VOL. 7, No. 2, June, 2000
Researchers Screen Perennial Species for Soybean Cyst Nematode Resistance
Despite the development of new resistant varieties, soybean cyst nematode (SCN) remains the most damaging soybean pathogen across the Midwest. In fact, SCN probably causes as much yield reduction in soybeans as all other pathogens combined.
"The development of resistant soybean varieties as a practical approach for reducing losses has been complicated by the need to find resistance to specific races of SCN," says Glen Hartman, USDA plant pathologist at the University of Illinois. "Unfortunately, none of the resistant varieties developed so far have resistance to all races of SCN."
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| Research Associate Bob Campbell counts the number of cysts in a petri dish under strong magnification. This technique provides a standardized procedure for measuring resistance to SCN in the wild perennial soybean as part of the major screening process underway at the NSRL. |
According to Hartman, the potential for development of new virulent nematode populations makes it essential for researchers to discover new, more diverse sources of SCN resistance genes.
"The problem is compounded by the likelihood that most of the resistance genes available in the cultivated soybean have already been utilized," he says. "We now know that even the new source of resistance found in the cultivar Hartwig is not immune to all SCN populations. That fact indicates that the high level of resistance from that source is not durable and that species other than the cultivated soybean may provide sources of unique resistance."
He notes that two of the most promising sources for new genes are the wild annual progenitors of the soybean, Glycine soja, and the wild perennial species from the subgenus Glycine. The wild perennials include 16 species that are indigenous to Australia and grow in diverse geographic areas and climatic conditions.
"Although the wild annual relatives of the soybean may provide some new sources of resistance to SCN, those genes probably will turn out not to be as unique as what may occur in the wild perennial species" he says. "Until recently, none of the wild perennial species had been screened for resistance to SCN."
U of I plant geneticist Ted Hymowitz, working in collaboration with scientists from the University of Arkansas, however, has now found immunity to SCN in several accessions of the wild perennials. The immunity in these accessions has recently been confirmed in follow-up studies by Greg Noel, USDA nematologist at the U of I.
Hartman notes that the most promising of these species is G. tomentella. Additional screening also was conducted by Hymowitz and his collaborators on a number of hybrid lines produced by crossing this species with the cultivated soybean.
"They evaluated more than 70 derived fertile lines and found that several showed strong resistance to SCN," Hartman says. "They concluded that resistance from the wild perennials had been transferred into these new lines, which can be crossed with cultivated soybean lines."
Working in collaboration with Hymowitz and Noel, Hartman and his research team have launched a new two-year project in the U of I’s Department of Crop Sciences aimed at finding the best sources of SCN resistance in G. tomentella. Key support for this effort is being provided by the Illinois Council on Food and Agricultural Research (C-FAR).
As part of this project, they are screening more than 300 accessions of G. tomentella for resistance to SCN races 1, 3, and 14. They also are attempting to determine the chromosome number of the resistance source so that crosses between the wild perennials and the cultivated soybean will be more likely to produce fertile hybrids.
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"A greenhouse procedure has already been developed to give a standardized and uniform test with a large differential between susceptible and resistance controls," Hartman says. "Plants are established in three-inch pots in a non_inoculated medium. A plug of soil is removed, and the hole is then filled with soil infested with mature cysts. Five weeks after inoculation, the cysts are collected in a culture dish, and the total number of cysts counted under a stereomicroscope at 120 magnification."
He notes that resistant, moderately resistant, and susceptible accessions have been identified for each race of nematode. In some cases, an accession may be resistant to one race of nematode but not to another. Initial results compiled by research associate Bob Campbell seem to indicate a correlation between resistance and the number of chromosome sets in the nucleus.
Similar screening of both the wild annual species and the other perennial species is also underway in Noel’s laboratory. To date, he has tested 30 accessions of the wild annual soybean and 170 accessions of the perennial species.
"Most of the wild annual soybeans we evaluated were susceptible to SCN," Noel says. "A few accessions expressed a low to moderate level of resistance that is not adequate to use for developing SCN-resistant varieties. At the same time, all of the perennial species had at least one accession that was immune to SCN."
Noels points out, however, that differences in chromosome numbers between the perennial soybean and the domestic soybean will require complicated procedures to incorporate resistance from the perennial soybean into commercial varieties.
"In the second phase of our research, we hope to determine the mode of inheritance of resistance to SCN and ultimately transfer these new sources of resistance into soybean varieties," Hartman says. "Most of all, we hope that this research will one day set the stage for soybean breeders to begin using germplasm from the wild perennial species in their regular breeding programs."
Additional details on this research is available on the Internet by following the links at www.soydiseases.uiuc.edu.
Thousands of Soybean Insect Species Caught in Information Center Web
Few insects associated with soybeans have escaped the attention of the Soybean Insect Research Information Center (SIRIC) located at the National Soybean Laboratory at the University of Illinois. More than 8,000 species are covered by the SIRIC electronic database, now available for the first time on the Internet at http://insectweb.inhs.uiuc.edu/Soy/Siric/.
With scientific and research literature that includes documents dating from the nineteenth century and "gray literature," or documents outside the mainstream publishing channels, SIRIC offers free access to the largest collection of publications on soybean insects. Lynn Hanson, a librarian working with the project, expects the database to be used most often by researchers, growers, crop consultants and Extension staff, but noted that it is available to anyone with an Internet connection.
"This project has made an effort to collect widely, even obscure publications, in order to offer complete coverage of the topic," Hanson says.
Before the website, staff received telephone calls and letters, conducted searches and then mailed out results. "This is faster for the user," she says. "It's a rich and valuable resource that we're glad to be making more widely available."
Hanson's expertise in library science is reflected in the user_friendly database design. More than 8,000 species names and subject terms are organized hierarchically in a thesaurus to allow for more precise searching. Entomologists provided their expertise in selecting and organizing the subject terms and in indexing the documents.
According to members of the team, SIRIC is intended to be the "first line of defense against outbreaks of new soybean pests." If exotic insect species are found in soybeans, for instance, the agricultural community could turn to SIRIC for information.
Odds are that the SIRIC database could help users identify the species, weaknesses in the their life cycles and effective management strategies. The team estimates SIRIC information could save two to five years of research time typically needed to evaluate an insect problem and to implement corrective measures.
Entomologists Edward Armbrust, Michael Irwin and William Ruesink lead the SIRIC Team. SIRIC is a project of the Illinois Natural History Survey's Center for Economic Entomology and the Office of Research in the College of Agricultural, Consumer and Environmental Sciences.
The project has been supported by the Illinois Soybean Checkoff Board, the National Soybean Research Laboratory, and Information Systems and Technology Strategic Research Initiative of the Illinois Council on Food and Agricultural Research (C_FAR). The U of I Graduate School of Library and Information Science developed the Web search interface.
U of I Researchers Lead Major Study on How Herbicides Affect Soybean Yields
Soybean researchers at the University of Illinois are taking a close look at the effects of herbicides on yields as part of a major three-year project funded by the soybean checkoff boards in Illinois and Iowa.
The study is one of five components in a project being conducted by 30 scientists at six universities on the various factors that affect yields in soybeans. Research is being carried out at a total of nine locations in Illinois, Iowa, and Wisconsin.
As part of this project, researchers are focusing on how herbicides modify plant reactions to soybean cyst nematodes (SCN) and the soil-borne diseases, Rhizoctonia root rot, brown stem rot, and sudden death syndrome.
At each location in the study, researchers are comparing four to six soybean varieties that are resistant or susceptible to SCN or the soil-borne diseases. They also are planting conventional, Roundup-Ready, and STS-resistant varieties. Weed control includes both pre-emergence and post-emergence herbicides.
"We are paying special attention to SCN because it is the number one pest of soybeans," says Wayne Pedersen, plant pathologist at the U of I’s National Soybean Research Laboratory. "If there is one constant in soybean production, it is that SCN needs to be controlled first. It has become quite clear that heavy SCN populations will worsen the effects of stress on the plants from herbicide applications."
Pedersen notes that findings from the first two years of the study also indicate that the SCN level had a significant effect on yields.
"The research clearly showed the value of resistant varieties in heavily infested fields," he says. "Yields were significantly higher for resistant varieties when SCN populations were large. One ‘take-home’ message from this research is that soybean growers should test their fields to determine the levels of SCN. Managing SCN ultimately will mean increased bushels of soybeans to sell at harvest."
He adds that the recovery from herbicide stress is delayed when there are high concentrations of SCN. In some cases, the plants may never recover. Preliminary results further indicate that the choice of herbicides may even alter SCN populations at harvest time.
"While the data need to be examined further, the practical significance of these findings is that any stress--like weather or damage from herbicides--may affect a plant’s ability to fight off other stresses, such as diseases, insects, or SCN," Pedersen says. "The final result for the grower is lower yields."
Pedersen also emphasizes the need for growers to take strong measures to control weeds in their fields.
"The importance of weed control is not only to eliminate the competition to soybeans but to minimize the growth of pathogens," he says. "Stresses of any kind--even competition for light and water--will open the way for additional problems. Also, we know that Rhizoctonia root rot, white mold, and SCN will all reproduce on weed hosts as well as on soybeans."
The researchers have also found that there appeared to be greater herbicide injury and slower recovery in soybean fields with high SCN populations.
"This was dramatically illustrated in comparing test plots this year," Pedersen says. "In a plot with a heavy concentration of SCN, a susceptible variety did not recover from a herbicide treatment even after 25 days. A resistant variety planted in the same field recovered from the same treatment in only ten days. Meanwhile, in another plot with low levels of SCN, the two soybean varieties showed no difference."
He points out that, prior to this study, there had been only a limited understanding of how weed management systems affect soybean health.
"We know that nature is complex and that most production variables affect other variables," Pedersen says. "Better understanding of these interactions will help producers make informed decisions in their weed, nematode, disease, and insect management programs."
NSRL Expands Research Program on Major Soybean Diseases
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| Darin Eastburn, associate professor of plant pathology, pauses during research at his new laboratory facility. His recent appointment to a faculty position specializing in soil-borne diseases has provided a major boost to the plant pathology program at the NSRL. |
The plant disease program in the National Soybean Research Laboratory (NSRL) at the University of Illinois recently received a major boost with the addition of a new faculty position specializing in soil-borne pathogens.
"Soybeans will be my major focus because many of the important diseases, such as sudden death syndrome, brown stem rot, and white mold, are caused by soil-borne fungi," says Darin Eastburn, associate professor of plant pathology in the U of I’s Department of Crop Sciences. "I plan to deal with problems that are directly applicable to what growers are doing in the field. I also want to look in-depth at some of the more basic issues involved in the development of these diseases."
Eastburn will focus much of his effort on better understanding how factors in the environment impact the development of soybean diseases and how variations in disease come about in the fungi. Such information could be especially important for soybean breeders by allowing them to know exactly how many different pathogens they need to include in their screening procedures for disease resistance.
"I think that joining the NSRL provides a great opportunity that will allow me to draw on the expertise of scientists who are already familiar with problems in the growers’ fields and those who are working on molecular and biochemical aspects of disease development," Eastburn says. "We are all addressing the same basic problems but are approaching them in different ways. By working together as a team, we can accomplish much more than if we tried to do it alone."
As part of his research program, Eastburn is currently studying what components in the soybean roots provide resistance to diseases such as sudden death syndrome.
"We want to understand what there is that is different in the development of the root system in a resistant variety from that in a susceptible variety," he says. "The research also is examining how infection differs in the root systems of resistant and susceptible varieties. The development of disease symptoms has been looked at mostly from foliar perspective. We want to look more clearly at what is happening in the root system."
Another project is focusing on the detection of mycoviruses that may infect various disease-causing fungi. Confirmation of their presence would mark the first step toward their use for a biological control.
"We especially want to examine the pathogen that causes sudden death syndrome to see if there are mycoviruses present," Eastburn says. "If there are, then the next step will be to determine if those viruses have any impact on the ability of the fungi to cause disease. As with all our work, the access to new facilities and the partnership with other researchers at the NSRL will make our task much less difficult."
NSRL to Play Role in Expanding Use of Soy Protein in Human Diets
The rapid growth of the world population, along with improving national economies and the shortage of protein in the diets in many countries, has created a unique opportunity to dramatically increase human consumption of soybean protein, according to Pradeep Khanna, program coordinator with the National Soybean Research Laboratory at the University of Illinois.
"In the developed countries, the demand for edible soy protein is being driven largely by increased awareness of the health benefits of soy and a conscious effort to eat healthy foods," Khanna says. "Recently the U.S. Food and Drug Administration has authorized a health claim on food labels linking soy protein with reduced risk of heart disease. This has resulted in significant interest from food companies to meet the need for more soy-based foods."
He notes, however, that the systems are not in place to meet the demand for increased soy protein in many of the developing countries. Although often overlooked, those countries represent some of the largest potential markets in the world for soy protein.
"An overwhelming proportion of the world population lives in those countries which have a substantial shortage of protein," Khanna says. "Nevertheless, the direct participation of the U.S. food industry in those areas is often very limited. Therefore, it is important for the other sectors of the soybean industry to focus attention on the needs of the developing countries."
With support from the Illinois Soybean Checkoff Board, researchers from the NSRL have already been involved in planning and conducting studies to analyze market and humanitarian opportunities so as to increase the export of U.S. soybeans and to meet the need for protein in many countries.
"Our economists also have been working on an analysis of the global demand for protein under different scenarios for population growth and economic development during the next 25 years," Khanna said. "Initial results from the study indicate that there will be an explosive growth in the demand for protein over the next two decades. The most dramatic growth in demand likely will come from Asia, Africa, and South America, and soy is ideally suited to fulfill that demand."
He notes that the NSRL staff also has been working to increase awareness among the major private volunteer organizations on how they can use soy protein beneficially in their humanitarian programs.
"One specific step would be to provide hands-on experience with soy protein foods and their preparation for key leaders from those organizations," Khanna says. "In this effort, we would hope to work with some of the most experienced volunteer organizations in the world."
Depending on the exact needs of an organization, the NSRL can organize training sessions for their volunteers and professional staffs designed specifically for a target country or region. Much of this work will focus on use of innovative products made with soy flour and textured soy protein.
Many of those efforts will be coordinated across different countries with support from the United Soybean Board through the International Soy Protein Program. This collaborative project, which is headed by the American Soybean Association, is aimed at increasing human consumption of soy protein in developing countries and other new markets, thereby creating added opportunities for exporting soybeans and providing higher economic returns to U.S. soybean producers.
"Incorporating soy protein in human diets in these new markets will not adversely affect the demand for animal protein," Khanna says. "A large part of the increased demand will come from segments of society that do not consume meat, largely due to economic and cultural reasons. Most soy-fortified food, such as soy-fortified tortillas in Mexico or fortified wheat flour in India, do not compete with meat products."
The NSRL will also play a key role in developing Internet-based marketing support and product development resources for the International Soy Program. Those resources will allow the private voluntary organizations, government agencies, and other interested groups to identify potential market segments and marketing practices and to focus specifically on countries identified for the program.
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| Director of the NSRL and the Soybean Industry Chair for Agricultural Strategy, Steven T. Sonka. |
Soybean diseases are of great economic importance to soybean producers worldwide. A conservative estimate is that eleven percent of the world's soybean production is lost to diseases each year. At the NSRL, considerable emphasis is devoted to studying soybean diseases and to conducting applied and basic research that aids in the development of efficient disease management strategies.
Throughout their history, a key strength of Land Grant Colleges of Agriculture has been the ability to leverage research funding from several sources. A recent evaluation of the funding support for the NSRL plant pathology effort provides a vivid illustration that this capability exists yet today. Significant funding for this program comes from the Illinois, regional and national soybean checkoff programs, the USDA (including its National Research Initiative), and the State of Illinois (including its Council for Food and Agricultural Research).
In addition to providing funding stability, this diversity of funding insures that the program's research efforts stay attuned to a broad range of stakeholder interests. Doing so is a key element leading to the long run sustainability of the Land Grant System. A new brochure, NSRL Soybean Pathology, which contains the data discussed here and other elements of the research program, is available upon request. Simply e-mail us at the address noted in this issue of the Bulletin.
Steven Sonka
NSRL Director and Soybean Industry Chair in Agricultural Strategy
The NSRL Bulletin is published three times a year by the National Soybean Research Laboratory at the University of Illinois, 170 Environmental and Agricultural Sciences Building, 1101 W. Peabody Drive, Urbana, IL 61801; telephone (217)244-1706; e-mail nsrl@uiuc.edu; FAX (217)244-1707. Steven T. Sonka, director; Robert J. Wynstra, editor; Lisa Sheppard, contributing editor; David Riecks, photographer; Lynn Hawkinson Smith, graphic designer.
Unless otherwise stated, articles may be reproduced or quoted if credit is given to the NSRL Bulletin. The National Soybean Research Laboratory at the University of Illinois is an affirmative action and equal opportunity institution.