Cyst Density Research Articles

Modelling the population dynamics of the toxic dinoflagellate Alexandrium tamarense in Hiroshima Bay, Japan. II. Sensitivity to physical and biological parameters

Using the numerical model developed in a previous paper [Υamamoto et al. (2002c) J. Plankton Res., 24, 33-47], the sensitivity of population dynamics of Alexandrium tamarense to physical and biological parameters was analysed. Horizontal and vertical diffusions led to the dispersion of dense A. tamarense populations in the surface layer of the innermost portion of the bay. Temperature and salinity influenced the timing of the A. tamarense bloom due to its stenothermal and steno-haline characteristics. Although increasing the light intensity caused the bloom of A. tamarense to begin earlier, it lowered the cell density at the bloom peak as a result of phosphate depletion in the ambient water. Both increasing the cyst density and the excystment rate had little influence on the population dynamics of A. tamarense vegetative cells. Increasing the phosphate concentration led to increases in cell density of A. tamarense, indicating that growth is phosphate-limited. Oysters, which are cultured intensively in this bay, appear to stimulate the bloom of A. tamarense through the regeneration of phosphorus from their faeces/pseudofaeces. The phosphorus reduction measure that has been taken since 1980 and the recent construction of a large dam are discussed as important factors that may influence the population dynamics of A. tamarense.

Pseudoenhancement of simulated renal cysts in a phantom using different multidetector CT scanners.

We undertook this study to determine whether pseudoenhancement of renal cysts occurs on scans obtained with multidetector CT (MDCT) scanners and whether the effect is influenced by scanning parameters. A kidney phantom with varying attenuation was created to simulate different levels of renal parenchymal enhancement (150 and 250 H). Two water-filled cylinders simulating renal cysts-one with a 5-mm diameter and one with a 15-mm diameter-were suspended in the "kidney." After validating the pseudoenhancement effect produced in our phantom model with a single-detector helical CT scanner, we investigated the effect with matrix array and adaptive array MDCT scanners using detector configurations of 1.25 and 2.5 mm and beam pitches of 0.75:1.0 and 1.5:1.0 at an effective reconstructed slice thickness of approximately 3 mm. Three sets of experiments were performed at each setting, and mean cyst density was measured. Data were statistically analyzed using the Student's t test and multiple logistic regression analysis when appropriate. Although pseudoenhancement was observed with MDCT scanners, the effect was statistically significant only for scans depicting the smaller cyst at a background renal density of 250 H on the matrix array MDCT. Modulation of scanning parameters did not alter these findings. Pseudoenhancement was significantly higher with the matrix array MDCT scanner than with the adaptive array MDCT scanner (p < 0.05). In our phantom model, high levels of renal enhancement produced pseudoenhancement in small renal cysts with different models of MDCT scanners, irrespective of pitch or detector configuration.

Distribution and density of cysticerci of Taenia solium by muscle groups and organs in naturally infected local finished pigs in Tanzania

The distribution and density of cysticerci of Taenia solium among distinct carcass sites was determined in 24 naturally infected finished pigs from Mbulu district, Tanzania. The heart, tongue, internal and external masseters, triceps brachii, lungs, liver, kidneys, psoas, diaphragm and brain of each pig as well as the muscles from the forelimb, hind limb, abdomen, head and thorax from one half of each pig carcass were all designated as distinct carcass sites and sliced in such a way that all fully developed cysts could be revealed and enumerated (i.e. each slice was less than 0.5 cm thick). The carcasses harboured from 76 to 80,340 cysts in total. Carcass sites which harboured the highest proportion of cysts were those of the hind and forelimbs (mean: 27.7 and 24.5%, respectively, of the total cysts in the carcass), while lower proportions were found in the tongue, heart, triceps brachii, and diaphragm (7, 3.6, 2 and 2, respectively). Relative cyst density was calculated for the different carcass sites by dividing the mean proportion of the total weight of the tissue groups into the mean proportion of cysts located in that site. The cysticerci in the examined distinct carcass sites were found in the following order of relative density: psoas muscles (10.5), internal masseter (8.1), external masseter (7.1), triceps brachii (4.9), forelimb (4.0), head muscles (3.8), tongue (3.4), hind limb (3.2), diaphragm (2.4), heart (1.9), abdominal muscles (1.3), trunk muscles (1.1), brain (1.0) and oesophagus (0.3). The proportion of cysts expected to be found at the surfaces exposed by visual examination or incision at meat inspection was calculated using an indirect method, which incorporated the area revealed by incision and visual inspection of an organ and the proportion of cysts located in the particular organ. It was estimated that 10.6% of the cysts would be located at inspected sites if regulations were followed carefully.

Cyst ornamentation in aquatic invertebrates: a defence against egg-predation

Eggs, including encysted embryos (cysts) of aquatic invertebrates may not only be thick-walled, but also provided with various external ornamentations such as spines and honeycombings. We argue that these provide protection, additional to that of the walls themselves, against invertebrate predators, and test this idea by offering intact (honeycombed) and decapsulated cysts of Chirocephalus diaphanus to the carnivorous flatworm Mesostomasp. Except at the lowest density of cysts, when intact as well as decapsulated cysts seem to be poorly detected by the (tactile?) searching system of the flatworms, intact cysts were relatively immune from predation. Similar causes elicit similar responses: the defences that occur in eggs are essentially similar to those present in adults of rotifers and various branchiopod microcrustaceans, copepods (marine species), and ostracods. Circumstantial evidence suggests that egg defences may vary in intensity with predation pressure. In some cases, they might be predator-inducible.

Early recurrence from stereotactic aspiration ofa colloid cyst of the third ventricle

The case of a 66 year old woman who underwent successful stereotactic aspiration of a symptomatic colloid cyst of the third ventricle, but who had recurrence after only 5 weeks, is presented. Stereotactic aspiration is a well established technique for th e treatment of colloid cysts, however disagreement exists regarding its efficacy. Two factors, both from pre-operative CT, help to predictsuccess from aspiration: the cyst's density and size. The literature reports that recurrence after successful stere otactic aspiration should not occur for many years.

Relationships Between Tillage and Spatial Patterns of Heterodera glycines

ABSTRACT The dynamics of Heterodera glycines spatial patterns were studied under different tillage systems in two naturally infested soybean fields in Iowa from 1994 to 1997. At each location, there were four different tillage treatments (conventional tillage, reduced tillage, ridge tillage, and no tillage). Soil samples were taken from 98 contiguous quadrats (5.2 m(2)) per plot in the fall of 1994, before any tillage was performed, and in the spring of the following 3 years shortly after planting. Cysts were extracted from soil samples by elutriation and counted, and eggs were extracted from cysts and enumerated. Spatial patterns of H. glycines populations were characterized by geostatistical analysis and variance-to-mean (VM) ratios. Semivariance values were calculated for cyst and egg densities and semivariograms were constructed. In general, there was greater spatial dependence among cyst populations than egg populations. In one field with a strongly aggregated initial H. glycines population, tillage practices resulted in changes in spatial patterns of H. glycines populations, characterized by spherical-model semivariogram parameters (sill, nugget effect, and range of spatial dependence). These parameters indicated increasing aggregation over time in no tillage and ridge tillage treatments, but decreasing aggregation in reduced and conventional tillage treatments. There was an increase of 350% in sill values (maximum semivariance) for cyst populations after 3 years of no tillage, but in the conventional tillage treatment, sill values remained unchanged or decreased over time as tillage was implemented. Semivariograms for cyst and egg population densities revealed strong anisotropy (directional spatial dependence) along soybean rows, coincident with the direction of tillage practices. VM ratios for cyst counts increased each year in the no tillage and ridge tillage treatments, but decreased for 2 years in reduced tillage and conventional tillage treatments. Final VM ratios for cyst and egg counts were highest in the no tillage treatment. In a second field, with low initial aggregation of H. glycines populations, there was little measurable change in semivariogram parameters after 3 years of no tillage, but in the conventional tillage treatment, populations became less aggregated, as the range, sill, and the proportion of the sill explained by spatial dependence decreased for cyst population densities. Our results indicated that in soybean fields with initially aggregated populations of H. glycines, no tillage and ridge tillage systems promoted aggregation of the nematode population, whereas conventional and reduced tillage systems resulted in a less aggregated spatial pattern.

Effect of coexistence of Penicillium frequentans (westling) with Globodera rostochiensis (Woll.) behrens on potato

The aim of two‐year‐long pot experiments was to investigate the influence of P. frequentans on the growth of over‐ground parts, the intensity of assimilation and transpiration of plants, as well as ths influence on the yield of potato bulbs. It was determined how the above fungus influenced the populaüon of G rostochiensis, the influence being characterized by the density change of cysts, eggs, and larvae in the soil. Experiments in vitro allowed to determine the wholesomeness of cysts, eggs, and larvae (J2) that were in direct contact with the mycelium ofP. frequentans. It was stated that presence of P. frequentans intensified the development of plants and relevantly stimulated their growth, especially in the initial vegetation phase, as compared with the remaining combinations (Fig. 1). Positive effect of P. frequentans on the growth of potato yield was proved, in comparison with the control, and by co‐occurrence of the fungus with G. rostochiensis, also in comparison to the combination with nematodes only (Fig. 2). Pot experiments confirmed the antagonistic effect of P. frequentans on the population of G. rostochiensis. Presence of P. frequentans in the ground caused namely a relevant diminution of density of cysts, eggs and larvae (Tab. II), as well as morphological changes by females, which was connected with size reduction of the cysts (Tab. III). Experiments in vitro confirmed the destructive effect of P. frequentans on the cysts of G. rostochiensis (Tab. IV).

Observations on Alexandrium tamarense (Lebour) Balech and Other Dinoflagellate Populations in Golfo Nuevo, Patagonia (Argentina)

The toxic dinoflagellate Alexandrium tamarense and other dinoflagellate species were studied, along with water temperature and nutrient concentrations, from September 1995 to December 1998 in the Golfo Nuevo, Chubut, Argentina. Nutrient concentrations were low, showing a peak of high concentration in winter and a phase of depletion in late spring and summer. Dinoflagellates tended to be abundant during spring and summer, when Prorocentrum micans was the most important species. Other dinoflagellates were Pyrophacus horologium and Dinophysis acuminata. Ceratium tripos, C. fusus and C. horridum were present during the autumn, and a C. tripos peak up to 5.9 X 103 cell l -1 was observed in May 1997. Alexandrium tamarense showed strong interannual variation, the highest concentration being found in spring (September-October) 1995, with densities up to 15 X 103 cells l -1 . The second A.tamarense peak was observed during October-November 1998 with maximal densities up to 5 X 103 cells l -1 . Moderately high A. tamarense cyst densities, up to 300 cysts cm -3 of sediment, were found in the deep zone of the Golfo Nuevo basin. Among meteorological variables, increased late winter rain and higher solar radiation during spring may have influenced A. tamarense blooms.

Quantification and longitudinal trends of kidney, renal cyst, and renal parenchyma volumes in autosomal dominant polycystic kidney disease.

ABSTRACT.: The aims of this study were to assess the accuracy and reproducibility of volumetric determinations of total kidney, renal cyst, and renal parenchymal volumes, using fast electron-beam computerized tomography scanning, and to determine the rate of change of these volumes. Nine patients with autosomal dominant polycystic kidney disease (ADPKD) and serum creatinine < or = 1.3 mg/dl and/or an initial iothalamate clearance > or = to 60 ml/min per 1.73 m(2) were imaged weekly over a 3-wk period (total of 3 times). Approximately 8 yr later, they returned for follow-up studies. The kidney volume estimation technique involved a manual segmentation (perimeter drawing) of the kidneys and a semiautomatic threshold approach, using a histogram analysis of the peak densities of renal parenchyma and renal cysts. At entry, total kidney and renal cyst volumes correlated positively with age, while renal parenchymal volumes and GFR correlated negatively with age. The average coefficient of variation values for the three initial consecutive measurements of total kidney, renal cyst (actual and as a percent of total volume), and renal parenchymal volume were 3.4, 7.2, 5.3, and 5.6%, respectively. During the 8 yr of follow-up, total kidney and renal cyst volumes increased, while renal parenchymal volumes and GFR declined. The rate of increase in total kidney and renal cyst volumes varied markedly from patient to patient. There was a significant correlation between rate of increase in renal cyst volume and the rate of decline in GFR. The patients with an initial urine protein/osmolality ratio >0.13 mg/L per mosmol per kg had a significantly higher increase in renal volume and decline in GFR than those with a lower ratio. In summary, the results of this pilot study suggest that: (1) electron-beam computerized tomography is capable of measuring total kidney, renal cyst, and renal parenchymal volumes reproducibly; (2) total kidney and renal cyst volumes increase, while parenchymal volumes decrease with time; (3) the increase in cyst volume correlates best with the decline in renal function; and (4) renal volumes appear to be good surrogate markers for disease progression in ADPKD.

"Air bubble": a new diagnostic CT sign of perforated pulmonary hydatid cyst.

The greatest difficulty in the CT diagnosis of perforated pulmonary hydatid cyst (PPHC) is the increase in the attenuation numbers following infection. Because of the solid density of infected hydatid cysts, the differentiation from an abscess or neoplasm is usually impossible. The aim of this study was to evaluate the value of "air bubble" as a new CT sign in the diagnosis of PPHC. Sixty-five patients (28 men and 37 women) with PPHC were included in the study. As a control group, 55 patients who had malignant (n = 36) or non-malignant (n = 19) pulmonary diseases were also examined. Radiological diagnosis with classical CT findings was made in only 38 of 65 patients (58.5 %) with PPHC. Air bubble sign was positive in 54 of the patients with PPHC (sensitivity 83.1 %) but only 3 of 55 patients in control group (specificity 94.5 %). When we analyzed the CT scans with classical CT findings including air bubble, the diagnosis of PPHC was made in 61 of patients (93.8 %). It is concluded that "air bubble sign" is a valuable CT finding in the diagnosis of PPHC.

A Model for Infestation Foci of Potato Cyst Nematodes Globodera rostochiensis and G. pallida

ABSTRACT Infestation foci of potato cyst nematodes (Globodera rostochiensis and G. pallida) in the provinces of Zeeland, Friesland, Groningen, and Drente of the Netherlands were sampled to validate a model describing infestation foci based on data from Flevoland. Eighty-two fields were presampled to locate infestation foci using a coarse sampling grid (8 x 3 m). Parts of 37 fields containing one or more foci were sampled intensively by extracting at least 1.5 kg of soil per square meter (1.33 x 0.75 m). Forty foci were analyzed for spatial distribution characteristics of cysts using multiple regression with generalized linear models and classical linear models. The results showed that the data from all investigated cropping areas fit well to an exponential model with two parameters, the length and width gradient parameters. Significant differences in these parameter values between cropping areas could not be demonstrated. As both parameters follow a normal distribution, the probability of any combination can be described by a bivariate normal distribution. Gradient parameters were correlated, but significant correlations between these parameters and certain variables such as the nematode species involved, the time interval between sampling and the last potato crop, soil type, cropping frequency, and cyst density in the focus center could not be demonstrated.

Sedimentation of free and attached Cryptosporidium oocysts and Giardia cysts in water.

Experimental analysis of the sedimentation velocity of Cryptosporidium parvum oocysts and Giardia lamblia cysts was compared with mathematical description of their sedimentation velocities by using measurements of (oo)cyst size and density and the density and viscosity of the sedimentation medium to determine if the sedimentation kinetics of freely suspended oocysts of C. parvum and cysts of G. lamblia can be described by Stokes' law. The theoretically calculated sedimentation kinetics showed a good agreement with the experimentally observed kinetics. Both showed a decline in sedimentation velocity over time, caused primarily by variation in (oo)cyst density. The initial apparent sedimentation velocities in Hanks balanced salt solution at 23 degrees C was 0.35 micron . s-1 for oocysts and 1.4 micron . s-1 for cysts. (Oo)cysts that enter the surface water environment by discharges of biologically treated sewage may be attached to sewage particles, and this will affect their sedimentation kinetics. Therefore, (oo)cysts were mixed with settled secondary effluent. (Oo)cysts readily attached to the (biological) particles in effluent; 30% of both cysts and oocysts attached during the first minutes of mixing, and this fraction increased to approximately 75% after 24 h. The sedimentation velocity of (oo)cysts attached to secondary effluent particles increased with particle size and was (already in the smallest size fraction [1 to 40 micron]) determined by the sedimentation kinetics of the effluent particles. The observed sedimentation velocities of freely suspended (oo)cysts are probably too low to cause significant sedimentation in surface water or reservoirs. However, since a significant proportion of both cysts and oocysts attached readily to organic biological particles in secondary effluent, sedimentation of attached (oo)cysts after discharge into surface water will probably be a significant factor in the environmental ecology of C. parvum and G. lamblia. Attachment to particles influences not only sedimentation of (oo)cysts in surface water but also their behavior in drinking water treatment processes.

Comparison of Black-Spot Disease Metapopulations in the Central Stonerollers of Two Warm-Water Streams

ABSTRACT Central stonerollers (Campostoma anomalum) were collected October 1994 through September 1995 from two third-order, warm-water Tennessee streams, Blackburn Fork and Spring Creek. Total lengths and numbers of externally-visible black-spot cysts were recorded for infected fish. Mean cyst densities, variance-to-mean ratios, and prevalence rates were consistently higher in Blackburn Fork than in Spring Creek. Peaks in prevalence and variance-to-mean ratios from Blackburn Fork occurred in September and January, respectively. Peak prevalence in Spring Creek occurred in October 1994. No trends in variance-to-mean ratios were observed in Spring Creek. Differences in black-spot metapopulations were due to cercarial transmission rates and undetermined abiotic factors.

An Economical, Portable System for Hatching Brine ShrimpArtemiaspp

Abstract Design and construction of a portable, inexpensive hatching system for brine shrimp Artemia spp. is described. The system design is based on batch culture methodology, which is easily customized to the feeding requirements of a larval system and optimizes the nutritional value of brine shrimp. This system can be set up quickly and provides stable temperature and aeration under a variety of external conditions. Harvest and separation of nauplii is facilitated by the shape of the culture vessel and placement of a light near the bottom of the vessel. During 14-d feeding trials, mean percent hatch of brine shrimp nauplii was 71% (59–81%) at 24 h and 83% (74–94%) at 28 h. Hatching rate was consistent across a range of initial cyst densities.

下水中のＧｉａｒｄｉａシストおよびＣｒｙｐｔｏｓｐｏｒｉｄｉｕｍオーシスト濃度と下水処理における除去性

In order to investigate the occurrence of Giardia cysts and Cryptosporidium oocysts in raw sewage and the removal in sewage treatment processes, we conducted a field survey at 9 sewage treatment plants. The results can be summarized as follows : 1) In all plants, Giardia cysts were detected in raw sewage and effluent of primary sedimentation. Cyst densities in raw sewage ranged from 130 to 5,500 cysts·l-1 (geometric mean 1,350 cysts·l-1). Cyst densities in effluent of primary sedimentation ranged from 150 to 5,200 cysts·l-1 (geometric mean 800cyst·l-1). 2) Cryptosporidium oocysts were detected from only one raw sewage sample with the density of 28 oocysts·l-1. 3) Indicator bacteria counts tested, C.perfringens spores, coliforms and E.coli, were statistically correlated with Giardia cyst densities and the most significant relationship was observed between C.perfringens spore counts and Giardia cyst densities. 4) No correlation was observed between Giardia cysts removal and indicator bacteria removal. However, significant relationship was observed between average removal of C.perfringens spores and Giardia cysts. These results indicated that C.perfringens spores can be useful indicator for the evaluation of protozoan densities and removal. 5) Turbidity appeared to be the most appropriate indicator for Giardia cysts removal in activated sludge treatment process.

Distribution of Taenia saginata cysts by muscle group in naturally infected cattle in Tanzania

The distribution of Taenia saginata cysts among organs and muscle groups was determined by slicing the heart, masseters, liver and muscles of the half carcass of 21 naturally infected Zebu cattle from Morogoro abattoir, Tanzania. The carcasses harboured from 1 to 310 cysts. In the muscle groups, normally considered predilection sites, the heart and Musculus triceps brachii harboured the highest proportions of cysts (mean 17% and 12%, respectively, of the total cysts in the carcass) while lower proportions were found in the tongue, masseters and psoas muscles (3%, 2% and 5%, respectively). A relatively high proportion was found in the liver (10%). Relative cyst density was calculated for the different muscle groups by dividing the mean proportion of total weight of the muscle group into the mean proportion of cysts located in that site. The cysticerci in the examined tissues were found in the following order of relative density: heart (10.4), tongue (2.1), masseters (1.9), M. triceps brachii (1.7), liver (1.4), M. psoas (1.3), hindlimb muscles (0.71), trunk muscles (0.67), and other forelimb muscles (0.32). The proportion of cysts expected to be found at the surfaces exposed by visual examination or incision at meat inspection was calculated using an indirect method, which incorporated the area revealed by incision and visual inspection of an organ and the proportion of cysts located in the particular organ. It was estimated that 17% of the cysts would be located at an inspected site if the regulations were followed carefully. Based on cyst density, we recommend that the heart should be paid particular attention during meat inspection.

Renal expression of a transforming growth factor-α transgene accelerates the progression of inherited, slowly progressive polycystic kidney disease in the mouse

Polycystic kidney disease (PKD) is a prevalent inherited disease in human beings. The pathogenesis of PKD is as yet unclear. The epidermal growth factor family of proteins has been implicated in PKD based largely on in vitro data. To determine whether these growth factors contribute to the progression of inherited PKD in vivo, we crossed mice with a transgene for human transforming growth factor-α (TGF-α, a member of the epidermal growth factor (EGF) family) and mice with the pcy gene (which causes a slowly progressive form of PKD very similar to human autosomal dominant PKD). Renal expression of the TGF-α transgene in cystic mice (homozygous for the pcy gene) accelerated the development of PKD as shown by an increased kidney weight as a percent of body weight and an increased volume density of renal cysts at 8.5 weeks of age. However, renal expression of the TGF-α transgene did not appear to precociously initiate cyst development (at 6.5 weeks), nor did it cause an increase in the final degree of renal enlargement (at 29 weeks). Thus TGF-α accelerated the enlargement of cysts once initiated. At 8.5 weeks of age, renal expression of the TGF-α mRNA correlated positively with the amount of renal enlargement. At all time points studied, cystic kidneys exhibited increased expression of c-myc mRNA as compared with phenotypic normal kidneys, consistent with PKD being a hyperplastic disease of renal tubules. However, the renal expression of c-myc in 8.5 week cystic kidneys, with or without the transgene, did not correlate with the degree of renal enlargement. The results of this study suggest that EGF-like proteins may accelerate the progression of inherited renal cystic disease. However, the final degree of cystic change is dictated by the primary disease process rather than by the continued presence of growth factor.

Effect of lovastatin on the development of polycystic kidney disease in the han:SPRD rat

Proliferation of tubular epithelial cells is a major element leading to cyst formation in Han:SPRD rats with autosomal dominant polycystic kidney disease (PKD). ras proteins are important in the control of renal cell proliferation, and ras gene expression is increased in PKD. Farnesyl pyrophosphate, an intermediate in the conversion of acetyl-CoA to cholesterol, is required for the activation of ras guanosine triphosphate (GTP)-binding proteins that are important in the execution of several cellular functions, including cell proliferation. 3-Hydroxy-3-methyl-glutaryl coenzyme A reductase inhibitors, such as lovastatin, reduce farnesyl production in responsive cells and thereby have potential for ameliorating the accelerated epithelial cell proliferation of PKD. We administered lovastatin to heterozygous (Cy/+) Han:SPRD rats (4 mg/kg/d subcutaneously) from age 4 to 10 weeks, a period of rapid cystic disease progression in these animals. Untreated male Cy/+ rats developed larger cystic kidneys and had more severe renal functional impairment than females, as reported previously. In males, lovastatin significantly decreased cystic kidney size (referenced to body weight), the volume density of cysts, and the serum urea nitrogen level 14.5%, 24.4%, and 25.6/%, respectively. The corresponding changes in females were insignificant, and lovastatin had no effect on kidney weight or serum urea nitrogen in homozygous (+/+) normal male animals. On the basis of these results we conclude that lovastatin diminishes the severity of PKD in heterozygous male Han:SPRD rats.

Field Population Dynamics of Soybean Cyst Nematode on Resistant and Susceptible Soybeans and Their Blends

Soybean cyst nematode (Heterodera glycines Ichinohe) (SCN) become an increasing problem in the upper midwest. In order to develop appropriate practices to manage SCN populations it is important to understand the population dynamics of SCN under field conditions. Soybean cyst nematode population dynamics were determined in naturally infested commercial soybean [Glycine max (L.) Merr.] fields in southern Minnesota on a monthly basis during 1991 and 1992 for an adapted susceptible (S) and a SCN Race 3 resistant (R) cultivar and three blends (25% R:75% S; 50% R:50% S; 75% R: 25% S). Population dynamics differed between sites and years. In 1991, fields with similar initial cyst densities were compared. Densities of second‐stage juveniles (J2) peaked in August at one site and gradually declined throughout the growing season at the other. Total cyst production was lower at the site where J2 densities declined. In 1992, fields with high and low initial egg densities were compared. SCN population densities increased when initial densities of J2 and eggs were low and decreased when initial J2 and egg densities were high. Physiological race of the nematode influenced population dynamics on resistant plants. The cyst index under field conditions for the resistant cultivar was 10 (moderately resistant) against Race and 32 (moderately susceptible) against Race 1. The blends generally lowered SCN population densities, but not significantly. Final egg density and cyst production for the resistant cultivar were significantly lower than the susceptible cultivar at each site. The use of SCN resistant cultivars alone or in a 75:25% mixture with a susceptible cultivar (25%) is recommended as a SCN population management strategy to delay shifts from one race to another thus prolonging the effectiveness of resistant cultivars.

Effect of Wheat Residue and Tillage onHeterodera glycinesand Yield of Doublecrop Soybean in Kentucky

A study (1990 to 1992) was conducted in western Kentucky to determine the effects of wheat (Triticum aestivum «Clark») residue and minimal- (two disking) or no-tillage on soybean cyst nematode (Heterodera glycines) cyst and egg population densities and yield of the H. glycinessusceptible soybean (Glycine max) cultivar Pennyrile. In each year, cyst densities at soybean planting were unaffected by the presence of residue from a prior winter wheat crop; however, harvest population densities were lower in plots with wheat residue compared with those without residue. Across residue treatments, tillage had no effect on harvest densities of cysts in any year. Differences in egg densities, determined only in 1992, were similar to differences detected in cyst densities for both residue and tillage. Minimum-tillage of wheat residue significantly reduced the «residue effect» in 1990 and 1991; however, plots with wheat residue had fewer cysts at harvest than plots without residue in both years regardless of tillage method. Neither residue nor tillage affected soybean yields. Results indicate that producers who have the option to no-till doublecrop soybean following wheat may have an advantage in long-term management of H. glycines