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To build a better soybean.

Soybeans can be found today, in one form or another, in a wide array of food and industrial products. But until the early 1900's, soybeans were virtually unheard of in the United States. Those grown here were used as forage or as green manure to enrich the soil.

Much of the credit for crating a commercial market for soybeans is given to A.E. Staley, who, in 1922, modified his corn processing plant in Decatur, Illinois, and announced that he would buy all of the soybeans that could be grown.

Today, Staley would have his hands full: U.S. farmers in 1992 produced nearly 2.2. billion bushels of this versatile crop on more than 62 million acres in 26 states.

"As the potential uses for soy-based products increase, there is a desire to breed new soybean varieties to meet specific market need," says Howard J. Brooks, associate deputy administrator of plant sciences for USDA's Agricultural Research Service.

Whether it's increasing yields, breeding plants that are genetically resistant to pests, or boosting protein and oil levels in soybeans, ARS researchers throughout the country have a significant hand in soybean production.

For agronomist Joseph Burton at the ARS Soybean and Nitrogen Fixation Research Laboratory in Raleigh, North Carolina, the goal is increasing the protein content of soybeans without decreasing yield.

"Usually, when soybeans are bred in an attempt to increase protein, total seed yield suffers," he says.

Soybeans' normal protein level is about 41 percent on a dry-weight basis. Burton has successfully upped this to 45.5. percent and is now working on the yield part of the problem.

With a classical breeding approach using restricted index selection, scientists are able to evaluate and select two or more traits simultaneously, instead of just one. They are having some success in increasing yields without affecting protein.

Burton has now completed six 2-year cycles in which 200 promising genotypes are planted in each of two locations. The best-yielding 10 percent, which also have higher seed protein concentrations, are then interbred and replanted. Using statistical analysis of seed yield and protein content, the scientists have developed an index for evaluating subsequent genotypes for the two desired characteristics.

"In past years, we've had yields that were only 5 percent less than Young, a currently planted commercial soybean variety, but with about a 46-percent protein level," Burton says.

Potential markets for high-protein varieties include the animal feed industry and producers of soy-based food for human consumption.


Soybeans' Future

In the future, making decisions to guide soy breeding programs such as Burton's may be as simple as consulting a map.

A team of ARS scientist at Ames, Iowa, is mapping the soybean genome to determine the whereabouts of the genes on its chromosomes. Plant geneticist Randy C. Showemaker says having such a map will "take some of the gamble out of genetics.

"Breeders are tossing the dice every time they make a cross," he says. "We want to stack the deck in our favor."

Just as mile markers can tell you where you are on a highway, these genome maps can tell a scientist where to find the genes responsible for economically important traits such as the protein and oil contents of the soybean seed.

These are both quantitative traits, Shoemaker explains, which means that more than just a single gene determine the levels produced. So scientists are using molecular probes that distinguish specific fragments of DNA to identify the genes responsible for the protein and oil content.

Genetic maps will allow breeders to identify key genes that will, in turn, help them successfully combine multiple traits to make advances much more quickly.

Thus far, Shoemaker and colleagues have mapped five of seven genes responsible for resistance/susceptibility to different races of phytophthora root rot, a disease that attacks the soybeans's vascular system and eventually kills the plant. Phytophthora can cost growers a tremendous amount of money in lost yields.

"Using molecular probes, we analyzed six of the seven genes and were able to map five of them," Shoemaker says.

In Stoneville, Mississippi, scientists have found a new genetic source of resistance to phytophthora rot. a germplasm line that resists several races of the pathogen that causes the disease was found in the USDA Soybean Germplasm Collection at Urbana, Illinois.

"This germplasm line contains a gene to fight phytophthora rot that is different from other genes currently being used by plant breeders to prevent the disease," says Thomas C. Kilen, the geneticist in charge of ARS' Soybean Production Research Unit at Stoneville. "It shows a resistance to some races of the pathogen that has not been seen in other lines."

Kilen has also found that the genes for phytophthora resistance and brown pod wall color are on the same chromosome, but not closely linked. By selecting for pod wall color, breeders may be able to indirectly select for phytophthora root rot resistance.

"The benefits of this will be limited, though, since the genes are not closely linked," Kilen says. "However, this knowledge will help further efforts to map the soybean genome."

Bad-Tasting Leaves

In other work at Stoneville, Kilen and coworkers have developed a new soybean with leaves that apparently taste so bad that insects, given a choice, won't bite into them. But the beans themselves are not altered, and the oil and meal taste fine.

Lavone Lambert, an entomologist at Stoneville, conducted studies that show the leaves and pods of this soybean plant contain a substance harmful to insects, but not to humans or livestock.

Mexican bean beetles, corn earworms, velvetbean caterpillars, soybean loopers, and beet armyworms - in fact, most major soybean insect enemies - do not fare well on the new variety.

Farmers may be able to save millions of dollars each year, just by planting the bad-tasting, pest-resistant bean. Insect damage, in terms of yield loss and control costs in only nine southern states, recently averaged more than $85 million.

"In addition to cost savings to farmers, the environment will benefit from less pollution if they don't have to use pesticides," says Kilen.

The hunt for insect-resistant soybeans has been ongoing for more than two decades, he adds.

Invisible Underground Attack

Warding off soil-borne nematodes is another important research goal.

Several ARS scientists are searching for genes to incorporate into soybeans to better thwart Heterodera glycines, the soybean cyst nematode. There are nine known SCN races, or types, in the United States.

This minute worm invades roots, disrupting the flow of water and nutrients in the plants and reducing yields Females are lemon-shaped and change in color from white to brown as they mature and die, to form cysts. The cysts are filled with eggs or hatched juveniles. The juveniles penetrate plant roots and develop into adults in about a month. As they develop, the females rupture the root surface.

The appearance of yellow, stunted plants in an oval formation in the field usually signals that soybean cyst nematodes have reduced normal root nodulation and root growth.

"Right now, the best way to fight this nematode is by crop rotation and using resistant varieties," says plant pathologist Gregory R. Noel, of the ARS Crop Protection Unit in Urbana.

Plants may be infested with SCN at any time during the growing season, but the most devastating attacks occur 1 to 2 months after planting. While chemicals are available to control the pest, prohibitive costs generally limit their use.

Some producers try to improve yields of SCN-stricken beans by irrigating. But Larry G. Heatherly, an agronomist at Stoneville, found that irrigation during the soybean reproductive period will not alleviate SCN stress.

"Growers with infested fields should be discouraged from expending resources to irrigate those fields," he says.

Both germplasm - soybean lines for use by breeders - and fully developed soybean varieties with new sources of SCN resistance are being developed by Noel and University of Illinois soybean breeder Cecil Nickell.

Since 1982, seven new varieties and four germplasm lines have been released. Some were developed with cooperation from the University of Missouri.

Lawrence D. Young, a plant pathologist in the ARS Nematology Research Unit in Jackson, Tennessee, released germplasm last year that resist the race 2 nematodes that primarily infest soybean fields in Maryland and Tennessee. The new soybean line also shows varying degrees of resistance to other nematode races.

"This line has good productivity, but the yield is not competitive with the best cultivars," said Young. "Our idea was to release the line so commercial breeders could cross it with their productive lines and give them nematode resistance."

Getting Enough Nitrogen

Like all living organisms, the soybean has specific needs that must be met for it to thrive. Carbon dioxide, sunlight, water, and nutrients are all "musts" for a healthy plant. Crops generally get their supply of nitrogen from the soil, but the soybean has another way to obtain this essential nutrient. A symbiotic nitrogen fixation system located in the roots takes gaseous nitrogen from the air and converts it to ammonium, a form usable by the plant.

To accomplish this, "A soil bacterium known as Bradyrhizobium japonicum invades the roots and forms nodules ," explains James F. Harper, the plant physiologist in charge of the Plant Physiology and Genetics Research Unit at Urbana. "It's inside these nodules that nitrogen fixation takes place.

The bacteria obtain carbon compounds - primarily the common sugar sucrose - from the plant and return nitrogenous compounds to it, as well as to the soil.

Genetic selection has now pinpointed a mutant soybean line that has two to four times more nodules that the average plant. Harper is attempting to produce these extra nodules on a normal soybean root system to provide more nitrogen to the plant and possibly release more nitrogen to the soil.

Increased nodulation may be good news for farmers who plant corn in rotation after soybeans. It might allow them to cut nitrogen fertilizer applications, reducing both costs and the possibility of groundwater contamination. Nodulation is also likely to get a boost from mutant B. japonicum bacteria. L. David Kuykendall, a microbiologist at the Beltsville (Maryland) Agricultural Research Center and W. James Hunter, a microbiologist at the Crops Research Laboratory, Fort Collins, Colorado, have patented a mutant strain of the bacterium that improves nitrogen fixation in soybeans by increasing nodulation.

"In 2 years of field studies in Upper Marlboro, Maryland, we've obtained a statistically significant 25-percent increase in nodulation and a numerical increase in seed yield on plants inoculated with the new bacterium, as compared with another strain known as USDA 110," says Kuykendall.

Previously, USDA 110 was identified as the best strain for use as an inoculant - a commercial product consisting of the bacterial cells plus a peat-based carrier.

Seed yield increases were also obtained in field tests conducted by Urbana Laboratories in St. Joseph, Missouri, and Fort Dodge, Iowa. Tom Wacek, a microbiologist in charge of research and development for Urbana Laboratories, says the results are encouraging and promises more field tests.

New Germplasm, and Allelopathy

If U.S. soybeans of the future are high-yielding and resistant to insects and disease or have more nitrogen nodules than ever before, China may be at least partially responsible.

For the first time in history, the People's Republic of China has released a large quantity of soybean seed from its germplasm collection. The USDA Soybean Germplasm Collection at Urbana, Illinois, is the new home for the seed. Some 500 accessions have been acquired, to date, and 500 more are expected within the next year or so.

It's all part of a two-way information exchange between the United States and China. According to the agreement, the U.S. receives soybean germplasm in exchange for the opportunity for a Chinese scientist to work side-by-side with an ARS scientist for a year and the provision of new laboratory equipment for China.

Discussions leading to this exchange have been ongoing for nearly 10 years. ARS, the University of Illinois, Iowa State University, the Illinois Soybean Program Operating Board, and the Iowa Soybean Promotion Board were all partners in the final agreement with the Chinese Academy of Agricultural Sciences. Each will contribute $10,000 a year for 2 years to cover expenses.

"The overall benefits of this exchange will most likely be long-term." says Randall L. Nelson, curator of the Urbana soybean collection.

When Chen Yi Wu, a scientist from the Institute of Crop Germplasm Resources in Beijing, China, arrived in Urbana to work with Nelson, he brought with him seed from 500 soybean varieties gathered from 9 provinces in central China.

Test plots planted and harvested in 1992 gave Nelson his first opportunity to analyze the new seeds. But with just one growing season completed, the researchers are still uncertain of the benefits of these new accession.

"There may be genes in these varieties to fight diseases and insects, and to improve oil and protein content," Nelson says, "but it will be a while before we really know what we have."

Once soybean seed is in the ground, producers wage constant battles with nature.

One fight is against weeds. Farmers traditionally use herbicides and tillage practices to control weeds. However, Reid Smeda, a plant physiologist in the Weed Biology and Management Research Unit at Stoneville, Mississippi, is looking at cover crops that exude toxic substances - allelochemicals - as an alternative method to fight weeds.

"It's known that some cover crops can suppress weeds, but it's uncertain how long the effect will last and how the soybean crop will be affected," Smeda says.

In the initial year of testing, field plots were planted with sorghum-sudangrass in early spring and killed using the herbicide glyphosate after the grass grew 6 to 7 feet high. The glyphosate was applied to soybean plots at a rate of 1 pound per acre 2 weeks, 1 week, and 1 day before planting with a no-till drill. Crop residue was flattened to minimize its interference with light received by emerging soybean plants.

"Weed suppression was greater than 90 percent up to 60 days after establishment," Smeda syas. "And the soybean yields in plots where sorghum-sudangrass was killed 1 week or 1 day before planting were within 2 bushels per acre yield of a plot that had no cover crop and was hand weeded."

Poor soybean germination reduced yields in the plot planted 2 weeks after the cover crop was killed, although weed suppression in this plot was satisfactory. In an additional plot not planted with a cover crop, weeds were not managed. Yields from that plot were the lowest of those included in the test.

Besides sorghum/sudangrass, researchers have ongoing tests with fall-seeded cover corps, such as rye, hairy vetch, and annual ryegrass. These are killed in the spring.

"Combining the allelopathic potential of cover crops and the capacity for the soybean canopy to shade out weeds may allow producers to use postemergence herbicide on an as-needed basis, rather than apply herbicides at planting or before planting," Smeda says.

Ensuring Adequate Water

Year in and year out, producers watch the skies, hoping the rainfall will be enough to produce a bumper crop. And it's this water that limits soybean yields year after year.

That's why Richard Cooper, an ARS agronomist at Wooster, Ohio, and Norman Fausey, a soil scientist at Columbus, Ohio, have developed a subirrigation/drainage system for soils that also sometimes need drainage of excess water. The system uses these same drainage tubes to put water back into the soil during periods of drought.

The tubes are generally 4-inch, corrugated plastic. The prevailing practice in the Midwest, according to Fausey, is to allow 40 to 80 feet between drainage lines. However, it the lines are to double as a subirrigation system, they need to be spaced 20 to 40 feet apart.

"The goal is to maintain a constant water table," says Cooper. "The ability to control water availability and maintain yields year after year is important to soybean producers."

"And a good water supply is essential," Fausey adds. "A surface reservoir that stores water, a major river or other body of water, or an existing high-capacity well are all possible options.

"Ordinarily, drainage lines discharge into a stream, but to use the lines for subirrigation, a control valve is put on the discharge outlet. Then water is added into the drainage system through a standpipe - a vertical pipe that runs from the soil surface into the drainage system. The water flows back into the field and maintains the water table so there is a constant moisture supply at the root zone."

The biggest challenge in using this system, says Fausey, is knowing when to switch back and forth between the drainage and irrigation modes. So other scientists are working to develop a sensor that would be put in the system to help farmers make that decision.

The subirrigation/drainage system is already commercially available. In fact is being uses on 20,000 to 30,000 acres in Michigan. But its cost may cause some farmers to shy away from the idea. In Ohio, adding more lines to an existing drainage system may cost about $500 per acre, while starting from scratch may cost as much as $1,000 an acre.

However, the cost of the subirrigation/drainage system can be recouped through higher and more stable yields year after year, Copper says.

Eight years of studies have shown that soybeans irrigated in this manner yield an average 75 bushels per acre, compared to an average of 50 bushels for nonirrigated soybeans. And other crops will also benefit from a plentiful water supply. Corn yeilds may be boosted 50 to 60 bushels per acre, Cooper says.

Irrigation is more or less a must in the lower Mississippi Delta, where a considerable number of soybean acres are planted on clay soils. Without irrigation, yields are often less than 22 bushels per acre.

"It's common knowledge that irrigation will boost yields," says Heatherly. "But producers need to know how long they should irrigate and which varieties perform best under irrigation."

Field studies were conducted at Stoneville from 1987 through 1991 to determine when to stop furrow irrigation, how selected varieties perform under flood irrigation, and if early-planted soybeans respond to furrow irrigation.

The tests show that ending furrow irrigation at the mid-podfill stage is sufficient to maximize seed yield during dry years. "Irrigating beyond that time is not economical," Heatherly says.

Flood irrigations 2 days long during the period between beginning bloom and full seed stage in dry seasons increased yield by over 32 bushels per acre for unadapted varieties in maturity group VI.

Soybean varieties are grouped according to maturity dates. If planted before a recommended date, soybeans will flower earlier and for a longer period of time than normal, but the plants will abort the seed pods.

In 3 of 4 years, furrow irrigation more than doubled seed yield from maturity group III and IV varieties planted in mid-April to mid-May.

In a relatively wet year, only one irrigation still provided an average seed yield increase of more than 7 bushels per acre.

"A nonirrigated plot showed that early-season planting of these varieties may help avoid drought during the usually dry summer months," says Heatherly.

Another irrigation study indicates that furrow irrigation can be used to maximize yields and germination of soybeans grown for seed. So Heatherly recommends that growers looking for the highest quality seed for planting select seed that is produced by irrigated culture.

Sunlight's Critical, Too

The amount of sunlight is also a factor in soybean production. "Soybeans are very responsive to photoperiods, or the amount of daylight they receive," says Edgar E. Hartwig, a plant breeder at Stoneville.

But now, thanks to Hartwig's research, soybean growers in the southern states have a new variety that is much more flexible about daylength.

Named "Vernal," the variety is resistant to several major soybean diseases. It also has a unique flowering characteristic that allows it to be planted anytime from March to late August in the Rio Grande Valley and from mid-April to late June at Stoneville. Ideally, days should be 14-1/2 hours or longer when soybean plants emerge, to allow full growth before flowering.

Flowering usually occurs in 30 days or less after emergence, if days are sufficiently short. Day length is influenced by the time of the year and proximity to the equator.

The new variety has a delayed flowering characteristic that permits good growth when planted under short-day conditions.

At Stoneville, if Vernal is planted in mid-May, it acts as a normal group VI, maturing in mid-October. If it's planted April 20, the crop will grow at a similar rate, but will mature in late September, like a group V variety. Yields, though, are higher when planted April 20, than in mid-May. The 4-year average of the irrigated April planting is 55 bushels per acre, compared to 45 bushels per acre for the irrigated mid-May Planting.

"Vernal gives producers another management alternative," says Hartwig. "Because it can be planted earlier in the year, when soil moisture is optimal, farmers may be able to plant soybeans after another crop. They didn't have that opportunity in the past."

"While research aimed at improving soybean production is important, it would be for naught without the many food and industrial markets for the crop," says Howard Brooks. "As long as there is a demand for soybeans, ARS research can play a vital role in developing new and improved varieties, and finding the most efficient production methods."

The USDA Soybean Germplasm Collection

When soybean breeders throughout the world need assistance with their breeding programs, they often turn the Randall L. Nelson.

Nelson is the curator of the U.S. Department of Agriculture's Soybean Germplasm Collection housed on the University of Illinois campus at Urbana, Illinois.

In 1991, The USDA Soybean Germplasm Collection at Stoneville, Mississippi, was consolidated with the Urbana collection.

"We get requests for germplasm from public and private breeders throughout the world," says Nelson. "During the past 10 years, we've averaged about 15,000 requests a year."

Generally, breeders requesting germplasm receive a packet of seed similar in size to those containing seeds for home gardening.

More than 14,000 germplasm lines - including varieties of both the common soybean, Glycine max, and the wild G. soja - are maintained in the collection. Stored in a controlled environment to ensure viability, seeds of G. max may be kept for 10 years and G. soja for 15. To maintain a supply of quality seed, aging specimens are periodically replaced by growing and harvesting new seed.

"Every time a variety is grown, more than a dozen traits are carefully monitored to maintain purity," says Nelson.
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Title Annotation:includes article on the Soybean Germplasm Collection; research
Author:Garrietts, Marcie
Publication:Agricultural Research
Date:Oct 1, 1993
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