Experiments were conducted in the greenhouse to assess root galling and egg production of three root-knot nematode species, Meloidogyne arenaria, M. incognita, and M. javanica, on several weeds common to Florida agricultural land. Weeds evaluated were Amaranthus retroflexus (redroot pigweed), Cyperus esculentus (yellow nutsedge), Eleusine indica (goosegrass), Portulaca oleracea (common purslane), and Solanum americanum (American black nightshade). Additionally, although it is recommended as a cover crop in southern regions of the U.S., Aeschynomene americana (American jointvetch) was evaluated as a weed following the detection of root galling in a heavy volunteer infestation of an experimental field in southeastern Florida. Weeds were propagated from seed and inoculated with 1000 nematode eggs when plants reached the two true-leaf stage. Tomato (Solanum lycopersicum ‘Rutgers’) was included as a positive control. Aeschynomene americana and P. oleracea roots supported the highest number of juveniles (J2) and had the highest number of eggs/g of root for all three species of Meloidogyne tested. However, though P. oleracea supported very high root levels of the three nematode species tested, its fleshy roots did not exhibit severe gall symptoms. Low levels of apparent galling, combined with high egg production, increase the potential for P. oleracea to support populations of these three species of root-knot nematodes to a degree that may not be appropriately recognized. This research quantifies the impact of P. oleracea as a host for M. arenaria, M. incognita, and M. javanica compared to several other important weeds commonly found in Florida agricultural production, and the potential for A. americana to serve as an important weed host of the three species of root-knot nematode tested in southern regions of Florida.
Aeschynomene americana; Amaranthus retroflexus; Cyperus esculentus; Eleusine indica; Florida; host status; nematode reproduction; Portulaca oleracea; root-knot nematodes; Solanum americanum
Use of resistant cultivars is a desirable approach to manage the peanut root-knot nematode (Meloidogyne arenaria). To incorporate resistance into commercially acceptable cultivars requires reliable, efficient screening methods. To optimize the resistance screening protocol, a series of greenhouse tests were done using seven genotypes with three levels of resistance to M. arenaria. The three resistance levels could be separated based on gall indices as early as two weeks after inoculation (WAI) using 8,000 eggs of M. arenaria per plant, while four or more weeks were needed when 1,000–6,000 eggs/plant were used. High inoculum densities (over 8,000 eggs/plant) were needed to separate the three resistance levels based on eggs per gram of root within eight WAI. A gall index based on percentage of galled roots could separate the three resistance levels at lower inoculum levels and earlier harvest dates than other assessment methods. The use of eggs vs. second-stage juveniles (J2) as inoculum provided similar results; however, it took three to five more days to collect J2 than to collect eggs from roots. Plant age affected gall index and nematode reproduction on peanut, especially on the susceptible genotypes AT201 and D098. The genotypes were separated into their correct resistance classes when inoculated 10 to 30 days after planting, but were not separated correctly when inoculated on day 40.
Arachis hypogaea; assessment date; host-plant resistance; inoculation date; inoculum level; inoculum type; Meloidogyne arenaria; method; peanut; resistance evaluation; root-knot nematode
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
Twenty Sesame indicum and four S. radiatum accessions in the USDA Plant Introduction collection were evaluated for reaction to the root-knot nematode, Meloidogyne incognita race 3, at two initial egg densities under greenhouse conditions. All sesame accessions produced considerably fewer root galls than the tomato cultivar Rutgers. Gall numbers varied slightly among accessions at the higher infestation density with even less variation at the lower density. Egg mass indices indicated little reproduction. Seventy percent of the accessions weighed less at the higher egg density than at the lower egg density. All the sesame accessions tested are resistant to M. incognita and have the potential for use as rotational crops for suppressing this nematode.
germplasm; host reaction; Meloidogyne incognita; nematode; plant breeding; resistance; sesarne; southern root-knot nematode
An in vitro root explant tissue culture technique is described for determining susceptibility of tomato (Lycopersicon esculentum Mill.) breeding lines and cultivars to the root-knot nematode Meloidogyne incognita. Root explants were taken from 2-day-old seedlings cultured for 30 days at 28 C on Gamborg's B-5 medium with or without nematode inoculum. The remaining portion of the root and stem from the excised root explants was transferred to soil in pots and grown to maturity in the greenhouse. In vitro root explants were evaluated for growth and occurrence of juveniles, adults, and egg masses. The regenerated plants were used to produce more seed, The proposed technique is simple, reliable, and adapted to routine screening of large numbers of F₁ and F₂ samples, and it utilizes less space than tests performed on intact plants in the greenhouse or growth chamber. Evidence is presented also on the breakdown of resistance to M. incognita under high temperature stress using this in vitro root explant technique.
Culture; Lycopersicon esculentum; Meloidogyne incognita; nematode; resistance; root-knot nematode; temperature
Meloidogyne enterolobii is widely considered to be an aggressive root-knot nematode species that is able to reproduce on root-knot nematode-resistant tomato and pepper cultivars. In greenhouse experiments, M. enterolobii isolates 1 and 2 from Switzerland were able to reproduce on tomato cultivars carrying the Mi-1 resistance gene as well as an N-carrying pepper cultivar. Reproduction factors (Rf) ranged between 12 and 109 depending on the plant cultivar, with M. enterolobii isolate 2 being more virulent when compared to isolate 1. In contrast, M. arenaria completely failed to reproduce on these resistant tomato and pepper cultivars. Although some variability in virulence and effectiveness of root-knot nematode-resistance genes was detected, none of the plant cultivars showed Rf values less than 1 or less than 10% of the reproduction observed on the susceptible cv. ‘Moneymaker’ (Rf = 23-44) used to characterize resistance. The ability of M. enterolobii to overcome the resistance of tomato and pepper carrying the Mi-1 and the N gene makes it difficult to manage this root-knot nematode species, particularly in organic farming systems where chemical control is not an option.
Capsicum annuum; resistance; root-knot nematodes; Solanum lycopersicon
Ten cultivars of watermelon were evaluated for their response to a Puerto Rican population of Meloidogyne incognita under greenhouse conditions in a 2-year study (1989 and 1990). Ten-day-old seedlings were planted in steam-sterilized soil in 15-cm-d plastic pots. The nematode inoculum consisted of 10,000 eggs and (or) second-stage juveniles (J2)/plant. The cultivars were Sugar Baby, Charleston Gray, Seedless, Prince Charles, Charleston 76, Jubilee, Florida Giant, Royal Charleston, Royal Sweet, and Royal Jubilee, with tomato cv. Rutgers included as a susceptible check. A completely randomized design with 10 replications was used. Fifty-five days after soil infestation, root-gall indices, numbers of nematode eggs per root system, and J2 per 250 cm³ of soil were recorded. All cultivars were susceptible. Sugar Baby had the lowest root-gall index, egg and J2 numbers, and a reproductive factor (Rf) of 2.89. Rf differed (P ≤ 0.05) among cultivars and ranged up to 7.36. Sugar Baby, Seedless, and Florida Giant showed the lowest susceptibility to M. incognita, whereas Charleston 76 and Charleston Gray were the most susceptible.
Citrullus lanatus; fruits; host status; Meloidogyne incognita; nematode; Puerto Rico; root-knot nematode; susceptibility; vegetables; watermelon
The efficacy of the nematode parasite Paecilomyces lilacinus, alone and in combination with phenamiphos and ethoprop, for controlling the root-knot nematode Meloidogyne javanica on tobacco and the ability of this fungus to colonize in soil under field conditions were evaluated for 2 years in microplots. Combinations and individual treatments of the fungus grown on autoclaved wheat seed, M. javanica eggs (76,000 per plot), and nematicides were applied to specified microplots at the time of transplanting tobacco the first year. Vetch was planted as a winter cover crop, and the fungus and nematicides were applied again the second year to specified plots at transplanting time. The fungus did not control the nematode in either year of these experiments. The average root-gall index (0 = no visible galls and 5 = > 100 galls per root system) ranged from 2.7 to 3.9 the first year and from 4.3 to 5.0 the second in nematode-infested plots treated with nematicides. Plants with M. javanica alone or in combination with P. lilacinus had galling indices of 5.0 both years; the latter produced lower yields than all other treatments during both years of the study. Nevertheless, the average soil population densities of P. lilacinus remained high, ranging from 1.2 to 1.3 × 106 propagules/g soil 1 week after the initial inoculation and from 1.6 to 2.3 × 104 propagules/g soil at harvest the second year. At harvest the second year the density of fungal propagules was greatest at the depth of inoculation, 15 cm, and rapidly decreased below this level.
biocontrol; ethoprop; 1,3-dichloropropene; fenamiphos; fungal egg parasite; Meloidogyne javanica; nematicide; Nicotiana tabacum; Paecilomyces lilacinus; root-knot nematode; tobacco; vetch; Vicia vilIosa
The effects of soil management systems on root-knot nematode (Meloidogyne incognita) eggs and gall incidence on tomato (Lycopersicon esculentum) and cucumber (Cucumis sativus) following tomato were evaluated. Soil was collected from a replicated field experiment in which six management systems were being assessed for vegetable production. Soil management systems were conventional production, organic production, bahiagrass (Paspalum notatum) pasture, bahiagrass: Stylosanthes (Stylosanthes guianensis) pasture, bare ground fallow, and weed fallow. Soil was collected from field plots and used in greenhouse experiments. Identification of egg-parasitic fungi and the incidence of root-knot nematode galling were assessed both on tomato and cucumber planted in the same pots following the removal of tomato plants. Organic, bare ground fallow and conventional production treatments reduced galling both on tomato and on cucumber following tomato. Although no treatment consistently enhanced egg-parasitic fungi, management system did affect egg viability and the types of fungi isolated from parasitized eggs.
biological control; cropping systems; cucumber; Cucumis sativus; fungal egg parasites; Lycopersicon esculentum; Meloidogyne incognita; root-knot nematode; tomato
Eight commonly cultivated Ixora species or cultivars were tested for their suitability as hosts and their level of tolerance to Meloidogyne incognita race 1 and M. javanica in a greenhouse study. Twenty weeks postinoculation with 5,000 eggs per pot, M. incognita race 1 and M. javanica produced galls and formed egg masses on roots of all eight Ixora species or cultivars tested. However, only M. javanica-infected 'Petite Yellow' and 'Maui' had decreases (P ≤ 0.05) in root wet weights, suggesting that the other cultivars were more tolerant to these root-knot nematode species. Differential host suitability to each Meloidogyne species was based on the relative number of galls, galls per gram root weight, egg masses, and second-stage juveniles produced per plant. 'Bonnie Lynn,' 'Maui,' and 'Petite Red' were good to excellent hosts for both Meloidogyne spp. Ixora coccinea was a good host for M. incognita race 1 but less suitable for M. javanica. 'Singapore' and 'Petite Yellow' were poor hosts for M. incognita race 1 but excellent hosts for M. javanica. 'Nora Grant' and I. casei 'Super King' were poor hosts for both species of root-knot nematodes.
host-parasite relationship; Ixora spp.; Meloidogyne incognita race 1; M. javanica; nematode; ornamental; root-knot nematode; woody ornamental
Resistance of pepper species (Capsicum annuum, C. baccatum, C. chinense, C. chacoense, and C. frutescens), cultivars and accessions to the root-knot nematodes Meloidogyne incognita race 2 and M. javanica, and their graft compatibility with commercial pepper varieties as rootstocks were evaluated in growth chamber and greenhouse experiments. Most of the plants tested were highly resistant to M. javanica but susceptible to M. incognita. Capsicum annuum AR-96023 and C. frutescens accessions as rootstocks showed moderate and relatively high resistance to M. incognita, respectively. In M. incognita-infested soil in a greenhouse, AR-96023 supported approximately 6-fold less nematode eggs per gram root and produced about 2-fold greater yield compared to a nongrafted commercial variety. The commercial variety grafted on AR-96023 produced a yield as great as the non-grafted variety in the root-knot nematode-free greenhouse. Some resistant varieties and accessions used as rootstocks produced lower yields (P < 0.01) than that of the non-grafted variety in the noninfested greenhouse. Use of rootstocks with nematode-resistance and graft compatibility may be effective for control of root-knot nematodes on susceptible pepper.
Capsicum spp.; graft compatibility; Meloidogyne incognita; Meloidogyne javanica; nematode control; pepper; resistance; root-knot nematodes; rootstock
Seven-day-old seedlings of two cultivars (Cristalina and UFV ITM1) of Glycine max were inoculated with 0, 3,000, 9,000, or 27,000 eggs of Meloidogyne incognita race 3 or M. javanica and maintained in a greenhouse. Thirty days later, plants were exposed to ¹⁴CO₂ for 4 hours. Twenty hours after ¹⁴CO₂ exposure, the root fresh weight, leaf dry weight, nematode eggs per gram of root, total and specific radioactivity of carbohydrates in roots, and root carbohydrate content were evaluated. Meloidogyne javanica produced more eggs than M. incognita on both varieties. A general increase in root weight and a decrease in leaf weight with increased inoculum levels were observed. Gall tissue appeared to account for most of the root mass increase in seedlings infected with M. javanica. For both nematodes there was an increase of total radioactivity in the root system with increased levels of nematodes, and this was positively related to the number of eggs per gram fresh weight and to the root fresh weight, but negatively related to leaf dry weight. In most cases, specific radioactivities of sucrose and reducing sugars were also increased with increased inoculum levels. Highest specific radioactivities were observed with reducing sugars. Although significant changes were not observed in endogenous levels of carbohydrates, sucrose content was higher than reducing sugars. The data show that nematodes are strong metabolic sinks and significantly change the carbon distribution pattern in infected soybean plants. Carbon partitioning in plants infected with nematodes may vary with the nematode genotype.
carbohydrates; carbon partitioning; Glycine max; Meloidogyne incognita; Meloidogyne javanica; nematode; photoassimilate translocation; root growth; soybean
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.
biological control; dwarf tomato; Meloidogyne incognita; Pochonia chlamydosporia; root-knot nematode; Solanum lycopersicon; suppressive soil; Triticum aestivum; wheat
Two Hawaiian isolates of Steinernema feltiae MG-14 and Heterohabditis indica MG-13, a French isolate of S. feltiae SN, and a Texan isolate of S. riobrave TX were tested for their efficacy against the root-knot nematode, Meloidogyne javanica, in the laboratory and greenhouse. Experiments were conducted to investigate the effects of treatment application time and dose on M. javanica penetration in soybean, and egg production and plant development in tomato. Two experiments conducted to assess the effects of entomopathogenic nematode application time on M. javanica penetration demonstrated that a single application of 10⁴ S. feltiae MG-14 or SN infective juveniles per 100 cm³ of sterile soil, together with 500 (MG-14) or 1,500 (SN) second-stage juveniles of M. javanica, reduced root penetration 3 days after M. javanica inoculation compared to that of a water treatment. Entomopathogenic nematode infective juveniles applied to assess the effects on M. javanica egg production did not demonstrate a significant reduction compared to that of the water control treatment. There was no dose response effect by Steinernema spp. On M. javanica root penetration or egg production. Steinernema spp. did not affect the growth or development of M. javanica-infected plants, but H. indica MG-13-treated plants had lower biomass than untreated plants infected with M. javanica. Infective juveniles of S. riobrave TX, S. feltiae SN, and MG-14 but not those of H. indica MG-13 were found inside root cortical tissues of M. javanica-infected plants. Entomopathogenic nematode antagonism to M. javanica on soybean or tomato was insufficient in the present study to provide a consistent level of nematode suppression at the concentrations of infective juveniles applied.
behavior; heterorhabditis; Meloidogyne javanica; root penetration; Steinernema; suppression
Forty-three open-pollinated maize varieties were tested for resistance to the southern root-knot nematode, Meloidogyne incognita race 4, in greenhouse tests. An experiment repeated on five different planting dates assessed nematode reproduction 60 days after inoculation with 3,000 eggs per plant. Tebeau and Old Raccoon showed consistently high levels of resistance in all plantings, with the lowest reproduction factor (RF) values (0.2 and 0.4) and low numbers of eggs per gram of fresh root (222 and 955). Bill Dailey Variety and Sheppard Corn had the same level of resistance to M. incognita as the resistant hybrid, Mp307 x Mp707, but they were less consistent in different plantings. Levi Mallard, African Bushman, and Field's White Variety were the most susceptible varieties with RF values of 3.1-3.3 and 2,479-3,678 eggs per gram of fresh root.
corn; maize; Meloidogyne incognita; resistance; southern root-knot nematode; Zea mays
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.
clover; Meloidogyne graminicola; Meloidogyne incognita; nematode; pathogenicity; resistance; rice root-knot nematode; southern root-knot nematode; Trifolium spp.
Ten cultivars and 13 germplasms of white clover (Trifolium repens) were evaluated in the greenhouse for resistance to the southern root-knot nematode, Meloidogyne incognita race 4. One hundred plants of each cultivar or germplasm were rated for percentage of the root system galled (PRSG) at 60 days after inoculation with root-knot nematode eggs. Tillman (9%) and SRVR (19%) had the highest percentage of resistant plants (PRSG = 0 or 1 on a scale of 0-5 ) for the cultivars and germplasms, respectively. No resistant plants were selected from the cultivars California Ladino or Sacramento, or from the germplasms Brown Loam population or Brown Loam Synthetic #6. Resistant plants identified in this study were used to initiate are current selection program for resistance to M. incognita.
clover; Meloidogyne incognita; nematode; resistance; southern root-knot nematode; Trifolium repens
Plant protoplast technology is being investigated as a means of transferring root-knot nematode resistance factors from Solanum sisymbriifolium into the susceptible S. melongena. Solanum sisymbriifolium plants regenerated from callus lost resistance to Meloidogyne javanica but retained resistance to M. incognita. Tomato plants cloned from leaf discs of the root-knot nematode resistant 'Patriot' were completely susceptible to M. incognita, while sections of stems and leaves rooted in sand in the absence of growth hormones retained resistance. Changes in resistance persisted for three generations. It is postulated that the exogenous hormonal constituents of the culture medium are modifying the expression of genetic resistance.
review; protoplast; callus; Solanum sisymbriifolium; Solanum melongena; eggplant; tomato; Meloidogyne incognita; Meloidogyne javanica; root-knot nematodes; somatic hybridization
Greenhouse and field microplot studies were conducted to compare soybean shoot and root growth responses to root penetration by Heterodera glycines (Hg) and Meloidogyne incognita (Mi) individually and in combination. Soybean cultivars Centennial (resistant to Hg and Mi), Braxton (resistant to Mi, susceptible to Hg), and Coker 237 (susceptible to Hg and Mi) were selected for study. In the greenhouse, pot size and number of plants per pot had no effect on Hg or Mi penetration of Coker 237 roots; root weight was higher in the presence of either nematode species compared with the noninoculated controls. In greenhouse studies using a sand or soil medium, and in field microplot studies, each cultivar was grown with increasing initial population densities (Pi) of Hg or Mi. Interactions between Hg and Mi did not affect early plant growth or number of nematodes penetrating roots. Root penetration was the only response related to Pi. Mi penetration was higher in sand than in soil, and higher in the greenhouse than in the field, whereas Hg penetration was similar under all conditions. At 14 days after planting, more second-stage juveniles were present in roots of susceptible than in roots of resistant plants. Roots continued to lengthen in the greenhouse in the presence of either Mi or Hg regardless of host genotype, but only in the presence of Mi in microplots; otherwise, responses in field and greenhouse studies were similar and differed only in magnitude and variability.
soybean cyst nematode; root-knot nematode; Glycine max; root penetration; root length; microplots; Heterodera glycines; Meloidogyne incognita
Solid CO₂ (dry ice) was added to pots containing soil that was infested either with eggs of the root-knot nematode, Meloidogyne incognita, or with tomato (Lycopersicon esculentum 'Rutgers') root fragments that were infected with various stages of the nematode. Two hours after dry ice was added, thermocouples in the soil recorded temperatures ranging from -15 °C to -59 °C. One day after treatment with the dry ice, the temperature of the soil was allowed to equilibrate with that of the greenhouse, and susceptible tomato seedlings were planted in pots containing infested soil treated or untreated (controls) with dry ice. After 5 weeks, roots were removed from the pots and nematode eggs were extracted and counted. Plants grown in soil infested with eggs and receiving dry ice treatment had less than 1% of the eggs found in the controls; plants from soil infested with root fragments and receiving dry ice treatment had less than 4% of the eggs found in controls. Dry ice used to lower soil temperature may have potential as a cryonematicide.
carbon dioxide; control; cryogen; cryonematicide; dry ice; Lycopersicon esculentum; Meloidogyne incognita; nematicide; nematode; population dynamics; root-knot nematode; temperature; winter survival
Changes in root- and leaf-soluble proteins were investigated in tomato after invasion by the root-knot nematode Meloidogyne javanica, or in barley and wheat after invasion by the cereal cyst nematode Heterodera avenae. Infection of susceptible tomato plants by M. javanica did not cause any change in the soluble-protein composition of leaves or roots compared with uninoculated plants at an early infection stage. No pathogenesis-related proteins (chitinase, glucanase, or P-14) were induced in the leaf apoplast. Changes in leaf proteins were not observed after invasion of wheat cultivars by H. avenae, whereas, in barley, a few changes in intercellular leaf proteins were recorded in resistant cultivars. These changes, however, were not the same among different H. avenae-resistant cultivars. Protein changes were found at an early stage of infection in barley and wheat roots infected with H. avenae, but no difference was found between resistant and susceptible cultivars.
barley; cereal cyst nematode; chitinase; glucanase; Heterodera avenae; Hordeum vulgate; Lycopersicon esculentum; Meloidogyne javanica; nematode; pathogenesis-related proteins; root-knot nematode; tomato; Triticum aestivum; wheat
Inula viscosa is a perennial plant that is widely distributed in Mediterranean countries. Formulations of I. viscosa extracts were tested for their effectiveness in control of Meloidogyne javanica in laboratory, growth chamber, microplot, and field experiments. Oily pastes were obtained by extraction of dry leaves with a mixture of acetone and n-hexane or n-hexane alone, followed by evaporation of the solvents. Emulsifiable concentrate formulations of the pastes killed M. javanica juveniles in sand at a concentration of 0.01% (paste, w/w) or greater and reduced the galling index of cucumber seedlings as well as the galling index and numbers of nematode eggs on tomato plants in growth chamber experiments. In microplot experiments, the hexane-extract formulation at 26 g paste/m2 reduced nematode infection on tomato plants in one of two experiments. In a field experiment, a reduction of 40% in root galling index by one of two formulations was observed on lettuce plants. The plant extracts have potential as a natural nematicide, although the formulations need improvement.
botanical nematicide; Inula viscosa; management; Meloidogyne javanica; nematode; phytochemical; root-knot nematode; sesquiterpenic acid
Effects of gamma-irradiation on the root-knot nematode Meloidogyne javanica were investigated. A dose of 7.5 kGy killed all second-stage juveniles (J2) within 1 day after treatment. Egg hatch was completely inhibited at 6.25 kGy. A bioassay on tomato measuring galling and egg production was used to determine the infectivity of irradiated J2 and J2 hatched from irradiated eggs. The J2 and eggs irradiated with a dose of 4.25 kGy did not induce galls or reproduce on tomato plants. When nematodes were exposed to combined irradiation and heat treatment, no synergistic effect on J2 or eggs was measured. Heat treatment at 49° C for 10 minutes or 20 minutes without irradiation immobilized J2 and prevented egg development. Irradiation rates needed to kill or incapacitate M. javanica were high and may be impractical as a quarantine measure.
Cobalt-60; control; dose; gamma-irradiation; heat treatment; kGy; Meloidogyne javanica; quarantine; root-knot nematode
The susceptibility of 22 plant species to Meloidogyne marylandi and M. incognita was examined in three greenhouse experiments. Inoculum of M. marylandi was eggs from cultures maintained on Zoysia matrella “Cavalier” or Cynodon dactylon x C. trasvaalensis “Tifdwarf”. Inoculum of M. incognita was eggs from cultures maintained on Solanum lycopersicum ‘Rutgers’. In each host test the inoculum density was 2,000 nematode eggs/pot. None of the three dicot species tested (Gossypium hirsutum, Arachis hypogaea, and S. lycopersicum) were hosts for M. marylandi but, as expected, M. incognita had high levels of reproduction on G. hirsutum and S. lycopersicum. Meloidogyne marylandi reproduced on all of the 19 grass species (Poaceae) tested but reproduction varied greatly (P = 0.05) among these hosts. The following grasses were identified for the first time as hosts for M. marylandi: Buchloe dactyloides (buffalograss), Echinochloa colona (jungle rice), Eragostis curvula (weeping lovegrass), Paspalum dilatatum (dallisgrass), P. notatum (bahiagrass), Sorghastrum, nutans (indiangrass), Tripsacum dactyloides (eastern gamagrass), and Zoysia matrella (zoysiagrass). No reproduction of M. incognita was observed on B. dactyloides, Cyndon dactylon (common bermudagrass), E. curvula, P. vaginatum (seashore paspalum), S. nutans, T. dactyloides, Z. matrella or Z. japonica. Reproduction of M. incognita was less than reproduction of M. marylandi on the other grass species, except for the Zea mays inbred line B73 on which M. incognita had greater reproduction than did M. marylandi (P = 0.05) and Stenotaphrum secundatum (St. Augustinegrass) on which M. incognita and M. marylandi had similar levels of reproduction.
dicots; grasses; Meloidgyne marylandi; M. incognita; hosts; Poaceae; root-knot nematode
Rooted cuttings of Chrysanthemum morifolium 'Yellow Delaware' (Fusarium-susceptible) and 'White Iceberg' (Fusarium-resistant) were greenhouse-grown in: (i) non-infested soil; (ii) soil infested with Fusarium oxysporum alone; (iii) soil infested with Meloidogyne incognita, M. javanica or M. hapla; and (iv) each nematode separately plus the fungus. All nematode species infected roots of both cultivars and caused characteristic root-knot symptoms but did not appreciably affect growth meassured by plant weight. Nematodes did not break Fusarium wilt resistance of 'White Iceberg'; however, wilt symptoms appeared earlier and were more severe among 'Yellow Delaware' plants inoculated with Meloidogyne javanica and F. oxysporum than with similar combinations of the fungus and M. incognita or M. hapla or with the fungus alone.