Complete Characterization of the Race Scheme for Heterodera glycines

One hundred thirty-eight isolates of Heterodera glycines from nine states in the United States, People's Republic of China, and Indonesia were tested on the four standard soybean race differentials. A total of 12 variants were found, including the five races described previously. The seven variants that did not correspond to one of the described races and reports from other areas of populations that could not be classified are evidence that the present race classification system needs to be fully characterized. Eleven additional races are described; this expands the total to 16 races, the maximum possible using the four prescribed differentials and a + or - rating for each. The seven new races are designated as 6, 9, 10, 13, 14, 15, and 16. This complete characterization of the race scheme will allow for immediate communication of the discovery of the remaining four races plus the identification of previous undescribed races.

Influence of Calonectria crotalariae on Reproduction of Heterodera glycines on Soybean

Calonectria crotalariae enhanced root penetration of Lee 74 (susceptible) and Centennial (resistant) soybeans by juveniles of race 3 of Heterodera glycines. Numbers of cysts in and on the roots of Lee 74 increased during the first 30 days in the presence of the fungus. Percentage of root infection by the fungus increased at 40 days in Lee 74 in the presence of the nematode. Numbers of cysts in soil at 80 and 120 days after inoculation with both organisms accounted for the significantly increased nematode population levels on Lee 74. In the presence of the fungus on the resistant cultivar, significantly increased levels of cysts were recovered from soil at 120 days. Fungus infection of Centennial roots also infected with the nematode increased from 58 to 86% at 120 days. An inoculum timing study in which Lee 74 was infested with the nematode and fungus individually, sequentially, and in combination at days 0 and 35 indicated that enhanced nematode reproduction was related more to early plant-fungus than to early plant-fungus-nematode interaction(s).

Effect of Within-field Variation in Soil Texture on Heterodera glycines and Soybean Yield

The influence of soil texture on Soybean yield in the presence of Heterodera glycines was investigated by comparing yields of susceptible cultivars with a resistant cultivar for 2 years. Soybean yield was negatively correlated with increasing sand content (P = 0.05). Yields of susceptible cultivars were suppressed with increasing sand content. Final nematode population densities were lowest in plots with greatest sand content. Soybean infection by SCN, as determined by the number of cysts 30 days after planting, was not consistently related to soil texture over 2 years. Initial nematode population density was positively related to soybean yield the first year and negatively related to soybean yield the second, probably a result of greater yield suppression by H. glycines in plots with greater sand content.

Current research on the major nematode problems in Japan

AMONG IMPORTANT NEMATODE SPECIES OCCURRING IN JAPAN, CURRENT RESEARCH ACHIEVEMENTS WITH THE FOLLOWING FOUR NEMATODES ARE REVIEWED: 1) Soybean cyst nematode (SCN), Heterodera glycines - breeding for resistance, race determination, association with Cephalosporium gregatum in azuki bean disease, and isolation of hatching stimulant. 2) Potato-cyst nematode (PCN), Globodera rostochiensis - pathotype determination (Ro 1), breeding for resistance, and control recommendations. 3) Pinewood nematode (PWN), Bursaphelenchus xylophilus - primary pathogen in pine wilt disease, life cycle exhibiting a typical symbiosis with Japanese pine sawyer, Monochamus alternatus, and project for control. 4) Rice root nematodes (RRN), Hirschmanniella imamuri and H. oryzae - distribution of species, population levels in roots, and role of these nematodes in rice culture.

Detection of Intraspecific Diversity of Heterodera glycines Using Isozyme Phenotypes

Twelve populations of Heterodera glycines from the United States (8), China (2), Japan (1), and Colombia (1) were surveyed for phenotypic intraspecific variability in 42 enzyme systems. Activity of 20 enzymes was detected following isoelectric focusing in polyacrylamide gels of extracts from mass homogenates and single females. Five enzymes, aspartate aminotransferase, phosphoglucose isomerase, alpha- and beta-esterases, and hexokinase were the most useful for detecting intraspecific variability. Phenotypic variability between single females was best demonstrated with alpha- and beta-esterases and acid phosphatase enzyme systems. These results suggest that isoelectric focusing in conjunction with sensitive enzyme systems can be used to detect phenotypic variation between individual nematodes from the same population. The unusual phenotypic variability detected in the H. glycines population from Virginia indicates that the genetic diversity of this population is complex.

A Modified Screening Test for Determining Heterodera glycines Resistance in Soybean

A modified version of a standard greenhouse bioassay for determining soybean cyst resistance in soybean plants is described. White plastic laundry tubs served as microplots for rearing large numbers of nematodes in a confined space; up to 3 million eggs of each generation were collected per tub. Before screening, SCN populations were evaluated on susceptible and resistant soybean to characterize female development; these were periodically retested. Screening tests took place in Todd planter flats (120 plants per flat). Test plants were inoculated with 1,200 eggs per plant and evaluated for resistance 33-37 days after inoculation. The plants were pruned at the cotyledonary node which resulted in a greatly reduced root system. Staining the roots in Toluidine Blue created contrast with the white females and facilitated counting. Greenhouse space was conserved, and the labor to set up and maintain the screening test was reduced.

Soybean Response to Ethylene Dibromide in a Soil Infested with Meloidogyne arenaria and Heterodera glycines

One susceptible and six nematode-resistant soybean cultivars were evaluated in the field for their effects on seed yield, nematode populations, and response to the fumigant nematicide, ethylene dibromide. The soil was a loamy sand infested with Meloidogyne arenaria and Heterodera glycines. Cultivars significantly affected yield and numbers of H. glycines but did not affect M. arenaria numbers. Fumigation increased yield and reduced M. arenaria numbers but did not affect numbers of H. glycines. The interaction between cultivars and fumigation was significant for yield but not for nematode numbers.

Results of annual phytoparasitic nematode surveys of arkansas soybean fields, 1978-1986

Results of surveys from 1978 to 1986 to estimate and identify nematodes in Arkansas soybean fields are presented. The seven most common nematode species in the fields were Heterodera glycines, Quinisulcius acutus, Pratylenchus scribneri, P. alleni, Helicotylenchus pseudorobustus, Tylenchorhynchus ewingi, and Xiphinema americanum. Other nematodes identified from these fields were Pratylenchus brachyurus, P. vulnus, P. zeae, Tylenchorhynchus canalis, T. goffarti, T. martini, Helicotylenchus dihystera, Scutellonema bradys, Xiphinema chambersi, X. rivesi, Hoplolaimus galeatus, H. magnistylus, Paratrichodorus minor (P. christiei), Paratylenchus projectus, P. tenuicaudatus, Criconemella macrodora, C. ornata, and Meiodorus hollisi.

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.

Soybean Response to a Planting-Time Application of Ethylene Dibromide in a Soil Infested with Meloidogyne incognita, M. arenaria, and Heterodera glycines

A field study was conducted to evaluate one susceptible and six nematode-resistant soybean cultivars for their effects on seed yield, nematode populations, and response to a fumigant nematicide, ethylene dibromide. The soil was a sandy loam, and the field was infested with a mixture of Meloidogyne incognita, M. arenaria, and Heterodera glycines. Soybean cultivars significantly affected yield and juvenile numbers of Meloidogyne spp. but did not affect the H. glycinesjuvenile population. Fumigation increased yield and numbers of H. glycines juveniles, whereas the numbers of Meloidogyne spp. juveniles were decreased. The interaction between cultivars and fumigation treatment was significant for yield but not for nematode numbers.

Ultrastructure of Esophageal Gland Secretory Granules in Juveniles of Heterodera glycines

Ultrastructural observations of the feeding sites of soybean cyst nematode juveniles 3 days after inoculation of soybean roots revealed the presence of feeding tubes in the host cell syncytium. Feeding tubes, which were extruded from the stylet tips, were formed by products of secretory granules that originated in the dorsal esophageal gland and accumulated in the ampulla of the gland extension. Granules traversing the space between the gland cell and the ampulla were regulated in their movement by two sets of sphincter-like muscles located anterior and posterior to the metacorpus pump chamber. Sections through the sphincter muscles revealed obliquely arranged fibers, which in a contracted mode caused microtubules in the gland extension to be tightly packed and devoid of granules.

Effects of aldicarb on nematodes, early season insect pests, and yield of soybean

The effects of aldicarb on soybean cyst (Heterodera glycines) and root-knot (Meloidogyne incognita and M. arenaria) nematode populations, early season insect pests and soybean (Glycine max) yield were evaluated in five field experiments in northern and southern Alabama. Aldicarb significantly (P = 0.05) reduced nematode populations in only two cases: M. arenaria in Centennial soybean in the Wiregrass site and M. incognita in Bedford soybean in a Tennessee Valley site. No significant difference (P = 0.05) in mean percentage main stem or petiole girdling by threecornered alfalfa hopper (Spissistilus festinus) or in mean number of plants damaged by lesser cornstalk borer (Elasmopalpus lignosellus) occurred among treatments in any experiment. Soybean yields were significantly (P = 0.05) increased in only two cases: in the nematode susceptible Essex and Cobb cultivars planted in the Tennessee Valley and Gulf Coast sites, respectively. Unusually dry 1986 weather conditions may have reduced the activity of aldicarb.

Effect of Heterodera glycines on Charcoal Rot Severity in Soybean Cultivars Resistant and Susceptible to Soybean Cyst Nematode

Field experiments were conducted in two soil types in northeastern Kansas to evaluate the influence of Heterodera glycines on the severity of charcoal rot in group III soybean cultivars resistant and susceptible to soybean cyst nematode race 3. Resistant cultivars Asgrow 3307 and Fayette and susceptible cultivars Asgrow 3127, Harper, Pella, Sprite, and Williams 82 were planted in carbofuran-treated and nontreated plots. Heterodera glycines and the charcoal rot fungus, Macrophomina phaseolina, were suppressed by carbofuran treatment in loamy sand, but not loam soil, and by nematode-resistant cultivars in both soils. Root densities of the fungus were positively correlated with nematode densities and negatively correlated with seed yield at both locations. Results indicate that H. glycines infection can increase colonization of soybean roots by M. phaseolina which may increase losses due to charcoal rot.

Population Density and Spatial Pattern of Heterodera glycines in Relation to Soybean Phenology

Population dynamics of Heterodera glycines (SCN) were influenced by initial nematode population density in soil, soybean root growth pattern, soil type, and environmental conditions in two field experiments. Low initial populations (Pi) of SCN increased more rapidly during the growing season than high Pi and resulted in greater numbers of nematodes at harvest. Egg and juvenile (J2) populations increased within 2-6 weeks after planting when early-season soil temperatures were 20 C and above and were delayed by soil temperatures of 17 C or below in May and early June. Frequencies of occurrence and number of nematodes decreased with increasing depth and distance from center of the soybean row. Spatial pattern of SCN paralleled that of soybean roots. Higher clay content in the subsoil 30-45 cm deep in one field restricted soil penetration by roots, indirectly influencing vertical distribution of SCN. Shoot dry weight was a good indicator of the effect of SCN on seed yield. Root dry weight was poorly correlated with soybean growth and yield. The relationship of yield (seed weight) to Pi was best described by a quadratic equation at one site, but did not fit any regression model tested at the second site.

Response of Soybean to Heterodera glycines Races 1 and 2 in Different Soil Types

Experiments were conducted for 3 years at four locations and 1 year with six soil types at a common location in North Carolina to determine damage and control-cost functions for Heterodera glycines races 1 and 2 on soybean. In the experiments on native loamy sand and sandy soils, tolerance limits for initial population densities were 0 or very low, whereas in a muck, the tolerance limit was 315 eggs/500 cm(3) soil. The aggressive race 2 was more damaging than race 1 in Lakeland sand and Norfolk loamy sand. The crop response was not different between races in the Appling sandy clay loam and Belhaven muck. Soybean yield responses to H. glycines were linear in six soil types in microplots at a common site. The amount of damage varied among these soil types, with lowest yields in the muck because of severe drought stress in this soil. An exponential function adequately described soybean yield response relative to nematode control with increasing rates of aldicarb in Norfolk loamy sand. Treatment with aldicarb in the Lakeland sand decreased the effective egg population of H. glycines but had only a minor effect in the muck.

Nonhost root penetration by soybean cyst nematode

A total of 66 plants in 50 species were inoculated with eggs and juveniles of soybean cyst nematode, Heterodera glycines. Roots were stained and observed for penetration and development of the nematode. Twenty-six plants were not penetrated; twenty-three were penetrated, but there was no development of the nematode; eight were penetrated with some nematode development; two were penetrated and had considerable nematode development, but few nematodes, if any, matured; and seven were penetrated with many nematodes maturing. The penetration of nonhosts may imply some susceptibility and that populations eventually would build up on the penetrated plants. Plants not penetrated may be useful as rotation plants because no reproduction would occur.

Structural Changes Associated with Resistance of Soybean to Heterodera glycines

Subcellular responses to infection by Race 3 of Heterodera glycines in susceptible ('Lee') and resistant ('Forrest' and 'Bedford') soybean cultivars were compared. Syncytial formation, initiated in susceptible as well as resistant soybean cultivars, was characterized by wall perforations, dense cytoplasm, and increased endoplasmic reticulum, In susceptible plants, syncytia developed continuously until nematode maturity. This included hypertrophy of nuclei, increase of rough endoplasmic reticulum in early stages of infection, and formation of wall ingrowths at a late stage of infection. In the resistant reaction in Forrest, a necrotic layer surrounded syncytium component cells demarcating them from surrounding normal cells and leading to syncytial necrosis. Wall appositions were prominently formed near the necrotic layer, and the cytoplasm of the syncytium component cells was extremely condensed. The whole syncytium became necrotic at a late stage of infection. Bedford had nuclear degeneration prior to cytoplasmic degradation. Chromatin was often scattered throughout the syncytial cytoplasm. Finally the whole syncytium became degenerated with plasmalemma completely detached from the syncytial cell walls. The differences in resistant responses reflect a difference in genetic composition of the soybean cultivars tested.

Effects of Heterodera glycines and Meloidogyne incognita on Early Growth of Soybean

Greenhouse and field microplot studies were conducted to compare soybean shoot and root growth responses to root penetration by Heterodera glycines (Hg) and Meloidogyne incognita (Mi) individually and in combination. Soybean cultivars Centennial (resistant to Hg and Mi), Braxton (resistant to Mi, susceptible to Hg), and Coker 237 (susceptible to Hg and Mi) were selected for study. In the greenhouse, pot size and number of plants per pot had no effect on Hg or Mi penetration of Coker 237 roots; root weight was higher in the presence of either nematode species compared with the noninoculated controls. In greenhouse studies using a sand or soil medium, and in field microplot studies, each cultivar was grown with increasing initial population densities (Pi) of Hg or Mi. Interactions between Hg and Mi did not affect early plant growth or number of nematodes penetrating roots. Root penetration was the only response related to Pi. Mi penetration was higher in sand than in soil, and higher in the greenhouse than in the field, whereas Hg penetration was similar under all conditions. At 14 days after planting, more second-stage juveniles were present in roots of susceptible than in roots of resistant plants. Roots continued to lengthen in the greenhouse in the presence of either Mi or Hg regardless of host genotype, but only in the presence of Mi in microplots; otherwise, responses in field and greenhouse studies were similar and differed only in magnitude and variability.

A comparison of techniques useful for preparing nematodes for scanning electron microscopy

Second-stage juveniles of Meloidogyne incognita were prepared by several different techniques for scanning electron microscopy (SEM). Sequential fixation in the cold (4-8 C) was superior to rapid fixation at room temperature, glutaraldehyde and glutaraldehyde-formalin were better fixatives than formalin alone, and critical point drying with carbon dioxide or Freon gave similar results that were only slightly better than air drying with Freon. Freeze drying sequentially fixed nematodes from 100% ethanol in liquid propane produced the best preserved specimens with the fewest artifacts. Specimens of various free-living and plant-parasitic nematodes were prepared for SEM by freeze drying. This technique was adequate for most genera but unsatisfactory for a few. Although each genus may require a different procedure for optimum preservation of detail, sequential fixation with glutaraldehyde and freeze drying are comparable and often superior to commonly used techniques for preparing nematodes for SEM.

Effects of Interactions among Heterodera glycines, Meloidogyne incognita, and Host Genotype on Soybean Yield and Nematode Population Densities

The effects of host genotype and initial nematode population densities (Pi) on yield of soybean and soil population densities of Heterodera glycines (Hg) race 3 and Meloidogyne incognita (Mi) race 3 were studied in a greenhouse and field microplots in 1983 and 1984. Centennial (resistant to Hg and Mi), Braxton (resistant to Mi, susceptible to Hg), and Coker 237 (susceptible to Hg and Mi) were planted in soil infested with 0, 31, or 124 eggs of Hg and Mi, individually and in all combinations, per 100 cm(3) soil. Yield responses of the soybean cultivars to individual and combined infestations of Hg and Mi were primarily dependent on soybean resistance or susceptibility to each species separately. Yield of Centennial was stimulated or unaffected by nematode treatments, yield of Braxton was suppressed by Hg only, and yield suppressions caused by Hg and Mi were additive and dependent on Pi for Coker 237. Other plant responses to nematodes were also dependent on host resistance or susceptibility. Population densities of Mi second-stage juveniles (J2) in soil were related to Mi Pi and remained constant in the presence of Hg for all three cultivars. Population densities of Hg J2 on the two Hg-susceptible Cultivars, Braxton and Coker 237, were suppressed in the presence of Mi at low Hg Pi.

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.

Effects of Temperature on Development of Heterodera glycines on Glycine max and Phaseolus vulgaris

Soybean cyst nematode resistant 'Fayette' and susceptible 'Williams 79' soybeans (Glycine max) and resistant 'WIS (RRR) 36' and susceptible 'Eagle' snap beans (Phaseolus vulgaris) were used in determining the effects of host and temperature on the development, female production, sex ratios, and host response to Heterodera glycines. Temperatures were maintained constant at 16, 20, 24, 28, and 32 C using water-filled tanks. The most rapid development and greatest female production occurred between 20 and 28 C. The equation DS = 5(10)x(2)y(2) - 3(10)x(2)y - 2.8(10(3))x(2) - 1.94(10(2))y(2) + 0.4288x + 1.0220y - 12.7185, where DS = developmental stage, X = time, and Y = temperature, predicted the developmental stage of the nematode and accounted for 84% of the variation. Male : female ratios did not differ within this range and were generally less than one. At all temperatures the resistant soybean produced the greatest number of necrotic responses to H. glycines infection, followed by the resistant snap bean. The susceptible soybean and snap bean produced the fewest necrotic responses.

Heterodera glycines-Soybean Association: A Rapid Assay Using Prun Seedlings

A 16-day bioassay to determine compatible and incompatible associations of soybeans and cyst nematodes is described. This permits large-scale experiments in the laboratory. Seedlings are placed between two sheets of moist paper towelling so that the root tips are even with the bottom edge. The towelling is then rolled and set on the surface of cyst-infested soil. Radicles are permitted to grow through the soil for 24 hours after which cotyledons and apical portions are trimmed to retard root growth. The plants are assembled in bundles and maintained in aerated water in test tubes for 15 days before counts of emerged nematodes are taken. This system is economical in both space and labor.