Three new species of Bunonematidae (Bunonema husseyi, Rhodolaimus dimorphus, R. stephaniae) and one of Plerygorhabditidae (Pterygorhabditis panoplus) are described from Georgia and Tennessee. The juvenile external morphology of P. panoplus is described and illustrated. A lectotype of P. pakistanensis is designated and the two species compared, and the dissimilar nature of cuticular tubercles in Bunonema and Rhodolaimus is discussed.
Bunonema; Rhodolaimus; Pterygorhabditis; microbivores; taxonomy
Of 12 stylet-bearing nematodes used for inoculations, Pratylenchus penetrans, P. brachyurus, P. vulnus, Ditylenchus destructor, Meloidogyne incognita, M. javanica, and M. hapla reproduced on Pinus ponderosa, while Xiphinema index, Aphelenchus avenae, Paratylenehus neoamblycephalus, Tylenchulus semipenetrans, and Macroposthonia xenoplax did not. P. vulnus, P. brachyurus, P. penetrans, A. avenae, D. destructor, T. semipenetrans, and P. neoamblycephalus significantly suppressed both the shoot and root wet weights of ponderosa pine seedlings obtained from stands in five different locations. X. index significantly suppressed root wet weights, M. xenoplax siguificantly suppressed shoot wet weight, and M. incognita, M. javanica, and M. hapla suppressed neither at the inoculation levels used. Injurious nematodes tended to suppress root growth more than shoot growth. Seedlings from two locations produced greater shoot growth wet weight than did seedlings from the other three locations. The more injurious nematodes tended to cause an increase in the water content of shoots. Frequency analyses of seedling population shoot-root ratios indicated that ponderosa pine seedlings could be selected for better shoot-root ratios as well as for resistance to several pathogenic nematodes.
A tetraploid single-cyst isolate of Heterodera glycines from a field population from Indiana has been propagated in the greenhouse on Lee soybeans since its discovery, in 1973. The tetraploid isolate has n = 18 chromosomes, compared with n = 9 of the diploid H. glycines; it has larger cysts and larvae, but shows the same level of parasitism and host range as the diploid population from which it apparently evolved. Association of chromosomes is irregular at metaphase I, with quadrivalents, trivalents, and univalents often observed in addition to the bivalents. The second maturation division is usually normal. About 80% of the mature oocytes (just before fertilization) have n = 18, and the other 20% have n = 17 or 19. Reproduction of the tetraploid isolate is exclusively by cross-fertilization. The discovery of such a tetraploid provides an experimental tool for the study of polyploidy in nematodes. Many amphimictic plant-parasitic nematodes are suspected of representing polyploids.
soybean cyst nematode; crossfertilization
Seedlings of Corchorus capsularis (cv. C4444) were inoculated with Meloidogyne incognita, Hoplolaimus indicus, and a fungus pathogen of jute, Macrophomina phaseoli, separately and in all possible combinations. The significant damage of jute plants caused individually by the pathogens was aggravated when the fungus was associated with either of the nematode species. M. incognita alone caused greater damage than either H. indicus or Macrophomina phaseoli alone. Plants inoculated with M. incognita and Macrophomina phaseoli were more severely damaged than plants inoculated with H. indicus and the fungus. Plant growth was minimum and disease symptoms were maximum when all pathogens acted together. In the presence of the fungus, M. incognita produced fewer galls. The reproduction of H. indicus was not influenced by the other organisms.
Heterodera canadensis n. sp. is described and illustrated from the roots of spike-rush, Eleocharis acicularis (L.) R. &S., in Deschenes, Quebec. This new abullate species is related to Heterodera graminophila Golden and Birchfield, 1972, but differs significantly in cyst shape, cone top structures, body length of the second-stage larva (520-600 μm, vs. 380-400 for H. graminophila) and tail length (110-120 μm, vs. 57-67 for H. graminophila). A taxonomic key based on cyst and second-stage larva characters is provided for identification of the fifteen species in the Heterodera goettingiana group.
Nematode taxonomy; morphology
Negative charges on the outer cuticular surface of Meloidogyne javanica females were visualized with electron microscope labelling techniques. Evidence is presented that the electronegative charge is not borne on neuraminic acid. Ruthenium red staining indicated acid mucopolysaccharides on the outer surface. A surface coat, or glycocalyx, external to the outer cuticle membrane was demonstrated.
ferritin labelling; Ruthenium red staining; cuticle surface negative charge
Two new species of plant-parasitic nematodes from Costa Rica are described. Helicotygenchus styloeercus n. sp., from soil around roots of banana at Coto, is distinguished hy the female tail, which bears a large pillarlike ventral projection. Rotylenchus phaliurus n. sp., from soil artmnd roots of Dioscoroea sp. at Sixaola, differs from R. caudaphasmidius in having the conus equal to or more than half the spear length, and large terminal annules on the female tail.
Nematode taxonomy; spiral nematodes; yam; banana
Mesomermis camdenensis n. sp. is described from larvae of Simulium tuberosum (lundstroem) collected in Camden Valley Creek, Washington County, New York. This species possesses a barrel-shaped vagina, vulval flap. two short separate spicules, terminal mouth, six longitudinal chords, six cephalic papillae, large sexually dimorpbic anaphids, an esophagns of uniform width which extends for less than one-third of the body length, and a cone-shaped tail directed ventrally without appendage. Juveniles also are described and illustrated.
A detailed morphological comparison with the mermithid M. flumenalis Welch is presented. The most pronounced morphological differences between these species are in the shape of the vulva, juvenile tail, and infective stage. Cross-mating trials support the integrity of the new species.
The life cycle of M. camdenensis is closely synchronized with that of its primary host, S. tuberosum larvae. Infected S. tuberosum larvae were first collected in May. Emergence of postparasites from late instars took place from mid-June through mid-October. Sampling data indicate a lower susceptibility to infection among S. venuslum Say larvae.
taxonomy; bionomics; Mesomermis spp.; Simulium tuberosum
Soil application of DBCP (l,2-dibromo-3-chloropropane) and foliar applications of oxamyl (methyl N',N'-dimethyl-N-[(methylcarbamoyl)oxy]-l-thiooxamimidate) were compared for control of Tylenchulus semipenetrans in a grapefruit (Citrus paradisi) orchard, DBCP reduced nematode populations and increased fruit growth rate, fruit size at harvest, and yield compared to the untreated controls in the 2 years following treatments. Foliar applications of oxamyl reduced nematode populations and increased fruit growth rate slightly the first year, but not in the second. Foliar applications of oxamyl did not improve control attained by DBCP alone. Soil application of aldicarb [2-methyl-2-(methylthio)propionaldehyde-O-(methylcarbamoyl)oxime] or DBCP to an orange (C. sinensis) orchard reduced T. semipenetrans populations in the 3 years tested and increased yield in 1 of 3 years. Aldicarb treatment reduced fruit damage caused by the citrus rust mite, Phyllocoptruta oleivora. Aldicarb, applied at 5.7 or 11.4 kg/ha, by disk incorporation or chisel injection, was equally effective in controlling nematodes, improving yields, fruit size, and external quality. In a grapefruit orchard, chisel-applied aldicarb reduced nematode populations and rust mite damage and increased yields in both years and increased fruit size in one year. The 11.4-kg/ha rate was slightly more effective than the 5.7-kg/ha rate. Aldicarb appears to be an adequate substitute for DBCP for nematode control in Texas citrus orchards and well-suited to an overall pest management system for Texas citrus.
citrus nematode; grapefruit; oranges; citrus rust mite; Phyllocoptruta oleivora
Greenhouse tests were conducted to determine the effects of two kinds of Meloidogyne hapla inoculum on the growth and quality of carrot roots, and the protection afforded in each case by nonfumigant nematicides in organic soils. For all treatments the percentage of carrots damaged was greater with larvae alone as inoculum than with larvae and eggs, indicating that most of the damage occurs early during formation of the taproot. Fosthietan, aldicarb, and oxamyl at 4 and 6 kg ai/ha protected the roots during formation and gave a lasting control of root-knot nematode. There was some nematode damage to the roots with phenamiphos and carbofuran at 4 and 6 kg ai/ha. Isazophos, diflubenzuron, and fenvalerate gave little protection to carrot roots and did not control root-knot nematode effectively.
Meloidogyne hapla; fosthietan; aldicarb; oxamyl; carbofuran; phenamiphos; isazophos; fenvalerate; diflubenzuron; chemical control
Histological responses to Meloidogyne incognita infection in Rhizobium nodules of clover, horsebean, lupine, and pea were investigated. The formation of giant cells in vascular bundles of nodules and roots, and the basal connection of the nodule, were usually associated with abnormal xylem and/or deformed xylem strands. However, giant cells did not disturb or prevent the development of nodular tissues. Areas in which galls formed, wall thickness of giant cells, and number of giant cells around the nematode head varied with plant species. Ranking by gall size and giant-cell wall thickness was horsebean > lupine and pea > clover. The multinucleate condition in giant cells resulted from repeated mitoses without subsequent cytokinesis. The resulting nuclei agglomerated in irregularly shaped masses in some giant cells.
Meloidogyne incognita; histopathology; pathogenesis; host-parasite relationship
Sixty-five soybean varieties were tested in the field for resistance to Rotylenchulus reniformis. Criteria for resistance or susceptibility were root necrosis, nematode recovery from roots and soil, and egg production. Nine varieties were resistant, 13 moderately resistant, 26 moderately susceptible, and 17 susceptible. Linear correlations between resistance rating and each assessment parameter were highly significantly positive, suggesting that any of the parameters could be used to identify resistance. There were also highly significant positive linear correlations between any two combinations of parameters, indicating that they were reciprocally related.
soybean resistance; screening; Rotylenehuhts reniformis; reniform nematode; assessment parameters; statistical correlations
A field study was made of the effects of a residual nematicide (phenamiphos), a fumigant (methyl bromide), and fallowing on the number of root lesion nematodes (Pratylenchus penetrans), forage yields of alfalfa, and the occurrence of Fusarium spp. in plant roots and soil. Fallowing controlled nematodes initially, but by the end of the second growing season, nematode numbers were as high as in plots which had grown a nematode-susceptible crop. Forage yield was greater in fallowed plots only for the first cut in the year after seeding. Fusarium in alfalfa roots and soil was not reduced by fallowing. Phenamiphos reduced nematode numbers, increased forage yields in 2 of 4 years, and reduced Fusarium infections of taproots. Soil fumigation with methyl bromide gave the best control of nematodes and Fusarium and gave significantly higher forage yields for the 4 years of study following fumigation. The 34% increase in alfalfa yield from fumigated plots over the 4 years indicates that the yield of alfalfa is being reduced significantly by microorganisms. The study does not establish the relative contributions of the root lesion nematodes and Fusarium spp. to the reduction.
alfalfa; root lesion nematode; population dynamics; control; nematode-fungus-host interaction
Attempts to develop defined in vitro culture systems for the growth, reproduction and development of free-living nematodes have yielded much basic information about their nutritional requirements and biochemistry. Requirements for sterol and heme have been identified suggesting that some nematodes lack de novo synthesis of these molecules. Possible pathways of metabolism of these nutritional requirements can be derived from in vitro experiments that use a variety of sterol and heine sources as supplements to the culture mediuin. These pathways are reviewed as well as the possible role of sterol and heme in the biology of free-living and parasitic nematodes, Since these molecules must be acquired dietarily, the possible involvement of lysosomal enzymes in digestion is discussed. Also considered is the possibility that lysosomal enzymes change when nematodes are fed on a heine protein source.
Hemoglobin; cholesterol; cathepsin D; acid protease; free-living; plant and animal parasitic nematodes
The influences of a vesicular-arbuscular mycorrhiza (Glomus etunicatus) and burrowing nematode (Radophohts similis), alone and in combination, on the growth of rough lemon (Citrus limon) seedlings were studied in the greenhouse. Growth of mycorrhizal seedlings was significantly greater than that of nonmycorrhizal seedlings or seedlings inoculated with R. sindlis. Mycorrhizal stimulation of seedling growth was inhibited by nematode infection. When seedlings were inoculated with G. etunicatus arid R. similis, suppression of seedling growth by R. similis was less on VAM seedlings than on nonmycorrhizal seedlings, Nonmycorrhizal seedlings infected with R. similis were significantly smaller than nonmycorrhizal seedlings free of R. similis. Vesicle formation and mycelia growth were less in nematode-infected roots.
Endomycorrhizae; burrowing nematode; rough lemon
Greenhouse studies have shown that when rough lemon (Citrus limon) seedlings infected with TyIenchulus semipenetrans were transplanted into soil infested with Glomus mosseae, the mycorrhizal fungus infection increased seedling growth compared to nonntycorrhizal seedlings. Tylenchulus semipenetrans significantly suppressed seedling growth below that of mycorrhizal seedlings. Histological observations of nematode-free mycorrhizal roots showed that hyphae penetrated the epidermis and invaded the cortex, giving rise to arbuscules and vesicles. Nematode infection sites in T. semipenetrans-infected roots grown in soil infested with G. mosseae did not show evidence of vesicle development in the cortex but did show arbuscule development.
mycorrhizae; citrus nematode; rough lemon
There has been much work on plant-feeding nematodes, and less on other soil nematodes, their distribution, abundance, intrinsic properties, and interactions with biotic and abiotic factors. Seasonal variation in nematode fauna as a whole is correlated with factors such as moisture, temperature, and plant growth; at each site nematode distribution generally reflects root distribution. There is a positive correlation between average nematode abundance and primary production as controlled by moisture, temperature, nutrients, etc. Soil nematodes, whether bacterial feeders, fungivores, plant feeders, omnivores, or predators, all influence the populations of the organisms they feed on. Although soil trematodes probably contribute less than 1% to soil respiration they may play an important role in nutrient cycling in the soil through their influence on bacterial growth and plant nutrient availability.
ecology; energetics; microcosms; nutrient cycling; primary production
In a soil temperature study, population increase on 'Clark 63' soybeatt was most rapid at 30 C in Pratylenchus alleni, P. brachyurus, P. cofleae, P. neglectus, P. scribneri, and P. zeae and at 25 C in P. penetrans and P. vulnus. The last two were the only species that reproduced at 15 C. Populations of all species increased over the range of 20-30 C, except those of P. neglectus at 20 C and P. coffeae, which was not tested below 25 C. Only P. brachyurus, P. neglectus, P. scribneri and P. zeae reproduced at 35 C. At their optimum temperatures, P. scribneri exhibited the greatest population increase, 1248-fold, and P. penetrans the least, 32-fold. This is the first report of soybean as a host for P. vulnus.
Pratylenchus alleni; P. brachyurus; P. coffeae; P. neglectus; P. penetrans; P. scribneri; P. wtlnus; P. zeae; lesion nematodes; host-parasite relationships; ecology; susceptibility; Glycine max
The wave forms and activity patterns of Caenorhabditis elegans were examined on agar in the presence of known chemical attractants (NaCl) and repellents (D-tryptophan), and in thermal gradients. Total activity was reduced in both attractants and repellents. Different combinations of transfers between chemicals were investigated. Two thresholds were found for NaCl: 10-3 M NaC1 caused reduced activity; 10⁻⁵ M NaCl increased reversals. D- or L-tryptophan influenced neither orientation nor the ability of thermally acclimatized individuals to remain at their eccritic temperature.
Behaviour; wave patterns; movement; thermotaxis; chemotaxis; neurobiology
In healthy cotton, except for random occasional occurrence in cortical cells, terpenoid aldehydes (TA) are localized in the epidermis and, even there, are absent from the tip 2-4 cm of the root. Since constitutive TA do not occur in the endodermis and stele of the root, they cannot be effective agents against the development of the sedentary stage of the root-knot nematode, Meloidogyne incognita. Within 4 days after inoculation with the root-knot nematode, infection-induced TA accumulated in the endodermis and outer stele. These induced TA were thus localized where they could be effective against the sedentary stage of the nematode. Infection-induced TA accumulation was more rapid and occurred in more stele cells in a resistant cotton cultivar than in two susceptible cultivars.
TA extracts from cotton were inhibitory to nematode movement. All second-stage larvae exposed to 1,000 ppm TA for 3 h became rigid, made no movement, and appeared dead. Washing these larvae to remove the TA and incubating them for an additional 24 h did not change their appearance. Shorter exposure times or lower TA concentrations allowed some larvae to recover. Exposing larvae to 10 ppm of TA for 24 h had little effect on them. TA extracted from G. arboreum, a cotton that does not methylate TA, were slightly less inhibitory to the root-knot nematode than TA extracted front G. hirsutum which partially methylates TA.
Gossypol-like; resistance; gossypium; host-parasite interactions; toxicants; antibiotic compounds
Relative to nematicides with greater fuming capabilities, 1,2-dibromo-3-chloropropane (DBCP) moved nonuniformly through soil. DBCP concentrations in soil were reduced by low soil temperature and the presence of lime or roots within the soil profile, Applications by either water or chisel injection provided DBCP movement to 120 cm and below. Concentrations were least persistent in the upper 15 cm of the field surface and in one situation where application was not followed by irrigation. Values for Henry's Constant are reported for DBCP at a range of solution temperatures. Certain advantages and disadvantages of soil atmosphere sampling of DBCP are discussed.
degradation; soil temperature; sorption
Hyphae of Dactylella oviparasitica proliferated rapidly through MeIoidogyne egg masses, and appressoria formed when they contacted eggs. The fungus probably penetrated egg shells mechanically, although chitinase production detected in culture suggested that enzymatic penetration was also possible. In soil, D. oviparasitica invaded egg masses soon after they were deposited on the root surface and eventually parasitized most of the first eggs laid. Occasionally the fungus grew into Meloidogyne females, halting egg production prematurely. The fungus parasitized eggs in the gelatinous matrix or eggs freed from the matrix and placed on agar or in soil. Specificity in nematode egg parasitism was not displayed, for D. oviparasitica parasitized eggs of four Meloidogyne spp., Acrobeloides sp., Heterodera schachtii, and Tylenchulus semipenetrans. In tests in a growth chamber, parasitism by D. oviparasitica suppressed galling on M. incognita-infected tomato plants.
biological control; appressorium; chitinase; Heterodera schachtii; Tylenchulus semipenetrans