Effects of Biosolid Soil Amendment on Heterodera glycines Populations.

The high degree of parasitic variability in Heterodera glycines and its distribution in a wide range of soybean production systems present multiple challenges for management, which necessitate increased understanding of the biology of H. glycines. Soil amendments are being considered either as stand-alone and/or as part of integrated management approaches. A recycled municipal biosolid with nutrition supplement and liming qualities, N-Viro Soil (NVS) has potential as a multi-purpose soil amendment. In three greenhouse experiments, the effects of 0, 1.0 or 4.0 g NVS/100 cm(3) of sandy loam soil on three H. glycines populations (GN1, GN2 and GN3) were investigated on soybean grown for 557 +/- 68 degree-days (base 10 degrees C). The response of the three H. glycines populations to NVS treatment varied by experiment. The overall numbers of preadult stages and cysts generally decreased with increasing levels of NVS in all experiments, and the high rate was more effective than the low rate in suppressing H. glycines numbers. This suggests that the high NVS treatment can affect the three populations in the experimental soil type under controlled conditions. Field studies to determine efficacy of the soil amendment in a wide range of environments should be initiated.

Assessing Heterodera glycines-Resistant and Susceptible Cultivar Yield Response.

The soybean cyst nematode Heterodera glycines (SCN) is of major economic importance and widely distributed throughout soybean production regions of the United States where different maturity groups with the same sources of SCN resistance are grown. The objective of this study was to assess SCN-resistant and -susceptible soybean yield responses in infested soils across the north-central region. In 1994 and 1995, eight SCN-resistant and eight SCN-susceptible public soybean cultivars representing maturity groups (MG) I to IV were planted in 63 fields, either infested or noninfested, in 10 states in the north-central United States. Soil samples were taken to determine initial SCN population density and race, and soil classification. Data were grouped for analysis by adaptation based on MG zones. Soybean yields were 658 to 3,840 kg/ha across the sites. Soybean cyst nematode-resistant cultivars yielded better at SCN-infested sites but lost this superiority to susceptible soybean cultivars at noninfested sites. Interactions were observed among initial SCN population density, cultivar, and location. This study showed that no region-wide predictive equations could be developed for yield loss based on initial nematode populations in the soil and that yield loss due to SCN in our region was greatly confounded by other stress factors, which included temperature and moisture extremes.

Germplasm Evaluation of Glycine max for Resistance to Fusarium solani, the Causal Organism of Sudden Death Syndrome.

Sudden death syndrome (SDS) is an important soybean disease that potentially can be controlled by host plant resistance. In this study, over 800 soybean plant introductions (PIs), lines, and cultivars were screened for resistance to Fusarium solani. Of 728 PIs from China, PI 567.374 had mean foliar SDS severities significantly (P = 0.05) lower than PI 520.733 (resistant check) in both growth-chamber and greenhouse tests. In addition, PIs 567.315, 567.441C, 567.650B, and 567.664 had mean SDS severity ratings significantly (P = 0.05) lower than PI 520.733 in a growth-chamber test. Of 16 soybean cyst nematode-resistant entries tested, 5 had values lower than the resistant check, PI 520.733, with cv. Hartwig significantly lower in the first trial. In trial two, no entries were lower than the resistant check, although cvs. Bell and Hartwig were not significantly different from PI 520.733. In another experiment, few soybean cultivars or experimental lines had SDS severity ratings lower than PI 520.733 in any one of three trials. Some of the newly acquired PIs from China that exhibited low foliar SDS severity ratings may provide the sources of resistance needed to develop new SDS-resistant soybean breeding lines and cultivars.

Soybean Cyst Nematode Reduces Soybean Yield Without Causing Obvious Aboveground Symptoms.

Field experiments were conducted at locations in northern and southern Illinois, central Iowa, and central Missouri from 1997 to 1999 to investigate the effects of Heterodera glycines on soybean growth, development, and yield. A wide range of infestation levels was present at all locations. Two locally adapted cultivars, one resistant to H. glycines, were grown at each location. Cultivars were planted in alternating four-row strips with 76 cm between rows. For each cultivar, 20 1-m-long single-row plots were sampled every 2 weeks starting 4 weeks after planting. Infection by H. glycines reduced plant height and leaf and stem weight on the resistant cultivars in the first 12 weeks after planting, and delayed pod and seed development 12 to 14 weeks after planting. Biomass accumulation was not reduced on the susceptible cultivars until 10 weeks after planting; reduction in pod and seed development occurred throughout the reproductive stages. Susceptible cultivars produced significantly lower yields than resistant cultivars, but the yield reductions were not accompanied by visually detectable symptoms.

Soybean Cyst Nematode Reproduction in the North Central United States.

An experiment was conducted in Heterodera glycines-infested fields in 40 north central U.S. environments (21 sites in 1994 and 19 sites in 1995) to assess reproduction of this nematode. Two resistant and two susceptible soybean cultivars from each of the maturity groups (MG) I through IV were grown at each site in 6.1 m by 4 row plots. Soil samples were collected from each plot at planting and harvest and processed at Iowa State University to determine H. glycines initial (Pi) and final (Pf) population densities as eggs per 100 cm3 of soil. Overall, reproduction (Pf/Pi) of H. glycines on susceptible cultivars in all MG was similar. Reproduction was higher on MG III and IV susceptible cultivars than on those in MG I and II. Resistant MG I and II cultivars reduced nematode population densities more consistently than those in MG III and IV. Reproduction of the nematode was similar among sites within the same maturity zone (MZ), defined as the areas of best adaptation of the corresponding MG. Nonetheless, careful monitoring of nematode population densities is necessary to assess changes that occur over time in individual fields.

Comparison of 'Fayette' Soybean, Aldicarb, and Experimental Nematicides for Management of Heterodera glycines on Soybean.

The efficacies of Heterodera glycines-resistant 'Fayene' soybean and aldicarb for managing H. glycines were compared to the experimental nematicides DS-47187 10F, DS-47357 10F, DS-48145 10F, DS-48165 10F, DS-46995 10F and 5G, and DS-38697 5G during 1981-83. Yield of Fayette was greater than yield of the H. glycines-susceptible cultivar treated with nematicide in 1981 and 1983. Yield of aldicarb-treated soybean was greater than yield of soybean treated with experimental nematicides in 1983. There were no yield differences in 1982. Fewer white females were recovered from Fayette 5 weeks after planting than from soybean treated with nematicides in 1981 and 1982, but not in 1983. Fewer white females were recovered from aldicarb-treated soybean than from experimental nematicide-treated soybean in 1983 but not in 1981 and 1982. In 1983 numbers of first generation white females at 5 weeks and the ratio of those white females to gravid cysts at planting were negatively correlated with soybean yield when soybean was severely damaged by the nematode, but the ratio of final eggs and second-stage juveniles to initial eggs and second-stage juveniles was not correlated with yield.

Evaluation of Thuringiensin for Control of Heterodera glycines on Soybean.

The efficacy of ABG-6162A (1.5 L formulation of thuringiensin) for control of Heterodera glycines on soybean (Glycine max cv. Williams 82) was evaluated in the greenhouse at rates of 0, 10, 100, 500, and 1,000 ppm a.i. and in a field experiment at rates of 0, 3.4, 10.2, and 20.3 g a.i./100 m of row applied in an 18-cm-wide band. In the greenhouse, the 100-ppm rate was as effective as an equivalent rate of aldicarb and caused no phytotoxicity, but the higher rates of thuringiensin were highly phytotoxic. In the field experiment, numbers of females recovered from plots treated with thuringiensin at the 3.4-g and 10.2-g rates were greater (P

Inability of a Seed Treatment with Pseudomonas cepacia to Control Heterodera glycines on Soybean.

A commercial seed treatment containing Pseudomonas cepacia was applied to Glycine max cv. Williams 82 (susceptible to Heterodera glycines) and was compared to Fayette soybean (resistant to H. glycines) for control of H. glycines at two locations in Illinois. The soil at the first location was sandy in texture and the field was irrigated, whereas the soil at the second location was a silty clay loam and the field was not irrigated. At both locations there was no yield increase associated with the seed treatment , but yield of Fayette was significantly (P < 0.05) greater than Williams 82 regardless of treatment.

Scanning Electron Microscopy of Vulval Cones of Heterodera glycines and Three Related Cyst Nematode Species.

Vulval cones of four closely related Heterodera species - H. glycines (races 1-5), H. lespedezae, H. schachtii, and H. trifolii - were examined using scanning electron microscopy. Numbers of dorsal and ventral radial ridges, total radial ridges, perineal ridges, and preanal ridges were useful in differentiating the five races of H. glycines and the other three species. Most of the populations differed significantly (P < 0.01) using the Waller-Duncan k-ratio t-test for mean separation of the five characters. H. glycines races 2, 4, and 5 were most similar. H. schachtii and H. trifolii were most dissimilar to each other and to H. lespedezae and H. glycines. Two additional qualitative characters were also useful in differentiating the populations. The shallower, shorter radial ridges of H. glycines provided a basis for separation from the other three species. Width and smoothness of the perineal ridges were useful in differentiating both races and species.

Comparative Electrophoretic Analyses of Soluble Proteins from Heterodera glycines Races 1-4 and Three Other Heterodera Species.

Modified polyacrylamide gel and SDS-polyacrylamide gel electrophoretic systems using a low molarity tris-HCl buffer and equal pH of homogenizing buffer and stacking gel provided improved stacking for separation of soluble proteins from Heterodera schachtii, H. trifolii, H. lespedezae, and H. glycines races 1, 2, 3, and 4, compared with previous studies with cyst nematodes, The four Heterodera species were easily distinguished using the polyacrylamide gel system, but H. trifolii and H. lespedezae had similar protein patterns. H. glycines races were not separable by that system. The SDS-polyacrylamide gel system produced different protein patterns for all four Heterodera species although H. trifolii and H. lespedezae differed by only a single band, suggesting that these two may be subspecifically related. A protein band unique to H. glycines races 3 and 4 was not detected in SDS-polyacrylamide gel profiles from races 1 and 2. Molecular weight determinations were 55,000 for distinctive proteins in profiles of H. trifolii and 75,000 for H. glycines races 3 and 4.

Pathogenicity of Criconemella curvata to Alfalfa.

Large populations of Criconemella curvata and extended experimental periods were required to adversely affect yield of 'Moapa 69' alfalfa. C. curvata ectoparasitic feeding caused a reduction in feeder root numbers and tap root size and small lesions on tap and secondary roots. Greater reproduction occurred at 27 C than at 22 C, but the effect of the nematode on alfalfa growth was the same at both temperatures.

First Report of Pasteuria sp. Attacking Heterodera glycines in North America.

Endospores of a Pasteuria sp. were observed on Heterodera glycines second-stage juveniles and males recovered from soil in microplots in which nematode populations had been declining for several years. Conventional scanning electron microscopy was used to observe and measure endospores on second-stage juveniles (J2) of both a race 3 and a race 4 population. Endospores were elipsoidal; those attached to J2 of race 3 measured (X) 4.2 x 3.7 mum with a height of 2.0 mum, and those on race 4 were 4.3 x 3.7 mum with a height of 2.3 mum. Measurements taken under light microscopy indicated that endospores attached to J2 of race 3 were 5.0 x 4.8 mum with a height of 2.2 mum. The velutinous exosporium of the H. glycines-infecting P. nishizawae from Japan was not visible in the Illinois isolate. Differences in endospore morphology and the apparent inability of the Illinois isolate to complete its life cycle in females indicate that the Japanese and Illinois isolates are distinct species of Pasteuria.

Population Development of Heterodera glycines and Soybean Yield in Soybean-maize Rotations Following Introduction into a Noninfested Field.

An 11-year field study was initiated in 1979 to monitor population development of Heterodera glycines. Fifty cysts of a race 5 population were introduced into plots in a field with no history of soybean production and that had been in sod for 20 years. Soybean cultivars either susceptible or resistant to H. glycines were grown either in monoculture or rotated with maize in a 2-year rotation. During the first 5 years, resistant cultivars with the Peking source of resistance were planted. After year 5, monocuhure of Peking resistance resulted in 18 cysts/250 cm(3) of soil, whereas populations resulting from the continuous cropping of susceptible soybean resulted in 45 cysts/250 cm(3). Some plots in all treatments, including control plots, were contaminated at the end of year 5. Crop rotation delayed population development of H. glycines. During years 6 through 11 cv. Fayette (PI88.788 source of resistance) was planted. In year 6 numbers of cysts declined to 1/250 cm(3) of soil in the treatment consisting of monocultured Fayette. At the end of year 10, cysts were below the detection level in all treatments in which Fayette was planted. Yield of susceptible soybean in monoculture with or without H. glycines infestation was lower beginning in year 6 when compared to yield of soybean grown in rotation and remained lower throughout the duration of the experiment except for 1987 (year 9). Yields of susceptible and resistant soybean were different each year except for drought years in 1980 and 1988. From 1979 to 1982 differences in yield were due to lower yield potential of resistant cultivars. Except for the drought year, yield of cv. Fayette was greater than susceptible Williams 82 during years 6 through 11.

Hatch and Emergence of Heterodera glycines in Root Leachate from Resistant and Susceptible Soybean Cultivars.

Egg hatch and emergence of second-stage juveniles (J2) of Heterodera glycines races 3 and 4 from cysts exposed to soybean root leachate of cv. Fayette (resistant to H. glycines) and H. glycines-susceptible cultivars A2575, A3127, and Williams 82 were determined in three sets of experiments. In the first experiment, cysts of both race 3 and race 4 were exposed to leachate of 8-week-old plants for a 2-week period. In the second experiment, cysts from populations of races 3 and 4 were raised on cultivars A2575, A3127, and Williams 82. Cysts then were exposed to leachate from 8-week-old plants for a 2-week period in all possible race-per-cultivar combinations. In the third experiment, cysts of races 3 and 4 were exposed at 4-day intervals to leachate from plants as the plants developed 7 to 59 days after planting. In experiments 1 and 2, leachate from 8-week-old Williams 82 and A3127 stimulated more hatch and emergence of H. glycines than leachate from A2575, Fayette, or the control. In the first experiment, cumulative hatch and emergence were greater for race 3 than for race 4. In experiment 2, no apparent relationship developed between leachate from a cultivar and the population developed on that cultivar in terms of stimulation of hatch and emergence. In the third experiment, A2575 stimulated more hatch and emergence of both race 3 and race 4 than A3127, Fayette, and Williams 82. Leachate from Fayette stimulated less hatch and emergence of both race 3 and race 4. Hatch and emergence were greatest during the initial 12 days of the experiment.

Peroxidase and 6-phosphogluconate dehydrogenase in resistant and susceptible cotton infected by Meloidogyne incognita.

Assays of specific activities and electrophoretic separations of multiple forms of 6-phosphogluconate dehydrogenase and peroxidase in cotton resistant and susceptible to Meloidogyne incognita were conducted 6 days after inoculation. Specific activities were greater in infected than in uninfected roots and also were greater in the resistant cultivar, 'Clevewilt 6-3-5,' than in the susceptible culti.var, 'M8.' In uninfected roots, peroxidase activity was greater in Clevewilt roots than in M8 roots, but activity of 6-phosphoglueonate dehydrogenase was the same. Multiple forms of peroxidase and 6-phosphogluconate dehydrogenase were separated and resolved by polyacrylamide gel electrophoresis. These experiments demonstrated the occurrence of altered metabolism upon infection and differences in enzyme activity between resistant and susceptible cultivars.

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.

Evaluation of Soybeans in Maturity Groups I-IV for Resistance to Heterodera glycines.

Forty-seven private and public soybean (Glycine max) cultivars in maturity groups I, II, III, and IV were evaluated in the field for resistance to Heterodera glycines race 3 and race 4 at two sites, Kilbourne and Urbana, Illinois. The soil at Kilbonrne was an irrigated sand infested with race 3. The soil at Urbana was a nonirrigated silty clay loam infested with race 4. Yield of nematode-susceptible controls was reduced at both locations, and yield differences were observed among the other cultivars. Soybeans grown in sand yielded less than the soybean grown in silty clay loam. Although populations of H. glycines recovered at planting were lower at Kilbourne than at Urbana, a greater percentage of loss in yield was associated with the sand at Kilbourne. Several soybean cultivars had a high level of resistance to both populations of H. glycines.

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 cm(3) 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.

Scanning Electron Microscopy of Second-Stage Juvenile Cephalic Morphology in Heterodera glycines Races.

Scanning electron microscopy (SEM) was used to compare juvenile cephalic morphology of the five described races of Heterodera glycines. Races 1, 2, 3, and 4 were obtained in the United States and race 5 was obtained from Japan. Differences in the gross morphology o f labial discs; ventral, dorsal and lateral lips; amphidial apertures; and fissures on the labial disc o f some specimens were observed. There was considerable interracial and intraracial variation which precluded separation o f juveniles of H. glycines races by SEM.

Population Dynamics of Heterodera glycines in Conventional Tillage and No-Tillage Soybean/Corn Cropping Systems.

The effects of no-tillage (NT), conventional tillage (CT), and crop rotation on soybean yield and population dynamics of Heterodera glycines were compared during a 7-year study in a silty clay loam soil with 6% organic matter. Either H. glycines-resistant 'Linford' soybean or susceptible 'Williams 82' soybean was rotated with corn and grown on 76-cm-wide rows in both tillage systems. Soybean was planted in 1994, 1996, 1998, 1999, and 2000. Yield of Linford was significantly greater than Williams 82 in all years. Soybean yield was affected by tillage in 1999 and 2000. No-tillage production tended to support more reproduction (R = number of eggs at harvest/number of eggs at planting) on both cultivars. The largest R for Williams 82 were in 1998: 58.35 for NT plots and 11.78 for CT plots. For Linford, the largest R were 12.09 for NT plots in 1996, and 3.71 for CT in 1999. When corn was planted, R decreased more in NT. When soybean was planted in years subsequent to 1994, numbers of eggs at harvest (Pf) were greater for Williams 82 NT than for Williams 82 CT or Linford in both tillage systems; however, crop rotation with corn negated these population increases. The soil became suppressive to H. glycines in 1999 and was suppressive in 2000. After the 3 years of continuous soybean, Pf per 250 cm[sup3] soil were 2,870 for Williams 82 NT, 791 for Williams 82 CT, 544 for Linford NT, and 990 for Linford CT in 2000, compared with Pf of 13,100 for Williams 82 NT, 15,000 for Williams CT, 2,360 for Linford NT, and 2,050 for Linford CT in 1994. Describing population dynamics solely on the basis of R was not adequate, but also required independent examination of initial populations following overwintering and Pf after the growing season. Planting soybean either NT or CT in rotation with corn did not result in long-term increases in numbers of H. glycines eggs.