Life cycle and mating behavior of <Emphasis Type="Italic">Helicotylenchus multicinctus</Emphasis> (Nematoda: Hoplolaimidae) on excised <Emphasis Type="Italic">Musa cavendishii</Emphasis> roots

The life cycle and mating behavior of Helicotylenchus multicinctus (Nematoda: Hoplolaimidae) were observed in vitro on excised roots of Musa cavendishii in gnotobiotic culture. Eggs hatched into juveniles whose appearance and structure were similar to those of the adults. Juveniles grew in size and each juvenile stage was terminated by a molt. H. multicinctus had four juvenile stages. The first molt occurred outside the egg shortly after hatching. After the final molt the juveniles differentiated into adult males and females. Mating was required for reproduction. After mating, fertilized females began to lay eggs. The life cycle from second stage juvenile to second stage juvenile was completed in 39 days.     

Development of Meloidogyne chitwoodi on Wheat

Postinfection development of Meloidogyne chitwoodi from second-stage juveniles (J2) to mature females and egg deposition on ''Nugaines'' winter wheat required 105, 51, 36, and 21 days at 10, 15, 20, and 25 C. At 25 C, the J2 induced cavities and hyperplasia in the cortex and apical meristem of root tips with hypertrophy of cortical and apical meristem cell nuclei, 2 and 5 days after inoculation. Giant cells induced by late J2 were observed in the stele 10 days after inoculation. Clusters of egg-laying females were common on wheat root galls 25 days after inoculation. Juveniles penetrated wheat roots at 4 C and above, but not at 2 C, when inoculum was obtained from cultures grown at 20 C, but no penetration occurred at 4 C when inoculum was stored for 12 hours at 4 C before inoculation. In northern Utah, J2 penetrated Nugaines wheat roots in the field in mid-May, about 5 months after seedling emergence. M. chitwoodi eggs were first observed on wheat roots in mid-July when plants were in blossom. Only 40% of overwintered M. chitwoodi eggs hatched at 25 C.     

In Vitro Culture and Feeding Behavior of Belonolaimus longicaudatus on Excised Zea mays Roots

A greenhouse population of the sting nematode, Belonolaimus longicaudatus, obtained from an infested golf course in California''s Coachella Valley, was surface-decontaminated and cuhured on excised roots of Zea mays supported by Gamborg''s B5 medium. At 26-27 °C the females laid eggs, and newly emerged juveniles of the second generation completed three molts within 29 days after egg deposition. Sixty days after inoculation with 60 females and 40 males, an average of 529 nematodes and 83 eggs were recovered from the culture. The feeding process consisted of probing, stylet penetration, ingestion, and stylet retraction. Feeding seemed to be necessary before egg deposition or molting occurred. The sting nematode was observed feeding exclusively as an ectoparasite and preferably at the region of cell division and elongation. Vigorous feeding by many nematodes usually caused discoloration of root tips and termination of growth.     

Penetration and Development of Meloidogyne incognita in Roots of Resistant and Susceptible Corn Genotypes

Rates of penetration and development ofMeloidogyne incognita race 4 in roots of resistant (inbred Mp307, and S4 lines derived from the open-pollinated varieties Tebeau and Old Raccoon) and susceptible (Pioneer 3110) corn genotypes were determined. Seedlings grown in styrofoam containers were inoculated with 5,000 eggs of M. incognita. Roots were harvested at 3-day intervals starting at 3 days after inoculation (DAI) to 27 DAI and stained with acid fuchsin. Penetration of roots by second-stage juveniles (J2) at 3 DAI was similar for the four corn genotypes. Meloidogyne incognita numbers in Tebeau, Old Raccoon, Mp307, and Pioneer 3110 peaked at 12, 12, 15, and 27 DAI, respectively. Nematode development in the resistant genotypes was greatly suppressed compared to Pioneer 3110. Resistance to M. incognita in these genotypes appears to be expressed primarily as slower nematode development rather than differences in J2 penetration.     

In vitro Cultivation of the Entomogenous Nematode Filipjevimermis leipsandra

The mermithid nematode, Filipjevimermis leipsandra, was successfully cultivated to the preadult stage in Schneider''s Drosophila medium supplemented with 20% fetal bovine serum. Upon transfer to a solid substrate the preadults continued to develop into ovipositing adult females. Four molts were observed. The first molt occurred in the egg. The second occurred after 6-8 days in culture during which the very thin cuticle was shed completely. The third molt occurred after 18-20 days in culture; the cuticle was retained by the third-stage nematode. This stage was considered comparable to the preadult stage that emerges from host larva, Diabrotica spp. The fourth molt occurred within 12 days after the preadult was transferred from the liquid medium to a solid substrate. Adult females began ovipositing viable eggs 1-3 days after the final molt.     

Population Dynamics of Meloidogyne chitwoodi on Russet Burbank Potatoes in Relation to Degree-day Accumulation

Population dynamics of Meloidogyne chitwoodi were studied for 2 years in a commercial potato field and microplots. Annual second-stage juvenile (J2) densities peaked at harvest in mid-fall, declined through the winter, and were lowest in early summer. In the field and in one microplot study, population increase displayed trimodal patterns during the 1984 and 1985 seasons. Overwintering nematodes produced egg masses on roots by 600-800 degree-days base 5 C (DD₅) after planting. Second-generation and third-generation eggs hatched by 950-1,100 DD₅ and 1,500-1,600 DD₅, respectively, and J2 densities rapidly increased in the soil. A fourth generation was observed at 2,150 DD₅ in 1985 microplot studies. Tubers were initiated by 450-500 DD₅, but J2 were not observed in the tubers until after the second generation hatched at 988-1,166 DD₅. A second period of tuber invasion was observed when third generation J2 hatched. The regional variation in M. chitwoodi damage on potato may be explained by degree-day accumulation in different potato production regions of the western United States.     

Efficacy of Ethoprop on Meloidogyne hapla and M. chitwoodi and Enhanced Biodegradation in Soil

Responses of egg masses, free eggs, and second-stage juveniles (J2) ofMeloidogyne hapla and M. chitwoodi to ethoprop were evaluated. The results indicated that J2 were the most sensitive, followed by free eggs and egg masses. In general, M. chitwoodi was more susceptible to ethoprop than M. hapla. Ethoprop at 7.2 μg a.i./g soil protected tomato roots from upward migrating M. chitwoodi for 5 weeks. The zone of protection was extended to 10 and 20 cm below the root zone when 3.6 and 7.2 cm water were applied over 8 days. Ethoprop at 1.8, 3.6, and 7.2 μg a.i./g soil degraded faster and killed fewer M. chitwoodi J2 in potato field soil previously exposed to ethoprop than in unexposed soil or sterilized exposed soil. The enhanced biodegradation property of the exposed soil lasted 17 months after the last application of ethoprop. The limited downward movement of ethoprop in the soil, migration of M. chitwoodi J2 into the treated zone, presence of resistant life stage(s) at the time of application, and loss of efficacy due to enhanced biodegradation may have a significant effect on the performance of ethoprop.     

Histopathology of Root-knot Nematode (Meloidogyne incognita) Infection on White Yam (Dioscorea rotundata) Tubers

White yam tissues naturally and artificially infected with root-knot nematodes were fixed, sectioned, and examined with a microscope. Infective second-stage juveniles of Meloidogyne incognita penetrated and moved intercellularly within the tuber. Feeding sites were always in the ground tissue layer where the vascular tissues are distributed in the tubers. Giant cells were always associated with xylem tissue. They were thin walled with dense cytoplasm and multinucleated. The nuclei of the giant cells were only half the size of those found in roots of infected tomato plants. Normal nematode growth and development followed giant cell formation. Females deposited eggs into a gelatinous egg mass within the tuber, and a necrotic ring formed around the female after eggs had been produced. Second-stage juveniles hatched, migrated, and re-infected other areas of the tuber. No males were observed from the tuber.     

Differences in Hatching of Heterodera glycines Egg-mass and Encysted Eggs in vitro

Hatching studies with Heterodera glycines typically have been conducted with a mixture of egg-mass and encysted eggs. Laboratory research was conducted to compare hatching of H. glycines eggs from external egg masses with that of eggs extracted from within females and cysts (encysted eggs). Egg-mass eggs were collected by soaking infected soybean roots in 0.5% sodium hypochlorite, and encysted eggs were collected from females and cysts dislodged from the same roots with a stream of water. Eggs were incubated at 25 °C in deionized water, 3.0 mM ZnSO₄solution, or one of three synthetic H. glycines hatch inhibitors, mad hatched juveniles were counted every other day for 22 days. Samples of eggs collected at the beginning and end of all experiments were analyzed to determine extent of embryo development. Egg-mass eggs hatched more rapidly than encysted eggs during the first 16 days, but not thereafter. Throughout the experiments, hatch of egg-mass eggs in deionized water was greater than that of encysted eggs. From day 8 to day 22, egg-mass eggs were less sensitive than encysted eggs to the hatch inhibitor 2-(2''-carboxyethyl)-5-[carboxy(hydroxy)methylidenyl]cyclopentanone. A greater proportion of egg-mass eggs contained vermiform juveniles than did encysted eggs at the beginning of the experiments, but not at the end. Results indicated that H. glycines egg-mass and encysted eggs have different hatching behaviors that cannot be explained entirely by differences in embryological development.     

Stage-specific Population Development and Fecundity of Paratrichodorus minor

A conceptual model of the life cycle of Paratrichodorus minor consisting of the egg stage, four juvenile stages, and the adult stage was proposed. Development of an individual from one stage to the next was described by a probability distribution defined by the mean length of time spent in the stage and the standard deviation associated with the mean duration. Experiments were conducted to estimate stage durations, stage-specific survivorships, and a fecundity rate for females. Eggs hatched on agar plates at a mean time of 53.3 ± 7.3 degree-days using a basal threshold of 10 C (DD₁₀) with a range of 40-64 DD₁₀ after deposition. Forty-five percent of the eggs observed ultimately hatched. Of the eggs that died, 44% died before the nematode form could be observed in the egg and 56% died after movement had been observed. First generation population peaks following inoculation with first-stage juveniles occurred at 28 DD₁₀ for second-stage juveniles, 67 DD₁₀ for third-stage juveniles, 109 DD₁₀ for fourth-stage juveniles, and 143 DD₁₀ for adults. Adult males are rare and were never observed in these studies. The fecundity rate was 0.784 eggs/(female-DD₁₀⁻¹), but the maximum length of the egg-laying period was not determined. The minimum egg-laying period was 73-113 DD₁₀, and minimum egg production was 57-86 eggs per female. The preovipositional period for adult females was estimated to be 79 DD₁₀. In the presence of a host, total population numbers increased, but in the absence of a host, the population declined to 33 % of the initial level after 300 DD₁₀.     

The Role of Microbes Associated with Chicken Litter in the Suppression of Meloidogyne arenaria

The role of microbes associated with chicken litter in the suppression of Meloidogyne arenaria in amended soil was investigated. Amended soil treatments were prepared, including combinations of sterile and nonsterile chicken litter and soil. Microbial biomass in different treatments was compared by measuring carbon dioxide evolution. There was less CO₂ evolved in sterile litter than in nonsterile litter treatments. Tomato seedlings cv. Rutgers were transplanted into soil mixtures and inoculated with 2,000 M. arenaria eggs. After 10 days, fewer second-stage juveniles (J2) had penetrated the roots in soils amended with nonsterile litter than sterile litter. The effects of sterile and nonsterile litter-amended soil solutions on M. arenaria eggs and J2 were observed over a period of 6 days. A lower percentage of eggs remained apparently healthy in nonsterile than in sterile-amended soil solutions over 6 days. Microbial degradation of the egg shells was apparent. Fewer J2 survived in sterile- and nonsterile-amended-soil solutions as compared to water controls.     

Penetration and Development of Meloidogyne arenaria on Two New Grape Rootstocks

Penetration, development, and reproduction of a virulent ''Harmony'' population of Meloidogyne arenaria was studied on two nematode-resistant grape rootstocks 10-17A and 6-19B. ''Cabernet Sauvignon'' was used as a susceptible control for comparison. Plants were inoculated with 100 freshly hatched second-stage juveniles (J2) of M. arenaria. Greater numbers of J2 penetrated roots of ''Cabernet'' than 10-17A, and none penetrated roots of 6-19B 4 days after inoculation (DAI). At 7 DAI, vermiform J2 advanced to sausage-shaped J2 in roots of ''Cabernet,'' penetrated roots of 6-19B, and had egressed from roots of 10-17A. Resistant rootstocks expressed hypersensitive responses to penetrating J2 along the root epidermis, among the cortical cells, and along the differentiating vascular bundles. At 13 DAI, 68% of the J2 had attained globose stage in roots of ''Cabernet,'' whereas there was no development of vermiform J2 in roots of the other two rootstocks. The nematodes reproduced only in roots of ''Cabernet.'' Lack of development of J2 in roots of the two resistant grape rootstocks might be the result of a hypersensitive response to J2 feeding.     

Differential Response of Thor Alfalfa to Meloidogyne chitwoodi Races and M. hapla

Second-stage juveniles (J2) of races 1 and 2 of Meloidogyne chiiwoodi and M. hapla readily penetrated roots of Thor alfalfa and Columbian tomato seedlings; however, few individuals of M. chitwoodi race 1 were able to establish feeding sites and mature on alfalfa. Histopathological studies indicate that J2 of race 1 either failed to initiate feeding sites or they caused cell enlargement without typical cell wall thickening. The protoplasm of these cells coagulated, and juveniles of race 1 did not develop beyond the swollen J2 stage. A few females of race 1 fed on small giant cells and deposited a few eggs at least 20 and 30 days later than M. chitwoodi race 2 and M. hapla, respectively. Failure of race 1 to establish feeding sites was related to egression of J2 from the roots. The M. chitwoodi race 1 J2 egression from alfalfa roots was higher than egression of race 2 and M. hapla. Egression of J2 of M. chitwoodi races 1 and 2 from tomato roots was similar and higher than that of M. hapla. Thus egression plays an important role in the host-parasite relationship of M. chitwoodi and alfalfa.     

Ultrastructure of Phasmid Development in Meloidodera floridensis and M. charis (Heteroderinae)

Phylogenetic characters for Heteroderinae Luc. et al., 1988 are evaluated in Meloidodera which is believed to have primarily ancestral characters. Phasmid ultrastructure is observed in second-stage juveniles (J2), third-stage juvenile males, fourth-stage juvenile males, and fifth-stage males of Meloidodera floridensis and M. charis. Phasmid secretion occurs inside the egg before the J1-J2 molt. Before J2 hatch, concentric lamellar membranes occur within the sheath and socket cells. Some membranes become lamellae of the sheath cell plasma membrane; others become multilamellar bodies. During early molting, plasma membrane lamellae disappear and a distal dendrite segment appears in a rudimentary canal. After the molt, the distal dendrite is not present within the canal. The phylogenetic utility of phasmid features is discussed. In both species the ampulla shape and size between molts are stable features in juveniles and males. The posthatch J2 sheath cell receptor cavity may vary in a species specific manner, but comparative morphology requires precise timing after hatch.     

Reproduction and Development of Meloidogyne incognita and M. javanica on Guardian Peach Rootstock

Guardian peach rootstock was evaluated for susceptibility to Meloidogyne incognita race 3 (Georgia-peach isolate) and M. javanica in the greenhouse. Both commercial Guardian seed sources produced plants that were poor hosts of M. incognita and M. javanica. Reproduction as measured by number of egg masses and eggs per plant, eggs per egg mass, and eggs per gram of root were a better measure of host resistance than number of root galls per plant. Penetration, development, and reproduction of M. incognita in Guardian (resistant) and Lovell (susceptible) peach were also studied in the greenhouse. Differences in susceptibility were not attributed to differential penetration by the infectivestage juveniles (J2) or the number of root galls per plant. Results indicated that M. incognita J2 penetrated Guardian roots and formed galls, but that the majority of the nematodes failed to mature and reproduce.     

Effect of Gamma-irradiation and Heat on Root-knot Nematode,Meloidogyne javanica

Effects of gamma-irradiation on the root-knot nematode Meloidogyne javanica were investigated. A dose of 7.5 kGy killed all second-stage juveniles (J2) within 1 day after treatment. Egg hatch was completely inhibited at 6.25 kGy. A bioassay on tomato measuring galling and egg production was used to determine the infectivity of irradiated J2 and J2 hatched from irradiated eggs. The J2 and eggs irradiated with a dose of 4.25 kGy did not induce galls or reproduce on tomato plants. When nematodes were exposed to combined irradiation and heat treatment, no synergistic effect on J2 or eggs was measured. Heat treatment at 49° C for 10 minutes or 20 minutes without irradiation immobilized J2 and prevented egg development. Irradiation rates needed to kill or incapacitate M. javanica were high and may be impractical as a quarantine measure.     

Overwintering Stages of Meloidogyne incognita in Vitis vinifera

The overwintering of Meloidogyne incognita in and around Vitis vinifera cv. French Colombard roots was studied in a naturally infested vineyard at the Kearney Agricultural Center, in a growth chamber, in inoculated vines in microplots at the University of California, Davis, and in a greenhouse. Infected roots were sampled at intervals from onset of vine dormancy until plants accumulated about 800 degree days (DD - base 10 C). Embryogenesis within eggs, classified as less than or more than 16 cells and fully differentiated, and numbers of juveniles (second to fourth stage) and preovipositional and mature (egg-laying) adult stages in roots were determined. All stages were present at the onset of dormancy. Juveniles and immature females were not recovered during the dormant period. Mature females and eggs were always present in roots, although the number of mature females generally decreased with time after onset of dormancy. In contrast, in a greenhouse experiment that accumulated comparable DD without the host plant going through dormancy, the number of mature females increased. After bud break, the number of eggs per female increased and all nematode stages were found in host roots. Eggs in all stages of embryogenesis were observed at all times of sampling, indicating that females overwinter and are capable of laying eggs when conditions improve in the spring and need to be considered in nematode management decisions.     

Effects of Acibenzolar-S-Methyl Application to Rotylenchulus reniformis and Meloidogyne javanica

Effects of acibenzolar-s-methyl, an inducer of systemic acquired resistance in plants, on Rotylenchulus reniformis and Meloidogyne javanica in vitro and in vivo were determined. A single foliar application of acibenzolar at 50 mg/liter (5 ml of solution per plant) to 7-day-old cowpea or soybean seedlings decreased R. reniformis and M. javanica egg production by 50% 30 days after inoculation. The mechanism of acibenzolar on plant-parasitic nematodes was then investigated. Acibenzolar at 50 to 200 mg/liter did not affect movement of R. reniformis and M. javanica or penetration of second-stage juveniles (J2) of M. javanica on cowpea. However, M. javanica development was slowed and fecundity was reduced in plants treated with acibenzolar. On average, 50% of J2 that penetrated acibenzolar-treated cowpeas developed into mature females with eggs, whereas the other 50% exhibited arrested development. The number of eggs per egg mass was 450 in water-treated cowpeas, whereas the number declined to 250 in acibenzolar-treated plants. Acibenzolar may be responsible for stimulating the plants to express some resistance to the nematodes.     

Stage-specific Differences in Lectin Binding to the Surface of Anguina tritici and Meloidogyne incognita

The occurrence and distribution of several lectin binding sites on the outer surfaces of eggs, preparasitic second-stage juveniles (J2), parasitic second-stage juveniles (PJ2), females, and males of two tylenchid nematodes, Anguina tritici and Meloidogyne incognita race 3, were compared. In both species, a greater variety of lectins bound to the eggs than to other life stages; lectin binding to eggs was also more intense than it was to other life stages. Species-specific differences also occurred. More lectins bound to the amphids or amphidial secretions of M. incognita J2 than to the amphids or amphidial secretions of A. tritici J2. Lectins also bound to the amphids or amphidial secretions of adult male and female A. tritici, but binding to the cuticle occurred only at the head and tail and was not consistent in all specimens. Canavalia ensiformis and Ulex europaeus lectins bound specifically to the outer cuticle of M. incognita. Several other lectins bound nonspecifically. Oxidation of the cuticle with periodate under mild conditions, as well as pretreatment of the nematodes with lipase, markedly increased the binding of lectins to the cuticle of A. tritici J2 but not, in most cases, to M. incognita J2 or eggs of either species.     

Reproduction,Chromosome Number,and Postembryonic Development of Panagrellus redivivus (Nematoda: Cephalobidae)

Panagrellus redivivus (L.) T. Goodey reproduced amphimictically; the sexual primordia of males had nine chromosomes, those of females had ten. Eggs contained five chromosomes, sperm four or five. There were four molts, all after hatching. The sexes could be separated at the second molt by development of a lobe of somatic cells in the gonad, anteriorly in males, posteriorly in females. The lobe in males reflexed posteriorly at the third molt and joined the rectum at the fourth molt. Third molt females had a thickened vaginal primordium and at the fourth molt the spermathecal and uterine primordia were evident. The uterus elongated enormously in the adult. The 15 ventral chord nuclei between esophagus and rectum in the first stage increased to approximately 63 during the first molt; specialized nuclei, not evident until the third molt, participate in vaginal lining formation in fourth molt females. Sperm were first produced at the late fourth molt. Eggs, not produced until after copulation, hatched within the uterus.