Duration: 10/01/1999 to 09/30/2004

Administrative Advisor(s):

NIFA Reps:

Non-Technical Summary

Statement of Issues and Justification

Nematodes, particularly the soybean cyst nematode (SCN), Heterodera glycines, are chronic problems for corn/soybean production systems in the North Central region. The distribution of SCN expands every year and the number of affected producers has risen dramatically within the last ten years. Soybean cultivars with resistance to SCN are available and extremely important t SCN management, but even resistant genotypes allow some nematode reproduction and do not achieve their full yield potential when the initial inoculum exceeds 5000 eggs/I 00 cm3 soil (Franci & Dropkin, 1986). The goal of our previous project, NC-215, was to determine the rates and the biological basis of overwinter survival of SCN and other nematodes in the region in order to devise strategies able to accelerate population decline following harvest. Our collective experience was that, unlike the southern states where SCN populations decline 25-40% during the winter (Riggs & Wrather, 1992), SCN in the North Central region is so well adapted to cold and freezing conditions that survivorship over the winter often approaches 100%. Even so, SCN and other nematode population densities decline every year a host crop is not planted and rotating to nonhost crops is the common denominator of all successful nematode management programs. The problem faced by North Central producers is that economics prevent a nonhost rotation of sufficient duration to reduce SCN population densities to levels which allow profitable soybean production. The purpose of the present project will be to devise control tactics and programs which accelerate the attrition of established nematode populations based on a comprehensive understanding of the factors and timing of events responsible for nematode persistence.

Justification:

Plant parasitic nematodes are serious constraints to agricultural production in the north central United States. One or more nematode species is pathogenic to every important annual agronomic crop species grown in the region, including soybean, corn, oats, potato, wheat, sugarbeet, and sorghum, and to a number of regionally important perennials such as alfalfa and fescue. Lesion nematodes (Pratylenchus spp.), dagger nematodes (Xiphinema spp.), lance nematodes (Hoplolaimus spp.), needle nematodes (Longidorus spp.), root-knot nematodes (Meloidogyne spp.) and sting nematodes (Belonolaimus sp.) are responsible for extensive damage and the current or pending loss of chemical control and unavailability of host resistance demands a shift in research focus to nematode ecology and biologically-based control.

The SCN caused an estimated annual soybean yield loss of 1,322,000 Mg (48,600,000 bushels) worth $243 million at $5/bushel from 1989 to 1991 in the North Central Region alone, according to the NCR-137 Committee on Soybean Diseases (Doupnik, 1993). More current regional estimates are not available, but the estimated distribution of SCN in the region has grown every year since 1991 (Tyika, Phytopathology in-press). The United Soybean Board describes SCN as the most serious pathogen of soybean in the U.S. Evidence of the importance of SCN to the region include the formation of the SCN Coalition by the North Central Soybean Research Program (NCSRP) and the release of a 24-page special report entitled, "Let's declare war on cyst nematodes!" by the trade magazine Soybean Digest.

The power of a collective approach to nematode; problems is demonstrated through the efforts of the SCN Coalition, a collaboration of the qualified soybean boards, university researchers, and industry partners in 12 North Central states. This initiative has defined and capitalized on the mechanisms of information transfer to north central soybean producers. One important outcome has been to provide a regional framework for the site-specific, information and recommendations that researchers in individual states make to their clientele. This regional context is extremely important because producers are increasingly influenced by a private sector that is not constrained by state boundaries. Cooperative research distinguishes the common versus regionally variable phenomena among nematode populations, and maximizes the productivity of a small cadre of nematologists, which amounts to 2.0 or less FTE per state.

The collaborators of this proposed regional project are involved in production research, funded by the qualified state soybean boards and the NCSRP, to help producers select appropriate cultivars and soybean management practices to produce profitable soybeans on SCN-infested land. Our educational efforts, funded by the soybean checkoff through the SCN Coalition, are reaching producers through magazine and radio ads, a toll-free hotline, and special publications. Because SCN is well adapted to the intermittent availability of its host, understanding the basis for its persistence is crucial for manipulating its population dynamics for devising long-term solutions to the production problems caused by nematodes in the region. Investing regional funds in fundamental research to add leverage to our current production research and information transfer initiatives will advance sustainable nematode management programs in the North Central region.

Related, Current and Previous Work

The SCN Coalition, the formal title of the educational arm of the project entitled "Development and Implementation of a Plan to Eliminate Losses Due to Soybean Cyst Nematode in the North Central Region" funded by the NCSRP, has launched an aggressive mass media campaign to convince producers to have then soil tested for the SCN. The SCN Coalition produces educational materials including pamphlets, slide sets, a website, and telephone hotline, recruits industry partners, and communicates to clientele information about SCN, its impact on soybean production, and appropriate management recommendations. Each state has also organized a statewide SCN Coalition which enlists cooperatives, consultants, seed dealers, and Cooperative Extension to accomplish technology transfer to producers through local meetings, newsletters, and media releases.

The NCSRP-funded project also includes a research project to determine the effect of tillage regime and row spacing on the yield gain of SCN-resistant soybean varieties in diverse environments representative of the North Central region. A common experiment was planted in 1997 and 1998 and will be planted again in 1999 in nine North Central states (Kansas, Indiana, Illinois, Iowa, Michigan, Minnesota, Missouri, South Dakota, Wisconsin), Arkansas, and Ontario, Canada. Prior to this project, the NCSRP funded another research initiative to demonstrate the yield benefit of planting SCN-resistant varieties in the region.

There are three other regional projects studying nematodes. The project for the North East region (pending) "Biologically Based IPM Systems for Management of Plant Parasitic Nematodes" is conceptually related to this proposal, but the focus is on understanding the biology of specific organisms intended for use as biological controls of nematode pests of vegetables fruits ornamentals, and tobacco.

In contrast to these other projects, our proposed project will be the only one directed primarily toward nematode ecology and its exploitation for crop management. It will complement the SCN research funded by the private sector, but is broader in that it targets the entire complex of nematodes parasitic on soybean and endeavors to implement control strategies consistent with cropping systems in the North Central region.

Related Previous Work:

The incidence and severity of SCN infestations have increased every year in the U.S. since SCN was first detected in 1954. Examples of current estimates for the number of infested acreage in the North Central states demonstrate the importance of this pest to midwest agriculture; 82% of fields in Illinois, 74% of Iowa, 71% of Missouri, 53% of Minnesota (Soybean Digest 1998-Tylka et al., -in press Phytopathology). Population densities of SCN eggs, representing the initial inoculum (Pi) for the soybean crop, are frequently in excess of 5,000 eggs/100 cm3 soil. Yield loss of soybean is proportional to Pi (Franci & Dropkin, 1986). The Pi is a function of the suitability of the previous crop for nematode reproduction and the survival rate during the absence of a host. Studies starting with large Pi have not successfully reduced SCN population densities using host resistance (Fraud & Wrather, 1987; Young & Hartwig, 1992), even though there is generally a yield advantage for resistant varieties. For example, Wheeler et al., in Ohio (1997) found SCN population densities increased up to five-fold on resistant varieties planted in highly infested soybean plots. In contrast when SCN population densities were low at the time the rotation of resistance genes was introduced in the cropping sequence, the populations declined to below the detection level (Noel & Edwards 1996). In addition to the size of the nematode population in a particular field, the allelic frequencies for parasitism expressed in a population are important. The number of genes that express parasitic capability in the nematode are not defined completely, but it is known that multiple host/parasite genes are involved in the establishment of successful nematode infections.

Adaptations of SCN and other nematodes responsible for the persistence of nematode populations in the absence of a host: In the absence of a host, SCN persists in the egg stage. The egg population consists of a range of developmental stages from single-celled to the fully developed second-stage juvenile (J2), the stage that hatches from the egg. A proportion of the eggs produced within a growing season hatch and reinvade the host plant. In the fall, most eggs enter dormancy and do not hatch until appropriate plant host signals are received. Even under optimum conditions some eggs remain dormant for long periods of time, and the proportions of egg populations that remain dormant increases with latitude. When a nonhost was planted, population densities of SCN declined 75% in one year in the south (Slack et al., 1981). The rate of population attrition is much less in the north (NC-215 committee, persnl. comm. The slow decline may be because most eggs survive the winter, or because they remain dormant and do not hatch.

Long-term studies of SCN survival in the midwest show that the nematode does not hatch at a rate sufficient to reduce Pi in short term (1-2 year) rotations. Thus, rotation intervals in northern soybean production areas must be longer than those recommended for southern environments. This reduced flexibility in rotation design can have serious economic consequences. An obvious approach to the problem is to increase the hatching rate of SCN, but no successful attempts have been reported. In early spring, egg populations from northern Missouri or Iowa field sites have a high proportion of early embryo stages and hatch at a rate of <5% after 14 days in glass distilled water at 27 C. Following exposure to soybean root leachate, development to J2 within the egg occurs rapidly and the hatching rate increases to > 80% (Walk and Niblack, unpub.) The nature of the processes that occur following the host signal is unknown (Perry, 1989). Hatching rates increase when eggs are exposed to zinc (Tefft and Bone, 1984), and may be mediated through a metalloenzyme, leucine aminopeptidase or pseudocollagenase (Tefft and Bone, 1985), but this has not been demonstrated. Exposure to relatively high levels of zinc in the field does not affect hatching rates in the absence of soybean (Behm et al., 1995). Assuming hatching is enzyme-mediated, one or more of the proteins produced or activated upon exposure to soybean root leachate should be candidates for a "hatching enzyme" and therefore essential to characterize, with the ultimate goal of manipulating SCN hatching in the absence of soybean.

Most studies consider SCN eggs collected from the field as homogeneous populations, but there is increasing evidence that the duration of dormancy and genetic disposition to hatching varies considerably within a spatial cohort of eggs. Both the timing and extent of eclosion of SCN eggs in water differed among a SCN egg cohort collected from fallow microplots one year after they were produced versus an egg cohort produced the same year (MacGuidwin, unpubl). Even eggs reared in greenhouse culture exhibit a range of hatch phenotypes, and selective rearing can produce "rapid hatchers" by repeatedly subculturing the first juveniles eclosed within a population (Niblack, personal comm.). Some differences in rates of egg hatch have been observed among races of H. glycines, but were not consistent among experiments (Sikora & Noel, 1996). Variation in egg hatch of H. schachtii led Zheng and Ferris (1991) to propose four types of dormancy, but the study did not identify whether the mechanism responsible for the hatch phenotypes was time, genetic disposition, or some other factor. A study in gene expression during stimulation and hatching of the potato cyst nematode, Globodera rostochiensis, found that changes were most apparent during or after hatching, rather than before (Jones et al., 1997).

Biologically based attrition of nematode populations: Natural enemies of nematodes include fungi, bacteria, and some microscopic animals such as insects, mites, and nematodes. Among these organisms, fungi and bacteria are more likely to be candidates as biological control agents. Many soil-borne fungi are demonstrated antagonists of nematodes, including trapping fungi that form special devices to capture and kill nematodes, endoparasites of vermiform nematodes, fungi colonizing eggs and females of sedentary endoparasitic nematodes such as SCN, and fungi that produce antibiotics to nematodes (Stirling, 1991). A number of fungal species have been isolated from SCN in the North Central region during the past two decades (Can-is et al., 1989; Kim and Riggs, 1991), but only a few have been tested in controlled conditions for their pathogenicity to SCN (Chen et al., 1996; Kim and Riggs, 1991; Meyer et al., 1990). Rhizosphere bacteria may compete with plant parasitic nematodes or alter the root environment to deter the entry of nematodes into roots (Oostendorp and Sikora, 1989; Tian et al., 1995). Pasteuria sp. has been detected from four locations in Michigan and a new species of Pasteuria has been discovered parasitizing Heterodera glycines in Illinois. It is currently being described by USDA/ARS.

Naturally occurring biological control of SCN has been described for specific sites in the midwest (Cams et al., 1989; Riggs) and elsewhere (Chen et al., 1996; Liu and Wu, 1993) but the role of antagonists in suppressing the increase of SCN is largely unknown. In Michigan, a population of Pasteuna sp. was found parasitizing a Tyienchus sp., two endospore forms were detected parasitizing a Hemicycliophora sp., and another isolate was discovered in the MSU greenhouse (Bird, persni. comm.). Nematologists at MSU initiated a Pasteuria research program in 1997 and to date have surveyed 50 soybean fields using molecular diagnostics, but none have been found associated with the SCN. The suppression of the cereal cyst nematode by egg-parasitic fungi has been well documented in Europe (Kerry, 1975; Kerry and Crump, 1977; Kerry et al., 1982) Paecilomyces lilacinus, isolated from SCN in China, has been developed as a biological control agent called "Soybean Root Bio-Protectant" and applied in over 30,000 acres of soybean in China (Lis et al., 1996).

Many experiments were conducted before 1980 on the use of organic matter to enhance control of plant parasitic nematodes. Most of these early experiments did not result in acceptable control. The hypothesis offered to support this work is that organic matter enhances the activity of trapping fungi and predaceous nematodes and mites. Ecological studies provided no simple conclusion (Cooke, 1968) and a recent resurgence in studies on the effect of soil amendments on nematodes have focused on the enzymatic activities of microorganisms (Kokalis-Burells and Rodriguez-Kabana, 1994) and plant degradation products (Mojtahedi et al., 1993). Lazzeri et. al., (1993) demonstrated in vitro nematicidal activity of glucosinolates, degradation products of Brassica spp. to the sugarbeet cyst nematode, Heterodera schachtii.

The impact of agricultural activities on the persistence of nematode populations associated with nonhost crops: An essential component of successful management of SCN and other nematodes is crop rotation to nonhost crops. Phytophagous nematodes are obligate parasites which persist in juvenile life stages in the absence of a host. Population increase through nematode reproduction only occurs when an appropriate and adequate food supply is available. Some SCN eggs hatch in the absence of a host resulting in the death of the J2, but the extent to which untimely eclosion contributes to population attrition has not been documented. Literature citing variation in the decline of SCN under different nonhost crop rotations is limited and it is the collective experience of the NC-215 Committee that the rate of decline of egg densities is lower on corn than on legumes (alfalfa and clover), potato, sugarbeet, and small grains; however, this relationship needs to be validated and the contributing factors responsible for the phenomenon identified. A study in Wisconsin used different rotations to create a range of SCN population densities to establish the dose/response benefit of planting SCN-resistant soybean (MacGuidwin et al., 1995). Economic models for managing nematodes with crop rotations have been developed for other crops (Burt & Ferris, 1996), and could be modified for SCN-infested soybean once rates of population attrition are available.

Tillage effects on SCN and other nematodes have been examined when the crop expected to be damaged by nematode parasitism is planted (Hershman & Bachi, 1995; Koenning, et al., 1995; Niblack et al, 1995; Noel & Edwards, 1996). Both no-till and conventional tillage alter the physical environment of the resident nematode communities, and various species in diverse taxa are affected differently (Gallaher, et al., 1988; McSorley & Gallaher, 1993; Minton, 1986). The effect of tillage in the rotation years has received limited attention for SCN, particularly in regards to its impact on the biological activity of soil. Biocontrol has been enhanced by manipulation of the soil environment and the addition of suppressive plant and animal products (Stirling, 1991) so it is not unreasonable to hypothesize that the increased residue associated with no-till can alter the rate of nematode population density decline. Surface residues lower soil temperature and increase soil moisture, conditions which impact the microbial communities in soil.

Herbicide use is another factor known to affect SCN egg population densities. The post-emergence herbicide Blazer inhibited egg hatch in laboratory assays (Wong et al., 1993). The stimulatory effects of other herbicides, such as diallate, have been demonstrated for other cyst nematodes (Kraus & Sikora, 1983). Field studies in Arkansas (Riggs and Oliver, 1982) and Illinois (Kraus et al., 1982) showed greater egg hatch and population increase of SCN in herbicide-treated plots than in control plots, but the population decline of SCN was enhanced in a North Carolina study when herbicides were applied in combination with a nematicide (Schmitt et. al., 1983).

Objectives

1. Determine the impact of cultural factors on the attrition of nematode populations.
   
2. Determine the biological factors responsible for the attrition of nematode populations.
   
3. Characterize and understand egg dormancy.
   
4. 
   

Methods

Measurement of Progress and Results

Outputs

Outcomes or Projected Impacts

• Soybean producers can expect yield increases of 5 to 20 bushels per acre when they switch to a SCN- resistant variety. For example, a recent article in Soybean Digest reported an increase of $91 per acre for Iowa farmer Ron Heck (1998). Experience and research shows that these yield gains cannot be sustained unless SCN population densities are kept in check and the nematode population does not show a genetic shift in response to selection pressure exerted by host resistance. The proposed project will identify some of the key factors responsible for the persistence of SCN and other nematodes and consequently, aspects of the nematode or environment that can be manipulated to enhance population decline. Using a biologically-based approach to manipulate SCN inoculum level (egg population densities) is consistent with the regional priorities for IPM (14.5-1). The specific information the project will generate on the relationship between biological and edaphic factors and SCN decline addresses the priority of assessing inoculum variability for field crops (14.3.1).</P> <P>Recommendations for managing SCN in the North Central Region currently include a generic recommendation to practice crop rotation and to plant SCN-resistant soybean once economic thresholds are surpassed. The proposed project will refine those recommendations considerably by providing detail on the value of specific nonhost crops, the duration of the rotation necessary to achieve adequate decline in SCN populations, and the importance of tillage for SCN management. Lowering SCN populations to economically manageable levels of Pi for the soybean year will not only increase yields in the short term; it will also decrease the likelihood of a genetic shift in the SCN population. Therefore, one expected outcome of the proposed project will be to help prolong the utility of many resistant soybean varieties for the region. </P> <P>A focus on nematode population reduction will result in cost savings for soybean production, particularly in regards to weed control. A common, but generally missed, symptom of SCN infestations is that soybean canopies are slow to close allowing weeds to become established. Lowering the nematode pressure for both resistant and susceptible varieties will decrease herbicide use from current levels. </P> <P>Information generated from the proposed project will be communicated regionally through the activities of the SCN Coalition. Venues will include a web page, pamphlets, and the popular press. The information also will be immediately available to industry partners of the coalition in a format suitable for their educational programs. The results of experiments and testing for biological antagonists will be communicated to scientific as well as lay audiences. The soil assays for fungi antagonistic to SCN by participating states will constitute a level of survey activity not previously achieved within the region.

Milestones

(0):0

Projected Participation

View Appendix E: Participation

Outreach Plan

Organization/Governance

An election is held every year to select the Secretary of the NC-215 Committee. After serving one year, the Secretary becomes the Vice-Chair, and then the Chair. The Chair writes the annual report, and prepares an agenda for and resides over the annual meeting. The Vice-Chair assists the Chair and participates in local arrangements for the meeting. The Secretary takes, prepares, and distributes the minutes for the meeting, and compiles mailing lists. Project leaders are responsible for collecting and compiling results for each project objective. Since 1994, members of the NC-215 Committee have been involved in regional research projects funded by the North Central Soybean Research Program and meet annually. The meeting of the NCSRP-funded group provides additional opportunity to discuss research goals and progress relative to NC-215.

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Attachments

Land Grant Participating States/Institutions

AR, IA, IL, IN, KS, MI, MN, NE, SD, WI

Non Land Grant Participating States/Institutions

USDA ARS