Cuticle Ultrastructure of Criconemella curvata and Criconemella sphaerocephala (Nemata: Criconematidae)

Cuticle ultrastructure of Criconemella curvata and C. sphaerocephala females is presented; males were available only in the second species. Ultrathin sections revealed three major zones: cortical, median, and basal. The cortical zone in the females consists of an external and internal layer. In C. curvata the external layer is trilaminate and at each annule it is covered by a multilayered cap. In C. sphaerocephala the trilaminate layer is lacking and the external cortical layer includes an osmophilic coating. In both species the internal layer consists of alternate striated and unstriated sublayers. The median zone is fibrous with a central lacuna and the zone is interrupted between the annules. The basal zone of the cuticle is striated and narrower between each annule. The cuticle of the C. sphaerocephala male is typical of Tylenchida, except under both lateral fields; the striated layer becomes forked at the first incisure and the innermost two prongs of the fork overlap each other, resulting in a continuous striated band.     

Degree-day Models for Predicting Egg Hatch and Population Increase of Criconemella xenoplax

A degree-day model was derived to predict egg hatch for Criconemella xenoplax. Eggs collected from gravid females were incubated in distilled water at constant temperatures of 10-35 C. Sixty-six percent of all eggs hatched between 13 and 32 C, and 42% hatched at 10 C. All eggs aborted above 32.5 C. Between 25 and 32 C, 8.5 ± 0.5 days were required for egg hatch. Degree-day requirement for egg hatch at 10-30 C was estimated to be 154 ± 5 with a base of 9.03 ± 0.04 C. This base of 9 C was adopted in studies of the relationship between degree-days and nematode population increase on Prunus seedlings grown 9-11 weeks in a greenhouse. Degree-day accumulations were based upon daily averages from maximum and minimum air temperatures. Ratios of final to initial population densities exhibited an exponential pattern in relation to degree-day accumulations with proportionate doubling increment of 0.100 ± 0.049 every 139 ± 8 degree-days. These results provide a means of predicting nematode population increase under greenhouse conditions and a basis for choosing sampling intervals when evaluating nematode multiplication.     

Evaluation of Host Suitability in Prunus for Criconemella xenoplax

Methods were developed for screening Prunus selections for host suitability to Criconemella xenoplax. The relative host suitability of selections was based upon a doubling accumulation value (β) that was defined as the number of degree-days (base 9 C) required for doubling of an increment of the initial nematode population. The β value characteristic for C. xenoplax (139 ± 8 degree-days) on suitable hosts was similar to the average β value determined for several peach rootstocks known to be suitable hosts. The β values were 144 ± 21 for Halford, 141 ± 16 for Lovell, and 138 ± 10 for Nemaguard. A higher value for β could indicate poorer host suitability or resistance of a selection to C. xenoplax. All of 369 Prunus accessions tested, including eight accessions that had survived well on a field site infested with C. xenoplax, were suitable hosts. Apparently, resistance to C. xenoplax was not a factor in survival of the accessions planted in the field. Seedlings from P. besseyi, P. pumila ''Mando'', and two interspecific hybrids, Redcoat and Sapalta IR 549-1, failed to support nematode population increase in 44-81% of tests conducted, but all selections supported population increase in some tests. These accessions may have resistance mechanisms that are active only under specific conditions.     

Tests for Transmission of Prunus Necrotic Ringspot and Two Nepoviruses by Criconemella xenoplax

In two of three trials, detectable color reactions in ELISA for Prunus necrotic ringspot virus (PNRSV) were observed for Criconemella xenoplax handpicked from the root zone of infected peach trees. Criconemella xenoplax (500/pot) handpicked from root zones of peach trees infected with PNRSV failed to transmit the virus to cucumber or peach seedlings. The nematode also failed to transmit tomato ringspot (TomRSV) or tobacco ringspot viruses between cucumbers, although Xiphinema americanum transmitted TomRSV under the same conditions. Plants of peach, cucumber, Chenopodium quinoa, and Catharanthus roseus were not infected by PNRSV when grown in soil containing C. xenoplax collected from root zones of PNRSV-infected trees. Shirofugen cherry scions budded on Mazzard cherry seedling rootstocks remained symptomless when transplanted into root zones of PNRSV-infected trees. Virus transmission was not detected by ELISA when C. xenoplax individuals were observed to feed on cucumber root explants that were infected with PNRSV and subsequently fed on roots of Prunus besseyi in agar cultures. Even if virus transmission by C. xenoplax occurs via contamination rather than by a specific mechanism, it must be rare.     

Association of Criconemella xenoplax and Fusarium spp. with Root Necrosis and Growth of Peach

Criconemella xenoplax, Fusarium solani, and F. oxysporum caused necrosis of Nemaguard peach feeder roots in greenhouse tests. Root necrosis was more extensive in the presence of either fungus than wtih C. xenoplax alone. Shoot growth and plant height were less for plants inoculated with F. oxysporum or F. solani than for plants inoculated with the fungi plus C. xenoplax. Neither synergistic nor additive effects on root necrosis or plant growth occurred between C. xenoplax and the fungal pathogens.     

Peach Leaf Senescence Delayed by Criconemella xenoplax

Fall annual leaf senescence of peach was delayed in the field and in microplots in the presence of Criconemella xenoplax. Soil from the rhizosphere of orchard trees with greener leaves had ca. 2.5 × more nematodes than soil around trees in a more advanced state of fall senescence. In microplots, monoclonal antibody enzyme immunoassay (EIA) of leaf cytokinins indicated that concentration of zeatin riboside-like substances and chlorophyll content were greater in leaves of trees growing in nematode-infested soil than in trees in uninfested soil. EIA also indicated the presence of substances resembling trans-zeatin, zeatin riboside, dihydrozeatin, and dihydrozeatin riboside-like substances in whole body homogenates of C. xenoplax. Levels of zeatin-like substances were present in the nematode in greater levels than the other related substances.     

An Assay for Hirsutella rhossiliensis Spores and the Importance of Phialides for Nematode Inoculation

A spore assay was developed to measure the relative density of spores of the nematophagous fungus Hirsutella rhossiliensis in soil. Orchard soil containing H. rhossiliensis-parasitized Criconemella xenoplax was placed in vials and incubated for 0-120 days before the addition of probe nematodes, Heterorhabditis heliothidis juveniles. After 18 hours, H. heliothidis were extracted from the soil and examined for adhering spores of H. rhossiliensis. No spores were detected when H. heliothidis were added to freshly mixed soil, but the percentage of H. heliothidis with spores increased rapidly if soil was incubated undisturbed. Because mixing soil detaches spores from phialides, the results indicate that spores must be attached to phialides to adhere to nematodes. The spore assay was compared with a plate assay that measures the population density of H. rhossiliensis-parasitized C. xenoplax. Results from the two assays were highly correlated, suggesting that spores occur in three phases: reserves in nematodes that may be converted into spores; spores on phialides and therefore capable of adhering to nematodes; and spores detached from phialides and thus incapable of adhering to nematodes.     

Parasitism of Nematodes by the Fungus Hirsutella rhossiliensis as Affected by Certain Organic Amendments

Experiments were conducted to determine whether the addition of organic matter to soil increased numbers of bacterivorous nematodes and parasitic activity of the nematophagous fungus Hirsutella rhossiliensis. In a peach orchard on loamy sand, parasitism of the plant-parasitic nematode Criconemella xenoplax by H. rhossiliensis was slightly suppressed and numbers of C. xenoplax were not affected by addition of 73 metric tons of composted chicken manure/ha. In the laboratory, numbers of bacterivorous nematodes (especially Acrobeloides spp.) and fungivorous nematodes increased but parasitism of nematodes by H. rhossiliensis usually decreased with addition of wheat straw or composted cow manure to a loamy sand naturally infested with H. rhossiliensis. These results do not support the hypothesis that organic amendments will enhance parasitism of nematodes by H. rhossiliensis.     

Additional Hosts for the Ring Nematode,Criconemella xenoplax

Some common legumes and weeds indigenous to peach orchards in South Carolina were tested in greenhouse experiments to determine their host suitability for Criconemella xenoplax. Legumes that were hosts for the nematode were dwarf English trefoil (Lotus corniculatus var. arvensis), big trefoil (L. uliginosis), birdsfoot trefoil (L. corniculatus), narrowleaf birdsfoot trefoil (L. tenuis), ball clover (Trifolium nigrescens), rose clover (T. hirtum), subterranean clover (T. subterraneum), striate lespedeza (Lespedeza striata), and partridge pea (Cassiafasciculata). Most nonleguminous plants tested did not support population increases, but small increases were observed on orchardgrass (Dactylis glomerata), broadleaf signalgrass (Brachiaria platyphylla), purslane (Portulaca oleracea), and Carolina geranium (Geranium carolinianum). Results indicate that leguminous plants probably should not be used as ground cover or rotation crops for plants that are injured by C. xenopax.     

Suppression of Cyst Nematode by Natural Infestation of a Nematophagous Fungus

Penetration of cabbage roots by Heterodera schachtii was suppressed 50-77% in loamy sand naturally infested with the nematophagous fungus Hirsutella rhossiliensis. When Heterodera schachtii was incubated in the suppressive soil without plants for 2 days, 40-63% of the juveniles had Hirsutella rhossiliensis spores adhering to their cuticles. Of those with spores, 82-92% were infected. Infected nematodes were killed and filled with hyphae within 2-3 days. Addition of KCl to soil did not increase infection of Heterodera schachtii by Hirsutella rhossiliensis. The percentage of infection was lower when nematodes were touched to two spores and incubated in KCl solution than when nematodes naturally acquired two spores in soil.     

Population Trends and Vertical Distribution of Plant-Parasitic Nematodes Associated with Vitis labrusca L. in Michigan

Nematode population trends and vertical distribution were monitored in a southwest Michigan vineyard (Vitis labrusca cv. Concord) from 1976 through 1983. Shallow (20 cm) and deep (90 cm) applications of 1,3-dichloropropene applied at 281 (shallow) plus 658 or 1,122 (deep) liters/ ha provided excellent control of Xiphinema americanum, Criconemella xenoplax, and Meloidogyne hapla. Populations of X. americanum remained below detectable levels for the entire 8-year experimental period where the fumigant was applied. X. americanum and C. xenoplax populations exhibited multiyear cycling in nonfumigated plots. M. hapla was first detected in 1978 and increased in prominence from 1980 through 1982. Criconemella spp. were commonly parasitized by an endoparasitic fungus. Parasitism was monitored and reported as an indication of nematode population quality.     

Seasonal Population Fluctuation of Xiphinema americanum and X. rivesi in New York and Pennsylvania Orchards

The population fluctuation and composition of Xiphinema americanum (sensu stricto) and X. rivesi were studied in a New York apple orchard (only X. americanum present), a Pennsylvania apple orchard (both X. americanum and X. rivesi present), and a Pennsylvania peach orchard (X. americanum, X. rivesi, and X. californicum present). Few clear trends in population fluctuation or composition were observed. The adult female was the predominant stage in most sample periods, and the reproductive period was limited to late spring and early summer. Only a few of the females at any sample period were gravid. All stages were present throughout the year, and all stages overwintered. Eggs in soil were not monitored. In the Pennsylvania apple orchard, X. americanum and X. rivesi were easily separated by morphological characteristics; however, the two species did not display differences in population structure or composition. The predominance of adults, the relatively low reproductive rates, and the association of these species with stable habitats suggest that the life strategies of X. americanum and X. rivesi are K-selected as opposed to r-selected.     

Impact of a Nematode-parasitic Fungus on the Effectiveness of Entomopathogenic Nematodes

The impact of the nematode-parasitic fungus Hirsutella rhossiliensis on the effectiveness of Steinernema carpocapsae, S. glaseri, and Heterorhabditis bacteriophora against Galleria mellonella larvae was assessed in the laboratory. The presence of Hirsutella conidia on the third-stage (J3) cuticle of S. carpocapsae and H. bacteriophora interfered with infection of insect larvae. Conidia on the J3 cuticle of S. glaseri and on the ensheathing second-stage cuticle of H. bacteriophora did not reduce the nematodes'' ability to infect larvae. The LD₅₀ values for S. carpocapsae, S. glaseri, and H. bacteriophora in sand containing H. rhossiliensis were not different from those in sterilized sand when Galleria larvae were added at the same time as the nematodes. However, when Galleria larvae were added 3 days after the nematodes, the LD₅₀ of S. glaseri was higher in Hirsutella-infested sand than in sterilized sand, whereas the LD₅₀ of H. bacteriophora was the same in infested and sterilized sand. Although the LD₅₀ of S. carpocapsae was much higher in Hirsutella-infested sand than in sterilized sand, the data were too variable to detect a significant difference. These data suggest that H. bacteriophora may be more effective than Steinernema species at reducing insect pests in habitats with abundant nematode-parasitic fungi.     

Management of Root-knot Nematodes by Phenamiphos Applied through an Irrigation Simulator with Various Amounts of Water

Phenamiphos (6.7 kg a.i./ha) was applied via an irrigation simulator to squash at planting (AP) and 2 weeks after planting (PP), and to corn AP and 1 week PP to manage root-knot nematodes (Meloidogyne incognita). The nematicide was applied with 0.25, 0.64, 1.27, and 1.91 cm surface water/ ha to a Lakeland sand in which the soil moisture was at or near field capacity. Based on efficacy and crop response, no additional benefits resulted when phenamiphos was applied in volumes of water greater than 0.25 crn/ha. The cost of applying each 0.25 cm of water over a hectare is approximately $1.08, or a 92% reduction in nematicide application cost over conventional methods ($13.50/ha). Low root-gall indices and high yields from squash and corn indicate more effective nematode management when phenamiphos was applied AP rather than PP. Results from this method of applying phenamiphos suggest that certain nematicides could be used as salvage alternatives when nematodes are detected in crops soon after planting. For multiple-pest management, nematicides, other compatible biocides, and fertilizers could be applied simultaneously with sprinkler irrigation.     

Vertical Distribution of Three Nematode Genera in a Bentgrass Putting Green in Central Illinois

A study was conducted to determine the vertical distribution of Tylenchorhynchus nudus, Criconemella curvata, and Helicotylynchus cornurus in the upper 5 cm of bentgrass (Agrostis palustris cv. Penncross) putting green turf. The effect of fenamiphos on the vertical distribution of these species also was examined. Experimental design was a split-plot in which whole-plots were fenamiphos treated (0.11 kg a.i./100 m²) or untreated, and sub-plots were two strata (depths of 0-2.5 crn and 2.5-5.0 cm). Soil samples were collected during the growing season for 2 years after treatment to determine root weight and number of nematodes. Root weight was greater in the upper stratum on all sampling dates in both years. When differences between strata in population density were observed, T. nudus, C. curvata, and H. cornurus were more concentrated in the upper stratum. Vertical distribution of T. nudus, C. curvata, and H. cornurus was similar to the distribution of root weight. The difference in population density of H. cornurus between upper and lower strata was affected by fenamiphos on some dates, whereas differences between strata were unaffected for T. nudus and C. curvata. Double arcsine transformed proportions of the total populations of T. nudus, C. curvata, and H. cornurus in the upper stratum on each sampling date indicated no differences between fenamiphos treated and untreated plots in 1989 or 1990.     

Host Range and Ecology of Isolates of Pasteuria spp. from the Southeastern United States

Isolates of Pasteuria penetrans were evaluated for ecological characteristics that are important in determining their potential as biological control agents. Isolate P-20 survived without loss of its ability to attach to its host nematode in dry, moist, and wet soil and in soil wetted and dried repeatedly for 6 weeks. Some spores moved 6.4 cm (the maximum distance tested) downward in soil within 3 days with percolating water. The isolates varied greatly in their attachment to different nematode species and genera. Of five isolates tested in spore-infested soil, three (P-104, P-122, B-3) attached to two or more nematode species, whereas B-8 attached only to Meloidogyne hapla and B-I did not attach to any of the nematodes tested. In water suspensions, spores of isolate P-20 attached readily to M. arenaria but only a few spores attached to other Meloidogyne spp. Isolate P-104 attached to all Meloidogyne spp. tested but not to Pratylenchus scribneri. Isolate B-4 attached to all species of Meloidogyne and Pratylenchus tested, but the rate of attachment was relatively low. Isolate P-Z00 attached in high numbers to M. arenaria when spores were extracted from females of this nematode; when extracted from M. javanica females, fewer spores attached to M. arenaria than to M. javanica or M. incognita.