Population Dynamics of Criconemoides simile on Soybean

Custer and Hood soybean cultivars were inoculated with nine levels of Criconemoides simile ranging from 300 to 20,600 nematodes per plant. Rate of reproduction decreased as inoculum level was increased beyond 900-2,000 nematodes. Final population density was influenced by both composition and level of inoculum. There was an indication that substance(s). inhibitory to larvae, accumnlated in soil in which Hood was grown for 11 months, Significant reduction of fresh weight of roots of Hood, but not Custer, occurred at population densities of 37,000 and 44,700 nematodes per plant.     

Field Interrelationships among Heterodera glycines,Pratylenchus scribneri,and Three Other Nematode Species Associated with Soybean

Field experiments were conducted in 1982 and 1983 to assess interactions between Heterodera glycines and Pratylenchus scribneri on soybean in southern Illinois. Soybean cyst nematode susceptible cultivar Williams 79 and resistant cultivar Fayette were treated or not treated with aldicarb 15G. Initial population densities were 35 H. glycines cysts containing eggs, 100 P. scribneri, 30 Helicotylenchus pseudorobustus, 225 Paratylenchus projectus, and 85 Tylenchorhynchus martini per 250 cm³ soil in 1982, whereas in 1983 populations were 11 H. glycines cysts, 330 P. scribneri, and 620 H. pseudorobustus. In both years H. glycines populations increased on nontreated Williams 79, decreased on both treated and nontreated Fayette, and remained at initial levels on treated Williams 79. Recovery of P. scribneri per gram dry root was different between nontreated cultivars in 1982 but not in 1983. Aldicarb treatment suppressed soil and root populations of P. scribneri on both cultivars in both years. Populations of H. pseudorobustus, P. projectus, and T. martini at harvest indicated little population increase on either nontreated cultivar. In 1982 H. glycines caused yield suppression but P. scribneri did not, as differences in yield occurred between cultivars but not between aldicarb treatments. In 1983, however, there were no yield differences between cultivars, but aldicarb application resulted in yield increase in both cultivars. In 1983 the yield increase resulting from P. scribneri control was approximately 25%. No synergistic effect on yield was observed between H. glycines and P. scribneri.     

The Interrelationship of Heterodera schachtii and Ditylenchus dipsaci on Sugarbeet

Heterodera schachtii significantly (P = 0.05) reduced sugarbeet root growth below that of uninoculated controls at 20, 24, and 28 C, and Ditylenchus dipsaci significantly (P = 0.05) reduced root growth below that of uninoculated controls at 16, 20, 24, and 28 C. A combination of H. schachtii and D. dipsaci significantly (P = 0.05) reduced root growth below that of single inoculations of H. schachtii at all temperatures and D. dipsaci at 20, 24, and 28 C. Single inoculations of H. schachtii and D. dipsaci significantly (P = 0.05) reduced top growth of sugarbeet below that of uninoculated controls at 20, 24, and 28 C, and 16, 20, 24, and 28 C, respectively. A combination of the two nematodes significantly (P = 0.05) reduced top growth below that of single inoculations of H. schachtii at all temperatures. However, a combination of the two nematodes failed to significantly (P = 0.05) reduce top growth below that of single inoculations of D. dipsaci at any temperature. Inoculations of either H. schachtii or D. dipsaci did not affect penetration of the other nematode, and D. dipsaci did not affect development and reproduction of H. schachtii. D. dipsaci did not reproduce on sugarbeet.     

Effects of Temperature on the Pathogenicity of Tylenchorhynchus clarus to Alfalfa and Observations on Feeding

The involvement of Tylenchorhynchus clarus in plant disease is reported. Addition of a suspension of surface-axenized nematodes reduced top and root growth of alfalfa. Reproduction of T. clarus was greater at 24 and 27 than at 21 C. The interaction of nematodes with temperature did not produce significant effects on alfalfa growth in the 4.5-mo experimental period. T. clarus fed endo- and ectoparasitically.     

Dynamics of Concomitant Populations of Hoplolaimus columbus,Scutellonema brachyurum,and Meloidogyne incognita on Cotton

Cotton seedlings grown in a greenhouse and a growth chamber were inoculated with Scutellonema brachyurum, Hoplolaimus columbus, and Meloidogyne incognita, singly and in all possible combinations, at two initial population (Pi) levels (100 and 300/100 cm³). S. brachyurum alone was not pathogenic to cotton at these population levels. It fed primarily as an ectoparasite but matured and reproduced within the root when it penetrated. Populations of S. brachyurum increased in the presence of H. columbus but were suppressed by M. incognita. H. columbus suppressed dry shoot weights of cotton (P = 0.05) at a Pi of 300/100 cm³ soil. Simultaneous inoculation of H. columbus with either M. incognita or S. brachyurum increased H. columbus populations over treatments with H. columbus alone, both at 60 and 90 d after inoculation. M. incognita suppressed cotton shoot weights significantly (P = 0.05) at both Pi levels. Inoculation with S. brachyurum increased M. incognita populations 60 d after inoculation, while H. columbus suppressed populations of M. incognita. Most larvae of M. incognita did not develop to maturity in the presence of H. columbus. Giant cells aborted and were necrotic 20-25 d after inoculation. Since M. incognita and H. columbus feed on different tissues, the inhibition of M. incognita may have resulted from a physiological effect of H. columbus on the host.     

Interactions Between Meloidogyne incognita and Pratylenchus brachyurus on Soybean

Interactions among Meloidogyne incognita, Pratylenchus brachyurus, and soybean genotype on plant growth and nematode reproduction were studied in a greenhouse. Coker 317 (susceptible to both nematodes) and Gordon (resistant to M. incognita, susceptible to P. brachyurus) were inoculated with increasing initial population densities (Pi) of both nematodes individually and combined. M. incognita and P. brachyurus individually usually suppressed shoot growth of both cultivars, but only root growth on Coker 317 was influenced by a M. incognita × P. brachyurus interaction. Reproduction of both nematodes, although dependent on Pi, was mutually suppressed on Coker 317. P. brachyurus reproduced better on Gordon than on Coker 317 but did not affect resistance to M. incognita. Root systems of Coker 317 were split and inoculated with M. incognita or P. brachyurus or both to determine the nature of the interaction. M. incognita suppressed reproduction of P. brachyurus either when coinhabiting a half-root system or infecting opposing half-root systems; however, P. brachyurus affected M. incognita only if both nematodes infected the same half-root system.     

Reproduction of Heterodera zeae and Its Suppression of Corn Plant Growth as Affected by Temperature

Reproduction of the corn cyst nematode (Heterodera zeae) and its effect on growth of corn (Zea mays) was studied in plant growth chambers at 24, 27, 30, 33, and 36 C. Reproduction of H. zeae increased directly with increase in temperature from 24 to 36 C. Fifteen-cm-d pots of corn seedlings inoculated with a mixture of 5,000 eggs + J2 and maintained for 8 weeks in growth chambers contained an average of 7,042 cysts + females at 36 C, but only 350 cysts + females at 24 C. Fresh weights of plants without nematodes were highest at 27 C and lowest at 36 C. Nematodes suppressed plant fresh weight by an average of 30% at 27 C and by 27% at 33 C but did not suppress plant weight at 36 C. Heterodera zeae has the highest reported temperature optimum for reproduction of any cyst nematode.     

Early Growth of Soybean as Altered by Heterodera glycines,Phenamiphos and/or Alachlor

Greenhouse and field experiments were conducted to determine the effects of phenamiphos and/or alachlor on early growth of soybean, root morphology, and infection and resurgence of Heterodera glycines (race 1). All tests were planted to ''Ransom'' soybeans. In greenhouse experiments without nematodes, root growth was inhibited at 5 days by alachlor treatments and at 10 days by phenamiphos treatments; with nematodes, phenamiphos treatments enhanced root growth. Phenamiphos also suppressed early penetration of soybean roots by H. glycines in the greenhouse. Early soybean growth parameters among treatments were generally similar in the field. Nematode penetration was limited with treatments containing phenamiphos at one location. Plants treated with only alachlor had less nematode infection than did the control; however, plants treated with herbicide/nematicide combinations had more nematode penetration than did plants treated with phenamiphos alone. Alterations of root growth and interference with the efficacy of phenamiphos are two processes by which alachlor may enhance soybean susceptibility or suitability to H. glycines.     

Pratylenchus penetrans Population Dynamics on Three Potato Cultivars

Reproduction of Pratylenchus penetrans on the potato cultivars Hudson, Katahdin, and Superior was determined in greenhouse and field microplot experiments. Although all three cultivars were good hosts for P. penetrans, differences in reproductive rate were found. In one greenhouse experiment, Katahdin plants inoculated with 1,500 or 15,000 P. penetrans per pot had larger population densities at harvest than did Superior; however differences between these cultivars were not significant in three other greenhouse experiments. In another experiment, population densities of P. penetrans on Hudson did not differ from those on Katahdin and Superior when inoculated with 270 and 5,080 nematodes per pot after 45 days in the greenhouse. However, population densities were usually higher on Hudson and Katahdin than on Superior in field microplots at four initial population densities during two seasons. Higher population densities on Hudson were detectable 304 days after planting in one of the two microplot studies. The juvenile:female and the male:female ratios were sometimes larger on Katahdin than on Superior, but differences were inconsistent. There was no evidence of resistance in the three cultivars evaluated, but reproduction was generally highest on Hudson and lowest on Superior.     

Effects of Temperature and Root Leachates on Embryogenic Development and Hatching of Meloidogyne chitwoodi and M. hapla

At 20 C the duration of the embryogenic development of Meloiclogyne chitwoodi and M. hapla was about 20 days. At 10 C the embryogenic development was 82-84 days for M. chitwoodi and 95-97 days for M. hapla. The effect of distilled water and root leachates of potato cv. Russet Burbank, tomato cv. Columbian, and wheat cv. Hyslop on the hatching of eggs of the two root-knot nematode species was investigated at 4, 7, 10, 15, 20, and 25 C (± 1 C). Cumulative egg taatch was no greater in root leachates titan in distilled water, but temperature did significantly affect egg hatch (P = 0.05). Less than 1% of the eggs of both nematode species hatched at 4 C. The percent cumulative hatch at 10 C was significantly less (P = 0.05) than at higher temperatures for both nematodes and significantly more (P = 0.05) M. chitwoodi eggs hatched than did M. hapla eggs. At 15 G the percent cumulative hatch of both species was significantly lower (P = 0.05) than that at 20 and 25 C. The percent cumulative egg hatch of two species did not differ at 25 C, but was higher (P = 0.05) at 25 C than at 20 C. At 7 C the emergence of M. chitwoodi juveniles was about seven times (P = 0.01) greater than that of M. hapla in distilled water.     

Relationships of Plant Parasitic Nematodes to Sites in Native Iowa Prairies

Soil samples were collected from three native Iowa prairies and analyzed for plant paiasitic nematodes and selected soil properties. Sites or nematodes were clustered with similarities related to habitat by a cluster analysis of site by nematode species and of nematodes by site. Some nematodes occurred in a wide range of prairie habitats, whereas others were more restricted. For example, greater numbers of Xiphinema americanum were in the low, well-drained sites than in the low wet sites or upland dry sites. Wet sites contained fewer nematodes than well-drained sites. Well-drained sites contained mainly Tylenchorhynchus maximus, Helicotylenchus pseudorobustus, and X. americanum. Wetter sites contained almost exclusively X. chambersi, H. hydrophilus, Telylenchus joctus, and an undescribed species of Tylenchorhynchus.     

Survival and Reproduction of Some Nematodes as Affected by Muck and Organic Acids

Fulvic, humic, acetic, N-bulyric, formic, lactic, and propionic acids were inhibitory to the survival or reproduction of Aphelenchus avenae, Aphelenchoides goodeyi, Helicotylenchus pseudorobustus, Meloidogyne hapla or Xiphinema americanum. Reproduction of H. pseudorobustus and M. hapla significantly increased with increasing amounts of muck added to sand, and with the initial amount of nematode inoculum. All acids except humic and fulvic were lethal, in vitro, to all nematode species tested. When A. goodeyi was treated with fulvic acid, reproduction was reduced significantly when compared with sodium humate or water treatments. Treatment of H. pseudorobustus with fulvic acid (pH 3.5) resulted in a greater reduction in reproduction in soil than did treatment with humic acid (pH 3.5).     

Effects of Rapeseed and Vetch as Green Manure Crops and Fallow on Nematodes and Soil-borne Pathogens

In a rapeseed-squash cropping system, Meloidogyne incognita race 1 and M. javanica did not enter, feed, or reproduce in roots of seven rapeseed cultivars. Both nematode species reproduced at low levels on roots of the third crop of rapeseed. Reproduction of M. incognita and M. javanica was high on squash following rapeseed, hairy vetch, and fallow. The application of fenamiphos suppressed (P = 0.05) root-gall indices on squash following rapeseed, hairy vetch, and fallow; and on Dwarf Essex and Cascade rapeseed, but not Bridger and Humus rapeseed in 1987. The incorporation of 30-61 mt/ha green biomass of rapeseed into the soil 6 months after planting did not affect the population densities of Criconemella ornata, M. incognita, M. javanica, Pythium spp., Rhizoctonia solani AG-4; nor did it consistently increase yield of squash. Hairy vetch supported larger numbers of M. incognita and M. javanica than rapeseed cultivars or fallow. Meloidogyne incognita and M. javanica survived in fallow plots in the absence of a host from October to May each year at a level sufficient to warrant the use of a nematicide to manage nematodes on the following susceptible crop.     

Host Range Assessment of Helicotylenchus pseudorobustus (Tylenchida: Hoplolaimidae) on Pasture Species

The host status of 15 commonly occurring pasture species for Helicotylenchus pseudorobustus was tested in a greenhouse trial. Only tall fescue, with and without Neotyphodium endophyte infection, was a good host (Pf/Pi = final/initial population > 1). Inoculation survival was tested in a second trial, which showed that only 10% of the H. pseudorobustus nematodes survived the first 7 days after inoculation. When the Pf/Pi was adjusted to account for a 10% survival, all of the grass and clover hosts tested had a Pf/Pi > 1. Both trials showed a positive correlation between increased numbers of H. pseudorobustus and free-living nematodes.     

Interaction between entomopathogenic nematodes and entomopathogenic fungi applied to third instar southern masked chafer white grubs,Cyclocephala lurida (Coleoptera: Scarabaeidae), under laboratory and greenhouse conditions

Four entomopathogenic nematode (EPN) species (Heterorhabditis bacteriophora Poinar, Heterorhabditis megidis Poinar, Jackson & Klein, Steinernema feltiae Filipjev and Steinernema riobrave Cabanillas, Poinar & Raulston) were tested for virulence against 3^rd instar southern masked chafer white grubs, Cyclocephala lurida Bland. H. bacteriophora and H. megidis, being the most virulent, were selected to evaluate the interaction with an entomopathogenic fungus (EPF), Beauveria bassiana (Balsamo) Vuillemin strain GHA or Metarhizium anisopliae (Metsch.) Sorokin strain F-52, under laboratory and greenhouse conditions. Nematodes and fungi were either applied alone or in combination, with nematodes added to fungi at different times. When applied alone, B. bassiana and M. anisopliae did not reduce grub numbers. Under laboratory conditions, additive interactions were found between H. megidis and B. bassiana, and between H. bacteriophora and B. bassiana or M. anisopliae in most combinations against chafer grubs; a few treatments showed synergism or antagonism. The combined effect did not differ significantly for nematode and fungal applications made simultaneously or at different times. Nematode infection and infective juveniles (IJs) production in grub carcasses were not significantly affected by the presence of a fungus. Efficacies of H. bacteriophora and M. anisopliae were affected by temperature, with grub mortality increasing at higher temperatures. Under greenhouse conditions, additive or synergistic interaction was found between H. bacteriophora and B. bassiana or M. anisopliae in different formulations in simultaneous applications or when the nematode was applied 4 weeks after the fungi, except between B. bassiana ES and H. bacteriophora. The impact of H. bacteriophora alone or in combination with M. anisopliae or B. bassiana on 3^rd instar C. lurida was comparable to that of an imidacloprid insecticide used as curative applications. More virulent fungal strains or species may be required to achieve a stronger interaction with nematodes in the management of C. lurida.     

Occurrence,Parasitism, and Pathogenicity of Nematodes Associated with Sycamore (Platanus occidentalis L.)

Ten species of stylet-bearing nematodes were recovered in a survey of sycamore (Platanus occidentalis L. ) stands in Georgia. Helicotylenchus, Xiphinema, and Criconemoides were the genera found most frequently. Populations of Hoplolaimus galeatus, Scutellonema brachyurum, Helicotylenchus dihystera and H. pseudorobustus increased on greenhouse-grown sycamore, but Trichodorus christiei, Xiphinema americanum, Meloidogyne hapla, M. arenaria and M. incognita did not. Hoplolaimus galeatus and S. brachyurum are semi-endoparasites; H. dihystera and H. pseudorobustus are migratory endoparasites. Hoplolaimus galeatus caused extensive root necrosis and marked decrease of fresh weights of seedling roots and tops. Helicotylenchus dihystera and S. brachyurum produced only qualitatively different sparse and unhealthy root growth. Helicotylenchus pseudorobustus caused only a reduction in root surface area.     

Distribution of Selected Plant Parasitic Nematodes Relative to Vegetation and Edaphic Factors

The occurrence of selected plant-parasitic nematodes in the hemlock-hardwood-white pine, boreal forest, tundra, and oak-hickory associations in some northern states was compared. Helicotylenchus platyurus and Xiphinema americanum were not found in the boreal forest and tundra, and occurred infrequently in the hemlock-hardwood-white pine areas. They were found frequently, however, in the oak-hickory forest of Iowa. It is questioned that vegetational differences among the areas account directly for the major differences in nematode occurrence. Presence and absence of nematodes and their numbers in the oak-hickory association were clustered by similarity coefficients by sites and correlated with soil pH, percentage organic matter, percentage sand-silt-clay, and field capacity. Of the soil factors measured, pH gave the strongest correlations with nematode numbers. Xiphinema chambersi was found only in soils with a pH between 4.5 and 6.4 while the largest numbers of H. platyurus, H. pseudorobustus, and X. americanum occurred in soil above pH 6.0.     

Influence of Soil Temperature on Meloidogyne incognita Resistant and Susceptible Cotton,Gossypium hirsutum

The degree of resistance by a cotton plant to Meloidogyne incognita is affected by soil temperature, particularly in moderately resistant cultivars, The total number of nematodes in the resistant and moderately resistant rools at 35 C was equal to, or greater than, the number in susceptible roots at 20, 25, or 30 C. A shift in numbers to developing and egg-bearing forms of nematodes in the susceptible cultivar as tentperature increased indicates development was affected by temperature rather than by genetic resistance mechanisms. However, the nematode resistant cultivar did not support maturation of nematodes until a soil tempurature of 35 C was attained. This indicated that resistance mechanisms are partially repressed at 35 C and differences in nematode development cannot be explained in terms of accumulated heat units. The moderately resistant cultivar was significantly more sensitive to the effects of high temperature than was the resistant cultivar.     

Interactions between Meloidogyne incognita,M. hapla,and Pratylenchus brachyurus in Tobacco

In a greenhouse pot experiment on the pathogenicity and interactions of Meloidogyne incognita, M. hapla and Pratylenchus brachyurus on four cultivars o f tobacco the cultivars ''Hicks'' and ''NC 2326'' were susceptible to each nematode and "NC 95'' and ''NC 2512'' resistant only to M. incognita.Mean heights of susceptible plants were depressed but fresh weight of tops did not differ significantly. Meloidogyne spp. increased fresh weight of susceptible (but not the resistant) roots.Reproduction of M. incognita was decreased in the presence of P. brachyurus in one case. M. hapla reproduction was less with either of the other nematodes in five out of eight cases. In 12 combinations involving P. brachyurus, reproduction of this species was depressed in seven, not affected in four and increased in one.Mechanisms involved in associative interactions were not identified but appeared to be indirect and to involve individual host-nematode responses.     

Interrelations between Meloidogyne javanica,Rotylenchulus reniformis,and Rhizobium Sp. on Vigna sinensis

The interactions of Meloidogyne javanica, Rotylenchulus reniformis, and Rhizobium sp. on cowpea seedlings were investigated. Upon simultaneous inoculation with the two nematode species, M. javanica invaded first but did not affect root invasion by R. reniformis. M. javanica populations increased less in competition with R. reniformis than when present alone. Preinvasion by R. renilormis significantly suppressed the number of M. javanica in the roots. Inoculation of M. javanica and/or R. reniformis with rhizobia did not affect nodulation. Nodule formation was hindered only when R. reniformis infection preceded rhizobial inoculation. Nitrogen nodules were formed on M. javanica galls. Nodules and M. javanica galls served as infection sites for both nematodes. Although R. reniIormis on the roots reduced the space for M. javanica infection, M. javanica is more competitive than R. reniformis and ultimately predominates as a result of its higher reproductive potential and shorter time spent in the soil before infection.