Influence of Population Densities of Heterodera schachtii on Sugar Beets Grown in Microplots

High initial population densities of Heterodera schachtii larvae (36 and 108/gm of soil) greatly retarded the seedling emergence of sugar beet ''Monogerm CSF 1971'' in Vineland fine sandy loam. In comparison with controls, initial population densities (P_i''s) of 1.7, 3.0, 6.2, and 14.4 larvae/gm of soil respectively reduced the weight of storage roots by 38, 56, 64, and 92%. Weights of tops also decreased with increases in P_i; weights of tap and small feeder roots tended to be higher at all P_i''s except the highest. Sucrose percentage was not affected by any initial nematode density. The populations were lower at midseason than at seeding, and at harvest had increased greatly, with respective populations of 339, 402, 222, and 140 larvae/gm of soil. At harvest, cysts/gm of soil and cysts/gm of root were respectively 4.4 and 72, 6.1 and 99, 6.1 and 191, and 5.8 and 140. The maximum rate of multiplication was 150-200. and maximum density was 400 larvae/gm of soil. The high pathogenicity and multiplication rate of the nematode was attributed to optimum temperature conditions and soil type.     

Self-interactions of Meloidogyne hapla and of Heterodera schachtii on Beta Vulgaris

Double inoculations of sugar beet with larvae of Meloidogyne hapla resulted in a higher galling incidence in only one treatment than did a single inoculation using the same number of larvae. Double inoculations with larvae of Heterodera schachtii, however, resulted in three- to five-fold more cysts in most cases than did single inoculations using the same number of larvae. In general, plants died more quickly after double inoculations than after single inoculations of the same total number of either nematode. Ratios of total soluble carbohydrates to reducing carbohydrates were lower in multiple inoculated treatments than in other treatments. Plants infected with M. hapla had lower quantities of B, K, and P in leaf tissue than noninoculated plants, but no differences were correlated with type of inoculation. Plants inoculated with H. schachtii had lower quantities of B, K, and Mg than noninoculated plants. Also, quantities of Mn, Cu, and Zn were much lower in plants inoculated twice with H. schachtii larvae than in plants inoculated with the same total number of larvae in a single dose.     

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.     

Potential for biological control of Heterodera schachtii by Pochonia chlamydosporia var. chlamydosporia on sugar beet

The biological control potential of an isolate of Pochonia chlamydosporia var. chlamydosporia against Heterodera schachtii was examined by assessing the percentage of females and cysts that became infected on water agar, the effect of culture filtrate on juvenile mobility, and the effects of the fungus on the final population of the nematode on sugar beet under greenhouse conditions. After 3 weeks at 20°C, 74 and 95% of the eggs within cysts and females, respectively, were colonised by the fungus on water agar. The full concentration of the fungal filtrate from cultures in malt extract broth killed only 12% of the juveniles after 24 h at 25°C. In the greenhouse experiment, adding 16,000 chlamydospores of the fungus per gram of soil as either colonised barley grains or spores reduced the final number of females on roots of sugar beet by 50 and 66%, respectively, after 3 months. The reproduction factor was reduced to ×2 in spore-treated soil compared with ×5 in the untreated control, and 18% of the eggs in spore-treated soil were colonised by fungal mycelium. Generally, P. chlamydosporia var. chlamydosporia was more efficient at reducing the nematode population when applied as spores without any substrate than when used as colonised barley grains.     

Effect of Phenamiphos on Heterodera schachtii and Meloidogyne javanica

Aqueous solutions of technical-grade phenamiphos [ethyl 3-methyl-4-(methylthio) phenyl (1-methylethyl) phosphoratnidale] were used in hatching chambers to test, under laboratory tory conditions, the effect of phenamiphos on the hatching and movement of Meloiclogyne javanica and Heterodera schachtii. Hatch of M. javanica and H. schachtii eggs was depressed 70 and 88% by nematicide at 0.48 and 4.80 μg/ml, respectively. The infectivity of second-stage larvae of both species was affected by concentrations as low as 0.01 μg/ml. At least 0.5 μg/ml was required to decrease the movement of larvae of M. javanica and H. schachtii. To decrease the movement of H. schachtii males toward females, 10 μg/ml was required. In a field experiment using a 15% granular formulation, 5 kg/ha a.i. significantly reduced infection of sugarbeet roots by H. schachtii.     

The Relationship of Plant Age,Soil Temperature,and Population Density of Heterodera schachtii on the Growth of Sugarbeet

There were direct relationships between inoculum density of Heterodera schachtii Schm. (nematode population density), initial soil temperature, the growth of sugarbeets in the greenhouse under controlled temperatures, and nematode populations. Heterodera schachtii was least pathogenic on plants inoculated at 6 wk of age and most pathogenic on plants grown from inoculated germinated seed (0 wk of age). In the field, H. schachtii was least pathogenic on sugarbeets grown at an initial soil temperature of 6 C and most pathogenic on those grown at an initial soil temperature of 24 C. The growth period for sugarbeets at the different soil temperatures was determined by heat units; since penetration of sugarbeet roots by H. schachtii larvae is accelerated at soil temperatures above 10 C, each hour-degree ahove 10 C was counted as one effective heat unit (HU). Using this guideline it was determined that root weight depressions in the greenhouse, for each degree-unit population (HU-UP) where unit population = one larvae/g soil, were 0.052, 0.09, 0.12, and 0.17 mg at initial soil temperatures of 6, 12, 18, and 24 C, respectively. Root weight depressions were 0.28, 0.23, 0.15, and 0.086 mg when plants were inoculated at 0, 2, 4, and 6 wk of age.     

Interrelationship of Heterodera schachtii and Meloidogyne hapla on Tomato

Invasion of tomato (Lycopersicon esculentum L.) roots by combined and sequential inoculations of Meloidogyne hapla and a tomato population of Heterodera schachtii was affected more by soil temperature than by nematode competition. Maximum invasion of tomato roots, by M. hapla and H. schachtii occurred at 30 and 26 C, respectively. Female development and nematode reproduction (eggs per plant) of M. hapla was adversely affected by H. schachtii in combined inoculations of the two nematode species. Inhibition of M. hapla development and reproduction on tomato roots from combined nematode inoculations was more pronounced as soil temperature was increased over a range of 18-30 C and with prior inoculation of tomato with H. schachtii. M. hapla minimally affected H. schachtii female development, but there was significant reduction in the buildup of H. schachtii when M. hapla inoculation preceded that of H. schachtii by 20 days.     

Influence of Planting Date on Damage to Soybean Caused by Heterodera glycines

Bragg soybeans were planted in nematicide-treated and nontreated plots on 15 May, 15 June, 1 July, and 15 July in 1980 and 1981 to determine the influence of planting date on damage caused by H. glycines. Although earlier studies showed the nematode was sensitive to high soil temperatures (> 34 C), late planting did not reduce damage caused by the nematode. Yields from plots treated with 1, 2-dibromo-3-chloropropane (57.5 kg a.i./ha) were 48, 118, 395, and 403% higher than yields from nontreated plots with planting dates of 15 May, 15 June, 1 July, and 15 July, respectively, when data were averaged over the 2 years. Increase in both seed size and number accounted for the yield increases in treated plots. Soil temperatures were highest during July in 1980, averaging 8.9 and 6.5 hours per day above 34 C at 10- and 20-cm depths, respectively. Larvae populations of H. glycines were reduced by the nematicide but not by late planting. These results indicate that damage caused by H. glycines may actually increase with later planting and that nematicides may be more beneficial when soybeans are planted late in a double-cropped production system.     

The effect of beet cyst nematode, Heterodera schachtii, on the yield of sugar beet in organic soils

In ten experiments on commercial sugar-beet crops grown on organic soils in 1984–86, a Genstat programme was used to examine the relationship between the initial population of Heterodera schachtii and sugar-beet root yield using the equation
Y = Ymin + (Ymax - Ymin) Z^pi-T
Fixing T = 200 eggs + juveniles 100 g^-1 soil and Z^T= 0.95, estimated values of Ymax varied from 49.2–67.1 t ha^-1 (129– 155% of the national average root yield for the years in which the experiments were carried out) and estimates of Ymin varied from 14.5–53.9 t ha^-1 (27–94% of Ymax). The estimated average root yield loss caused by the nematode was 6.95 t ha^-1.     

Effect of Age of Alfalfa Root on Penetration by Pratylenchus penetrans

Penetration by all migratory life stages of Pratylenchus penetrans into roots of alfalfa (Medicago sativa L. cv. Du Puits) was inversely proportional to tissue age. Two-day-old tissue in the root hair zone was penetrated twice as much as 10- or 20-day-old sections of the tap root. Age-related differences were also observed in branch roots; these differences were not affected by increasing the number of nematodes from 1 to 10 per inoculation site, nor by increasing the length of the incubation period from 6 to 96 h. Age-related differences were only significant with 3-wk-old plants, not with 2- and 1-wk-old seedlings. Nematodes entered roots at temperatures from 5 to 30 C with maximum entry at 20 C and minimum at 5 C. At all temperatures, except 5 C, penetration into young tissue (2 days) was significantly greater than into medium (10 days) and old (20 days) tissue. Females and third-stage larvae entered the different-aged root sections 122% and 83%, respectively, more than did males. Two-day-old seedlings of the alfalfa cultivars Vernal, Saranac, and Du Puits were penetrated equally by P. penetrans. Perhaps the inverse relationship between penetration and age of root is, in part, responsible for the increasing resistance or tolerance of plants to nematode damage as they grow older.     

Nodulation of Soybeans as Affected by Half-root Infection with Heterodera glycines

A split-root technique was applied to soybean, Glycine max (L.) Merr. cv. Lee 68, to characterize the nature of the nodulation suppression by race 1 of the soybean cyst nematode (SCN), Heterodera glycines. Root-halves of each split-root plant were inoculated with Rhizobium japonicum, and one root-half only was inoculated with various numbers of SCN eggs. Nodulation (indicated by nodule number, nodule weights, and ratio of nodule weight to root weight) and nitrogen-fixing capacity (indicated by rate of acetylene reduction) were systemically and variously suppressed on both root-halves of the split-root plant 5 weeks after half-root inoculation with 12,500 SCN eggs. Inoculation with 500 eggs caused this suppression only on the SCN-infected (+NE) root-half; nodulation on the companion uninfected (-NE) root-half was stimulated slightly. The +NE root-halves inoculated with 5,000 eggs were excised at 2-week intervals; nodulation on the remaining -NE root-halves was not different from that of the noninoculated control when measured 6 weeks after the SCN inoculation. Thus, the systemic suppression of nodulation was reversible upon the removal of the SCN. Similarly, application of various levels of KNO₃ to the -NE root-halves of the split-root plant did not alleviate the suppressed nodulation on the companion +NE root-halves, even though plant growth was much improved at certain levels of nitrogen (125 μg N/g soil). This indicated that the localized suppression of nodulation by SCN was caused by factors in addition to poor plant growth.     

Population Dynamics of Heterodera schachtii on Tomato and Sugar Beet

Experiments showed that development of male and female Heterodera schachtii on tomato and sugarbeet are disproportionately influenced by the nematode inoculum level and root size, which together determine the density of invading larvae. Slight overcrowding favored development of males over females, whereas severe overcrowding equally affected development of males and females. Differential population changes of host-selected races on tested cultivars was attributable to selective development of male and female nematodes.     

In-Vitro and In-Vivo Effects of Aldicarb on Survival and Development of Heterodera schachtii

Aqueous solutions of 5-500 μg/ml aldicarb inhibited hatching of Heterodera schachtii. Addition of hatching agents, zinc chloride, or sugarbeet root diffusate, to the aldicarb solutions did not decrease the inhibition of hatching. When cysts were removed from the aldicarb solufions and then treated for 4 wk in sugarbeet root diffusate, larvae hatched and emerged. Treatments of newly hatched larvae of H. schachtii with 5-100 μg/ml aldicarb depressed later development of larvae on sugarbeet (Beta vulgaris). Similar treatments with aldicarb sulfoxide had less effect on larval development, and aldicarb sulfone had no effect. Numbers of treated larvae that survived and developed were inversely proportional to concentration (0.1-5.0 μg/ml) and duration (0-14 days) of aldicarb treatments. Development of H. schachtii on sugarbeet grown in aldicarb-treated soil was inversely proportional to the concentration of aldicarb in the tested range of 0.75 - 3.0 μg aldicarb/g of soil. Transfer of nematode-infected plants to soil with aldicarb retarded nematode development, whereas transfer of plants first grownin treated soil to nematode-infested soil only slightly suppressed nematode development. Development of H. schachtii was inhibited in slices of storage roots of table beet (B. vulgaris), sugarbeet and turnip, (Brassica rapa), that had grown in soil treated with aldicarb.     

Comparative Morphometrics of Eggs and Second-Stage Juveniles of Heterodera schachtii and a Race of H. trifolii Parasitic on Sugarbeet in The Netherlands

Measurements of second-stage juveniles of Heterodera schachtii from California and The Netherlands and a race of H. trifolii from The Netherlands were obtained and compared to determine if these populations can be differentiated by morphometrics. Juvenile lengths of 10 specimens from each of 10 cysts of each population were measured. Dimensions of tail regions of 20 juveniles from individual cysts of H. schachtii (California) and a like number of juveniles of H. trifolii (The Netherlands) were also obtained. The mean lengths of juveniles of H. schachtii from California and The Netherlands were not significantly different, but similar measurements of H. schachtii and H. trifolii were different (P = 0.05). Mean dimensions of tail lengths, tail widths, tail hyaline lengths, and tail length/tail width were significantly greater for H. trifolii than for H. schachtii. Also, dimensions of eggs of H. trifolii were significantly greater than dimensions of H. schachtii eggs. The investigations established that H. schachtii can be readily differentiated from H. trifolii by morphometrics of eggs and juveniles, Minimum sample sizes required for specified confidence intervals for each criterion measured are provided.     

Extraction of Cysts and Eggs of Heterodera schachtii from Soil with an Assessment of Extraction Efficiency

Techniques are described for the extraction and enumeration of cysts and contained eggs from soil samples. The average recovery of cysts from seeded soil samples of differing soil texture was 82.7 ± 2.1%. Recovery from sandy clay soil samples seeded at 1 cyst/100 g soil was 63.4 ± 5.5%; at 4.2 cysts/100 g soil recovery was 89.6 ± 1.8%. Recovery of cysts from naturally infested clay soil was 88.3 ± 2.05%. Egg extraction efficiency for seeded samples was calculated as 78%, and for naturally infested soil was estimated as 83%.     

Changes in the Reproduction of Heterodera glycines on Different Lines of Glycine max

Selection for ability of soybean cyst nematode (SCN), Heterodera glycines, to reproduce on soybeans with different sources of resistance divides some SCN race 4 field populations into two distinct subpopulations. These subpopulations reproduce well on ''Bedford'' and plant introduction (PI) 88788 or PI 89772 and PI 90763 but not on both pairs of soybean lines. The ability of these subpopulations to reproduce on the four soybean lines was reversed by changing the soybean line used as a host during a second cycle of selection. When SCN populations previously selected for reproduction on Bedford and PI 88788 were selected for their ability to reproduce on D72-8927 and J74-88, the ability of these populations to reproduce on Bedford and PI 88788 decreased significantly and their ability to reproduce on PI 89772 and PI 90763 increased significantly. Conversely, when SCN populations, previously selected for reproduction on P189772 and P190763, were selected for their ability to reproduce on Bedford, the reproduction of these populations on Bedford increased significantly and reproduction on PI 89772 and PI 90763 decreased significantly. Selection for ability of a SCN race 4 field population to reproduce on soybean lines derived from SCN race 4 resistant PIs resulted in the same division of the field population into two distinct subpopulations. These data substantiate earlier proposals to rotate cultivars with different genes for SCN resistance as a means of managing SCN populations.     

Differences in the Response of Certain Weed Host Populations to Heterodera schachtii

Significant differences (P = 0.05) in nematode reproduction were observed among populations of Heterodera schachtii and weed collections of black nightshade, common lambsquarters, common purslane, redroot-pigweed, shepherdspurse, and wild mustard from Colorado, Idaho, Oregon, and Utah. Colorado weeds supported the greatest nematode development (P = 0.05). Weeds collected from Idaho and Utah were similar with respect to their response to H. schachtii with the exception of shepherdspurse. At increasing soil temperatures, a Utah redroot-pigweed collection showed a higher percent susceptibility to a Utah nematode population than to nematode populations from the other states (P = 0.05). There was a higher percentage of susceptible plants when the weed host population was collected from the same geographical area as the nematode inoculun.     

Population Dynamics of Dactylella oviparasitica and Heterodera schachtii: Toward a Decision Model for Sugar Beet Planting

A series of experiments were performed to examine the population dynamics of the sugarbeet cyst nematode, Heterodera schachtii, and the nematophagus fungus Dactylella oviparasitica. After two nematode generations, the population densities of H. schachtii were measured in relation to various initial infestation densities of both D. oviparasitica and H. schachtii. In general, higher initial population densities of D. oviparasitica were associated with lower final population densities of H. schachtii. Regression models showed that the initial densities of D. oviparasitica were only significant when predicting the final densities of H. schachtii J2 and eggs as well as fungal egg parasitism, while the initial densities of J2 were significant for all final H. schachtii population density measurements. We also showed that the densities of H. schachtii-associated D. oviparasitica fluctuate greatly, with rRNA gene numbers going from zero in most field-soil-collected cysts to an average of 4.24 x 10⁸ in mature females isolated directly from root surfaces. Finally, phylogenetic analysis of rRNA genes suggested that D. oviparasitica belongs to a clade of nematophagous fungi that includes Arkansas Fungus strain L (ARF-L) and that these fungi are widely distributed. We anticipate that these findings will provide foundational data facilitating the development of more effective decision models for sugar beet planting.     

In Vitro Hatch and Survival of Heterodera glycines as Affected by Alachlor and Phenamiphos

Heterodera glycines (race 1) eggs were exposed to aqueous solutions o f selected concentrations o f the herbicide alachlor and the organophosphate nematicide phenamiphos alone and in herbicide-nematicide combinations. Phenamiphos (0.5 μg/ml) + alachlor (0.063, 0.125, or 1.0 μg/ ml) treatments increased the incidence o f juvenile hatch over that of untreated controls at 18 days. At 18 and 25 days, phenamiphos (0.5 μg/ml) treatments contained more juveniles than did phenamiphos at 1.0 μg/ml. Phenamiphos (1.0 μg/ml) alone and in combination with alachlor (1.0 μg/ ml) suppressed hatch for 21 days and juvenile survival for more than 21 days. Alachlor treatments enhanced juvenile survival compared to the untreated control at 14 and 21 days. Technical alachlor gave results similar to those of the formulated product.     

Separation and Characterization of Heterodera glycines Acetylcholinesterase Molecular Forms

The composition and biochemical properties of acetylcholinesterases isolated from Heterodera glycines were determined. Heterodera glycines contains three separable AChE molecular forms that can be grouped into two classes corresponding to classes A and C found in some other nematode species. The apparent lack of class B AChE is unusual and may have significant behavioral ramifications. The class C enzyme isolated from H. glycines is similar to that from Meloidogyne arenaria and M. incognita but is somewhat more sensitive to AChE inhibitors such as eserine. Heterodera glycines possesses a larger percentage of its total acetylcholinesterase as class C than other nematodes thus far examined.