Soybean Cyst Nematode Population Density Research Articles

Soybean Cyst Nematode, Heterodera glycines, Populations Adapting to Resistant Soybean Cultivars in Kentucky.

Soybean cyst nematode (SCN), Heterodera glycines, is the most limiting biotic factor of soybean (Glycine max) production in Kentucky (KY). Unpublished results of a survey of commercial soybean fields in KY in the late 1980s indicated that H. glycines (HG) type 0 (race 3) was the most common HG type in the state. HG type 0 populations cannot reproduce (female index [FI] <10% compared with reproduction on a standard susceptible cultivar) on PI88788, which is the basis of H. glycines resistance in >90% of the soybean cultivars grown in the United States. Recent reports from Illinois (4), Missouri (3), and North Carolina (2) indicate that most populations of H. glycines in those states are now able to reproduce on resistant soybean cultivars derived from PI88788. Because cultivars derived from PI88788 are grown almost exclusively in KY to manage H. glycines, a limited survey was needed to update information on H. glycines populations. Most soybean fields in KY are grown in a 1-year rotation with corn (Zea mays), a nonhost crop for H. glycines. Therefore, the survey targeted fields that had most recently been in corn. Otherwise, fields were arbitrarily selected for sampling. Composite samples were collected in the fall of 2006 or the spring of 2007 and consisted of 20 soil cores (10 to 15 cm deep × 2.5 cm in diameter) collected following a zigzag pattern. Samples were mixed and stored at 4°C until processing. H. glycines cysts were extracted from soil by a sucrose centrifugation and flotation technique (1). Eggs were liberated by crushing cysts caught on a sieve (250-μm-diameter pores) with a rubber stopper. Liberated eggs were then collected, stained with acid fuchsin, and counted. Up to three samples from each county surveyed were sent to the University of Missouri Nematology Laboratory, Columbia, MO for HG type testing (3). A total of 139 samples, representing 19 major soybean-production counties in KY, were analyzed for H. glycines levels. H. glycines eggs were recovered from 106 (76%) samples and 16 (84%) counties. SCN population densities ranged from 38 to 4,275 eggs per 250 cm3 of soil. HG type tests were conducted on 20 populations from eight counties. HG types 1.2.5.7 (race 2) and 2.5.7 (race 1 or 5) were identified, with HG type 2.5.7 (race 1) being the most common (60% of populations screened). No HG type 0 populations were detected. All populations tested had a FI ≥10% on three of nine indicator lines (PI88788, PI209322, and PI548316). FIs on these indicators ranged from 15 to 80, 11 to 81, and 23 to 88%, respectively. Sixty percent of populations tested had FIs ≥30% on PI88788. Of the populations screened, 25 and 35% had FIs ≥10% on PI548402 (Peking) and Pickett, respectively. All populations tested had FIs = 0 on PI437654. Survey results indicate that cultivars deriving their H. glycines resistance from PI88788 may have reduced effectiveness in suppressing current H. glycines populations in KY. Consequently, producers may need to grow soybean cultivars derived from non-PI88788 resistance sources to successfully manage H. glycines in the future.

Purple Deadnettle (Lamium Purpureum) Emergence and Removal Time Effects on Soybean Cyst Nematode (Heterodera Glycines)

Abstract Purple deadnettle is an obligate winter annual weed and an alternate host of soybean cyst nematode (SCN). Field experiments were conducted using microplots to determine (1) the effect of purple deadnettle planting date and (2) the effect of purple deadnettle removal time on SCN egg population density in continuous no-tillage soybean. A population change factor (PCF) to assess treatment effects on SCN population densities was calculated by dividing the SCN population density at each sampling time (Pf) by the initial population density before treatments were applied (Pi). In the planting date experiment, purple deadnettle seeded on October 3, 11, and 18 resulted in PCF values ranging from 7.28 to 11.41, which were three- to fivefold higher than the PCF values for the weed-free control or purple deadnettle seeded on September 6, 20, and 27. Self-thinning of purple deadnettle seeded in September may have resulted in higher levels of SCN mortality compared to later seeding dates. In the removal time e...

Effect of Soybean Cyst Nematode (Heterodera glycines) Resistance Rotation on SCN Population Distribution, Soybean Canopy Reflectance, and Grain Yield

The soybean cyst nematode (SCN) is a serious pest that needs to be managed in soybean production. This pest is difficult to detect at its onset, as symptoms deleterious to the plant are not dramatic. This study was conducted to evaluate the effect of SCN resistance rotation on SCN distribution as well as on soybean canopy reflectance and grain yield. A 0.8 ha field was planted with soybeans under eleven resistance rotation treatments. Two sets of SCN counts and three airborne visible-infrared images were obtained during the 2004 season. An analysis of variance (ANOVA) indicated that the resistance rotation treatment explained 59% and 64% of variability in cyst and egg counts at planting, and 55% and 57% of variability in cyst and egg counts at harvest. The yield was lowest in all the plots under cultivar Manokin, and monoculture of Hutcheson or Hutcheson treated with the nematicide Temik, while the highest yields occurred in plots under cultivar Anand. The SCN population densities at planting and harvest and grain yield were correlated to the wide dynamic range vegetation index (WDRVI) at P < 0.1. However, there was no relationship between SCN population densities and normalized difference vegetation index (NDVI) and green NDVI (GNDVI) on any given date in the season. This study indicated that the resistance rotation was effective in managing SCN in the field. Remote sensing showed potential in identifying SCN damage under the low to moderate infestation. This study also elucidates the complex relationship between SCN population density in the soil and potential crop damage, and the difficulty in assessing SCN infestation.

Influence of Winter Annual Weed Management and Crop Rotation on Soybean Cyst Nematode (Heterodera Glycines) and Winter Annual Weeds

Abstract Certain winter annual weeds have been documented as alternative hosts to soybean cyst nematode (SCN), and infestations of such species have become common in no-till production fields in the Midwest. This research was conducted to determine the influence of herbicide- and cover-crop-based winter annual weed management systems and crop rotation on winter annual weed growth and seed production, SCN population density, and crop yield. Two crop rotations (continuous soybean and soybean-corn) and six winter annual weed management systems (a nontreated control, fall and spring herbicide applications, spring-applied herbicide, fall-applied herbicide, fall-seeded annual ryegrass, and fall-seeded winter wheat) were evaluated in no-tillage systems from fall 2003 to 2006 at West Lafayette, IN and Vincennes, IN. Fall or spring herbicide treatments generally resulted in lower winter annual weed densities than cover crops. Densities of henbit and purple deadnettle increased over years in the cover crop systems ...

Winter-Annual Weed Management in Corn (Zea mays) and Soybean (Glycine max) and the Impact on Soybean Cyst Nematode (Heterodera glycines) Egg Population Densities

Field research was conducted at Columbia and Novelty, MO, to determine the impact of winter-annual weed management systems on corn and soybean grain yields, winter-annual weed control, and soybean cyst nematode (SCN) egg population densities over the crop production cycle. Corn grain yield was not affected by winter-annual weed management systems. Soybean grain yield was not affected by winter weed management systems in 2001, but at Columbia in 2002 winter rye and Italian ryegrass reduced soybean grain yield 62 and 64%, respectively. Fall-applied simazine + tribenuron in corn and chlorimuron + sulfentrazone in soybean controlled winter-annual weeds greater than 99%. Fall-overseeded winter rye and Italian ryegrass in corn and overseeded Italian ryegrass in soybean controlled winter weeds 66 to 86%. In the soybean studies, race 4 SCN population densities increased (P = 0.08) in the nontreated control and remained stable (P = 0.55) with fall-applied chlorimuron + sulfentrazone from fall 2001 to spring 2002 while SCN population densities were reduced (P = 0.06) with spring-applied chlorimuron + sulfentrazone from fall 2002 to spring 2003. In the corn studies, none of the winter-annual weed management strategies reduced (P &gt; 0.22) race 2 SCN population densities except winter rye from fall 2001 to spring 2002 (P = 0.05). This research indicates that control of weed species considered to be weak alternative hosts for SCN affected SCN population densities some instances when race 4 SCN population densities were high in a continuous soybean production system or race 2 SCN population densities were low in a 2-yr corn production system.

Effect of Cover Crops Alfalfa, Red Clover, and Perennial Ryegrass on Soybean Cyst Nematode Population and Soybean and Corn Yields in Minnesota

The effects of alfalfa, red clover, and perennial ryegrass as cover crops on soybean cyst nematode (SCN) and soybean and corn yields were evaluated in Waseca, Lamberton, and Rosemount, MN. The cover crops were interseeded in soybean at 0 or 2 wks after planting soybean in 2002 and killed with herbicide before planting corn in 2003. As expected, SCN‐susceptible soybean supported higher SCN population density than SCN‐resistant soybean. Reduction of SCN population density by red clover (up to 40%) and alfalfa (up to 55%) was observed in some sampling occasions at Lamberton and Rosemount, probably due to reduced soybean growth, but the effect was inconsistent. No significant reduction of SCN population by the two crops was detected at Waseca. While perennial ryegrass did not affect SCN population density in most cases, up to 46% higher egg population densities were observed in the perennial ryegrass treatment as compared to the control at Waseca. SCN‐resistant soybean produced higher yield than susceptible soybean at all sites. While alfalfa reduced soybean yield at Lamberton (up to 50%) and Rosemount (up to 11%), red clover and perennial ryegrass reduced soybean yield only at Lamberton (up to 38%) and Waseca (up to 34%), respectively. No difference in corn yield was observed at Waseca. At Lamberton, alfalfa and red clover planted at the time of planting soybean reduced corn yield in the following year 17 and 13%, respectively, and perennial ryegrass planted 2 wks after planting soybean reduced corn yield 13%. At Rosemount, significant reduction of corn yield was observed with red clover (15–21%) interseeded in SCN‐susceptible soybean and with alfalfa (12%) and red clover (12%) interseeded in SCN‐resistant soybean at the time of planting soybean. The results suggest that an even later planting date of cover crops in soybean may reduce yield loss due to competition and make these cover crops more appropriate for use in the soybean‐corn rotation in Minnesota.

Rotation Crop Evaluation for Management of the Soybean Cyst Nematode in Minnesota

Crop rotation is an effective tactic for soybean cyst nematode (SCN) management. In the North Central region of the USA, corn is almost exclusively used as a nonhost rotation crop with soybean. This study was conducted to determine the effectiveness of crops common to or having potential use in the North Central region as rotation crops for managing SCN. Sixteen potential rotation crops and SCN‐resistant and susceptible soybeans were grown along with six fallow controls in three commercial field sites near Waseca, Lamberton, and Morris, MN, in 2001, and SCN‐susceptible soybean was grown on all plots in 2002. Nematode populations at planting, midseason, and harvest were measured both years; soybean yield was measured in 2002. There was large variability in SCN populations and soybean yields at the three sites. Nevertheless, significant treatment effects were detected at all sites. While all of the rotation crops lowered SCN populations compared with SCN‐susceptible soybean, there were only subtle differences among the individual rotation crops and among different groups of the crops. Leguminous nonhosts or poor hosts were best in reducing SCN population density. Corn, the most common rotation crop in Minnesota, was among the least effective in reducing nematode populations. There was an undetectable yield benefit from SCN management, although differences in yield were observed among the rotation crop treatments—probably due to agronomic factors. The data suggest that a single year of rotation of soybean with any of these crops before planting a susceptible soybean may not be sufficient in managing SCN.

The Spatial Distribution of Soybean Cyst Nematode in Relation to Soil Texture and Soil Map Unit

Evidence suggests that variation in soil texture may be key to explain the variability of soybean cyst nematode (Heterodera glycinesIchinohe) population density within infested fields and may be important to the delineation of soybean cyst nematode (SCN) management zones. The purpose of this work was to assess the spatial structure of soil texture in two fields of known SCN population density and its relationship to published soil survey maps and to quantify the relationship between soil texture and SCN population density variability across fields and over time. Cysts were extracted by elutriation from single‐core soil samples collected in a geostatistical sampling design. Soil texture analysis was performed using a modified hydrometer method. Classical and geostatistical tools were employed to characterize and map soil texture and correlate sand, silt, and clay with SCN population. Cyst population density was consistently higher in loamy sand than in sandy clay loam. Sand, clay, and silt in the soil were spatially structured and strongly correlated with SCN population density consistently over time. The number of eggs per cyst was not related to soil type or texture. This study demonstrates the value of soil survey maps as indicators of where SCN can be expected in an infested field and how the addition of site‐specific texture data can improve the spatial prediction of SCN. This study provides the basis for future experimentation to define soil texture tolerance limits for SCN and lays out foundations for new and integrated approaches to site‐specific management of SCN.

COUPLING SOYBEAN CYST NEMATODE DAMAGE TO CROPGRO–SOYBEAN

The soybean cyst nematode (SCN) Heterodera glycines Ichinohe is responsible for substantial economic losses in soybean (Glycine max L. Merr.) production throughout the U.S. Results from past efforts to quantify the severity of crop damage resulting from SCN are often subject to variable experimental conditions resulting from differences in weather, soil type, and cultivar. Because of the difficulty in accounting for these variables, a process–oriented crop growth simulation model was chosen as a platform for studying the dynamics of SCN damage and for transferring knowledge between crop production scenarios. The objective of this study was to develop and evaluate hypotheses for coupling SCN damage to the process–oriented crop growth model CROPGRO–Soybean. A monomolecular function was used to relate daily SCN damage to initial population density of SCN eggs. The equation was incorporated into the crop model in order to test two hypotheses of how SCN damage occurs. The first hypothesis was that SCN reduce daily photosynthesis (Pg), while the second hypothesis was that SCN reduce daily potential root water uptake (RWU). Canopy biomass data collected in 1997 and 1998 from a site in Iowa were used to estimate damage function parameters for two distinct coupling points, one applied to reduce daily photosynthesis (Pg) and the other applied to reduce daily potential root water uptake (RWU). Function parameters were estimated by minimizing the log transformation of root mean square error (RMSE) between predicted and measured canopy biomass collected every 2 weeks during the season in Iowa. Biomass data collected in 1997 and 1998 from an independent site in Missouri were used to validate the SCN damage models. The minimum root mean squared errors (RMSE) of canopy and grain biomass were 0.245 and 0.198 log10(kg ha –1 ), respectively, for the RWU coupling point, and 0.238 and 0.193 log10(kg ha –1 ), respectively, for the Pg coupling point at the independent site in Missouri. The damage functions transferred very well to the independent site. Validation showed that the Pg coupling point represented the variability of both canopy and final yield data slightly better than the RWU coupling point.

Crop Sequence Effects on Soybean Cyst Nematode and Soybean and Corn Yields

The soybean cyst nematode (SCN), Heterodera glycines Ichinohe, is a destructive pest of soybean, Glycine max (L.) Merr. Field research was conducted at Waseca and Lamberton, MN, from 1996 through 1999 to evaluate the effect of crop sequence on SCN population density and on crop yields. Cropping sequence treatments were (i) monocultures of corn (Zea mays L.), SCN‐resistant soybean, and SCN‐susceptible soybean; (ii) susceptible soybean rotated with 1, 2, or 3 yr of corn; (iii) resistant soybean rotated annually with corn; and (iv) rotation of corn–resistant soybean–corn–susceptible soybean. Egg density was determined at sowing and harvest, and crop yields were determined each year. In general, yields of resistant soybean were higher than susceptible soybean. Resistant soybean in annual rotation with corn produced the highest yield, and susceptible soybean in monoculture produced the lowest yield among all treatments. A longer period of corn in rotation resulted in higher yield of subsequent susceptible soybean in most instances. Yields of corn following corn were lower than following soybean. Egg density at the start of the study was 6994 and 14 000 eggs 100 cm−3 soil at Waseca and Lamberton, respectively. Average Pf/Pi (egg density at harvest/egg density at sowing) was 0.59 (0.23–0.86) for corn, 0.49 (0.21–0.73) for resistant soybean, and 3.3 (0.74–9.91) for susceptible soybean for all treatments at the two sites across the 4‐yr period. After 3 yr of corn, egg density decreased to 889 and 3695 eggs 100 cm−3 soil at Waseca and Lamberton, respectively. Annual rotation of resistant soybean and corn resulted in the lowest SCN population density and produced the highest yield of both crops.

Screening Isolates of Hirsutella Species for Biocontrol of Heterodera glycines

The fungi, Hirsutella rhossiliensis and Hirsutella minnesotensis, are two endoparasites of second-stage juveniles (J2) of the soybean cyst nematode (SCN), Heterodera glycines. The objective of this study was to screen for effective fungal isolates to control the nematode in laboratory and greenhouse assays. A total of 93 isolates of H. rhossiliensis and 25 isolates of H. minnesotensis were evaluated for parasitism of SCN J2 on cornmeal agar. Percentage of SCN J2 parasitized by the fungi varied among the fungal isolates. Most H. rhossiliensis isolates parasitized a high percentage of J2. The isolates of H. rhossiliensis obtained from bacteria-feeding nematodes, however, generally did not parasitize J2 on agar. H. minnesotensis parasitized fewer J2 on agar than did H. rhossiliensis . Forty isolates of H. rhossiliensis and four isolates of H. minnesotensis that parasitized a high percentage of J2 on agar were evaluated for their biocontrol potential in soil treated with microwave heating. Most isolates selected from the agar assay also parasitized a high percentage of J2 in the soil but there was variation among isolates. Pathogenicity of 14 isolates of H. rhossiliensis and four isolates of H. minnesotensis to the SCN was also investigated in the greenhouse using untreated field soil. Most isolates of H. rhossiliensis reduced SCN population density and increased plant growth when compared with 1% corn-grits control (culture media). One isolate (OWVT-1) of H. rhossiliensis reduced the SCN egg density by 95% and J2 density by 98% when compared with the control. Isolates of H. minnesotensis, however, neither reduced SCN density nor increased plant growth in the greenhouse.

A Method for Infesting Small Field Plots with Soybean Cyst Nematode

AbstractField experimentation with soybean cyst nematode (Heterodera glycines Ichinohe) is difficult, because of problems in obtaining plots with desired population densities. Therefore, a technique was developed for infesting small field plots with soybean cyst nematode. In 1990 and 1991, cysts, eggs, and infective juveniles were mixed with soil and applied with a commercial fertilizer spreader. Infected soybean [Glycine max (L.) Merr.] root segments were distributed by hand. Infested soil and roots were incorporated with a tractor‐drawn herbicide incorporator, and plots were planted to susceptible soybean. At‐planting egg densities in 1990 and 1991 averaged 184 and 100 eggs 100 cm−3 soil, respectively, representing 78 and 90% of expected egg densities. Resultant low densities of encysted eggs, which are highly aggregated, probably prevented detection of eggs in some plots. No soybean cyst nematode was detected in uninfested plots at planting, although some contamination was noted at harvest. This method may be appropriate for establishing soybean cyst nematode population densities for some small‐plot research.

Reproductive Advantage in Soybean Associated with Resistance to Soybean Cyst Nematode: Effects of Tolerance and Nematode Density

Natural selection is used by plant breeders to increase the frequency of desirable genotypes in a population. When soybean [Glycine max (L.) Merr.] populations segregating for resistance to soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) are grown on SCN‐infested soil, resistant genotypes produce more seed than susceptible genotypes. In a bulk‐harvested population this differential reproduction results in an increased frequency of resistant genotypes in the population. This research was conducted to determine the effects of tolerance to SCN and the frequency of resistant genotypes in the population on the effectiveness of natural selection for resistance to SCN. A second objective was to relate initial SCN population densities and parental pure‐stand yield ratios to the effectiveness of natural selection. Four 1:1 viable seed mixtures of resistant (R) and susceptible (S) genotypes were evaluated in four SCN‐infested fields for 2 yr. Two of the S genotypes were moderately tolerant and two were intolerant to SCN. The R genotypes in mixtures with moderately tolerant, S genotypes had an average reproductive advantage (ratio of R/S seed number) of 2.2 compared to 4.2 for R genotypes in mixtures with intolerant, S genotypes. In a second experiment, five ratios, 1:9, 3:7, 1:1, 7:3, and 9:1, of R to S genotypes were compared for two of the genotypic mixtures (‘Gordon’/‘ Bragg’ and Gordon/‘Wright’). The effectiveness of natural selection was not related to the frequency of the R genotype in the mixture. On an individual‐plot basis across the four mixtures the linear regression of the pure‐stand R/S yield ratios predicted 47% of the variation in reproductive advantage of R genotypes compared to 22% for log10 of initial density of SCN eggs. Effectiveness of natural selection for SCN resistance was dependent on the initial population density of SCN, the specific environmental conditions, and the tolerance level of the genotypes in the soybean population.