Studies on the structure of the cuticle of Tylenchorhynchus martini swarmers with electron microscopes revealed abnormal disruptive and eruptive morphological changes in most layers. Drastic effects of swarming on cuticular structure were reflected in the partial dissolution of cortical layer and matrix and in the irregular cracking of cortical sublayers in sublateral areas of the body. The occurrence of projections in the cortex was apparently unrelated to other changes. The structure of the cuticle of nonswarmers was intact and without any morphological changes.
swarming; cuticle; dissolution; cuticular projection
The effect of Tylenchorhynchus nudus on growth of Kentucky bluegrass was investigated under controlled environmental conditions in both a phytotron and a greenhouse. The nematode significantly reduced weights of clippings, crowns and roots. Pathogenicity was greater in sandy loam soil than in loam and was enhanced by submitting plants to nutrient and/or moisture stresses; soil nutrient level was most critical. The results suggest that T. nudus contributes significantly to summer decline of bluegrass lawns in South Dakota.
stunt nematode; soil moisture; soil fertility; soil type; Poa pratensis; pathogenicity
Two species of free-living nematodes, Panagrellus redivivus and Turbatrix aceti, were cultured axenically at control (20 C) and cold (10 C) temperatures. Oxygen consumption of worms from each population was measured manometrically on days 2 through 8 after exposure to these temperatures. In both species, the slope of the oxygen consumption curve for the controls was greater than that of the worms exposed to the cold on day 2. The slope of the curve of the cold-exposed worms gradually increased until day 7. At this time, the slope of the oxygen consumption curve from the cold-exposed worms exceeded or equaled that of the controls. This is taken as an indication of the onset of the cold-acclimated state in both species of worms by day 7.
A non-sodic, non-saline sandy loam soil was salinized to anion-cation ratios similar to those naturally occurring in Iraq and California. The interactions of saline soils (conductivities 4, 8, 12 and 16 mmhos/cm) with a moderately salt-tolerant plant (Lycopersicon esculentum 'Marimond') and a plant parasitic nematode (Meloidogyne javanica) were investigated. Plant parasitic nematodes were shown to be an important modifying influence within the plant environment, either accentuating or ameliorating salinity stress effects.
Criconemoides xenoplax and Meloidogyne incognita were the nematode species most frequently associated with peach in North Carolina. Other nematodes often found in high numbers on that crop were Pratylenehus vulnus, Helicotylenchus spp., Trichodorus christiei, Xiphinema amerieanum and Tylenchorhynchus claytoni. P. vulnus and P. penetrans reproduced well on rootstocks of 21 peach cultivars tested in the greenhouse. P. zeae, P. brachyurus, P. coffeae and P. scribneri decreased or increased only slightly in most instances. C. xenoplax increased as much as 330-fold and reproduced on all cultivars tested. In a field experiment with six peach cultivars and moderate numbers of P. brachyurus, P. vulnus, C. xenoplax, and M. incognita, only M. incognita caused significant stunting in 30 months. This nematode increased only on root-knot susceptible cultivars, whereas the other nematodes followed the same patterns observed in the greenhouse. In a second field experiment, seedlings were stunted significantly by high numbers of C. xenoplax during an 18-month period.
Crieonemoides xenoplax; Meloidogyne incognita; Pratylenchus vulnus; P. seribneri; P. coffeae; P. zeae; P. brachyurus
The pathogenic effects of Pratylenchus coffeae on growth and yield of tangelo (Citrus paradisi × C. reticulata) scions grafted on rough lemon (C jambhiri), sour orange (C. aurantium) and 'Cleopatra' mandarin (C. reticulata) rootstocks were evaluated under field conditions for 4 years. Pratylenchus coffeae on inoculated trees increased to significantly damaging population densities on rough lemon rootstock the second year, on sour orange the third and on Cleopatra mandarin the fourth year after planting. Mean growth reduction of P. coffeae-infected trees after 4 years was 80, 77 and 49%, respectively, for the three rootstocks. Noninoculated trees on rough lemon and sour orange rootstocks yielded significantly more fruit than comparable inoculated trees. Natural migration of P. coffeae occurred horizontally on roots for a distance of 4.5 m.
population densities; biology; nematode movement
Field populations of Xiphinerna americanum around roots of Syringa vulgaris 'President Lincoln' were larger in Marshall silty clay loam, a medially developed loess soil, than in Monona silt loam, a minimally developed loess soil. Most X. amerieanum occurred in the top 15 cm of soil, with few below 30 cm. Maximum numbers occurred in August of both years in the Marshall soil, and in August 1969 and June 1970 in the Monona soil. Population fluctuations during the growing season were coincident with changes in soil moisture content. Although the population fluctuation pattern was the same at each depth tested, the adult-to-juvenile ratio increased in one soil while it decreased in the other. Numbers of X. americanum decreased as root weights decreased within a soil profile, but they were not correlated with root weights over all soils and depths. More X. americanum were recovered from the Marshall than from the Monona soil, but fibrous root weights were greater in the Monona soil. Survival of X. americanum in soil columns in growth chamber experiments was better in the Marshall than in the Monona soil. Movement and survival were different in identically textured Monona A and B horizon soils. Factors related to the ion exchange sites may affect X. americanum.
cation exchange capacity; ions; movement
Host-parasite relationships of Meloidogyne incognita acrita and Pratylenchus penetrans were compared on three closely related cultivars of tomato: 'Nemared', resistant to root-knot nematodes; 'Hawaii 7153', moderately resistant; and 'B-5', susceptible. Root-knot nematode larvae induced typical galls on the roots of B-5; larvae that entered Nemared were walled-off by necrotic cells; both reactions occurred in Hawaii 7153. Lesion nematodes caused surface lesions which were initially similar on all cultivars. Five weeks after infection, they penetrated into the stele of the B-5 roots, whereas in Nemared and Hawaii 7153, injury was confined to the cortex. Chlorogenic acid was identified as the major phenofic compound in healthy tomato roots. Nemared contained the highest concentration of the acid and B-5 the lowest. Histochemical tests showed that chlorogenic acid was concentrated in the endodermis. The localized accumulation of chlorogenic acid and its oxidized products in host root cells infected by nematodes was concluded to be an important mechanism of resistance.
Lycopersicon esculentum; histochemistry; polyphenol oxidase
Two hundred thirty-five cultivated varieties, breeding lines and plant introductions of Arachis hypogaea and 12 accessions of wild Arachis spp. were tested for resistance to Meloidogyne hapla. Eight of the cultivated peanut lines were only moderately susceptible and four of the wild peanuts exhibited resistance. No resistance-breaking M. hapla populations were found among 10 geographical isolates tested.
northern root-knot nematode; Arachis hypogaea; Arachis spp.
The effect of soil water content on Rotylenchulus reniformis infectivity of 'Lee' soybean roots was investigated in an autoclaved sandy clay loam. Nematodes were introduced into soil masses maintained at constant soil water levels ranging from 3.4 to 19% by weight. Seedling growth and the soil water content-water potential relationships of the soil were determined. Nematode infectivity was greatest when the soil water content was maintained just below field capacity in the 7.2 (-1/3 bar) to 13.0% (-1/7 bar) ranges. Nematode invasion of roots was reduced in the wetter 15.5 (-1/10 bar) to 19.0% (-1 /2 0 bar) soil moisture ranges and in the dryer 3.4 (-15 bar) to 5.8% (-3/4 bar) soil moisture ranges.
plant growth; transpiration; nematode; water potential
Theratromyxa weberi, an amoeba, was isolated and cultured in the laboratory to determine the physical conditions that influence its predation on plant parasitic nematodes. In greenhouse tests, the amoeba was a poor biological control agent of the root-knot nematode, Meloidogyne incognita.
biological control; interaction; predation; Proteomyxida; Vampyrellidae; soil amoeba
Using a scanning electron microscope and an interference contrast microscope, distinct morphological differences were found in the terminal areas of white females and cysts of six species of the genus Heterodera (s.g. Globodera). Suffident differences to separate species were established on the basis of length of vulval aperture in the white female; arrangement, number and size of the perineal tubercles and vulval bodies in the white female; and presence or absence of a circumfenestral area and width of the cuticular grooves in the cyst.
cyst nematode; morphology
Laboratory experiments were conducted by applying 1,2-dibromo-3-chloropropane (DBCP) to sealed vials of soil infested with Meloidogyne javanica. A minimum initial concentration of 0.25 μg of DBCP/g of oven-dry soil killed all nematodes within 35 days. A concentration of 1.0 μg/g killed all nematodes within 28 days. The rate of degradation of this chemical was determined by treatment of steamed and nonsteamed dry soil in open and sealed vials. Extraction of tile chemical, followed by quantification by gas chromatography, showed approximately 100% of the amount applied recovered after 14 days in sealed vials without soil. With soil present, approximately 10% of the amount of chemical applied was recovered.
root knot; DBCP; chemical control; fumigant; bioassay
Amphids, and the cephalic and labial papillae of Meloidogyne incognita males were examined in detail by electron microscopy. Each amphid basically consists of an amphidial gland, a nerve bundle and an amphidial duct. The gland is a broad microvillous organ with a narrow anterior process, which is closely associated with the amphidial duct. A posterior process of the gland contains secretory organelles and proceeds along the esophagus with the lateral cephalic nerve bundle. The nerve bundle penetrates the broad portion of the gland and, subsequently, individual nerve processes (dendrites) separate from one another, thus forming the sensilla pouch which is enveloped by the gland. Anterior to the pouch, the dendrites converge as they enter and eventually terminate in the amphidial duct. The external opening of the duct is a broad slit which separates the cheek, the outermost part of the lateral lip, from the remainder of the lip region. M. incognita males have six inner labial papillae and four outer cephalic papillae which are each innervated by two and one cilia, respectively. In labial papillae, the cilia appear to terminate at the base of a pore opening, whereas in cephalic papillae each cilium terminates beneath the labial cuticle.
amphid; labial papillae; cephalic papillae; ultrastructure; amphidial gland; cilium; dendrite; receptor; microvillus; root-knot nematode
Plant extracts, made by grinding 2 g of fresh tissue in 5 ml of water, were toxic to Tylenchorhynchus dubius and Hoplolaimus spp. Such extracts from leaves and stems of bean (Phaseolus vulgaris L.) and leaves of tobacco (Nicotiana tabacum L.) were most toxic; those from leaves of corn (Zea mays L.), tomato (Lycopersicon esculentum Mill.) and rhododendron (Rhododendron catawbiense L.) were less toxic; and extracts of bean roots were nontoxic. Nematode movement slowed markedly within 1 hr in tobacco leaf extract, and within 4 hr in bean leaf extract; both extracts completely inactivated or killed 95% of the nematodes in 24 hr. Heating leaf extract 10 min at 80 C eliminated toxicity. Absorption of fusicoccin, a phytotoxin produced by Fusicoccum amygdali Del., increased the toxicity of tomato leaf extracts, whereas water extracts of acetone-extracted powder preparations of leaves were about 15-fold more toxic than water extracts of fresh tissue. Addition of homogenized leaves of bean, tobacco and tomato to soil significantly reduced nematode populations within 3 days.
The esophageal glands in the genus Pratylenchus occur in a large, single ventral lobe except for four populations in which a few specimens had the glands located dorsally. Apratylenchoides belli n. gen. n. sp. in the subfamily Radopholinae is proposed for a species having two esophageal glands in a large dorsal lobe and one gland in a smaller, shorter ventral lobe.
Second-stage larvae of Meloidodera floridensis kept in tap water developed without feeding into small, slender males. They completed three molts, and the molted cuticles remained superimposed. All organ systems were well developed in third- and fourth-stage male larvae. Structures in the head region such as cephalic framework, styler and esophagus were smaller and differed morphologically from those of second-stage larvae. Development of the male reproductive system was similar to that of other tylenchids, and sex was recognizable at the end of the second molt. Second-stage larvae, developing in pine roots, increased in size and molted three times to become ovoid to spherical females. Each larval stage had a stylet and fed actively. Sex could be determined at the end of the second molt. Detailed observations were made on the development of the reproductive system, cuticle, esophagus and tail region.
morphology; pine cystoid nematode
Heterodera achilleae n. sp., a member of the H. rostochiensis group, is described and illustrated from roots of yarrow, Achillea millefolium L. in Sarajevo, Yugoslavia. This new, round-cyst species differs from closely related species especially as follows: (1) from H. leptonepia, by having stouter larvae (a = 21), with longer styler (25 μ), and with outlet of dorsal esophageal gland averaging 5.7 μ from base o f styler; (2) from H. millefolii, in having excretory pore at base of neck and small, straight vulval slit of 5 μ; (3) from H. rostochiensis, in having a B/A ratio (Granek's ratio) of 1.6 ; (4) from H. tabacum, by longer female stylet, two annules on female head, and males with outlet of dorsal esophageal gland further back (5.7 μ). In addition, H. achilleae n. sp. differs from the latter three species in having prominent longitudinal striae on the anterior half, or more, of cysts and females.
taxonomy; morphology; new Heterodera species; Achillea millefolium
Particles of fanleaf and yellow mosaic viruses are reported in the lumen of the esophagus of Xiphinerna index. Differences in cuticular morphology suggest differences in charged receptor sites which may offer an explanation for virus location and orderly arrangement.
NEPO virus; morphology; esophagus; odontophore
Populations of Pratylenchus brachyurus on cotton were increased significantly in the presence of either Meloidogyne incognita or M. arenaria.This occurred with either simultaneous inoculation or prior invasion by M. incognita. P. brachyurus penetrated cotton roots previously invaded by, or simultaneously inoculated with, M. incognita, as well as, or better than, in the absence of M. incognita. Prior invasion by M. incognita, however, suppressed P. brachyurus populations on tomato, while it had no effect on alfalfa and tobacco. Populations of M. incognita on cotton were generally inhibited by the presence of P. brachyurus. Simultaneous inoculation with, or previous invasion by, P. brachyurus also inhibited root penetration by M. incognita. These findings emphasize the importance of host susceptibility in the study of concomitant nematode populations.
cotton, Gossypium hirsutum; tomato, Lycopersicon esculentum; alfalfa, Medicago sativa; tobacco, Nicotiana tabacum; Meloidogyne incognita; Meloidogyne arenaria; coinhabitants.
Scarified seeds of Medicago sativa L. 'Ranger' and 'Lahontan' alfalfa were allowed to imbibe water for 36 hr and then were inoculated with stem nematodes, Ditylenchus dipsaci Kühn. Seedlings were grown in sterilized Provo sand at 20 C and hypocotyl sections harvested at 1, 3 and 7 days. Evidence from electron micrographs indicated that cells of noninfected control plants contained normally developing chloroplasts bearing stroma, thylakoids, starch grains and plastoglobuli. The cytoplasm contained a nucleus, endoplasmic reticulum, vacuoles, mitochondria, ribosomes and dictyosomes. No morphological symptoms of nematode infection were observed in infected plants of either Ranger of Lahontan alfalfa 1 day after inoculation. Electron micrographs of tissue from the infected plants, however, indicated more osmiophilic bodies (lipid bodies) per cell than did the noninfected control, with more lipid bodies present in Ranger than in Lahontan. Three and 7 days after planting, swollen hypocotyls could be seen; the degree of swelling was greater in Ranger than in Lahontan. Electron micrographs of infected tissues indicated that both cultivars were undergoing the same kind of damage. Injured organelles were endoplasmic reticulum, chloroplasts and the nucleus. Histochemical staining indicated no changes in the middle lamellae.
fine structure; host-parasite interactions
Larvae of Meloidodera floridensis develop as females after feeding on pine roots, but become males under conditions of starvation. Seventy to 80% of the larvae kept in tap water at 23 C for 4 months underwent one or two molts, developing as males, and more than 50% became adult males. Ninety-six percent of the larvae that entered pine roots became females and only 4% developed as males. There is evidence that the latter did not feed on the roots. In comparison with tap water, solutions of cholesterol, testosterone propionate and β-estradiol did not significantly affect the percentage of larvae that developed into males. Larvae kept in soil without a host plant did not develop into males. Most of them exhausted their energy supply and died without undergoing any development. We conclude that sex expression in M. floridensis is to a large extent controlled by environmental factors. Under natural conditions of feeding on a host plant, larvae develop as females according to their genetic constitution (thelytokous organism). Under conditions of starvation, however, sexual differentiation proceeds toward the male direction, probably as a result of alteration of the hormonal balance of the larvae and the subsequent activation of different sites of genetic function.
postembryogenesis; development; hormones
Foliar applications of oxamyl (methyl N', N'-dimethyl-N-[(methylcarbamoyl)oxy]-l-thiooxamimidate) were applied 24 hr before transplanting seedlings to soil infested with Rotylenchulus reniformis. With a single application of oxamyl, tomato seedlings required 600 ppm to significantly inhibit R. reniformis penetration. Cotton seedlings, however, required a single application of 2400 ppm for significant inhibition of penetration, but only 600 ppm when two or more applications were used.
Gossypium hirsutum; L ycopersicon esculentum; Vydate®