Evaluation of Asteraceae Plants for Control of Meloidogyne incognita

Of the 56 species and 43 genera of Asteraceae tested, 9 were highly resistant or immune to Meloidogyne incognita and did not form root galls. Twenty-six species and six cultivars had 25% or fewer roots galled and were considered moderately resistant to M. incognita. Pre-planting Cosmos bipinnatus (F190), Gaillardia pulchella, Tagetes erecta, Tithonia diversifolia, or Zinnia elegans (F645) reduced root galling and M. incognita J2 in and around Ipomoea reptans. Amendment of soils with roots, stems, or leaves of G. pulchella was effective in controlling M. incognita on I. reptans. Tissue extracts of G. pulchella were lethal to various plant-parasitic nematodes but were innocuous to free-living nematodes. Root exudates of G. pulchella were lethal to J2 of M. incognita and were inhibitory to the hatch of eggs at the concentration of 250 ppm or higher. Gaillardia pulchella could be used to manage M. incognita as a rotation crop, a co-planted crop, or a soil amendment for control of root-knot nematode.     

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.     

In-vitro Assays of Meloidogyne incognita and Heterodera glycines for Detection of Nematode-antagonistic Fungal Compounds

In-vitro methods were developed to test fungi for production of metabolites affecting nematode egg hatch and mobility of second-stage juveniles. Separate assays were developed for two nematodes: root-knot nematode (Meloidogyne incognita) and soybean cyst nematode (Heterodera glycines). For egg hatch to be successfully assayed, eggs must first be surface-disinfested to avoid the confounding effects of incidental microbial growth facilitated by the fungal culture medium. Sodium hypochlorite was more effective than chlorhexidine diacetate or formaldehyde solutions at surface-disinfesting soybean cyst nematode eggs from greenhouse cultures. Subsequent rinsing with sodium thiosulfate to remove residual chlorine from disinfested eggs did not improve either soybean cyst nematode hatch or juvenile mobility. Soybean cyst nematode hatch in all culture media was lower than in water. Sodium hypochlorite was also used to surface-disinfest root-knot nematode eggs. In contrast to soybean cyst nematode hatch, root-knot nematode hatch was higher in potato dextrose broth medium than in water. Broth of the fungus Fusarium equiseti inhibited root-knot nematode egg hatch and was investigated in more detail. Broth extract and its chemical fractions not only inhibited egg hatch but also immobilized second-stage juveniles that did hatch, confirming that the fungus secretes nematode-antagonistic metabolites.     

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.     

Influence of Glomus intraradices and Soil Phosphorus on Meloidogyne incognita Infecting Cucumis melo

The interaction among Glomus intraradices, Meloidogyne incognita, and cantaloupe was studied at three soil phosphorus (P) levels in a greenhouse. All plants grew poorly in soil not amended with P, regardless of mycorrhizal or nematode status. In soil amended with 50 μg P /g soil, M. incognita suppressed the growth of nonmycorrhizal plants by 84%. In contrast, growth of mycorrhizal plants inoculated with M. incognita was retarded by only 21%. A similar trend occurred in plants grown in soil with 100 μg P /g soil. Mycorrhizal infection had no effect on the degree of root-knot gall formation and did not affect the number of nematode eggs per egg mass. Mineral levels in plant shoots generally declined as soil P levels increased and were not significantly influenced by G. intraradices or M. incognita.     

Viability of Heterodera glycines Exposed to Fungal Filtrates

Filtrates from nematode-parasitic fungi have been reported to be toxic to plant-parasitic nematodes. Our objective was to determine the effects of fungal filtrates on second-stage juveniles and eggs of Heterodera glycines. Eleven fungal species that were isolated from cysts extracted from a soybean field in Florida were tested on J2, and five species were tested on eggs in vitro. Each fungal species was grown in Czapek-Dox broth and malt extract broth. No toxic activity was observed for fungi grown in Czapek-Dox broth. Filtrates from Paecilomyces lilacinus, Stagonospora heteroderae, Neocosmospora vasinfecta, and Fusarium solani grown in malt extract broth were toxic to J2, whereas filtrates from Exophiala pisciphila, Fusarium oxysporum, Gliocladium catenulatum, Pyrenochaeta terrestris, Verticillium chlamydosporium, and sterile fungi 1 and 2 were not toxic to J2. Filtrates of P. lilacinus, S. heteroderae, and N. vasinfecta grown in malt extract broth reduced egg viability, whereas F. oxysporum and P. terrestris filtrates had no effect on egg viability.     

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.     

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

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

Effects of Planting Date,Small Grain Crop Destruction,Fallow, and Soil Temperature on the Management of Meloidogyne incognita

The effects of planting date, rye (Secale cereale cv. Wren Abruzzi) and wheat (Triticura aestivum cv. Coker 797), crop destruction, fallow, and soil temperature on managing Meloidogyne incognita race 1 were determined in a 2-year study. More M. incognita juveniles (J2) and egg-producing adults were found in roots of rye planted 1 October than in roots of rye planted 1 November and wheat planted 1 November and 1 December. Numbers of M. incognita adults with and without egg masses were near or below detectable levels in roots of rye planted 1 November and wheat planted 1 November and 1 December. Meloidogyne incognita survived the mild winters in southern Georgia as J2 and eggs. The destruction of rye and wheat as a trap crop 1 March suppressed numbers of J2 in the soil temporarily but did not provide long-term benefits for susceptible crops that followed. In warmer areas where rye and wheat are grown in winter, reproduction of M. incognita may be avoided by delaying planting dates until soil temperature declines below the nematode penetration threshold (18 C), but no long-term benefits should be expected. The temperature threshold may be an important consideration in managing M. incognita population densities in areas having lower winter soil temperatures than southern Georgia.     

Exposure Time to Lethal Temperatures for Meloidogyne incognita Suppression and Its Implication for Soil Solarization

Meloidogyne incognita eggs or J2 were incubated in test tubes containing sand:peat mix and immersed in a water bath heated to 38, 39, 40, 41, 42, 43, 44 and 45°C for a series of time intervals. Controls were maintained at 22°C. Nematodes surviving or hatching were collected from Baermann trays after three weeks of incubation. Regression analyses between percent survival or egg hatch and hours of heat treatment were performed for each temperature. Complete suppression of egg hatch required 389.8, 164.5, 32.9, 19.7 and 13.1 hours at 38, 39, 40, 41 and 42°C, respectively. Complete killing of J2 required 47.9, 46.2, 17.5 and 13.8 hours at 39, 40, 41 and 42°C, respectively. J2 were not completely killed at 38°C within 40 hours of treatment, but were killed within one hour at 44 and 45°C. Effect of temperature on nematode killing is not determined by heat units. Oscillating temperature between cool and warm did not interfere with the nematode suppressive effect by the heat treatment. Six-week solarization in the field during the summers of 2003 and 2004 in Florida accumulated heat exposure times in the top 15 cm of soil that surpassed levels required to kill M. incognita as determined in the water bath experiments. Although near zero M. incognita were detected right after solarization, the nematode population densities increased after a cycle of a susceptible pepper crop. Therefore, future research should address failure of solarization to kill nematodes in the deeper soil layers.     

Response of Resistant Soybean Plant Introductions to Meloidogyne incognita in Field Microplots

The response of two soybean plant introductions, PI 96354 and PI 417444, highly resistant to Meloidogyne incognita, to increasing initial soil population densities (Pi) (0, 31, 125, and 500 eggs/100 cm³ soil) of M. incognita was studied in field microplots for 2 years. The plant introductions were compared to the cultivars Forrest, moderately resistant, and Bossier, susceptible to M. incognita. Averaged across years, the yield suppressions of Bossier, Forrest, PI 417444, and PI 96354 were 97, 12, 18, and < 1%, respectively, at the highest Pi when compared with uninfested control plots. Penetration of roots by second-stage juveniles (J2) increased linearly with increasing Pi at 14 days after planting. At the highest Pi, 62% fewer J2 were present in roots of PI 96354 than in roots of the other resistant genotypes. Soil population densities of M. incognita were lower on both plant introductions than on Forrest. At 75 and 140 days after planting, PI 96354 had the lowest number of J2 in the soil, with 49% and 56% fewer than Forrest at the highest Pi. The resistance genes in PI 96354 should be useful in a breeding program to improve the level of resistance to M. incognita in soybean cultivars.     

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.     

Penetration Rates by Second-stage Juveniles of Meloidogyne spp. and Heterodera glycines into Soybean Roots

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.     

Penetration and Development of Meloidogyne incognita in Roots of Resistant and Susceptible Corn Genotypes

Rates of penetration and development ofMeloidogyne incognita race 4 in roots of resistant (inbred Mp307, and S4 lines derived from the open-pollinated varieties Tebeau and Old Raccoon) and susceptible (Pioneer 3110) corn genotypes were determined. Seedlings grown in styrofoam containers were inoculated with 5,000 eggs of M. incognita. Roots were harvested at 3-day intervals starting at 3 days after inoculation (DAI) to 27 DAI and stained with acid fuchsin. Penetration of roots by second-stage juveniles (J2) at 3 DAI was similar for the four corn genotypes. Meloidogyne incognita numbers in Tebeau, Old Raccoon, Mp307, and Pioneer 3110 peaked at 12, 12, 15, and 27 DAI, respectively. Nematode development in the resistant genotypes was greatly suppressed compared to Pioneer 3110. Resistance to M. incognita in these genotypes appears to be expressed primarily as slower nematode development rather than differences in J2 penetration.     

Histopathology of Selected cultivars of Tobacco infected with Meloidogyne species

Rates of nematode penetration and the histopathology of root infections in fluecured tobacco cultivars ''McNair-944,'' ''Speight G-28,'' and ''NC-89'' with either Meloidogyne arenaria, M. incognita, M. hapla, or M. javanica were investigated. Penetration of root tips by juveniles of all species into the M. incognita-resistant NC-89 and G-28 was much less than that on the susceptible McNair-944. Few juveniles of M. incognita were detected in resistant cultivars 7 and 14 days after inoculation. Infection sites exhibited some cavities and extensive necrotic tissue at 14 days; less necrotic tissue and no intact nematodes were observed 35 days after inoculation. Although some females of M. arenaria reached maturity and produced eggs, considerable necrosis was induced in the resistant cultivars. Meloidogyne hapla and M. javanica developed on all cultivars, but there was necrotic tissue at some infection sites in the resistant cultivars. The occurrence of single multistructured nuclei in the syncytia of most M. hapla infections differed from the numerous small nuclei found in syncytia caused by the other three species.     

Chemical-Mediated Toxicity of N-Viro Soil to Heterodera glycines and Meloidogyne incognita

N-Viro Soil (NVS) is an alkaline-stabilized municipal biosolid that has been shown to lower population densities and reduce egg hatch of Heterodera glycines and other plant-parasitic nematodes; but the mechanism(s) of nematode suppression of this soil amendment are unknown. This study sought to identify NVS-mediated changes in soil chemical properties and their impact upon H. glycines and Meloidogyne incognita mortality. N-Viro Soil was applied to sand in laboratory assays at 0.5%, 1.0%, 2.0%, and 3.0% dry w/w with a nonamended treatment as a control. Nematode mortality and changes in sand-assay chemical properties were determined 24 hours after incubation. Calculated lethal concentration (LC₉₀) values were 1.4% w/w NVS for second-stage juveniles of both nematode species and 2.6 and >3.0% w/w NVS for eggs of M. incognita and H. glycines, respectively. Increasing rates of NVS were strongly correlated (r² = 0.84) with higher sand solution pH levels. Sand solution pH levels and, to a lesser extent, the production of ammonia appeared to be the inorganic chemical-mediated factors responsible for killing plant-parasitic nematodes following amendment with NVS.     

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.     

Optimal Release Rates for Attracting Meloidogyne incognita,Rotylenchulus reniformis,and Other Nematodes to Carbon Dioxide in Sand

Movement of vermiform stages of Meloidogyne incognita, Rotylenchulus reniformis, Ditylenchus phyllobius, Steinernema glaseri, and Caenorhabditis elegans in response to carbon dioxide was studied in 40- and 72-mm-long cylinders of moist sand inside 38-mm-d acrylic tubes. Meloidogyne incognita, R. reniformis, and S. glaseri were attracted to CO₂ when placed on a linear gradient of 0.2%/cm at a mean CO₂ concentration of 1.2%. When CO₂ was delivered into the sand through a syringe needle at flow rates between 2 and 130 μl/minute, the optimal flow rate for attracting M. incognita and R. reniformis was 15 μl/minute, and maximal attraction of the two species from a distance of 52 mm was achieved after 29 and 40 hours, respectively. After 24 hours, a total CO₂ volume of 20 cm³ was sufficient to induce 96% of all M. incognita introduced to move into the half of the cylinder into which CO₂ was delivered and more than 75 % to accumulate in the 9 cm³ of sand volume nearest the source. Results indicate it may be possible to use a chemical or biological source of CO₂ to attract nematodes to nematicide granules or biocontrol agents.     

Effective Use of Marine Algal Products in the Management of Plant-Parasitic Nematodes

Algal extracts were ineffective against Meloidogyne spp., Panagrellus redivivus, and Neoaplectana carpocapsae at 1.0% aqueous concentrations, with the exception of Spatoglossum schroederi. S. schroederi killed Meloidogyne incognita, M. javanica, M. acrita, and Hoplolaimus galeatus at concentrations of 1.0, 0.75, and 0.50%. Extracts from S. schroederi at a concentration of 1.0% were ineffective against Hirschmanniella caudacrena and Belonolaimus longicaudatus. Spatoglossum schroederi, Botryocladia occidentalis, and Bryothamnion triquestrum when used as soil amendments at 0.5-1.0% concentrations (by weight) produced significant reduction of root gall development in tomato plants infected with M. incognita. Tomato plant growth was significantly improved by these algae, as well as by Caulerpa prolifera. Soil amendments of S. schroederi at concentrations of 0.5 and 1.0% significantly reduced root galling of tomato infected with M. incognita, M. arenaria, and M. javanica. Tomatoes grown in algal-soil mixture produced significantly heavier shoots and roots than plants raised in autoclaved soil. No significant differences in root-knot indices, nor in fresh and dry weights of tomato, were noted between the two concentrations of algal-soil mixture.