus longicaudatus; Pratylenchus brachyurus; Rhizoctonia solani; Fusarium oxysporum; double-cropped; minimum-tilled; irrigation; nematicides; ethylene dibromide; phenamiphos; aldicarb
Supernatant from a sonicated macerate of eggs of Heterodera glycines hydrolyzed L-leucine β-naphthylamide and L-leucine 7-amido-4-methylcoumarin. Rate of substrate hydrolysis was influenced by pH and increased with the duration of incubation. A Michaelis-Menten constant of 0.15 mM was obtained. Rate of substrate hydrolysis was decreased by freezing egg supernatant for 26 days or heating above 60 C for 5 minutes. When egg supernatant was incubated with six different substrates, L-leucine β-naphthylamide was hydrolyzed most readily and L-valine β-naphthylamide the least readily. The rate of substrate hydrolysis by egg supernatant was not increased by pretreatment of eggs with 3 mM zinc chloride for up to 14 days.
biochemistry; egg hatching; enzyme; Glycine max; soybean; nematode eggs
Overestimation of yield loss caused by Meloidogyne incognita on tobacco was calculated as a function of the statistical frequency distribution of sample counts. Sampling frequency distributions were described by a negative binomial model, with parameter k, and the resulting probability generating function was used to calculate discrete damage probabilities. Negative binomial damage predictions were compared to mean-density estimates of damage. Predictions based on mean density alone overestimate yield loss by values ranging from 300% at a k of 0.1 to less than 10% at a k of 1.0. Damage overestimation was described as an exponential function of k and mean density. Preplant sampling data for M. incognita were used to derive a linear model for the estimation of k from mean density, allowing the calculation of yield-loss overestimation based on one parameter, the field mean density. Overestimation of damage ranged from 288% at a density of 50 juveniles/500 cm³ soil, to 5% at a density of 1,000 juvelfiles/500 cm³ soil.
crop-loss estimation; negative binomial; nematode damage functions