1,3-Dichloropropene (1,3-D) and nonfumigant nematicides were evaluated for control of Meloidogyne spp. and soil and foliar insects in a tobacco pest management system. In a field with a high Meloidogyne spp. population density (root gall index 4.0 to 4.5 on a 0 to 10 scale in untreated controls), tobacco yields and crop values increased (482 kg/ha and $1,784/ha for 1, 3-D; 326 kg/ha and $1,206/ha for fenamiphos; 252 kg/ha and $933/ha for ethoprop) with nematicide application over an untreated control. In fields with a low population density of Meloidogyne arenaria or M. incognita (root gall index 2.3 to 2.5 in untreated controls), yields ranged from 1,714 to 2,027 kg/ha and were not altered by fumigant or nonfumigant nematicide application. Carbofuran, a soil-applied nonfumigant nematicide/insecticide, reduced the number of foliar insecticide applications required to keep insect populations below treatment threshold (3.8 vs. 4.5, respectively, for treated vs. untreated). Carbofuran reduced the cost ($23/ha) of foliar insecticide treatments when compared to an untreated control. Although nonfumigant nematicides provided some soil and foliar insect control, the cost of using a fumigant plus a lower insecticidal rate of a soil insecticide/nematicide was comparable to the least expensive non-fumigant nematicide when the cost of foliar insecticide applications was included in the cost estimates. Savings in foliar insecticide cost by use of soil-applied nonfumigant nematicide/insecticides were small ($23/ha) in comparison to potential value reductions by root-knot nematodes when the nonfumigant nematicides fenamiphos or ethoprop ($578/ha and $851/ha, respectively) were used instead of 1,3-D.
1,3-dichloropropene; Meloidogyne arenaria; M. incognita; M. javanica; nematicide; nematode management systems; Nicotiana tabacum; root-knot nematode; tobacco
Fergusobia nematodes and Fergusonina flies are mutualists that cause a variety of gall types on myrtaceous plant buds and young leaves. The biology of an isolate of the gall complex was studied in its native range in Australia for possible use in southern Florida as a biological control agent against the invasive broad-leaved paperbark tree, Melaleuca quinquenervia. Timed studies with caged Fergusonina flies on young branches of M. quinquenervia revealed that females are synovigenic with lifetime fecundities of 183 ± 42 (standard error; SE) eggs and longevities of 17 ± 2 days. None of the male flies but all dissected female flies contained parasitic female nematodes (range = 3-15), nematode eggs (12-112), and nematode juveniles (78-1,750). Female flies deposited eggs (34 ± 6; 8-77 per bud) and nematode juveniles (114 ± 15; 44-207 per bud) into bud apices within 15 days. Histological sections of shoot buds suggested that nematodes induce the formation of hypertrophied, uninucleate plant cells prior to fly larval eclosion. Enlarged size, granular cytoplasm, and enlarged nucleus and nucleolus characterized these cells, which appeared similar to those of other species galled by nematodes in the Anguinidae. Observations of ovipositional behavior revealed that female Fergusonina sp. create diagnostic oviposition scars. The presence of these scars may facilitate recognition of host use during specificity screening.
Australia; biocontrol; Diptera; Fergusobia; Fergusonina; Fergusoninidae; fly; gall development; life history; mutualism; Myrtaceae; Nemata; nematode; oviposition; Tylenchida
If, as Einstein said, "it is the theory which decides what we can observe," then "the species problem" could be solved by simply improving our theoretical definition of what a species is. However, because delimiting species entails predicting the historical fate of evolutionary lineages, species appear to behave according to the Heisenberg Uncertainty Principle, which states that the most philosophically satisfying definitions of species are the least operational, and as species concepts are modified to become more operational they tend to lose their philosophical integrity. Can species be delimited operationally without losing their philosophical rigor? To mitigate the contingent properties of species that tend to make them difficult for us to delimit, I advocate a set of operations that takes into account the prospective nature of delimiting species. Given the fundamental role of species in studies of evolution and biodiversity, I also suggest that species delimitation proceed within the context of explicit hypothesis testing, like other scientific endeavors. The real challenge is not so much the inherent fallibility of predicting the future but rather adequately sampling and interpreting the evidence available to us in the present.
evolution; nematode; phylogeny; speciation; species concepts; species delimitation; systematics; taxonomy
A molecular analysis of eight described species of seed gall nematode, along with six undescribed isolates from different hosts, has revealed a strong association between nucleotide sequence polymorphism and host status. Each anguinid nematode associated with a unique host produced a unique PCR-RFLP pattern for the ITS1 region. Anguina species that had been synonymized in the past, Anguina agrostis, A. funesta, and A. wevelli (Afrina wevelli), were readily discriminated. Two undescribed species from northern New South Wales and southeastern South Australia, reported to be vectors of Rathyaibacter toxicus in the disease called ''floodplain staggers,'' were differentiated by a single restriction enzyme, and both could be separated easily from A. funesta, the vector of R. toxicus in annual ryegrass toxicity. Other species differentiated in this study include A. agropyronifloris, A. graminis, A. microlaenae, A. pacificae, and undescribed species from host species Dactylis glomerata, Agrostis avenacea, Polypogon monospeliensis, Stipa sp., Astrebla pectinata, and Holcus lanatus. Phylogenetic analysis of the ITS1 region suggests that considerable anguinid genetic diversification has accompanied specialization on different host species.
Afrina wevelli; Anguina agrostis; Anguina tritici; diagnostics; nematode identification; PCR-RFLP; regulatory nematology; seed gall nematode
The composition of nematode communities (plant-parasitic and free-living) may be used as bioindicators of soil health or condition because composition correlates well with nitrogen cycling and decomposition, two critical ecological processes in soil. Maturity and trophic diversity indices withstand statistical rigor better than do abundances, proportions, or ratios of trophic groups. Maturity indices respond to a variety of land-management practices, based largely on inferred life history characteristics of families. Similarity indices may be more useful than diversity indices because they reflect taxon composition. Improving existing indices or developing alternative indices refined by a greater understanding of the biology of key taxa may enhance the utility of nematodes as bioindicators.
biodiversity; biomonitor; ecology; integrity; maturity index; monitoring; nematode; soil; trophic diversity
Pasteuria sp., strain S-1, is a gram-positive, obligate endoparasitic bacterium that uses the phytoparasitic sting nematode, Belonolaimus longicaudatus, as its host in Florida. The host attachment of S-1 appears to be specific to the genus Belonolaimus with development occurring only in juveniles and adults of B. longicaudatus. This bacterium is characterized from other described species of Pasteuria using ultrastructure of the mature endospore. Penetration, development, and sporogenesis were elucidated with TEM, LTSEM, and SEM and are similar to other nematode-specific Pasteuria. Recent analysis of 16S rDNA sequence homology confirms its congeneric ranking with other Pasteuria species and strains from nematodes and cladocerans, and corroborates ultrastructural, morphological, morphometric, and host-range evidence suggesting separate species status.
Belonolaimus longicaudatus; development; obligate nematode endoparasitic bacterium; Pasteuria sp. (s-1 strain); sporogenesis; sting nematode; ultrastructure
Trap crops that stimulate nematode egg hatching but not reproduction have been reported as an effective means for managing certain nematodes. Studies were carried out at two field sites each year in 1998 and 1999 to evaluate the potential of trapping the soybean cyst nematode (Heterodera glycines) with soybean and pea in the corn year to manage the nematode in Minnesota. The trap crops were planted on the same day as corn at each site and later killed with the herbicide glyphosate. Nematode egg densities were determined at planting, 1 and 2 months after planting, and at harvest. Treatments included four seeding rates (0, 124,000, 247,000, and 494,000 seeds/ha) of resistant soybean as a trap crop and four kill dates (3, 4, 5, and 6 weeks after planting). No effects of the trap-crop and kill-date treatments on H. glycines population density, corn yield, and the followingyear soybean yield were observed at the two locations. In a second study, the experiment included four trap-crop comparisons (resistant soybean at 494,000 seeds/ha, susceptible soybean at 494,000 seeds/ha, pea at 1,482,000 seeds/ha, and no trap crop) and five kill dates (3, 4, 5, 6 weeks after planting, and no-kill). At the Waseca site, egg density at harvest was lower where resistant soybean was grown for 6 weeks and where pea was grown for 5 and 6 weeks compared with where no trap crop was grown. Maintaining pea plants for more than 5 weeks, however, reduced corn yield by 20% at the Waseca site. At the Lamberton site, egg density at harvest was lower where the susceptible soybean was grown for 5 weeks compared with where no trap crop was grown. Even with significant reduction of eggs in some treatments, use of soybean and pea as trap crops in the corn year was not an effective means for managing H. glycines.
Glycine max; Heterodera glycines; management; pea; Pisum sativum; soybean; soybean cyst nematode; trap crop
In greenhouse pot experiments during summer 2000, 118 soybean cultivars were tested to determine their suitability as hosts for the reniform nematode, Rotylenchulus reniformis. The cultivars included 115 new entries into the Arkansas and Mississippi soybean variety testing programs and three entries submitted by an extension nematologist from Texas. Also included in the tests were the R. reniformis-resistant cultivars Forrest and Hartwig, the susceptible cultivar Braxton, and fallow R. reniformis-infested soil that served as controls. Total number of eggs and nematodes extracted from both the soil and roots from each pot and reproductive indices (Pf/Pi) were calculated for each cultivar. The ratio of the Pf/Pi of each cultivar to the Pf/Pi of Forrest (RF), and the log ratio[log10 (RF + 1)], are reported. Cultivars with reproductive indices that were greater than the reproductive index on Forrest were considered to be suitable hosts for R. reniformis. These data will be useful in the selection of soybean cultivars to use in rotation with cotton or other susceptible crops to help control the reniform nematode.
Glycine max; nematode; reniform nematode; reproductive index; rotation; Rotylenchulus reniformis; soybean
Phylogenetic analysis of new ribosomal DNA (rDNA) data for Heterodera mediterranea, H. hordecalis, H. carotae, and H. fici from Italy and H. ciceri from Syria, along with published data for other species, showed high bootstrap support for the following relationships: (((((H. carotae H. cruciferae) H. goettingiana) (((H. trifolii H. ciceri) H. mediterranea) ((H. avenae H. latipons) H. fici))) (Cactodera betulae H. hordecalis)) (Globodera rostochiensis G. pallida)). The rDNA sequence data were for the two internal transcribed spacers (ITS1 and ITS2) plus the 5.8S gene between them. These inferred relationships support the classic ''Goettingiana Group'' of H. carotae, H. cruciferae, and H. goettingiana. A clade comprised of Cactodera betulae and H. hordecalis is only distantly related to the other species in the analysis.
Heterodera; Heterodera carotae; Heterodera ciceri; Heterodera fici; Heterodera hordecalis; Heterodera mediterranea; ITS1; ITS2; phylogenetic analysis; ribosomal DNA; 5.8S gene
The effects of agricultural management on the soil nematode community were investigated in a field study at depths of 0 to 10 cm and 10 to 20 cm during a peanut (Arachis hypogaea) growing season in Israel. Nineteen nematode families and 23 genera were observed. Rhabditidae, Cephalobus, Eucephalobus, Aphelenchus, Aphelenchoides, Tetylenchus, Tylenchus, Dorylaimus, and Discolaimus were the dominant family and genera. Ecological measures of soil nematode community structure, diversity, and maturity indices were assessed and compared between the managed (by fertilization, irrigation, and pesticide application) and unmanaged fields. The total number of nematodes at a 10-cm depth during peanut-sowing, mid-season, and harvest periods was higher in the treated (managed) plot than in the control (unmanaged) plot. Bacterivores and fungivores were the most abundant trophic groups in both plots and both depths. The relative abundance of each group averaged 60.8 to 67.3% and 11.5 to 19.6% of the nematode community, respectively. Plant parasites and omnivores-predators at the 0 to 10-cm depth were much less abundant than any other two groups in our experimental plots. During the growing season, except the harvest period, populations of plant parasites and omnivores-predators at the 10 to 20-cm depth were lower in the treated plot than in the control plot. Maturity index (MI), plant-parasite index (PPI), and ratio of fungivores and bacterivores to plant parasites (WI) were found to be more sensitive indicators than other ecological indices for assessing the response of nematode communities to agricultural management in an Israeli agroecosystem.
agricultural management; agroecosystem; diversity; maturity index; nematode communities; peanut
The survival of eggs of the root-knot nematode Meloidogyne javanica was studied in a series of experiments comparing the infectivity of egg masses (EM) to that of separated eggs (SE). The EM or SE were placed in the centers of pots containing citrus orchard soil and incubated for 24 hours, 10 days, or 20 days. Following each incubation time, 10-day-old tomato plants were planted in each pot, and 3 to 4 weeks later the plants were harvested and the galling indices determined. In the EM treatments, galling indices of ca. 4.0 to 5.0 were recorded after all three incubation periods; in the SE treatments, the infectivity gradually declined to trace amounts by 20 days. Incubating EM and SE for 2 weeks in four different soil types showed the same pattern in all the soil types: EM caused heavy infection of the test plants while the infection rate from the SE was extremely low. Incubating EM and SE in soil disinfested with formaldehyde resulted in comparable galling indices in most treatments. In petri dish experiments, 100 mg of natural soil was spread at the perimeter of a Phytagel surface and EM or SE of M. incognita were placed in the center. Light microscopy revealed that within 5 to 10 days the SE were attacked by a broad spectrum of microorganisms and were obliterated while the eggs within the EM remained intact. Separated eggs placed within sections of gelatinous matrix (GM) were not attacked by the soil microorganisms. When selected microbes were placed on Phytagel surfaces with EM of M. incognita, electron microscopy demonstrated that at least some microbes colonized the GM. As the major difference between the EM and the SE was the presence of the GM, the GM may serve as a barrier to the invasion of some microorganisms.
biological control; Burkholderia cepacia; egg; electron microscopy; gelatinous matrix; Meloidogyne; Mortierella sp.; nematode; root-knot nematode
The European chafer Rhizotrogus majalis (Razoumowsky) feeds on turfgrass roots, causing major damage in the urban areas of northeastern North America. A laboratory study was conducted to determine the susceptibility of third-instar chafer larvae to four species of entomopathogenic nematodes (Steinernema glaseri, S. feltiae, S. carpocapsae, and Heterorhabditis bacteriophora). Only S. glaseri was virulent, and only at high numbers (LD50 = 294 nematodes/larva). Prolonged contact with nematodes increased host mortality. Optimal conditions for S. glaseri with respect to soil type and soil moisture were determined. Maximum larval mortality was obtained with 7% moisture and a 50/50 mixture of chernozem and sand. These results suggest that these nematodes currently have little potential for the biological control of the European chafer in turfgrass.
biological control; entomopathogenic nematodes; European chafer; turfgrass pest
The effects of crop rotation and the nematicides 1,3-dichloropropene (1,3-D), ethoprop, and fenamiphos on the relative frequency of Meloidogyne incognita race 3, M. arenaria race 2, and M. javanica and tobacco yields on a sandy loam soil were determined. Cropping sequences altered the species composition and population densities of Meloidogyne spp. Meloidogyne arenaria and M. incognita predominated when cotton, corn, sorghum, or rye-fallow preceded tobacco. Meloidogyne javanica and M. arenaria predominated when tobacco preceded tobacco. Sorghum, cotton, corn, or rye-fallow preceding tobacco enhanced yields compared to tobacco preceding tobacco in plots containing mixtures of Meloidogyne species. Sorghum supported minimal reproduction of any Meloidogyne spp. Application of 1,3-D increased tobacco yields and reduced root galling when compared to untreated controls. Both fenamiphos and ethoprop treatments were less effective than 1,3-D in controlling Meloidogyne spp. or increasing yields. A rotation crop x nematicide interaction was not observed. In continuous tobacco, use of the M. incognita-resistant tobacco cv. Coker 176 increased tobacco yields when compared to the M. incognita-susceptible cv. Coker 319 when 1,3-D was not applied.
corn; cotton; Meloidogyne arenaria; M. incognita; M. javanica; nematicide; root-knot nematode; rotation; rye; sorghum; tobacco
Guardian, Lovell, and Nemaguard peach rootstocks were evaluated for their susceptibility and growth response to two isolates of Pratylenchus vulnus. One nematode isolate was obtained from peach in Georgia (P. vulnus [GA-isolate]) and the other from apple in Idaho (P. vulnus [ID-isolate]). Nematode reproduction and pathogenicity as related to rootstock were determined 29 months after inoculation in outdoor microplots. All rootstocks were susceptible to both nematode isolates. Guardian supported a greater number of nematodes per gram dry root weight than Lovell or Nemaguard rootstocks. All rootstocks supported greater numbers of P. vulnus (GA-isolate) than P. vulnus (ID-isolate). Tree growth among the three rootstocks was similar in the presence of either P. vulnus isolate, but growth suppression was greatest in P. vulnus (GA-isolate) plots, intermediate in P. vulnus (ID-isolate) plots, and least in the uninoculated plots.
host-parasitic relationship; nematode; pathogenicity; peach; Pratylenchus vulnus; Prunus persica; resistance; root-lesion nematode; rootstock
1,3-Dichloropropene (1,3-D) is a likely alternative soil fumigant for methyl bromide. The objective was to determine root-knot nematode, Meloidogyne incognita, survival in microplots after exposure to 1,3-D for various periods of time in soil that have previously been amended with compost. The treatments were 1,3-D applied broadcast at 112 liters/ha and untreated controls in both compost-amended and unamended soil. Soil samples were collected from each microplot at 6, 24, 48, 72, and 96 hours after fumigation at three depths (0-15, 15-30, and 30-45 cm). One week after fumigation, six tomato seedlings were transplanted into each microplot and root galling was recorded 6 weeks later. Plants grown in fumigated compost-amended soil had more galls than plants from fumigated unamended soil at P ≤ 0.1. Gall indices from roots in fumigated soil amended with compost were not different from nonfumigated controls. Based on soil bioassays, the number of galls decreased with increasing time after fumigation in both compost-amended and unamended soil at 0-to-15 and 15-to-30 cm depths, but not at 30 to 45 cm deep. Higher soil water content due to the elevated levels of organic matter in the soil at these depths may have interfered with 1,3-D movement, thus reducing its efficacy.
compost-amended soil; deep sand soil; 1,3-dichloropropene; fumigation; Lycopersicon esculentum; Meloidogyne incognita; nematicide; nematode; root-knot nematode; tomato
The development of novel foods produced through agricultural biotechnology is a complex three-stage process: gene discovery, line selection, and product advancement to commercialization. The safety of genetically modified foods is an integral part of the overall developmental process throughout all of the stages. In the discovery stage, the safety of the gene, its source, and the gene products must be considered. If any questions arise at this stage, these questions must be answered later in the developmental process. During the line selection stage, the genetically modified seed progresses through a variety of greenhouse and field trials. At this stage, the biological and agronomic equivalence of the genetically modified crop to its traditional counterpart must be compared. While the evaluations made during this stage are not specifically directed toward a safety assessment, many potential products with unusual characteristics are eliminated during this stage of development. However, the elimination of products with unusual agronomic or biological characteristics enhances the likelihood that a safe product will be generated. Finally, in the pre-commercialization stage, the genetically modified product undergoes a detailed safety assessment process. This process focuses on the safety of the gene products associated with the introduced gene and any other likely toxicological or anti-nutrient factors associated with the source of the novel gene and the crop to which it was introduced. The safety of the genetically modified product for both food and feed uses is considered. Thus far, all of the genetically modified products brought into the marketplace have been subjected to such an intensive safety assessment. The safety assessment data have been reviewed by regulatory authorities around the world. The current generation of genetically modified products are quite safe for human and feed animal consumption.
allergen; antibiotic resistance; food safety; genetic engineering; safety assessment; substantial equivalence; toxicant
The terms ''soil health'' or ''soil quality'' as applied to agroecosystems refer to the ability of soil to support and sustain crop growth while maintaining environmental quality. High-quality soils have the following characteristics: (i) a sufficient, but not excess, supply of nutrients; (ii) good structure (tilth); (iii) sufficient depth for rooting and drainage; (iv) good internal drainage; (v) low populations of plant disease and parasitic organisms; (vi) high populations of organisms that promote plant growth; (vii) low weed pressure; (viii) no chemicals that might harm the plant; (ix) resistance to being degraded; and (x) resilience following an episode of degradation. Management intended to improve soil health involves creatively combining a number of practices that enhance the soil's biological, chemical, and physical suitability for crop production. The most important general strategy is to add plentiful quantities of organic matter—including crop and cover crop residues, manures, and composts. Other important strategies include better crop rotations, reducing tillage and keeping the soil surface covered with living and dead residue, reducing compaction by decreasing heavy equipment traffic, and using best nutrient management practices. Practices that enhance soil quality frequently reduce plant pest pressures.
soil health; soil organic matter; soil quality
Ultra-narrow row cotton studies were conducted during 1999 at two field sites in northern Florida. One site was naturally infested with Meloidogyne incognita Race 3 and the other with Rotylenchulus reniformis. The fumigant 1,3-dichloropropene (1,3-D) was applied broadcast at rates of 0, 16, 32, 48, 64, 80, and 96 kg ai./ha in replicated plots before planting Delta Pine 655 BRR cotton in 25-cm-wide rows. Post-harvest soil population densities at the root-knot nematode site had a significant (P ≤ 0.01) negative linear relationship to 1,3-D dosage level. Cotton lint yields at this site had a significant (P ≤ 0.01) positive linear relationship to 1,3-D dosage level. At the reniform nematode site, there was no relationship between post-harvest soil population densities of reniform nematodes and 1,3-D dosage level. However, significant (P ≤ 0.01) positive curvilinear relationships were found between both plant heights and lint yield to 1,3-D dosage levels.
1,3-dichloropropene; cotton; Gossypium hirsutum; Meloidogyne incognita; nematicide; reniform nematode; root-knot nematode; Rotylenchulus reniformis
In a 3-year field study, population densities of Belonolaimus longicaudatus and other plant-parasitic nematodes and crop yields were compared between potato (Solanum tuberosum) cropping systems where either sorghum-sudangrass (Sorghum bicolor × S. arundinaceum) or velvetbean (Mucuna pruriens) was grown as a summer cover crop. Population densities of B. longicaudatus, Paratrichodorus minor, Tylenchorhynchus sp., and Mesocriconema sp. increased on sorghum-sudangrass. Population densities of P. minor and Mesocriconema sp. increased on velvetbean. Sorghum-sudangrass increased population densities of B. longicaudatus and Mesocriconema sp. on a subsequent potato crop compared to velvetbean. Potato yields following velvetbean were not greater than following sorghum-sudangrass despite reductions in population densities of B. longicaudatus.
Belonolaimus longicaudatus; cover crop; cropping sequence; Dolichodorus heterocephalus; Hemicycliophora sp.; management; Meloidogyne incognita; Mesocriconema sp.; modeling; Mucuna pruriens; nematode; Paratrichodorus minor; population dynamics; potato; root-knot nematode; Solanum tuberosum; Sorghum bicolor × S. arundinaceum; sorghum-sudangrass; sting nematode; stubby root nematode; Tlenchorhynchus sp.; velvetbean
The purpose of this research was to compare the overwinter survival of populations of Heterodera glycines at different latitudes in the United States and the effect of changing latitudes before and after the initiation of dormancy. Soil samples infested with H. glycines were collected in August or October in 1992 to 1994 from soybean fields in two to four states (combinations of Arkansas, Florida, Minnesota, Missouri, and Wisconsin). The samples were mixed thoroughly, divided into subsamples, shipped to an overwinter location, and buried until time for processing. To determine survival, cysts, eggs, and second-stage juveniles were extracted from replicated subsamples and counted each month from December to May. Survival generally was between 50% and 100%, and often was best in the state of origin. In Florida, survival was at the 50 to 100% level in soil from most locations, and in Wisconsin was near 100%. Survival of H. glycines in Arkansas and Missouri varied more than at the other locations. In a separate test, survival in microplots in Arkansas, in a more natural environment than that of buried samples, was 70 to 94% for field isolates from Arkansas, Minnesota, and Missouri and 100% for isolates of races 1, 3, and 14 that had been maintained in a greenhouse for several years. Survival appears to be better than previous tests had indicated. High survival rates require cultivars with high levels of resistance and long-term rotations for management.
Heterodera glycines; nematode; overwintering; soybean cyst nematode; survival
Globodera rostochiensis and G. pallida responded similarly to hatch stimulation by potato root leachate, but proportionally more second-stage juveniles (J2s) of G. rostochiensis hatched than of G. pallida in response to picrolonic acid, sodium thiocyanate, alpha-solanine, and alpha-chaconine. Fractionation of the potato root leachate identified hatching factors with species-selective (active toward both species but stimulating greater hatch of one species than the other), -specific (active toward only one species), and -neutral (equally active toward both species) activities. In a comparison of two populations of each of the two potato cyst nematode (PCN) species, however, greater similarity in response to the individual hatching factors was observed among populations of different species produced under the same conditions than among different populations of the same PCN species. Smaller numbers of species-specific and species-selective hatching factor stimulants and hatching inhibitors than of hatching factors were resolved. In a study to determine whether the different hatching responses of the two species to the same root leachate were associated with different ratios of species-selective and species-specific hatching factors, G. rostochiensis pathotype Ro1 exhibited greater hatch than did G. pallida pathotype Pa2/3 in response to leachate from older plants (more than 38 days old), while G. pallida exhibited greater hatch in response to leachate from younger plants (less than 38 days old); the response of G. pallida pathotype Pal with respect to plant age was intermediate between the other two populations. Combined molecular exclusion-ion exchange chromatography of the root leachates from plants of different ages revealed an increase in the proportion of G. rostochiensis-specific and -selective hatching factors as the plants aged.
Globodera pallida; Globodera rostochiensis; glycoalkaloids; hatching factors; hatching factor stimulants; hatching inhibitors; potato cyst nematode; potato root diffusate; potato root leachate
The effects of the arbuscular mycorrhizal (AM) fungus Glomus mosseae on Heterodera glycines-soybean interactions were investigated in greenhouse experiments. Mycorrhizal and nonmycorrhizal soybean cultivars that were either resistant or susceptible to H. glycines were exposed to initial nematode population densities (Pi) of 0, 100, 1,000, or 10,000 eggs and infective juveniles. Soybean growth, nematode reproduction, and AM fungal colonization were determined after 35 (experiment I) and 83 (experiment II) days. Soybean shoot and root weights were reduced an average 29% across H. glycines Pi but were 36% greater overall in the presence of G. mosseae. Analyses of variance indicated that root colonization and stimulation of soybean growth by G. mosseae were inhibited at high H. glycines Pi, while the combined effects of the nematode and fungus on soybean growth were best described as additive in linear regression models. No evidence for increased nematode tolerance of mycorrhizal soybean plants was observed. Nematode population densities and reproduction were lower on a nematode-resistant soybean cultivar than on a susceptible cultivar, but reproduction was comparable on mycorrhizal and nonmycorrhizal plants. Root colonization by G. mosseae was reduced at high nematode Pi. The results suggest that nematode antagonism to the mycorrhizal symbiosis is a more likely consequence of interactions between H. glycines and AM fungi on soybean than is nematode suppression by the fungus.
arbuscular mycorrhizae; Glomus mosseae; Glycine max; Heterodera glycines; nematode-mycorrhizal interaction; soybean; soybean cyst nematode; vesicular-arbuscular mycorrhizae
Nematode occurrence at specific locations throughout a water catchment-irrigation system was determined. Soil samples were collected from five water source locations on the slopes of Olomana Mountain and Maunawili Valley and from about 40 plant species on 18 farms (56 ha of 480 ha irrigated by the reservoir). Water was sampled from the catchment reservoir at 0.3 m, 9 m, and 18 m (bottom). A farm irrigated with potable water was sampled and compared to areas of the same farm irrigated from the reservoir. Nematodes present in soil from the mountain and farms were root-knot (Meloidogyne spp.), lesion (Pratylenchus spp.), reniform (Rotylenchulus reniformis), stunt (Tylenchorhynchus sp.), ring (Criconema spp.), dagger (Xiphinema sp.), spiral (Helicotylenchus sp.), Tylenchus sp., Aphelenchus sp., and pin (Paratylenchus sp.) nematodes. The economically important genera Rotylenchulus, Meloidogyne, and Pratylenchus occurred in very low numbers (10, 41, and 10/250 cm³ soil, respectively) and in low frequency (10%, 25%, and 8% of the samples, respectively) in the mountain samples compared with high numbers (170-895/250 cm³ soil) from farms. Frequency of occurrence over all farms was near 40% for Meloidogyne and 80% for Rotylenchulus. No nematodes were detected in water from the reservoir. One sample from the outlets contained two specimens of plant-parasitic nematodes. The population densities of nematodes were not different between the soil samples collected from crops irrigated by potable or reservoir water.
Criconema; dagger nematode; Hawaii; Helicotylenchus; irrigation; lesion nematode; Meloidogyne; nematode; Paratylenchus; pin nematode; Pratylenchus; reniform nematode; ring nematode; root-knot nematode; Rotylenchulus; spiral nematode; watershed; Xiphinema
Meloidogyne incognita and M. arenaria reproduction and host plant tolerance were assessed in field and greenhouse experiments on seven holly cultivars including Ilex glabra 'Shamrock', I. vomitoria 'Schelling's Dwarf', I. cornuta 'Carissa', red holly hybrid (Ilex Little Red™), and I. crenata 'Compacta', 'Green Luster', and 'Helleri' as well as Japanese boxwood (Buxus microphylla) and two lantana cultivars (Lantana camara 'Miss Huff' and 'New Gold'). Boxwood had the highest M. arenaria and M. incognita gall rating of any of the plants evaluated. Gall ratings from M. arenaria and M. incognita on I. crenata 'Green Luster' and 'Helleri' were not different from boxwood. Ilex crenata 'Compacta' had less root galling than boxwood, but the roots averaged up to 20% galling by M. incognita and 30% galling by M. arenaria. Ilex glabra 'Shamrock', I. vomitoria 'Schelling's Dwarf', I. cornuta 'Carissa', Ilex Little Red™, and the two lantana cultivars had little or no root galling after 2 years of growth. Neither M. incognita nor M. arenaria affected the growth of any of the plants evaluated in the field or greenhouse. Reproduction of M. incognita was much lower than that of M. arenaria on the holly cultivars. Nematode reproduction in the greenhouse was greatest on the three I. crenata cultivars, followed by Ilex Little Red™ and B. microphylla. Ilex glabra 'Shamrock', I. vomitoria 'Schelling's Dwarf', I. cornuta 'Carissa', and L. camara 'Miss Huff' and 'New Gold' could be useful as Meloidogyne-resistant landscape plants.
boxwood; Buxus microphylla; holly; Ilex; Lantana; Meloidogyne arenaria; Meloidogyne incognita; ornamental; perennial; resistance; root-knot nematode