Several potential cover crops were evaluated for their susceptibility to Meloidogyne arenaria race 1, M. incognita race 1, and M. javanica in a series of five greenhouse experiments. No galls or egg masses were observed on roots of castor (Ricinus communis), cowpea (Vigna unguiculata cv. Iron Clay), crotalaria (Crotalaria spectabilis), or American jointvetch (Aeschynomene americana). Occasional egg masses (rating ≤1.0 on 0-5 scale) were observed on marigold (Tagetes minuta) in one test with M. incognita, on sesame (Sesamum indicum cv. Paloma) in a test with M. arenaria, and on sunn hemp (Crotalaria juncea cv. Tropic Sun) in 1 of 2 tests with M. incognita; otherwise, these crops were free of egg masses. Numbers of second-stage juveniles (J2) hatched from eggs per root system were low (≤10/pot) for the abovementioned crops. Egg-mass levels and numbers of hatched J2 of M. incognita on pearl millet (Pennisetum typhoides, Tifleaf II hybrid) were comparable to those on a susceptible tomato (Lycopersicon esculentum cv. Rutgers). In a test with M. arenaria, egg mass levels and numbers of J2 on Japanese millet (Echinochloa frumentacea) were similar to those on tomato. Japanese millet was susceptible to each of the nematode isolates tested. However, several of the crops evaluated were very poor hosts or non-hosts of the nematode isolates, including several legumes (cowpea, crotalaria, jointvetch, sunn hemp) that have potential use in both nematode and nitrogen management.
Aeschynomene americana; castor; cowpea; Crotalaria juncea; Crotalaria spectabilis; Echinochloa frumentacea; host-plant resistance; jointvetch; marigold; Meloidogyne arenaria; Meloidogyne incognita; Meloidogyne javanica; millet; nematode; nematode management; Pennisetum glaucum; Pennisetum typhoides; Ricinus communis; sesame; Sesamum indicum; sunn hemp; sustainable agriculture; Tagetes minuta; Vigna unguiculata
The effects of abamectin B1, diazinon, and methiocarb insecticides on Aphelenchoides fragariae and Ditylenchus dipsaci in Lamium maculatum, Phlox subulata, Rhododendron indicum, and Begonia × tuberhybrida were determined in a series of greenhouse experiments. Abamectin at 0.005 or 0.011 g a.i./liter (0.3 or 0.6 ml/liter Avid 0.15 EC), diazinon at 0.62 or 1.87 g a.i./liter (2.6 or 7.8 ml/liter KnoxOut GH), or methiocarb at 3.5 g a.i./liter (4.7 g/liter Mesurol) were applied in two to six weekly or biweekly applications to foliage until runoff. Diazinon and abamectin reduced both A. fragariae and D. dipsaci populations in Lamium and Phlox, especially after repeated applications. Diazinon was generally more effective than abamectin. While methiocarb reduced A. fragariae densities in Lamium, it was not as efficacious as diazinon or abamectin. Nematode populations varied widely between host plant species and over time. Management of high nematode populations was difficult, and none of the materials tested was effective against A. fragariae in azalea or begonia. Both abamectin and diazinon are currently registered for insect control in ornamentals and may be combined with cultural control tactics to manage foliar nematodes.
abamectin; Aphelenchoides fragariae; avid; azalea; begonia; diazinon; Ditylenchus dipsaci; KnoxOut; Lamium maculatum; Mesurol; methiocarb; nematicide; nematode; Phlox subulata; stem and bulb nematode
Tests of eight Dutch Meloidogyne chitwoodi isolates to the differential set for host races 1 and 2 in M. chitwoodi provided no evidence for the existence of host race 2 in the Netherlands. The data showed deviations from expected reactions on the differential hosts, which raised doubts of the usefulness of the host race classification in M. chitwoodi. The term ''pathotype'' is proposed for groups of isolates of one Meloidogyne sp. that exhibit the same level of pathogenicity on genotypes of one host species. We recommend that the pathotype classification be applied in pathogen-host relationships when several genotypes of a Meloidogyne sp. are tested on several genotypes of one host species. Three pathotypes of M. chitwoodi were identified on Solanum bulbocastanum, suggesting at least two different genetic factors for virulence and resistance in the pathogen and the host species, respectively. The occurrence of several virulence factors in M. chitwoodi will complicate the successful application of resistance factors from S. bulbocastanum for developing resistant potato cultivars.
biotype; Daucus carota; host race; intraspecific variation; Medicago sativa; Meloidogyne chitwoodi; nematode; pathogen-by-host interaction; pathotype; resistance; root-knot nematode; Solanum bulbocastanum; virulence
The effect of amending soil held at 3 different moisture levels with glucose, unsulfured molasses, or nutrient broth (0.3, 0.7, 3.2, 7.1 g carbon/100 g) on Tylenchorhynchus claytoni and T. dubius was investigated. When soil was held under saturated or flooded conditions in the absence of carbon amendments for 7 days, Tylenchorhynchus populations were 19% and 16%, respectively, of the controls. Carbon amendments at all levels tested precipitated a further decline in the nematode population to 1% or less of the unamended controls in 7 days. Two applications of molasses (7.4%, w/w) 3 days apart to nematode-infested soil held in Conetainers under mist for 7 days reduced Tylenchorhynchus spp. and Hoplolaimus galeatus densities to 7% and 3%, respectively, of the controls. Nematode densities in turfgrass field plots also declined following irrigation and repeated drenching with a molasses solution. Based on the observed decline in redox potential and pH in saturated soil, especially following carbon amendment, we propose that the activity of anaerobic fermentative bacteria was responsible for the reduction in nematode densities.
carbon; Hoplolaimus galeatus; moisture; molasses; nematode; pH; redox; Tylenchorhynchus claytoni; Tylenchorhynchus dubius
The influence of host cultivar on the lipid levels provided by a female to her progeny was investigated with Oil Red O stain and a quantitative image analyzer. A population of Globodera rostochiensis was multiplied at Toralapa Field Station in Bolivia on 25 different potato cultivars grown in that country. The mean neutral lipid content of newly formed second-stage juveniles varied significantly with cultivar over a 200% range. The corresponding range was only 18% and 28% for the same Bolivian and a UK population of G. rostochiensis, respectively, when both completed reproduction concurrently on 10 pot-grown European cultivars in the United Kingdom. Egg numbers per female varied with host for Bolivian cultivars that lack known partial resistance to Globodera spp. There was a 15-fold range between the most and least fecund nematode-host combinations (Kosi and Gendarme). The Bolivian G. rostochiensis population showed only a 2-fold range in mean eggs per cyst when grown on European cultivars in the UK. The fatty acid profiles of lipids from Bolivian G. rostochiensis cysts reared on Bolivian potato cultivars were dominated by C20 (37-64%) and C18 (28-46%) fatty acids and ranged from C14 to C22. The three major fatty acids detected were C20:4:, C20:1, and C18:1. Few differences between cultivars were observed. For a UK population of G. rostochiensis reared on ssp. tuberosum, higher relative percentages of C18 and monounsaturated fatty acids and lower relative percentages of C20 and polyunsaturated fatty acids were found.
Bolivia; fatty acid; fecundity; Globodera rostochiensis; lipids; nematode; neutral lipid; Oil Red O; potato; potato cyst nematode
A simple extraction method was developed for obtaining the white tip nematode, Aphelenchoides besseyi Christie, from single seeds of rice, Oryza sativa. The method was as follows: Individual rice seeds were split longitudinally and then transferred into single pipet tips. Tips containing a split seed were then singly placed upright in glass vials with water to extract the nematodes. This method was more efficient than the Baermann funnel technique and allowed nearly 100% recovery of living A. besseyi from single rice seeds within 4 hours.
Aphelenchoides besseyi; assay; extraction; methodology; nematode; nematode load; Oryza sativa; rice; white tip disease
Two hundred eighty-two soybean cultivars from the variety testing programs of Arkansas and Mississippi were tested in greenhouse pot experiments during summer 1998 to identify soybean cultivars with resistance to the reniform nematode, Rotylenchulus reniformis. Also included in the tests were the resistant cultivars Forrest and Hartwig, the susceptible control Braxton, and fallow infested soil, which were used as controls. Numbers of reniform nematode extracted from the soil and roots and the ratio of the numbers reproducing on each cultivar compared to the number reproducing on Forrest are reported. Cultivars with reproduction not significantly different from Forrest were classified resistant, whereas those with greater reproductive indices were considered susceptible. One of the 18 cultivars of relative maturity group (RMG) ≤4.4 was classified as resistant. For the 86 cultivars of RMG 4.5-4.9, 18 were found to be resistant. Of the 43 cultivars of RMG 5.0-5.4, 16 were resistant, while 43 of the 91 cultivars of RMG 5.5-5.9 were resistant. Fifteen of the cultivars with an RMG of ≥6.0 were classed as resistant. These data will be useful in the selection of soybean cultivars to use in rotation with cotton to help control the reniform nematode.
Glycine max; nematode; reniform nematode; reproductive index; resistance; rotation; Rotylenchulus reniformis; soybean; susceptibility
We determined the effects of crop residue on the persistence of an entomopathogenic nematode, Steinernema carpocapsae. During 2 consecutive years, nematodes were applied at rates of 2.5 × 10₄ and 1.0 × 10⁵ infective juveniles/m² to small field plots planted with corn. Nematode persistence was monitored by exposing Galleria mellonella larvae to soil samples from plots with and without crop residue (approximately 75% coverage of soybean stubble). Persistence of S. carpocapsae was significantly greater in crop residue plots than in plots without residue. In crop residue plots that received the higher rate of nematode application, larval mortality did not significantly decrease during the study period (3 to 5 days) and remained above 85%. In nematode-treated plots without crop residue, however, larval mortality fell from over 96% to below 11% and 35% in the first and second trials, respectively. The increased crop residue may have benefited nematode persistence through protection from desiccation or ultraviolet light. We conclude that increased ground cover in cropping systems (e.g., due to reduced tillage) may lead to increased insect pest suppression with entomopathogenic nematodes.
crop residue; entomopathogenic nematodes; mulch; nematode; Steinernema carpocapsae; survival; tillage
The free-living marine nematodes Leptosomatides brevicaudatus n. sp. and L. marinae were described and redescribed, respectively, from material collected in the northwest Pacific. Leptosomatides brevicaudatus n. sp. from Simushir Island differs from L. marinae in the ratio c8 (body length divided by tail length measured on the chord) and the length of the spicules. Leptosomatides marinae is redescribed from light microscopy (LM) observations of the type specimens and LM and scanning electron microscopy (SEM) observations of specimens from Hokkaido, Japan. It appears to be impossible to distinguish among some species of Leptosomatides because they are either insufficiently described or known only from females. Secondary sexual characters of males are essential for purposes of identification.
Leptosomatides brevicaudatus; Leptosomatides marinae; marine nematode; nematode; new species; SEM observation; subventral supplement; taxonomy
Three field trials were conducted to determine response of Meloidogyne javanica to tomato cultivars containing the Mi gene for resistance in sequential tests. Trials were conducted in spring and fall 1997 and spring 1998 on the same site. Tomatoes were grown on polyethylene mulch at a site initially treated with methyl bromide and then infested with M. javanica via drip tubing. Cultivars with the Mi gene were 'PSR 8991994' and 'Sanibel', and susceptible cultivars were 'Colonial' and 'Agriset 761'. The resistant cultivars greatly suppressed root galling in the three tests. Population densities of second-stage juveniles also were low in soil samples collected from resistant cultivars. Tomato fruit yields were significantly increased in only one test when using resistant cultivars. However, the susceptible cultivars are high-yielding and recommended for north Florida production, while the cultivars containing the Mi gene are not as well adapted. In the three successive crops, no evidence of resistance-breaking biotypes of M. javanica was observed. With further incorporation into adapted cultivars, the Mi gene resistance could be a valuable tool to manage M. javanica in north Florida stake tomato production.
Lycopersicon esculentum; Meloidogyne javanica; Mi gene; nematode; resistance; root galling; root-knot nematode; tomato
Two pot experiments, in consecutive years, were conducted under outdoor conditions during the wheat growing season to examine the relationship between increasing initial population densities (Pi: 0-3,000 cysts/pot) of Heterodera avenae and corresponding responses of wheat cv. Yecora Rojo. Results of both experiments were very similar. The nematode suppressed plant height, root and biomass dry weights, and grain yield at all Pi's studied. The suppression of these parameters, as well as the final nematode population densities (Pf), increased with increasing Pi levels. The reproduction factor (Pf/Pi) decreased as Pi increased but was always greater than 1.0. When data from both experiments were combined for regression analyses, inverse relationships were found between log10 (Pi + 1) and both plant growth and yield. These negative relationships were highly significant and adequately described by linear models. Final population (Pf) increased linearly with Pi. The wheat cultivar cv. Yecora Rojo was found to be highly vulnerable to damage and a good host for H. avenae.
cereal cyst nematode; growth; Heterodera avenae; nematode; pathogenicity; reproduction; reproduction; Triticum aestivum; wheat; yield
Field microplot, small plot, and greenhouse experiments were conducted to determine the effects of rotation crops on Pratylenchus penetrans, Meloidogyne hapla, and Rhizoctonia fragariae populations. Extraction of P. penetrans from roots and soil in microplots and field plots planted to rotation crops was highest for Garry oat, lowest for Triple S sorgho-sudangrass and Saia oat, and intermediate for strawberry, buckwheat, and canola. Isolation of R. fragariae from bait roots was highest for strawberry and canola after 2 years of rotation and lowest for Saia oat. Nematode extraction from roots of rotation crops in field soils was generally higher than from roots in microplots. Grasses were nonhosts of M. hapla. Strawberry, canola, and buckwheat supported root-knot populations over time, but there were no differences in nematode numbers regardless of crop after one season of strawberry growth. Garry oat, canola, and, to a lesser extent, buckwheat supported large populations of P. penetrans without visible root symptoms. Strawberry plants supported fewer nematodes due to root damage. Nematode numbers from soil were less than from roots for all crops. While there were similar trends for pathogen recovery after more than 1 year of strawberry growth following rotation, differences in pathogen density and fruit yield were not significant. In the greenhouse, P. penetrans populations in roots and soil in pots were much higher for Garry oat than for Saia oat. Total P. penetrans adult and juvenile numbers per pot ranged from 40 to 880 (mean = 365.6) for Garry oat and 0 to 40 (mean = 8.7) for Saia oat. Production of Saia oat as a rotation crop may be a means of managing strawberry nematodes and black root rot in Connecticut.
black root rot; buckwheat; canola; crop rotation; Fragaria × ananassa; lesion nematode; Meloidogyne hapla; nematode; oat; Pratylenchus penetrans; Rhizoctonia fragariae; sorgho-sudangrass; strawberry
Globodera millefolii and G. artemisiae are interesting because their type localities (Estonia and Russia, respectively) are geographically distant from those of the potato cyst nematodes and other Globodera species that seem to have originated in the Western world, and because the type host for each is a member of Compositae rather than Solanaceae. Sequence data for ITS1, ITS2, and 5.8S ribosomal DNA (ITS rDNA) for G. millefolii and G. artemisiae were nearly identical to sequence data for Cactodera salina from the rhizosphere of the estuary plant Salicornia bigelovii in Sonora, Mexico. The ITS rDNA sequences of these three species were all about 94% similar to those of two other Cactodera species for which ITS rDNA data were obtained. Phylogenetic analysis indicated that, based on the ITS rDNA data, G. millefolii and G. artemisiae are more closely related phylogenetically to the Cactodera species than to other nominal Globodera species. The molecular data further suggest that the genus Cactodera may comprise two or more morphologically similar but separate groups.
Cactodera; Cactodera salina; Globodera; Globodera artemisiae; Globodera millefolii; ITS1; ITS2; nematode; phylogenetic analysis; ribosomal DNA; rDNA; 5.8S gene
Seven populations of Heterodera trifolii from Arkansas, Kentucky, Pennsylvania, and Australia plus 3 or 4 single-cyst isolates (SCI) from each population were tested for reproduction on seven species of plants to compare the host preferences among and within populations. Common lespedeza, Kummerowia striata cv. Kobe, was a good host for all populations and isolates. Therefore, a plant was considered to be a host if the number of females produced on it was 10% or more of the number on Kobe. All seven populations reproduced on Trifolium repens and T. pratense. None reproduced on Beta vulgaris or Glycine max. One single-cyst isolate from the Australian population produced a few females on T. pratense. The Australian population maintained on carnation, Dianthus caryophyllus, produced females on carnation but not on curly dock, Rumex crispus. However, its subpopulation maintained on T. repens produced females on R. crispus but not on carnation. Four of the other six populations produced females on R. crispus, and four produced females on carnation. Differences in host range were observed among seven of the mother populations and their SCI, and among isolates within each population. Five host range patterns were found in populations and SCI of H. trifolii. Significant quantitative differences occurred among populations in the numbers of females on most hosts, between isolates and their original populations, and among isolates from the same population. SCI selected from white clover produced fewer females on a series of test hosts and had host ranges the same as or narrower than those of the original populations. However, SCI selected from Kobe lespedeza had more females on some hosts and had host ranges the same as or wider than those of the original populations. The host ranges of all populations and SCI of H. trifolii were different from those of populations and SCI of race 3 of H. glycines and H. lespedezae.
clover cyst nematode; Heterodera glycines; Heterodera lespedezae; Heterodera trifolii; host-parasite interaction; host range; nematode
The effects of Pratylenchus vulnus on growth and nutrition of Cadaman peach and Ishtara and Julior plum rootstocks were evaluated in a microplot experiment lasting two growing seasons. Cadaman peach was the only rootstock that showed suppressed growth for all growth parameters at the end of the first year. At the end of the second growing season, dry and fresh shoot weights as well as shoot length and root weights of Cadaman peach were reduced in nematode-inoculated microplots in comparison to uninoculated treatments. Stem diameter was not affected. Dry and fresh shoot weights were the only growth parameters affected by the nematode in Ishtara plum at the end of the second growing season, whereas Julior was not affected by P. vulnus infection. No nutrient deficiencies were detected by foliar analysis in any of the rootstocks and treatments. All the tested rootstocks were good hosts for P. vulnus, whose mean root population ranged from 1,670 (Cadaman) to 2,895 (Julior) nematodes/g of root.
nematode; nutrients; pathogenicity; peach; plum; Pratylenchus vulnus; Prunus; rootstocks; root-lesion nematode; tolerance
The suppression of Meloidogyne incognita by marigolds differed among six marigold cultivars and five soil temperatures. Tagetes signata (syn. T. tenuifolia) cv. Tangerine Gem and the Tagetes hybrid Polynema allowed reproduction and root galling when grown at 30 °C, and should not be used for control of M. incognita at temperatures close to 30 °C. Tagetes patula cultivars Single Gold and Tangerine and T. erecta Flor de Muerto, when grown within a 20-30 °C soil temperature range, significantly reduced root galling and nematode infestation of subsequent tomato compared to tomato following fallow. When grown at 10 °C or 15 °C, only one of the tested marigold cultivars (T. erecta CrackerJack at 15 °C) reduced M. incognita infection of subsequent tomato compared to tomato after fallow. Marigolds should be grown at soil temperatures above 15 °C to suppress M. incognita infection of a subsequent crop.
marigold; Meloidogyne incognita; nematode; root-knot nematodes; suppression; Tagetes; temperature
Four procedures were compared in their efficacy to extract juveniles of Anguina agrostis from commercial grass seed. The procedures included those currently used by the state regulatory laboratories of Oregon and California, as well as new tests developed to determine juvenile viability for the phytosanitary certification of fumigated grass seed. Eleven seed lots of Agrostis tenuis (bentgrass) and Dactylis glomerata (orchardgrass) naturally infested with varying levels of juveniles of Anguina were individually analyzed. Only one procedure, a new live recovery test, yielded nematodes in all 11 samples and is recommended as the best method for use by regulatory agencies. In comparison, although the other three extraction procedures resulted in greater numbers of Anguina agrostis juveniles per gram of seed, they failed to yield any nematodes in as many as four seed lots with low infection levels.
Anguina agrostis; assay; bentgrass; extraction procedures; nematode; orchardgrass; phytosanitary certification; regulatory nematology; seed-borne nematodes; technique
The persistence of Heterorhabditis megidis in soil was studied over a 4-week period. On days 0, 2, 14, and 28, infective juveniles (IJ) were extracted by centrifugal flotation, Baermann funnel, and baiting of soil with Tenebrio molitor larvae, which were then dissected. Extraction efficiencies on day 0 were 82% by centrifugal flotation, 56% by Baermann funnel, and 19.8% by bait insect. The relative efficiency of the three methods changed over time. The relationship between the density of nematodes in the soil and the proportion recovered by dissection was non-linear. Up to a dose of approximately 60 IJ/insect, less than 12% became established, while at higher doses (up to 200 IJ/insect) the invasion efficiency was 23%. Mortality of bait insects increased from day 0 to day 2, but decreased to day 28. A novel method of assessing soil pathogenicity by preparing a soil density series and calculating the dose of soil or IJ that kills 50% of the bait insects gave a similar pattern. This method is recommended as a means of tracking changes in pathogenicity over time when bait insect mortality in undiluted soil is at or near 100%. Two methods of preparing a series of Heterorhabditis IJ densities in soil, either by diluting the soil itself with IJ-free soil or by adding diluted suspensions of IJ to the soil, resulted in the same bait insect mortalities.
Baermann funnel; centrifugal flotation; dissection; entomopathogenic nematode; Heterorhabditis bacteriophora; Heterorhabditis megidis; infectivity; LD50; nematode; persistence; soil baiting; soil dilution; soil ecology; soil extraction
The activity of steinernematid entomopathogenic nematodes against Choristoneura rosaceana was evaluated under laboratory and field conditions. In petri dish trials, all instars were susceptible to Steinernema carpocapsae AII strain with LD50 values of 13, 5, 3, and 2 infective juveniles for the third-, fourth-, fifth-, and sixth-stage larvae, respectively. Steinernema riobrave 335, S. feltiae UK, S. carpocapsae AII, and S. glaseri 326 caused 85, 55, 45, and 8% mortality of third instars when exposed to the concentration of 25 infective juveniles per dish. When third instars were exposed to S. carpocapsae AII for 0, 1, 4, 8, 12, and 24 hours, larval mortality was 12, 13, 21, 47, 64, and 87%, respectively. At least 8 hours' exposure was required to cause a significant increase in mortality when compared with the control (water) and the 1 and 4-hour exposures. None of the tested adjuvants provided a significant improvement in the average total number and the average number of living S. carpocapsae AII per unit leaf area when compared to the water control. Under field conditions, foliar applications of S. carpocapsae AII at the rate of 2 × 10⁹ infective juveniles/ha provided 37, 19, and 13% larval control. At present, efficacy level and treatment cost preclude nematode applications as a sole treatment against this pest.
apple; biological control; Choristoneura rosaceana; entomopathogenic nematode; field; foliar application; Lepidoptera; oblique banded leafroller; Steinernema carpocapsae; S. feltiae; S. glaseri; S. riobrave; Tortricidae
Two new species of Actinolaimidae are described from China. Trachactinolaimus brevicaudatus n. sp. is 3.4-4.4 mm long; a = 40-60, b = 3.5-5.2, c = 20-21 in female and 34-39 in male; odontostyle length is 29-33 µm; spicules are 67-77 µm long; and the stoma has four onchia with numerous mural denticles. The female has a longitudinal vulva, and the male has 20 to 23 contiguous ventromedian supplements. Egtitus sinensis n. sp. is 1.7-2.2 mm long; a = 24-33, b = 3.1-3.9, c = 16-19 in female and 0.7-0.9 in male; odontostyle length is 25-29 µm; spicules are 55-56 µm long; and the prerectum 53-77 µm long. The cardia is short and blunt conoid, 13-19 µm long. The male has 12 to 13 ventromedian supplements at intervals of 2-3 µm.
Actinolaimidae; China; Dorylaimida; Egtitus sinensis; nematode; new species; taxonomy; Trachactinolaimus brevicaudatus
Chitin was used as soil amendment in fiberglass field microplots, alone or with one or a combination of two to three species of Hirsutella rhossiliensis, Paecilomyces marquandii, Verticillium chlamydosporium, Bacillus thuringiensis, and Streptomyces costaricanus. Sudangrass and rapeseed were planted as cover crops and incorporated into soil as green manure amendments. Chitin amendment alone increased the marketable yield of lettuce in 1995 and reduced root-galling ratings and the reproduction of Meloidogyne hapla in both 1995 and 1996. Green manure amendments of sudangrass and rapeseed increased total and marketable yields of lettuce, and decreased root-galling ratings and the reproduction of M. hapla in 1996. Hirsutella rhossiliensis in combination with chitin increased total yield of lettuce over the chitin amendment alone in 1995. The combination of B. thuringiensis, S. costaricanus, and chitin either with or without P. marquandii increased total yield of lettuce over the chitin amendment alone in 1996. In most cases, however, the nematode-antagonistic organisms did not improve lettuce yield or further suppression of M. hapla compared to the chitin amendment alone. The introduced fungi were recoverable from the infested soil. The rifampicin-resistant mutant of B. thuringiensis was not isolated at the end of the season.
Bacillus thuringiensis; biological control; chitin amendment; cover crop; green manure; Hirsutella rhossiliensis; Lactuca sativa; Meloidogyne hapla; nematode; northern root-knot nematode; Paecilomyces marquandii; Streptomyces costaricanus; Verticillium chlamydosporium
The effect of crop sequence on parasitism of second-stage juveniles (J2) of Heterodera glycines by Hirsutella rhossiliensis was investigated. Data were collected from plots of a long-term crop rotation experiment established in 1982. Crop sequences included (i) continuous monoculture of corn and soybean; (ii) annual rotation of the two crops; and (iii) 1, 2, 3, 4, or 5 years of each crop following 5 years of the other crop. The nematode J2 density and percentage of J2 parasitized by the fungus were determined at planting, midseason, and end of season in 1997 and 1998. A significant effect of the crop sequence on parasitism of J2 was observed at midseason in both years and at end of season in 1998. In plots of first-year soybean following 5 years of corn, fungal parasitism increased from an undetectable level at planting to 2% and 4% of J2 parasitized by ends of season in 1997 and 1998, respectively. Fungal parasitism was similar in plots of second-through-fifth-year soybean after 5 years of corn and in plots of soybean monoculture. Parasitism of J2 in the soybean plots in annual rotation with corn increased from undetectable and 2% at planting to 6% and 23% at midseason in 1997 and 1998, respectively. The effect of crop sequence on the fungal parasitism of J2 may be attributed to a density-dependent relationship between the parasite and its host. Season also affected the fungal parasitism; percentage of J2 parasitized by the fungus was the highest at midseason and the lowest at planting.
biological control; corn; crop rotation; crop sequence; Glycine max; Heterodera glycines; Hirsutella rhossiliensis; nematode; nematophagous fungus; soybean; soybean cyst nematode; Zea mays
The nematicide fosthiazate was evaluated over a 3-year period for management of Meloidogyne incognita race 3 (site 1) and M. arenaria race 2 (site 2) in flue-cured tobacco. Fosthiazate was applied broadcast and incorporated at rates ranging from 22 to 88 g a.i./100 m², and compared with the nematicides fenamiphos (67 g a.i./100 m²), 1,3-D (56.1 L/ha, 670 ml/100-m row), and an untreated control. Root-gall indices and leaf yields were averaged over the 3-year period. Root galling was negatively correlated in a linear relationship with fosthiazate application rate at sites 1 and 2. Leaf yields were positively correlated with fosthiazate application rate at site 1 and could be described by a quadratic equation. Leaf yields were greater at 33 and 88 g a.i./100 m² application rates (site 2) than the untreated control. Leaf yields in fosthiazate (88 g a.i./100 m²)-treated plots infested with M. incognita or M. arenaria were not different from plots fumigated with 1,3-D. Plants in plots with fosthiazate applied in a row band (1993) had a lower root-gall index than those in plots with the same rate of fosthiazate applied broadcast. Fosthiazate may provide an alternative to fumigation for control of M. incognita and M. arenaria.
1,3-D; fenamiphos; fosthiazate; Meloidogyne arenaria; Meloidogyne incognita; nematicide; nematode; root-knot nematode; tobacco
Bioengineering strategies are being developed that will provide specific and durable resistance against plant-parasitic nematodes in crops. The strategies come under three categories: (i) transfer of natural resistance genes from plants that have them to plants that do not, to mobilize the defense mechanisms in susceptible crops; (ii) interference with the biochemical signals that nematodes exchange with plants during parasitic interactions, especially those resulting in the formation of specialized feeding sites for the sedentary endoparasites—many nematode genes and many plant genes are potential targets for manipulation; and (iii) expression in plant cells of proteins toxic to nematodes.
cystatins; enzyme inhibitors; giant cells; hypersensitivity; lectins; natural resistance genes; nematodes; nematode genes; nematode-induced promoters; plant defense; plant genes; syncitia; synthetic resistance; toxins; transformation; transgenic plants