During a 1998-to-2001 survey from Arkansas, nine distinct species of Longidorus were found including five new species. Morphometrics of these nine species were used in a stepwise and canonical discrimination to select a subset of characteristics that best identified each species. Student's t test was applied to compare Longidorus breviannulatus Norton &Hoffman, 1975; L. crassus Thorne, 1974; L. diadecturus Eveleigh &Allen, 1982; L. fragilis Thorne, 1974; L. biformis Ye &Robbins, 2004; L. glycines Ye &Robbins, 2004; L. grandis Ye &Robbins, 2003; L. paralongicaudatus Ye &Robbins, 2003; and L. paravineacola Ye &Robbins, 2003 to examine interspecies variation and test for the most useful morphometric characters in species discrimination. Most of the morphometric characters were useful to differentiate species, but species identification could not be based on a single character because the morphometric character ranges often overlap. Stepwise discriminant analysis indicated that the guide ring position, head width, tail length, body length, odontostyle length, and anal body width were the most important variables. These were used to generate canonical variables in discriminating the species. The first three canonical variables accounted for 95% of the total variance. The scatterplots by the first three canonical variables grouped and separated the Longidorus species from Arkansas. Stepwise and canonical discriminant analyses were useful for examining the groupings and morphometric relationships of the nine Longidorus species.
Arkansas; canonical discriminant analysis; identification; Longidorus; morphometrics; stepwise discriminant analysis
During searches for pathogens to be used as classical biocontrol agents for Miconia calvescens (velvet tree), a devastating plant invader of Hawaii and French Polynesia, damaging angular leaf spots were found repeatedly. The etiological agent of this disease was identified as the nematode Ditylenchus drepanocercus. This nematode has a distinctive falciform appendage at the apex of the tail on both sexes, which allows easy identification. The nematodes were found in the lacunar parenchyma. Infected tissues have abnormally large cells (7 to 13 times the normal size). The lamina at infected areas is chlorotic, slightly thicker, and becomes necrotic with time. The best method of inoculation for this nematode was spraying plants with a suspension containing individuals of various stages on previously wounded leaves. Incubation period was determined to be 20 days.
aerial parasite; angular leaf-spot; biological control; Ditylenchus drepanocercus; invasive weed; Miconia calvescens; pathogenicity; taxonomy; velvet tree
The effects of the application of poultry litter at 0.0, 6.7, 13.4, and 20.1 tons/ha on population changes during the growing season on nematode communities were evaluated in two cotton production fields in North Carolina. Numbers of bactivorous nematodes increased at midseason in response to the rate at which litter was applied but decreased with increasing litter application rates at cotton harvest. Numbers of fungivores at cotton harvest were related positively to the rate of litter applied, and this affected a positive increase in the fungivore-to-bacterivore ratio at this sampling date. The rate at which poultry litter was applied resulted in an increase in the bacterivore to plant-parasite ratio, and this corresponded with increased cotton lint yield. Trophic diversity was increased by litter application rate at cotton harvest at one location but not at another. The plant-parasite maturity index was greater consistently at one site than at a second site where the Hoplolaimus columbus population density was above the damage threshold for cotton. The population density of H. columbus was suppressed with increasing rates of poultry litter application, but other plant-parasitic nematodes were affected marginally.
Columbia lance nematode; community structure; cotton; ecology; Gossypium hirsutum; Helicotylenchus dihystera; Hoplolaimus columbus; management; nematode; Paratrichodorus minor; poultry litter; population changes; Pratylenchus brachyurus; soil health; trophic groups
Two experiments were conducted in north-central Florida to examine the effects of various winter cover crops on plant-parasitic nematode populations through time. In the first experiment, six winter cover crops were rotated with summer corn (Zea mays), arranged in a randomized complete block design. The cover crops evaluated were wheat (Triticum aestivum), rye (Secale cereale), oat (Avena sativa), lupine (Lupinus angustifolius), hairy vetch (Vicia villosa), and crimson clover (Trifolium incarnatum). At the end of the corn crop in year 1, population densities of Meloidogyne incognita were lowest on corn following rye or oat (P ≤ 0.05), but no treatment differences were observed in year 2. Wheat was a good host to Paratrichodorus minor, whereas vetch was a poor host, but numbers of P. minor were not lower in vetch-planted plots after corn was grown. The second experiment used a split-plot design in which rye or lupine was planted into field plots with histories of five tropical cover crops: soybean (Glycine max), cowpea (Vigna unguiculata), sorghum-sudangrass (Sorghum bicolor × S. sudanense), sunn hemp (Crotalaria juncea), and corn. Population densities of M. incognita and Helicotylenchus dihystera were affected by previous tropical cover crops (P ≤ 0.05) but not by the winter cover crops present at the time of sampling. Plots planted to sunn hemp in the fall maintained the lowest M. incognita and H. dihystera numbers. Results suggest that winter cover crops tested did not suppress plant-parasitic nematodes effectively. Planting tropical cover crops such as sunn hemp after corn in a triple-cropping system with winter cover crops may provide more versatile nematode management strategies in northern Florida.
crop rotation; cropping systems; Helicotylenchus dihystera; Meloidogyne incognita; Mesocriconema ornata; M. sphaerocephala; nematode management; Paratrichodorus minor; Pratylenchulus brachyurus; P. scribneri; root-knot nematode; sustainable agriculture; weeds
The host status of 15 commonly occurring pasture species for Helicotylenchus pseudorobustus was tested in a greenhouse trial. Only tall fescue, with and without Neotyphodium endophyte infection, was a good host (Pf/Pi = final/initial population > 1). Inoculation survival was tested in a second trial, which showed that only 10% of the H. pseudorobustus nematodes survived the first 7 days after inoculation. When the Pf/Pi was adjusted to account for a 10% survival, all of the grass and clover hosts tested had a Pf/Pi > 1. Both trials showed a positive correlation between increased numbers of H. pseudorobustus and free-living nematodes.
Helicotylenchus pseudorobustus; host range; pasture species; spiral nematode; free-living nematodes
Of the many nematode species that parasitize citrus, Tylenchulus semipenetrans is the most important on a worldwide basis. Management of the citrus nematode remains problematic as no one tactic gives adequate control of the nematode. An overall management strategy must include such components as site selection, use of non-infected nursery stock, use of at lease one post-plant nematode control tactic, and careful management of other elements of the environment that may stress the trees. Nematicides continue to play a key role in management of this pest. Optimum results require careful attention to application techniques.
biological control; citrus; citrus nematode; Citrus paradise; nematicides; nematode management; host resistance; Poncirus trifoliate; soil solarization; swingle citrumelo; Tylenchulus semipenetrans
Evolutionary relationships among cyst nematodes based on predicted ß-tubulin amino acid and DNA sequence data were compared with phylogenies inferred from ribosomal DNA (ITS1, 5.8S gene, ITS2). The ß-tubulin amino acid data were highly conserved and not useful for phylogenetic inference at the taxonomic level of genus and species. Phylogenetic trees based on ß-tubulin DNA sequence data were better resolved, but the relationships at lower taxonomic levels could not be inferred with confidence. Sequences from single species often appeared in more than one monophyletic clade, indicating the presence of ß-tubulin paralogs (confirmed by Southern blot analysis). For a subset of taxa, good congruence between the two data sets was revealed by the presence of the same putative ß-tubulin gene paralogs in monophyletic groups on the rDNA tree, corroborating the taxon relationships inferred from ribosomal DNA data.
ß-tubulin; cyst nematodes; paralogous genes; ribosomal DNA
The entomopathogenic nematode species Steinernema feltiae and Heterorhabditis bacteriophora were compared for survival and infectivity of infective juveniles (IJ) collected with a standard White trap (i.e., emerging from hosts and accumulating in water) and later applied to sand (treatment A) to IJ allowed to emerge from hosts into sand (treatment C). Percentage IJ survival and infectivity was compared between treatments for S. feltiae IJ that emerged between days 1 to 3 and days 4 to 6. For H. bacteriophora, percentage IJ survival and infectivity was compared between treatments only for infective juveniles that emerged between days 4 to 6. For S. feltiae IJ percentage survival and infectivity decreased with time (P ≤ 0.05) and was greater (P ≤ 0.05) for IJ from treatment C than for IJ from treatment A. For H. bacteriophora IJ percentage survival decreased (P ≤ 0.05) and percentage infectivity increased (P ≤ 0.05) with time. While percent survival was higher (P ≤ 0.05) for treatment C than for A, percent infectivity was not different between treatments.
desiccation; Heterorhabditis bacteriophora; infectivity; Steinernema feltiae; survival
The long-term persistence and suppressiveness of Pasteuria penetrans against Meloidogyne arenaria race 1 were investigated in a formerly root-knot nematode suppressive site following 9 years of continuous cultivation of three treatments and 4 years of continuous peanut. The three treatments were two M. arenaria race 1 nonhost crops, bahiagrass (Paspalum notatum cv. Pensacola var. Tifton 9), rhizomal peanut (Arachis glabrata cv. Florigraze), and weed fallow. Two root-knot nematode susceptible weeds commonly observed in weed fallow plots were hairy indigo (Indigofera hirsuta) and alyce clover (Alysicarpus vaginalis). The percentage of J2 with endospores attached reached the highest level of 87% in 2000 in weed fallow, and 63% and 53% in 2002 in bahiagrass and rhizomal peanut, respectively. The percentage of endospore-filled females extracted from peanut roots grown in weed fallow plots increased from nondetectable in 1999 to 56% in 2002, whereas the percentages in bahiagrass and rhizomal peanut plots were 41% and 16%, respectively. Over 4 years, however, there was no strong evidence that endospores densities reached suppressive levels because peanut roots, pods, and pegs were heavily galled, and yields were suppressed. This might be attributed to the discovery of M. javanica infecting peanut in this field in early autumn 2001. A laboratory test confirmed that although the P. penetrans isolate specific to M. arenaria attached to M. javanica J2, no development occurred. In summary, P. penetrans increased on M. arenaria over a 4-year period, but apparently because of infection of M. javanica on peanut at the field site root-knot disease was not suppressed. This was confirmed by a suppressive soil test that showed a higher level of soil suppressiveness than occurred in the field (P ≤ 0.01).
Arachis hypogaea; biological control; Meloidogyne arenaria; M. javanica; nematode; Pasteuria penetrans; peanut; persistence; root-knot nematode; suppressive soil
The predominant root-knot nematode in New Zealand pastures is Meloidogyne trifoliophila, and a recurrent selection program in Trifolium repens has developed resistance to this species. No data are available, however, on the mechanisms of resistance in T. repens or resistant genotypes of T. semipilosum. The development of M. trifoliophila in roots of T. repens and T. semipilosum was examined weekly after a 2-day inoculation with eggs. More second-stage juveniles (J2) were found in two resistant genotypes of T. repens than in two susceptible ones 1 week after inoculation. J2 did not develop further in resistant genotypes, but in susceptible plants development proceeded to the adult stage, visible at 4 weeks after inoculation. The mode of action of resistance to M. trifoliophila in T. repens and in T. semipilosum was compared after a 24-hour inoculation with J2. Numbers of J2 per root tip ranged from 0 to 12 with a median of one for each species. At 24 hours after inoculation (HAI), similar numbers of J2 were seen in the cortex oriented toward the root tip in both resistant and susceptible genotypes of both plant species. At 48 HAI, accumulations of J2 were seen in the meristem in both resistant and susceptible genotypes of both plant species. At 72 HAI, differences in nematode responses were evident between resistant and susceptible genotypes of both plant species; in susceptible roots, J2 heads were embedded in the developing stele. At this time, a browning reaction in resistant genotypes of both plant species indicated a hypersensitive response, and differences in the reaction were recorded between T. repens and T. semipilosum. More study is needed to determine whether the resistance reaction in T. semipilosum is suitable for introgression or insertion into T. repens.
hypersensitive response; invasion; Kenya white clover; Meloidogyne trifoliophila; penetration; resistance; root-knot nematode; Trifolium repens; Trifolium semipilosum; white clover
While multiple genes are optimal for corroborating nematode phylogenies, only a few are commonly used. Here we examine the phylogenetic potential of the nuclear Hsp90 chaperone gene. We used degenerate primers to obtain partial Hsp90 sequences from several plant-parasitic and free-living nematodes. Hsp90 was single-copy in Heterodera glycines and Meloidogyne javanica, similar to the situation for Caenorhabditis elegans. The full-length H. glycines Hsp90 protein sequence showed homology to sequences from C. elegans and Brugia pahangi and to other eukaryotes, and contains several functionally important regions common to cytoplasmic Hsp90 proteins. The Hsp90 amino acid phylogeny supported the Coelomata hypothesis for metazoan evolution. Phylogenetic trees, substitution scatter plots, and statistics for phylogenetic signal were made for Hsp90, 18S small subunit (SSU), and 28S large subunit (LSU) over a limited but broad sampling of nematode taxa. Only the LSU data set failed to recover any of the expected topology and showed extensive substitution saturation. In an intensive sampling of plant-parasitic nematode taxa, the Hsp90 tree topologies were generally congruent with rDNA results and alignments were unambiguous. Hsp90 sequences may help strengthen branch support or clarify tree topologies when other molecules show ambiguous alignments, greater branch-length heterogeneity, or codon bias in certain taxonomic groups.
DNA; Hsp90; phylogenetics; protein; rDNA; saturation
In Caenorhabditis elegans the unc-87 gene encodes a protein that binds to actin at the I band and is important in nematodes for maintenance of the body-wall muscle. Caenorhabditis elegans mutant phenotypes of unc-87 exhibit severe paralysis in larvae and limp paralysis in the adult. We cloned and characterized a full-length cDNA representing a Heterodera glycines homolog of the unc-87 gene from C. elegans that encodes a protein that contains a region of seven repeats similar to CLIK-23 from C-elegans and has 81% amino acid identity with that of C. elegans unc-87 variant A. In the EST database clones labeled "unc-87'' encode mainly the 3' portion of unc-87, while clones labeled "calponin homolog OV9M'' contain mainly DNA sequence representing the 5' and middle transcribed regions of unc-87. A 1770 nucleotide cDNA encoding H. glycines unc-87 was cloned and encodes a predicted UNC-87 protein product of 375 amino acids. The expression of unc-87 was determined using RT-PCR and, in comparison to its expression in eggs, unc-87 was expressed 6-fold higher in J2 juveniles and 20-fold and 13-fold (P = 0.05) higher in nematodes 15 and 30 days after inoculation, respectively. In situ hybridization patterns confirmed the expression patterns observed with RT-PCR.
gene expression; Heterodera glycines; in situ hybridization; soybean cyst nematode; Unc-87
Belonolaimus longicaudatus and Hoplolaimus galeatus are considered among the most damaging pathogens of turfgrasses in Florida. However, the host status of seashore paspalum (Paspalum vaginatum) is unknown. Glasshouse experiments were performed in 2002 and 2003 to determine the tolerance of 'SeaIsle 1' seashore paspalum to a population of B. longicaudatus and a population of H. galeatus, and to compare to 'Tifdwarf' bermudagrass for differences. Both nematode species reproduced well on either grass, but only B. longicaudatus consistently reduced root growth as measured by root length. Belonolaimus longicaudatus reduced root growth (P ≤ 0.05) by 35% to 45% at 120 days after inoculation on both grasses. In 2003, higher inoculum levels of H. galeatus reduced root growth (P ≤ 0.05) by 19.4% in seashore paspalum and by 14% in bermudagrass after 60 and 120 days of exposure, respectively. Percentage reductions in root length caused by H. galeatus and B. longicaudatus indicated no differences between grass species, although Tifdwarf bermudagrass supported higher soil population densities of both nematodes than SeaIsle 1 seashore paspalum.
Belonolaimus longicaudatus; bermudagrass; Hoplolaimus galeatus; host status; lance nematode; Paspalum vaginatum; seashore paspalum; sting nematode; tolerance
Random amplified polymorphic DNA (RAPDs) were used to investigate the intraspecific variability among 19 geographic isolates of Globodera tabacum solanacearum from eight counties in Virginia and one county in North Carolina. Globodera tabacum tabacum, G. t. virginiae, and the Mexican cyst nematode (MCN) were included as outgroups. Six primers were used and 119 amplification products were observed. Each primer yielded reproducible differences in fragment patterns that differentiated the isolates and species. Hierarchical cluster analysis was performed to illustrate the relatedness among isolates and species. The average Jaccard's similarity index among isolates of G. t. solanacearum was 74%, possibly representing greater variation than that reported in the literature across different pathotypes of the potato cyst nematode, Globodera pallida, in studies where RAPD were also employed. The RAPD markers described here may be useful for the development of specific primers or probes that could improve the identification of TCN populations. Such improvements in the characterization of TCN genotypes would facilitate the effective deployment of existing and future resistant cultivars to control these economically important pests.
DNA fingerprinting; genetic variation; Globodera tabacum solanacearum; RAPD; tobacco cyst nematode; virulence
The Mesocriconema xenoplax population increased exponentially in a newly planted peach orchard. The rate of increase was greater on Nemaguard than on Lovell rootstock and was reduced by postplant nematicides. Population levels were more stable in an established almond orchard on Nemaguard rootstock. All life stages of the nematode were present year round; lower ratios of juveniles to adults in summer suggested adverse effects of temperature and dry soil. Also in summer, there was a smaller proportion of the population in the upper 30 cm of soil than at greater depths. Nematode dosage, average nematode density multiplied by accumulated degree-days (physiological time) of the sampling interval, was useful in quantifying nematode stress on trees and as an indicator of the nematode management effectiveness. The annual trajectory of the nematode dosage could be determined by two samplings, one in spring and one in fall. A nematode predator, the parasitic fungus Hirsutella rhossiliensis, did not regulate ring nematode populations in the newly planted orchard; a recovery period was necessary for increase in the prevalence of parasitism.
bacterial canker; Mesocriconema xenoplax; nematicides; nematode management; population regulation; Prunus; rootstocks; stress dosage
Entomopathogenic nematodes are used for biological control of insect pests. A method for improved cryopreservation of infective juvenile stage nematodes has been developed using Steinernema carpocapsae and Heterorhabditis bacteriophora. Optimum survival for both species was achieved with 12,000 infective juveniles/ml in glycerol and 7,500/ml in Ringer's solution. For S. carpocapsae, maximum survival also was observed with 60,000 infective juveniles/ml in glycerol and 25,000/ml in Ringer's solution. These concentrations resulted in 100% post-cryopreservation survival of S. carpocapsae and 100% retention of original virulence to Galleria mellonella larvae. This is the first report of achieving 100% survival of an entomopathogenic nematode after preservation in liquid nitrogen. Maximum survival of H. bacteriophora following cryopreservation was 87%.
concentration; cryobiology; cryopreservation; Heterorhabditis bacteriophora; Steinernema carpocapsae; survival
Previous surveys of vineyards had indicated that Mesocriconema xenoplax was present in 85% of vineyards in western Oregon, but yields were not depressed in established vines. Microplot studies were initiated in 1997 in a Willamette Valley vineyard to determine the impact of M. xenoplax on vine establishment. Plots were infested with 0.03, 0.6, and 3.0 M. xenoplax g-1 soil and planted with self-rooted Chardonnay and Pinot Noir vines. In November 2000, four growing seasons after planting, pruning weights, fine root weights, and fruit yield of vines planted in infested soil were reduced by 58%, 75%, and 33%, respectively, relative to control vines (planted in noninfested soil). In 1998 with ca 2000 degree-day base 9 °C accumulation, population densities increased 32-fold and 44-fold on 1-year-old Chardonnay and Pinot Noir vines, respectively. Nematode population dynamics and pruning data suggested that the carrying capacity of vines in microplots was 5 to 8 M. xenoplax g-1 soil. In November 2000, more than 80% of the fine root length was colonized by arbuscular mycorrhizal fungi in all treatments. The frequency of fine roots containing arbuscules (the site of nutrient transfer between plant and fungus), however, was depressed from 5% to 65% in plants infested initially with M. xenoplax as compared to controls. Competition for photosynthate within the root system is proposed as a possible mechanism by which nematodes suppressed arbuscule frequency.
arbuscule frequency; grape; Mesocriconema xenoplax; mycorrhizae; plant disease loss; population dynamics; ring nematode; Vitis vinifera
In a study of relationships among selected cyst-forming and noncyst-forming species of Heteroderoidea, combined sequences comprised of DNA from part of the conserved 18S ribosomal RNA gene (rDNA) plus the complete ITS rDNA segment were more similar to analyses based on the ITS data alone than to analyses based on the 18S data alone. One of the two noncyst-forming species, Ekphymatodera thomasoni, grouped with cyst-forming species of Heteroderoidea. Bilobodera flexa, also a noncyst-forming species, was separated from all the other taxa by a long branch. Afenestrata koreana, with a weakly sclerotized cyst, grouped closely with H. bifenestra. These observations suggest that phylogenetic analyses using molecular data may aid in our understanding of the evolution of cyst formation in nematodes, including the possibility of secondary loss. The usefulness of molecular phylogenetic analyses in nematodes may depend more on the particular selection of taxa than on mere addition of data from additional genes.
Afenestrata koreana; Bilobodera flexa; Cactodera betulae; Ekphymatodera thomasoni; Globodera; Heterodera bifenestra; ITS1; ITS2; nematode; phylogenetic analysis; ribosomal DNA; 5.8S gene; 18S gene
Soybean root cells undergo dramatic morphological and biochemical changes during the establishment of a feeding site in a compatible interaction with the soybean cyst nematode (SCN). We constructed a cDNA microarray with approximately 1,300 cDNA inserts targeted to identify differentially expressed genes during the compatible interaction of SCN with soybean roots 2 days after infection. Three independent biological replicates were grown and inoculated with SCN, and 2 days later RNA was extracted for hybridization to microarrays and compared to noninoculated controls. Statistical analysis indicated that approximately 8% of the genes monitored were induced and more than 50% of these were genes of unknown function. Notable genes that were more highly expressed 2 days after inoculation with SCN as compared to noninoculated roots included the repetitive proline-rich glycoprotein, the stress-induced gene SAM22, ß-1,3-endoglucanase, peroxidase, and those involved in carbohydrate metabolism, plant defense, and signaling.
Glycine max; Heterodera glycines; microarray; plant-pathogen interaction; SGMD; signaling pathway; soybean cyst nematode; soybean genomics microarray database; syncytium
Two greenhouse experiments were conducted to examine the effect of Crotalaria juncea amendment on Meloidogyne incognita population levels and growth of yellow squash (Cucurbita pepo). In the first experiment, four soils with a long history of receiving yard waste compost (YWC+), no-yard-waste compost (YWC-), conventional tillage, or no-tillage treatments were used; in the second experiment, only one recently cultivated soil was used. Half of the amount of each soil received air-dried residues of C. juncea as amendment before planting squash, whereas the other half did not. Crotalaria juncea amendment increased squash shoot and root weights in all soils tested, except in YWC+ soil where the organic matter content was high without the amendment. The amendment suppressed the numbers of M. incognita if the inoculum level was low, and when the soil contained relatively abundant nematode-antagonistic fungi. Microwaved soil resulted in greater numbers of M. incognita and free-living nematodes than frozen or untreated soil, indicating nematode-antagonistic microorganisms played a role in nematode suppression. The effects of C. juncea amendment on nutrient cycling were complex. Amendment with C. juncea increased the abundance of free-living nematodes and Harposporium anguillulae, a fungus antagonistic to them in the second experiment but not in the first experiment. Soil histories, especially long-term yard waste compost treatments that increased soil organic matter, can affect the performance of C. juncea amendment.
free-living nematode; nematode-trapping fungi; organic amendments; root-knot nematode; soil ecosystem; soil nutrient; sunn hemp; tillage
Strains of Caenorhabditis elegans obtained from their natural soil environment exhibit one of two forms of foraging behavior. Some strains forage solitarily and disperse evenly on a bacterial lawn. Other strains move rapidly until they encounter groups of conspecifics, and then slow their movement and join the group. Strains expressing these behaviors are globally widespread and have been isolated from the same location, suggesting a foraging polymorphism. We hypothesized that density-dependent selection maintains both foraging alleles in populations. Alternatively, both foraging alleles could be retained in populations through frequency-dependent selection. We tested both of these hypotheses by manipulating strain density and frequency, and observing changes in population density over time. Our results indicated that neither density- nor frequency-dependent selection appears to be responsible for the observed polymorphism. The clumping strain consistently out-competed the solitary strain over all treatment levels. We suggest other potential factors that may maintain both alleles in populations.
Caenorhabditis elegans; density-dependent selection; foraging behavior; frequency-dependent selection; polymorphism
In the study of the biological control of plant-parasitic nematodes, knowledge of the saprophytic ability of a nematophagous fungus is necessary to understand its establishment and survival in the soil. The objectives of this study were (i) to determine if the nematophagous fungus ARF (Arkansas Fungus) shows differential use of plant residues; and (ii) to determine if ARF still existed in the soil of a field in which ARF was found originally and in which the population level of Heterodera glycines had remained very low, despite 15 years of continuous, susceptible soybean. Laboratory studies of the decomposition of wheat straw or soybean root by ARF were conducted in two separate experiments, using a CO₂ collection apparatus, where CO₂-free air was passed through sterilized cotton to remove the microorganisms in the air and then was passed over the samples, and evolved CO₂ was trapped by KOH. Milligrams of C as CO₂ was used to calculate the percentage decomposition of the plant debris by ARF. Data indicated ARF decomposed 11.7% of total organic carbon of the wheat straw and 20.1% of the soybean roots in 6 weeks. In the field soil study, 21 soil samples were taken randomly from the field. Only 3 months after the infestation of the soil with H. glycines, the percentage of parasitized eggs of H. glycines reached 64 ± 19%, and ARF was isolated from most parasitized eggs of H. glycines. Research results indicated ARF could use plant residues to survive.
ARF; decompose; Heterodera glycines; nematophagous fungus; plant debris; soybean cyst nematode
The discovery of Meloidogyne mayaguensis is confirmed in Florida; this is the first report for the continental United States. Meloidogyne mayaguensis is a virulent species that can reproduce on host cultivars bred for nematode resistance. The perineal patterns of M. mayaguensis isolates from Florida show morphological variability and often are similar to M. incognita. Useful morphological characters for the separation of M. mayaguensis from M. incognita from Florida are the male stylet length values (smaller for M. mayaguensis than M. incognita) and J2 tail length values (greater for M. mayaguensis than M. incognita). Meloidogyne mayaguensis values for these characters overlap with those of M. arenaria and M. javanica from Florida. Enzyme analyses of Florida M. mayaguensis isolates show two major bands (VS1-S1 phenotype) of esterase activity, and one strong malate dehydrogenase band (Rm 1.4) plus two additional weak bands that migrated close together. Their detection requires larger amounts of homogenates from several females. Amplification of two separate regions of mitochondrial DNA resulted in products of a unique size. PCR primers embedded in the COII and 16S genes produced a product size of 705 bp, and amplification of the 63-bp repeat region resulted in a single product of 322 bp. Nucleotide sequence comparison of these mitochondrial products together with sequence from 18S rDNA and ITS1 from the nuclear genome were nearly identical with the corresponding regions from a M. mayaguensis isolate from Mayaguez, Puerto Rico, the type locality of the species. Meloidogyne mayaguensis reproduced on cotton, pepper, tobacco, and watermelon but not on peanut. Preliminary results indicate the M. mayaguensis isolates from Florida can reproduce on tomato containing the Mi gene. Molecular techniques for the identification of M. mayaguensis will be particularly useful in cases of M. mayaguensis populations mixed with M. arenaria, M. incognita, and M. javanica, which are the most economically important root-knot nematode species in Florida, and especially when low (<25) numbers of specimens of these species are recovered from the soil.
isozyme; Meloidogyne arenaria; M. incognita; M. javanica; M. mayaguensis; mitochondrial DNA; molecular diagnosis; morphology; nematode; root-knot nematode; taxonomy