Glycines Population Densities Research Articles

Biocontrol potential of Microbacterium maritypicum Sneb159 against Heterodera glycines.

The soybean cyst nematode Heterodera glycines (Ichinohe) is the most devastating pathogen affecting soybean production worldwide. Biocontrol agents have become eco-friendly candidates to control pathogens. The aim of this study was to discover novel biocontrol agents against H. glycines. Microbacterium maritypicum Sneb159, screened from 804 strains, effectively reduced the number of females in field experiments conducted in 2014 and 2015. The stability and efficiency of H. glycines control by Sneb159 was further assessed in growth chamber and field experiments. Sneb159 decreased H. glycines population densities, especially the number of females by 43.9%-67.7%. To confirm Sneb159 induced plant resistance, a split-root assay was conducted. Sneb159 induced local and systemic resistance to suppress the penetration and development of H. glycines, and enhanced the gene expression of PR2, PR3b, and JAZ1, involved in the salicylic acid and jasmonic acid pathways. This is the first report of M. maritypicum Sneb159 suppressing H. glycines infection. This effect may be the result of Sneb159-induced resistance. Our study indicates that M. maritypicum Sneb159 is a promising biocontrol agent against H. glycines. © 2019 Society of Chemical Industry.

Biological control of Heterodera glycines by spore-forming plant growth-promoting rhizobacteria (PGPR) on soybean

Heterodera glycines, the soybean cyst nematode, is the most economically important plant-parasitic nematode on soybean production in the U.S. The objectives of this study were to evaluate the potential of plant growth-promoting rhizobacteria (PGPR) strains for mortality of H. glycines J2 in vitro and for reducing nematode population density on soybean in greenhouse, microplot, and field trials. The major group causing mortality to H. glycines in vitro was the genus Bacillus that consisted of 92.6% of the total 663 PGPR strains evaluated. The subsequent greenhouse, microplot, and field trials indicated that B. velezensis strain Bve2 consistently reduced H. glycines cyst population density at 60 DAP. Bacillus mojavensis strain Bmo3 suppressed H. glycines cyst and total H. glycines population density under greenhouse conditions. Bacillus safensis strain Bsa27 and Mixture 1 (Bve2 + Bal13) reduced H. glycines cyst population density at 60 DAP in the field trials. Bacillus subtilis subsp. subtilis strains Bsssu2 and Bsssu3, and B. velezensis strain Bve12 increased early soybean growth including plant height and plant biomass in the greenhouse trials. Bacillus altitudinis strain Bal13 increased early plant growth on soybean in the greenhouse and microplot trials. Mixture 2 (Abamectin + Bve2 + Bal13) increased early plant growth in the microplot trials at 60 DAP, and also enhanced soybean yield at harvest in the field trials. These results demonstrated that individual PGPR strains and mixtures can reduce H. glycines population density in the greenhouse, microplot, and field conditions, and increased yield of soybean.

Intra- and interplot variability of Heterodera glycines population densities in experimental settings to soybean variety evaluations in Nebraska

The intra- and interplot variability of soybean cyst nematode (SCN; Heterodera glycines) population densities was characterized in three experimental areas in Nebraska in 2014. Through single-core cluster sampling of 4-m-long plots, a random pattern of SCN incidence (number of SCN-positive soil cores out of 10 per plot) within plots was suggested by the binomial distribution in one location. The detected randomness, however, was associated to the high SCN infestation level and tillage in the experimental area. In the other two experimental areas, the beta-binomial distribution adequately described SCN incidence (index of aggregation θ > 0; index of dispersion D > 1.0), suggesting the presence of an aggregated pattern within plots. Based on the properties of the fitted distributions, the intraplot aggregation of incidence affects the probability of cyst recovery during sampling and thereby the estimation of SCN population densities. At the interplot scale, correlogram analysis of 36 transects of 28 and 35 m showed that discrete foci of SCN population densities were spatially dependent with foci located up to 15 m away. This was confirmed by spatial autocorrelation, which indicated that SCN population densities in the 4-m-long plots were positively correlated with population densities of up to two contiguous plots. Interplot aggregation of SCN population densities suggests lack of independence among plots or experimental units. Altogether, the results of this study recommend that researchers conducting field experiments with H. glycines consider SCN spatial pattern, particularly, if rigorous comparisons among soybean varieties are sought. Consideration may comprise both the diagnostics of spatial dependence of SCN population densities in a prospective variety evaluation site, prior to spring sampling, and the subsequent allocation of varieties to plots based on their degree of spatial correlation. While limited to a single-year assessment, the information on SCN spatial pattern from the present study, coupled with that on soybean plant populations, row spacing, and soil conditions, can be useful to determine site suitability for a variety trial. The information could also be incorporated into statistical analysis to determine the number of replications needed to detect differences among varieties for their response to SCN.

Correlation between Soil pH, Heterodera glycines Population Densities, and Soybean Yield

Soybean cyst nematode (Heterodera glycines Ichinohe) is the most damaging pathogen of soybean [Glycine max (L.) Merr.] in the United States. Observations in fields suggest that high H. glycines population densities are associated with high soil pH, but H. glycines and soil pH have not been linked to soybean yield. The objective of our study was to assess the relationship between soil pH and H. glycines population densities and subsequent effect on yield. Experiments were conducted in Wisconsin from 1997 to 2000 and in Iowa from 1996 to 1998. Results were consistent among the experiments and showed a positive correlation between soil pH and H. glycines population densities and a negative correlation between yield and both soil pH and H. glycines population densities in both states. In the Wisconsin experiment, yield of both H. glycines–resistant and H. glycines–susceptible cultivars decreased as pH increased, but the decrease was less with H. glycines–resistant cultivars. Overall, results indicate that H. glycines population densities and the impact of nematode population densities on soybean yield are related to soil pH; however, the mechanism of these interactions is unknown.

Effect of rotation crops on hatch, viability and development of Heterodera glycines

AbstractRotation with non-host crops can be an effective method for reducing soybean cyst nematode (Heterodera glycines) populations in soybean cropping systems. Sunn hemp, Illinois bundleflower, oilseed rape, perennial ryegrass, red clover, corn and H. glycines-susceptible soybean were compared for their effects on H. glycines hatch, viability and development in laboratory and glasshouse experiments. In the laboratory experiments, root exudates in soil leachates, extracts from fresh plant tissues, and extracts from residues of sunn hemp, red clover and soybean stimulated hatch of second-stage juveniles (J2) of H. glycines. All crops appeared to contain hatch inhibitors as well. There was no apparent effect of the root exudates and extracts from any of the crops on egg viability in vitro. When the H. glycines J2 were exposed to root exudates and extracts for 72 h, only the extracts of fresh plants and plant residue from sunn hemp, red clover and soybean, and the extract of plant residue from oilseed rape reduced viability of J2. In glasshouse experiments, residues of all crops, except Illinois bundleflower, reduced egg population density, with sunn hemp providing the greatest reduction. Residues of sunn hemp, red clover, and perennial ryegrass added to soil reduced the reproduction factor, suggesting the residues not only reduced egg population density but also reduced nematode infectivity. While all crops allowed penetration by J2, minimal development (to third- or fourth-stage juveniles only) occurred only in sunn hemp, red clover, oilseed rape and Illinois bundleflower, and full development occurred only in soybean. The results suggest that sunn hemp and red clover were the most effective rotation crops for managing H. glycines, and that stimulating hatch of H. glycines J2 was the main mechanism involved in reducing the H. glycines population density.

Effects of Tillage Practices on Dissemination and Spatial Patterns of Heterodera glycines and Soybean Yield.

Two field experiments were conducted in central Iowa to assess the effects of tillage on Heterodera glycines dissemination and reproduction and soybean (Glycine max) yield. Plots in both experiments were artificially infested with equivalent numbers of H. glycines cysts. In one experiment, plots were left noninfested or received aggregated or uniform infestation, and a susceptible soybean cultivar was grown for 3 years. By the end of the first growing season and through the second, H. glycines population densities were consistently greater (P ≤ 0.05) in uniformly infested plots than in plots with aggregated infestations. No differences in soybean yield among the treatments were detected. In a second experiment, a 1-m2 area of each plot was infested with H. glycines cysts, susceptible soybeans were grown for four seasons, and crop residue was managed with either ridge-, conventional-, reduced-, or no-tillage. After 1 year, nematode population densities were significantly (P ≤ 0.05) greater in conventional- and reduced-tillage treatments than in no- and ridge-tillage treatments. After 2 years, H. glycines had been disseminated 6.9 m from the infestation site in conventional- and reduced-tillage treatments but only 0.5 and 1.4 m for no-tillage and ridge-tillage treatments, respectively. After 3 years, H. glycines population densities were 10 times greater in conventional- and reduced-tillage treatments than in the no-tillage treatment; conventional-tillage was the only treatment with yield significantly lower (P ≤ 0.05) than the noninfested control. Aggregation of H. glycines eggs was greater (P ≤ 0.05) in no- and ridge-tillage treatments than in conventional- and reduced-tillage treatments. Results indicate tillage can quickly disseminate H. glycines in newly infested fields, facilitating more rapid nematode reproduction and subsequent yield loss.

Soybean Stem Colonization by Genotypes A and B of Cadophora gregata Increases with Increasing Population Densities of Heterodera glycines.

Growth chamber experiments were conducted to investigate whether parasitism by increasing population densities of Heterodera glycines, the soybean cyst nematode, increases the incidence and severity of stem colonization by the aggressive genotype A and the mild genotype B of Cadophora gregata (Phialophora gregata), causal agents of brown stem rot of soybeans. Soybean genotypes with three combinations of resistance and susceptibility to H. glycines and genotype A of C. gregata were inoculated with each genotype of C. gregata alone or each genotype with two population densities of H. glycines eggs, 1,500 or 10,000 per 100 cm3 of soil. Stems of two H. glycines-susceptible soybeans were more colonized by both aggressive and mild genotypes of C. gregata in the presence of high than in the presence of low H. glycines population density.

Predators SuppressAphis glycinesMatsumura Population Growth in Soybean

The soybean aphid, Aphis glycines Matsumura, is an invasive pest of soybean, Þrst discovered in North America in 2000. We studied the ability of the existing predator community in soybean to suppress A. glycines population growthduring JuneÐAugust 2002, in Þeld studies using predator exclusion and sham cages or no-cage controls. Cages were infested with uniform initial densities of A. glycines adults, and subsequent populations of aphids and predators were monitored. After 2 wk, exclusion and sham cages were switched, with aphid and predator density followed for additional 2 wk. The experiment was repeated a second time, allowing observation of predator community response to bothlow and h ighdensity aph id populations over several time periods and stages of soybean development. Cages had minimal effects on temperature, relative humidity, or soybean growth. In contrast, predator communities and aphid populations were strongly affected by cage treatments. In the Þrst trial, the activity of foliar-foraging predators effectively prevented A. glycines population growthmaintaining populations below 10 aph ids per plant (adult nymphs) in sham cages, while populations exceeded 200 aphids per plant in exclusion cages. After cage switch, these high A. glycines populations in the former exclusion cages were rapidly colonized and reduced by nearly an order of magnitude within 2 wk by a combination of generalist and specialist predators. The second trial produced qualitatively similar results, but at much lower aphid densities. The most abundant predators in bothtrials included: Harmonia axyridis Pallas, Orius insidiosus (Say), and Leucopis spp. These studies demonstrate that existing predator communities comprised of a mixture of indigenous and naturalized species can suppress A. glycines population density in soybean. The impact of existing predator communities should be further investigated as a component of A. glycines management in United States soybean production systems.

Effect of crop rotation on soil population densities of Fusarium solani and Heterodera glycines and on the development of sudden death syndrome of soybean

The effect of crop rotation on the development of sudden death syndrome (SDS) of soybean and on the soil population densities of Fusarium solani and the soybean cyst nematode ( Heterodera glycines) was observed for four years in a field naturally infested with both pathogens. In 1989 all plots were planted to a soybean cultivar susceptible to both pathogens (cv. Lee 74). In 1990 and 1991, the plots were planted to one of the following crops: soybean cv. Lee 74, soybean cv. Hartz 6130 (resistant to both pathogens), sorghum, fescue, or wheat (not double-cropped). In 1992 all plots were planted to soybean cv. Lee 74. The parameters measured to determine rotation effects were severity of SDS over the season, the soil population densities of both pathogens, soybean yields and soybean seed weights. Rotation to any crop except soybean significantly reduced the H. glycines population densities in 1990 and 1991. In 1991, the H. glycines population densities began to rise in the nematode-resistant soybean treatment, but were lower than those in the susceptible soybean treatment. Averaged over all years, the F. solani population densities were significantly lower when sorghum or wheat were grown than when soybean or fescue were grown. Considering the whole season, the F. solani population densities were generally the highest at harvest. Negative correlations between SDS and yield were significant, as were positive correlations between SDS and population densities of F. solani. In 1992, SDS was very low in all treatments, but yields were highest in plots planted to non-soybean crops and lowest in plots planted to the susceptible soybean.

Impact of Crop Rotation and Tillage System onHeterodera glycinesPopulation Density and Soybean Yield

The long-term effects of no-till planting practices and rotation on the population dynamics of the soybean cyst nematode (Heterodera glycines) and soybean yield were investigated in field experiments over a period of 8 yr. The experiment was a 2 X 4 factorial, comparing no-till vs. conventional tillage practices in four cropping patterns (continuous soybean, a 1-yr rotation of corn and soybean, a rotation of 2 yr of corn followed by soybean, and a corn-wheat/soybean double-cropping system). Treatments were arranged so that each combination occurred every year after 1986. Soybean after 1 yr of corn had higher yields (P = 0.0001) than soybean after soybean. Two years of corn between soybean crops resulted in soybean yields higher than those after 1 yr of corn in only 2 out of 6 yr. The yields of soybean in the corn, wheat/soybean double-cropping system, however, were generally similar to monoculture soybean. No-till practices had positive or no effects on soybean yield early in the study, but yields of no-till soybean were lower (P = 0.01) than conventionally tilled soybean after several years because weed pressure was greater in no-till plots. Population densities of H. glycines were greater (P < 0.10) in conventionally tilled plots than in no-till plots in 1988 and 1990-1992. Numbers of H. glycines fluctuated in an unpredictable manner from year to year, possibly because of unidentified biological control agents or excessive moisture in certain years. H. glycines population densities declined in a predictable manner when a nonhost was planted