The effects of root diffusates of selected plants within the families Chenopodiaceae and Cruciferae and the hatching agent zinc chloride were tested for their effects on hatching and emergence of juveniles from cysts of Heterodera schachtii and a race of H. trifolii parasitic on Chenopodaceae and Cruciferae in The Netherlands. Although all diffusates strongly stimulated hatching of juveniles of H. schachtii, their effects on H. trifolii were less evident.
sugarbeet diffusate; zinc chloride; Beta spp; Chenopodiaceae; Cruciferae; sugarbeet nematode; clover cyst nematode
Various combinations of vertebrate and invertebrate tissue culture and microbiological media were utilized in an attempt to culture Romanomermis culicivorax (Mermithidae: Nematoda) in vitro. Most media were unsuitable and caused nematodes to become lumpy, vacuolated, and granular. Slow and limited growth and development of internal structures of the nematodes were obtained with variously supplemented Grace's tissue culture and Schneider's Drosophila media. In an enriched Grace's medium, development attained by the nematodes after 3-4 wk was comparable to 4-5-day-old parasites grown in vivo in the mosquito host, Culex pipiens. Two molts were observed in vitro. Maximum dimensions in vitro were 7.0-mm length and 87-μm width at the widest point. The stichosome, stichocytes, and trophosome developed prominently. A filiform tail and highly cuticularized tube persisted throughout the culture period in vitro.
Culex pipiens; Mermithidae; mosquito nematode
The influence of various c oncentrations of K⁺, nitrogen sources, and inoculation with root-knot nematode Meloidogyne javanica were evaluated in tomato plants. Increased potassium concentration increased top and root fresh weights of intact plants and fresh weights of excised roots. Nitrate-fertilized plants weighed more than plants receiving ammonium independent of the K level in the medium. Nematode counts on roots were not affected by nutritional differences in intact or excised roots. In intact roots a high percentage of males was recorded at low K⁺ levels, whereas in excised roots the proportion of males in the population rose as the K⁺ levels increased. Inoculated intact roots accumulated K⁺ when the level of potassium supply was low; infected excised roots contained less K⁺ than did nematode-free roots.
ammonium; nitrate; nutrition; physiology; potassium
The genetic nature of resistance and its epidemiologic effects on two Meloidogyne incognita populations were assessed in the F₁ hybrid tomato cv. Small Fry. The progeny of a Small Fry × Small Fry cross segregated in a 3:1 resistant:susceptible ratio, indicating the presence of a single, completely dominant resistance gene (LMiR₂) in Small Fry. In a subsequent experiment, infection frequency and the rate of development of primary infection on resistant Small Fry × Small Fry segregates were compared to those on susceptible segregates and the susceptible cultivar Rutgers. Suppression in both infection frequency and rate of development of primary infection was entirely attributable to gene LMiR₂. A single egg-mass population of M. incognita propagated for 12 generations on Small Fry showed an increased ability over the wild type population to parasitize plants containing the LMiR₂ gene but failed to completely overcome resistance. The relationship of this phenomenon to the genetics of the Lycopersicon esculentum-M. incognita interaction is discussed.
infection frequency; primary infection; selection; rate of development
Dolichodorus grandaspicatus n. sp., collected from soil about roots of a red maple (Acer rubrum L.) in a creek bottom near Ludwig. Johnson County, Arkansas, is described. It differs from two closely related species, D. marylandicus and D. heterocephalus, by the longer spike on the female tail, the lenght of the female tail, and the shape of the extrudable portion of the gubernaculum of the males. It further differs from D. marylandicus by having heavily sclerotized accessory pieces of the vuvla and from D. heterocephalus by having a shorter stylet.
taxonomy; morphology; new species
The relative susceptibility of four field crops to Criconemella ornata differed greatly in microplot tests. As few as 178 freshly-introduced C. ornata/500 cm³ of soil stunted peanut. In contrast, this nematode had no effect on the growth of corn or soybean. Large populations remaining after culture of peanut or corn enhanced the growth of tobacco. A problem of comparing the effects of a freshly introduced population of this nematode with large residual populations was encountered. Freshly extracted, greenhouse-grown inoculum caused the typical "yellows disease" on peanut, whereas much greater residual population densities following a poor host (tobacco) had little effect on the growth of peanut. It is suggested that many of the nematodes in the field following a poor host are dead. Peanut supported greater reproduction (up to 970-fold) than did other crops tested. Corn was intermediate, with a population increase as great as 264-fold; soybean and tobacco failed to maintain initial population densities.
tolerance limit; damage potential; host suitability; host sensitivity; Zea mays; Nicotiana tabacum; Glycine max; Arachis hypogea; nematode advisory services
Though in the past Xiphinema americanum has been the most commonly reported dagger nematode in the eastern United States, our studies revealed the presence in Pennsvlvania of a previously unrecognized and unreported species related to X. americanum, Morphometric data and photomicrographs establish the identity of this form as X. rivesi and show expected variations in populations of this species from various locations. Similar data and illustrations are given for X. americanum populations from Pennsylvania and other areas, showing variations and relationships. Xiphinema rivesi is widely distributed in the fruit producing area of south-central Pennsylvania and is also reported herein from raspberry in Vermont and apple in Maryland and New York. This species is frequently found in fruit growing areas of Pennsylvania associated with tomato ringspot virus-induced diseases and is also found associated with corn, bluegrass sod, and alfalfa.
Xiphinema americanum; X. rivesi; morphology; occurrence; fruit orchards; virus transmission
The effect of α-tocopherol on the reproductive capacity of the free-living nematode Turbatrix aceti was determined using three different culture methods: mass culture, pair culture. and single culture. Significant differences were observed between control and α-tocopherol cultured nematodes for all reproductive parameters measured. The reproductive period started at a significantly earlier time and the length of the reproductive period was significantly longer in α-tocopherol cultured nematodes. The average number of offspring was 34 in control cultures as compared to 55 in α-tocopherol cultures. The eggs of α-tocopherol cultured females showed a more regular outline and uniform distribution of yolk than did eggs from control females.
physiology; reproduction; α-tocopherol; vitamin E; oocytes
Custer and Hood soybean cultivars were inoculated with nine levels of Criconemoides simile ranging from 300 to 20,600 nematodes per plant. Rate of reproduction decreased as inoculum level was increased beyond 900-2,000 nematodes. Final population density was influenced by both composition and level of inoculum. There was an indication that substance(s). inhibitory to larvae, accumnlated in soil in which Hood was grown for 11 months, Significant reduction of fresh weight of roots of Hood, but not Custer, occurred at population densities of 37,000 and 44,700 nematodes per plant.
ring nematode; allelopathy
A FORTRAN computer program was developed to simulate nematode soil sampling strategies consisting of various numbers of samples per field, with each sample consisting of various numbers of soil cores. The program assumes that the nematode species involved fit a negative binomial distribution. Required input data are estimates of the mean and k values, the number of samples per field and cores per sample in the strategy to be investigated, and the number of times the simulation is to be replicated. Output consists of simulated values of the relative deviation from the mean and standard error to mean ratio, both averaged over all replications. The program was used to compare 150 simulated sampling strategies for Meloidogyne incognita, involving all combinations of two mean values (2.0 and 10.0 la.rvae/10 cm³ soil), three k values (1.35, 0.544, and 0.294), five different numbers of samples per field (1, 2, 4. 10, 20), and five different numbers of cores per sample (1, 2, 4, 10, 20). Simulations resulting from different mean values were similar, but best results were obtained with higher k values and 20 cores per sample. Relatively few 20-core samples were needed to obtain average deviations from the mean of 20-25%.
computer simulation; sampling error; spatial distribution; Meloidogyne incognita
The effects of organophosphates (mevinphos, phenamiphos, trichlorfon), carbamates (carbofuran, methomyl, oxamyl), a formamidine (chlordimeform), a synthetic pyrethroid (fenvalerate), a chlorinated hydrocarbon (methoxychlor). and an insect growth regulator (diflubenzuron) on in vitro development and reproduction of Neoaplectana carflocapsae were tested by incorporating each chemical into a nematode rearing medium. Organophosphates and carbamates adversely affected development and reproduction at concentrations ≥ 0.1 mg/ml. Phenamiphos was the most toxic, with no nematode reproduction at 0.01 mg/ml. Inoculated infective juveniles developed to adults with some of the organophosphates and carbamates, but limited or no reproduction occurred. Chlordimeform inhibited development at 1.0 mg/ml, while diflubenzuron, fenvalerate, and methoxychlor did not significantly (P > 0.05) reduced reproduction at 1.0 mg/ml. The organophosphate and carbamate nematicides in use for control of plant-parasitic nematodes may be toxic to N. carpocapsae in the soil.
organophosphates; carbamates; integrated pest management; biological control
Chemical control of the citrus nematode, Tylenchulus semipenetrans Cobb, has consistently increased yield of grapefruit on sour orange rootstock in Texas. In this study, data from chemical control tests conducted from 1973 to 1980 were analyzed to determine the relationship between nematode counts and grapefruit yield and fruit size. The correlation between yield and nematode counts was negative (r = -0.47) and highly significant (P < 0.01). The data best fit the exponential decay curve: y = 160.3e-0.0000429 where y = yield in kg/tree and x = nematodes/100 cm³ of soil. The correlation between fruit size and nematode counts was not significant because yield and fruit size were inversely related. Yield loss in an average untreated orchard was estimated to be 12.4 tons/ha. Economic loss to citrus nematode in Texas grapefruit, assuming no treatment and an average on-tree price of $60/ton, was estimated to be $13.2 million annually.
Tylenchulus semipenetrans; control; economics
Hoplolaimus magnistylus n. sp. is described and illustrated. It was found in soil around roots of soybean in Arkansas and Mississippi. It is similar to H. galeatus and H. concaudajuvencus. It differs from H. galeatus in all stages primarily by possession of a longer stylet. It differs from H. concaudajuvencus by the possession of rounded tails in second-stage juveniles vs. conically pointed tails with acute termini, having fewer subdivisions in female basal lip annules, and the greater distance from female anterior end to posterior end of esophageal lobes. Morphometrics and descriptions of second-, third-, and fourth-stage juveniles are given. A paratype female of H. sheri was examined and found to have six esophageal gland nuclei.
taxonomy; morphology; new species
The infectivity and development of four populations of Meloidogyne hapla were compared, at three temperatures, on tomato and two varieties of cucumber. A population from Canada produced few root-galls on cucumber and, except at 24 C, no larvae developed into adult females and produced egg masses. In contrast, a population with 45 chromosomes from America produced many galls on cucumber and small proportions of larvae became females and produced egg masses at 20 and 24 C. At 18 C this population produced no egg masses on cucumber, but a population from Britain and one from America with 17 chromosomes produced more egg masses at this temperature than at 20 or 24 C. Dissection of the galls showed that on cucumber many larvae died or their growth and development was slowed.
temperature; root-knot nematodes; cucumber; tomato
Sex differentiation was studied by examining the cellular structure of gonad primordia extracted from second-stage juveniles developing under different environmental conditions. In female jnveniles, divisions of the two somatic cells of the primordium occurred in mid-sccond stage and resulted in 12 cells. Two of them were differentiated as cap cells, two occupied the anterior central and eight the posterior central part of the V-shaped primordium. The two germinal cells divided at the 6-8 somatic-cell stage of the primordium; i.e., earlier than in any other plant-parasitic nematode. In male juveniles of similar developmental stage, divisions of somatic cells resulted in 10 cells: one cap cell at the posterior tip and nine cells at the anterior part of the rod-shaped primordium. Germinal cells divided at the 6-8 sontatic-cell stage. On the basis of gonad anatomy it was concluded that some female juveniles undergo sex reversal and proceed with further development as males. The degree of expression of intersexual features depends on the period at which sex reversal occurs. Sex reversal at an early period gives rise to males with one testis, almost indistinguishable front true males. Sex reversal at mid-second stage involves degeneration of the nucleus of one of the cap cells resulting in males with an atrophied testis and a well-developed testis. More delayed sex reversal results in males with two testes of approximately equal size. To explain these patterns of development, it is assumed that sex differentiation is hormonally controlled and that the environment influences hormonal balance by affecting gene expression.
sexuality; nematodes; postembryogenesis
The effects of Meloidogyne incognita or M. javanica at five initial inoculum levels of 20, 100, 200, 1,000, and 2,000 eggs and infective juveniles per seedling on 'Floradade,' 'Nemarex,' 'Patriot,' and 'PI 129149-2(sib)-5' tomatoes maintained at 25 or 32.5 C were studied. The number of egg masses on roots of the susceptible cultivar Floradade was similar for both species of root-knot nematodes at either 2.5 or 32.5 C soil temperatures. At 25 C, very low numbers of egg masses were produced by both species of root-knot nematodes on Nematex, Patriot, and Lycopersicon peruvianum PI 129149-2(sib)-5. At 32.5 C, the best inoculum level for assessing resistance in these tomato genotypes was 200 eggs and infective juveniles per seedling. With 28 days of incubation, this temperature and inoculum level produced quantitative differences in resistance for both species of Meloidogyne.
Lycopersicon; root-knot nematode
Annual postplanting applications of 40.7 kg/ha DBCP (1,2-dibromo-3-chloropropane) controlled Macroposthonia xenoplax (Raski, 1952) deGrisse and Loof, 1965 in peach tree short life sites, reduced bacterial canker incidence from 74% to 6%, and inreased the average life of the trees from 3.9 to 6.8 yr for a 7-yr test period. Hydrated lime at 5.5 kg per planting site reduced bacterial canker incidence from 81% 57 % and increased the tree longevity from 2.6 to 6.0 yr. Populations M. xenoplax were inversely correlated with tree longevity.
Romanomermis culicivorax juveniles were dissected out of Aedes aegypti larvae 7 days after infection and incubated under controlled conditions in isotonic saline containing a ¹⁴C-labeled fatty acid (palmitic acid), monoacylglycerol (glycerol monoolein), or triacylglycerol (glycerol tripalmate) nutrient source. The mermithid absorbed each of these lipids from the incubation medium, the rate of uptake being greatest for glycerol monoolein. No lipase activity was detected in whole nematode homogenates or in the media in which the nematodes were incubated. It is suggested that the nematode transports complex lipid molecules across its outer cuticle intact.
Aedes aegypti; fatly acid; lipase; mermithid; monoacylglycerol; nutrition; triacylglycerol
A simple, rapid, and inexpensive method for evaluation of host-parasite interactions, based on monoxenic cultures, is described. Axenic root explants of Glycine max (L.) Merr., cultured on a holidic agar medium, were inoculated with axenic second-stage larvae of Heterodera glycines Ichinohe, Race 3. A clear separation of susceptible and resistant cultivars, based on numbers of mature female nematodes present after 3 wk at 25 C, was observed. The method described should aid researchers in the evaluation of the host response to infection by H. glycines.
Spatial distributions of several species of plant-parasitic nematodes were determined in each of three fallow vegetable fields and in smaller subunits of those fields. Goodness of fit to each of several theoretical distributions was tested hy means of a X² test. Distributions for most species showed good agreement with a negative binomial model. An exception occurred with Crictmemella sp., which showed a better fit to the Neyman Type A distribution. For nematodes distributed according to the negative binomial model, the number of cores per composite sample needed to achieve specified relative errors was calculated. For a given nematode species, such as Quinisulcius actus (Allen) Siddiqi or Meloidogyne incognita (Kofoid &White) Chitwood, the k values for the negative binomial distribution increased as field size decreased, with the result that fewer cores were needed to achieve the same level of precision in a smaller field. Best results were achieved when the single sample was used to estimate populations in fields of 0.25-0.45 ha in size. When using only a single composite sample to estimate mixed populations of the nematodes studied here in a field of that size, approximately 22 cores per composite sample would be needed to estimate all population means within a standard error to mean ratio of 25%. Considerably, more cores were needed to maintain a given level of precision in fields of 1.0 ha or greater, and it may be necessary to subdivide larger unils (ca. 1.5 ha and up) for accurate sampling.
spatial distribution; negative binomial distribution; Neyman Type A distribution; Criconemella sp.; Helicotylenchus dihhystera; Meloidogyne incognita; Quinisulcius acutus; Rotylenchulus reniformis