Reproduction and Development of Meloidogyne incognita and M. javanica on Guardian Peach Rootstock

Guardian peach rootstock was evaluated for susceptibility to Meloidogyne incognita race 3 (Georgia-peach isolate) and M. javanica in the greenhouse. Both commercial Guardian seed sources produced plants that were poor hosts of M. incognita and M. javanica. Reproduction as measured by number of egg masses and eggs per plant, eggs per egg mass, and eggs per gram of root were a better measure of host resistance than number of root galls per plant. Penetration, development, and reproduction of M. incognita in Guardian (resistant) and Lovell (susceptible) peach were also studied in the greenhouse. Differences in susceptibility were not attributed to differential penetration by the infectivestage juveniles (J2) or the number of root galls per plant. Results indicated that M. incognita J2 penetrated Guardian roots and formed galls, but that the majority of the nematodes failed to mature and reproduce.     

Competition of Meloidogyne incognita and Rotylenchulus reniformis on Cotton Following Separate and Concomitant Inoculations

It has been hypothesized Rotylenchulus reniformis (Rr) has a competitive advantage over Meloidogyne incognita (Mi) in the southeastern cotton production region of the United States. This study examines the reproduction and development of Meloidogyne incognita (Mi) and Rotylenchulus reniformis (Rr) in separate and concomitant infections on cotton. Under greenhouse conditions, cotton seedlings were inoculated simultaneously with juveniles (J2) of M. incognita and vermiform adults of R. reniformis in the following ratios (Mi:Rr): 0:0, 100:0, 75:25, 50:50, 25:75, and 0:100. Soil populations of M. incognita and R. reniformis were recorded at 3, 6, 9, 14, 19, 25, 35, 45, and 60 days after inoculations. At each date, samples were taken to determine the life stage of development, number of egg masses, eggs per egg mass, galls, and giant cells or syncytia produced by the nematodes. Meloidogyne incognita and R. reniformis were capable of initially inhibiting each other when the inoculum ratio of one species was higher than the other. In concomitant infections, M. incognita was susceptible to the antagonistic effect of R. reniformis. Rotylenchulus reniformis affected hatching of M. incognita eggs, delayed secondary infection of M. incognita J2, reduced the number of egg masses produced by M. incognita, and reduced J2 of M. incognita 60 days after inoculations. In contrast, M. incognita reduced R. reniformis soil populations only when its proportion in the inoculum ratio was higher than that of R. reniformis. Meloidogyne incognita reduced egg masses produced by R. reniformis, but not production of eggs and secondary infection.     

Use of Entomopathogenic Nematodes to Suppress Meloidogyne incognita on Greenhouse Tomatoes

Tomato seedlings in a growth chamber were inoculated with 150 Meloidogyne incognita eggs and 25 infective juveniles (IJ)/cm² of Steinernema feltiae, S. riobrave, or Heterorhabditis bacteriophora. With the exception of seedling roots treated with H. bacteriophora, all seedlings treated with entomopathogenic nematodes had fewer M. incognita juveniles inside roots and produced fewer eggs than the control seedlings. Tomato plants in the greenhouse were infested with 4,000 M. incognita eggs and treated 2 weeks before, 1 week before, at the same time, 1 week after, or 2 weeks after with 25 or 125 IJ/cm² of S. feltiae, S. riobrave, or H. bacteriophora. Plants with pre- and post-infestation applications of S. feltiae or S. riobrave suppressed M. incognita. Plants treated with H. bacteriophora 1 week before and at the time of infestation suppressed M. incognita. Increasing the rate of H. bacteriophora and S. feltiae from 25 to 125 IJ/cm² improved M. incognita suppression.     

The long and the short of it: RNA-directed chromatin asymmetry in mammalian X-chromosome inactivation

Mammalian X-chromosome inactivation is controlled by a multilayered silencing pathway involving both short and long non-coding RNAs, which differentially recruit the epigenetic machinery to establish chromatin asymmetries. In response to developmentally regulated small RNAs, dicer, a key effector of RNA interference, locally silences Xist on the active X-chromosome and establishes the heterochromatin conformation along the silent X-chromosome. The 1.6 kb RepA RNA initiates silencing by targeting the PRC2 polycomb complex to the inactive X-chromosome. In addition, the nuclear microenvironment is implicated in the initiation and maintenance of X-chromosome asymmetries. Here we review new findings involving these various RNA species in terms of understanding Xist gene regulation and the establishment of X-chromosome inactivation.     

Population Development of Meloidogyne incognita on Soybean Defoliated by Pseudoplusia includens

Greenhouse studies examined population densities of Meloidogyne incognita race 4 on soybean (Glycine max ''Davis'') defoliated by larvae of soybean looper (Pseudoplusia indudens (Walker)). Plants were defoliated over a 2-week period beginning 5 weeks after seedlings were transplanted. Four groups of plants were infested with nematodes (5,000 eggs/pot) at 2-week intervals to allow harvesting of plants at 0, 2, 4, and 6 weeks postdefoliation (WPD). Plants in each group were harvested 4 weeks after nematode infestation. Root and nodule weights of defoliated plants were suppressed at 0 WPD, but differences were not detectable at 2, 4, and 6 WPD. Population densities of M. incognita were similar on defoliated and control plants at 0 WPD but were greater on defoliated plants at 4 and 6 WPD. Percentage hatching of eggs produced on the latter plants also was higher. Effects of insect-induced defoliation on development of M. incognita remained detectable even after soybean plant growth apparently returned to normal.     

Detection and Investigation of Soil Biological Activity against Meloidogyne incognita

Greenhouse experiments with two susceptible hosts of Meloidogyne incognita, a dwarf tomato and wheat, led to the identification of a soil in which the root-knot nematode population was reduced 5- to 16-fold compared to identical but pasteurized soil two months after infestation with 280 M. incognita J2/100 cm³ soil. This suppressive soil was subjected to various temperature, fumigation and dilution treatments, planted with tomato, and infested with 1,000 eggs of M. incognita/100 cm³ soil. Eight weeks after nematode infestation, distinct differences in nematode population densities were observed among the soil treatments, suggesting the suppressiveness had a biological nature. A fungal rRNA gene analysis (OFRG) performed on M. incognita egg masses collected at the end of the greenhouse experiments identified 11 fungal phylotypes, several of which exhibited associations with one or more of the nematode population density measurements (egg masses, eggs or J2). The phylotype containing rRNA genes with high sequence identity to Pochonia chlamydosporia exhibited the strongest negative associations. The negative correlation between the densities of the P. chlamydosporia genes and the nematodes was corroborated by an analysis using a P. chlamydosporia-selective qPCR assay.     

Effect of Meloidogyne incognita on Reproduction of Pratylenchus penetrans in Red Clover and Alfalfa

Roots of seedlings of red clover and alfalfa growing on 10⁻¹ Hoagland and Arnon solution agar were inoculated with various combinations of Meloidogyne incognita and Pratylenchus penetrans. Egg-laying by P. penetrans decreased as the number of nematodes, the ratio of entrant M. incognita to entrant P. penetrans, and the priority of invasion of roots by M. incognita increased. Embryogeny and hatching of eggs of P. penetrans, and development of larvae of M. incognita, were not affected. In red clover, the greatest red uction occurred when there were 65 entrant nematodes, the ratio of M. incognita:P. penetrans was 4:1 and M. incognita was inoculated four days prior to P. penetrans. In alfalfa, the less-favorable host for both nematodes, the greatest reduction occurred when there were 45 entrant nematodes, the ratio of M. incognita:P. penetrans was 2:1, and M. incognita was inoculated 4 days prior to P. penetrans.     

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.     

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.     

Interaction Between Meloidogyne incognita and Thielaviopsis basicola on Cotton (Gossypium hirsutum)

The effects of Meloidogyne incognita and Thielaviopsis basicola on the growth of cotton (Gossypium hirsutum) and the effects of T. basicola on M. incognita populations were evaluated in a 2-year study. Microplots were infested with M. incognita, T. basicola, or a combination of M. incognita and T. basicola. Uninfested plots served as controls both years. Seedling survival was decreased by the M. incognita + T. basicola treatment compared to the control. Meloidogyne incognita alone and M. incognita + T. basicola reduced plant height-to-node ratio for seedlings in both years. Seed cotton yield was reduced, and the length of time required for boll maturation was lengthened by M. incognita + T. basicola in 1994 and M. incognita both alone and with T. basicola in 1995. Position of the first sympodial node on the main stem was increased by M. incognita in both years and was higher for plants treated with M. incognita + T. basicola in 1995 in comparison to the control. The number of sympodial branches with bolls in the first and second fruiting position and the percentage of bolls retained in the second position were reduced both years by M. incognita + T. basicola compared to either the control or T. basicola alone. Orthogonal contrasts indicated that effects on height-to-node ratio, number of days to first cracked boll, and yield were significantly different for combined pathogen inoculations than with either pathogen alone. Meloidogyne incognita eggs at harvest were reduced by T. basicola in 1994 and 1995 compared to M. incognita alone. The study demonstrated a significant interaction between M. incognita and T. basicola on cotton that impacted the survival and development of cotton and the reproduction of M. incognita on cotton.     

Resistance to Meloidogyne spp. in Allohexaploid Wheat Derived from Triticum turgidum and Aegilops squarrosa

Expression of resistance to Meloidogyne incognita and M. javanica from Aegilops squarrosa was studied in a synthetic allohexaploid produced from Triticum turgidum var. durum cv. Produra and Ae. squarrosa G 3489. The reproductive rate of different races of M. incognita and M. javanica, expressed in eggs per gram of fresh root, was low (P < 0.05) on the synthetic allohexaploid and the resistant parent, Ae. squarrosa G 3489, compared with different bread and durum wheat cultivars. Reproduction of race 2 and race 3 of M. incognita and an isolate of M. javanica was studied on the synthetic allohexaploid and seven cultivars of T. aestivum: Anza, Coker 747, Coker 68-15, Delta Queen, Double Crop, McNair 1813, and Southern Bell. The latter six cultivars are grown in the southeastern United States and reportedly were resistant to M. incognita. Significant differences (P < 0.05) were detected in nematode reproduction on the seven bread wheat cultivars. Reproduction of M. incognita race 3 and M. javanica was highest on Anza. Reproductive rates on the six southeastern United States bread wheat cultivars varied both within and among nematode isolates. The lowest reproductive rates of the three root-knot isolates were detected in the synthetic allohexaploid.     

Stage-specific Differences in Lectin Binding to the Surface of Anguina tritici and Meloidogyne incognita

The occurrence and distribution of several lectin binding sites on the outer surfaces of eggs, preparasitic second-stage juveniles (J2), parasitic second-stage juveniles (PJ2), females, and males of two tylenchid nematodes, Anguina tritici and Meloidogyne incognita race 3, were compared. In both species, a greater variety of lectins bound to the eggs than to other life stages; lectin binding to eggs was also more intense than it was to other life stages. Species-specific differences also occurred. More lectins bound to the amphids or amphidial secretions of M. incognita J2 than to the amphids or amphidial secretions of A. tritici J2. Lectins also bound to the amphids or amphidial secretions of adult male and female A. tritici, but binding to the cuticle occurred only at the head and tail and was not consistent in all specimens. Canavalia ensiformis and Ulex europaeus lectins bound specifically to the outer cuticle of M. incognita. Several other lectins bound nonspecifically. Oxidation of the cuticle with periodate under mild conditions, as well as pretreatment of the nematodes with lipase, markedly increased the binding of lectins to the cuticle of A. tritici J2 but not, in most cases, to M. incognita J2 or eggs of either species.     

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.     

Influence of Initial Population Densities of Meloidogyne incognita on Three Chile Cultivars

The effects of Meloidogyne incognita on the Big Jim, Jalapeno, and New Mexico No. 6 chile (Capsicum annuum) cultivars were investigated in microplots for two growing seasons. All three cultivars were susceptible to M. incognita and reacted similarly to different initial populations of this nematode. Severe stunting and yield suppressions occurred at all initial M. incognita densities tested ranging from 385 to 4,230 eggs and larvae/500 cm³ soil. Regression analysis of the microplot data from a sandy loam soil showed yield losses of 31% for the 1978 season and 25% for the 1979 season for the three cultivars for each 10-fold increase in the initial population of M. incognita.