Extension Ag Update
September/October 2004
Articles Research Resources Internet Links Ag Facts Education

Research

Researchers Identify Gene with Resistance to Soybean Aphids

Rob Wynstra (217)333-9446, wynstra@uiuc.edu, Source: Glen Hartman (217)244-3258

Farmers across the Midwest could soon have high-yielding commercial varieties with effective resistance to soybean aphids as the result of a major breakthrough at the University of Illinois. After nearly three years of effort, a team of researchers at the U of I has identified a single-gene source of aphid resistance that can be easily crossed into elite commercial varieties.

The lead scientists in this effort are Glen Hartman, plant pathologist with the USDA's Agricultural Research Service at the U of I, Senior Research Associate Curtis Hill, and soybean breeder Brian Diers from the U of I's Department of Crops Sciences. Funding for this research has been provided by the Illinois Soybean Checkoff Board.

"This gene has been tested in both the greenhouse and the field and has consistently prevented colonization by soybean aphids," Hartman said. "Because it is a single dominant gene with identified DNA markers, it can be readily introduced into susceptible commercial soybean varieties by backcrossing using marker-assisted selection."

The methods for breeding plants with the aphid-resistance gene will be licensed for use in both public and private breeding programs. "Growers could have resistant varieties fairly quickly, especially if industry adopts this technology," Hartman said. "I think three to four years would be a reasonable time frame for that to happen."

The aphids were first discovered in large numbers in fields near the end of the 2000 growing season. After careful scientific investigation, they were identified as Aphis glycines, which had previously been reported only in Asia, Australia, and some Pacific islands. By 2003, this pest had emerged as a major problem for growers throughout the Midwest. "When the aphids infest a field, the most common means of control is to spray the field with an insecticide that can cost as much as 20 to 25 dollars per acre," Hartman said. "In 2003 alone, more than one million acres were sprayed in Illinois and more than three million acres in both Iowa and Minnesota. Once resistant commercial varieties are available, the savings to growers will be substantial."

As part of their initial screening process, the team evaluated the various commercial soybean varieties that had been submitted to the yield trials at U of I for resistance to the aphids. "After screening more than 700 varieties, we found that all of them were basically susceptible to this pest," Hartman said. "We also determined that there had not been any reported resistance from the germplasm screened in the part of the world where the aphids originated, which is China."

In the next step, they began screening about 100 cultivars that had been identified as the major genetic contributors to modern soybean varieties. Those ancestral lines account for more than 90 percent of the genetic variation in our current soybeans. "Luckily we found resistance in two different cultivars," Hill said." One is called Jackson, which is an old southern cultivar. Another was Dowling, which also is an old variety grown in the south."

As part of the experimental design, the resistant cultivars were tested in a specially designed field cage with several commercial varieties and were treated with an insecticide or left untreated. "Even with a large number of aphids present, we found virtually no difference in yield and agronomic traits whether these resistant lines were treated with an insecticide or not," Hartman said. "At the same time, the commercial varieties were severely damaged when they were not treated with an insecticide, with many of the plants actually dying."

The researchers followed that up with a series of laboratory and fields studies that identified the single dominant gene that carried resistance to the aphids. They also developed methods for identifying and breeding resistant plants using marker-assisted selection. "We were able to identify the specific region of the chromosome where the gene is located using genetic markers," Diers said. "Our team also confirmed that the resistance is conferred by a single major gene. We are now using that marker information to breed the resistance gene into adapted soybean varieties and testing whether there is any associated yield or agronomic drag associated with the gene. We hope to have resistant varieties available to farmers by 2008."

With assistance from the Office of Technology Management at the U of I, they have also applied for a patent and will soon be licensing this new technology to both university and industry breeders. "The idea of licensing is to make it a fair playing field for everyone," Hartman said. "Otherwise an individual company could take this research and patent the gene for itself. By licensing the technology to a large number of companies and public breeders, we can ensure that the benefits will reach growers across the Midwest as quickly and cheaply as possible." For more information check the website: http://www.otm.uiuc.edu/techs/techdetail.asp?id=267

Pasture Grass Fights Wheat Fungus Danger to Plants, Animals, People

Susan A. Steeves, (765) 496-7481, ssteeves@purdue.edu ,Source: Herbert Ohm, (765) 494-8072, hohm@purdue.edu

Resistance genes in the grass that replaced genes in wheat increased protection against Fusarium head blight, or wheat scab, the scientists said. In the December issue of the journal Theoretical and Applied Genetics the researchers also report that they located and mapped the small bits of DNA, or markers, associated with the resistance gene in the grass, called tall wheatgrass.

"In the past 10 or 15 years, the fungus Fusarium graminearum has emerged as one of the diseases of primary concern in wheat," said Herb Ohm, Purdue agronomy professor. "This is because the widespread practice of reduced tillage in fields provides a perfect environment for growth of the fungus."

Reduced tillage, meaning the soil is not plowed for planting, cuts farmers' costs and helps prevent erosion, he said. In the eastern United States, the upper Midwest and other places where large amounts of corn and wheat are both grown, Fusarium is a major problem, especially when the weather is warm and humid or rainy. Corn stalks left as natural mulch after harvest also foster fungus growth.

The fungus causes head blight that leads to major wheat crop losses. In 1996, crop losses due to Fusarium totaled at least $38 million just in Indiana, according to the U.S. Department of Agriculture.

"The disease has occurred most years since the early 1990s," Ohm said. "Its increase in frequency and severity coincide with reduced soil tillage, along with favorable weather warm, humid conditions for several weeks prior to and during wheat flowering in mid- to late-May." The fungus also produces a mycotoxin that sickens animals and people. Pigs, cattle, horses, poultry and people can develop vomiting, loss of appetite, diarrhea, staggering, skin irritation and immunosuppression when they eat grain or hay infected by Fusarium. The most severe cases can be fatal. Research has found evidence that these toxins may be cancer-causing. People usually ingest the fungus when they eat contaminated grains and cereals. According to the United Nations' Food and Agriculture Organization, people in developing countries face the greatest risk from Fusarium mycotoxins.

"Fusarium production of mycotoxins is a more serious problem than wheat production loss," Ohm said. "The toxin results in complete loss because you can't use the grain to make food for people or livestock."

The fungus can infect most cereal grains, including corn, wheat, barley and some oats. Replacement of the wheat gene was done with conventional crossbreeding and selection and didn't involve any genetic engineering. Because the two plants are closely related, the wheat is not altered, except for the added protection against Fusarium.

The newly identified resistance gene in the wheat grass is on a different chromosome in the genome than other known resistance genes used in wheat. This will enable researchers to combine the newly discovered effective resistance gene from wheatgrass with other genes that protect wheat against Fusarium. This breeding of a plant with more than one resistance gene is called gene pyramiding.

Now that Ohm and his team of researchers know they can combine the tall wheatgrass resistance gene with other resistance genes, they will try to produce a line of wheat with several genes resistant to Fusarium. The seed will then be available through the U.S. Department of Agriculture-Agricultural Research Service laboratory in Aberdeen, Idaho, that is a seed repository for wheat lines from around the world. The Ag Alumni Seed Improvement Association and Purdue Agricultural Research Programs provided funding for this research.

Varying Soil Conditions Can Impact Nutrient Levels

By Candace Pollock, (614) 292-3799, pollock.58@osu.edu, Source: Maurice Watson,
(330) 263-3755, watson.8@osu.edu, News and Media Relations, College of Food, Agricultural, and Environmental Sciences, The Ohio State University, Columbus: (614) 292-2011, Wooster: (330) 263-3775, http://ohioline.osu.edu/news/

This growing season's topsy-turvy weather may have impacted more than crop performance and subsequent yields. Maurice Watson, an Ohio State University Extension soil specialist with the Ohio Agricultural Research and Development Center (OARDC), said that the wet spring followed by a summer drought may have also affected soil nutrient concentrations.

As a result, growers should test their soil for nutrient availability following harvest to determine whether or not fertilizer is required before spring planting.

"Most growers test their fields to determine nutrient concentrations. We recommend testing every three years, so that growers over time get a feel for the natural variation of nutrient levels in the soil," said Watson. "This year is just more of a concern because of the extreme wet and dry conditions we encountered." Watson said that varying soil conditions affect a plant's ability to uptake nutrients effectively. Under extreme wet conditions, the oxygen supply to the roots is limited, affecting the uptake of nutrients, even though the nutrients are present in sufficient concentrations. Under drought conditions, plants are unable to take up nutrients because of the lack of water flow to the roots and the lack of growth or slow growth of the plant.

"Because of this year's drought, it is possible not as much fertilizer will be needed by next year's crop on a field that was sufficiently fertilized this year. In addition, it is possible that not enough fertilizer was applied this year because of the very wet spring," Watson said. "Despite either condition, a soil test will determine whether or not nutrients are at their optimum levels."

Watson said growers should mainly test for phosphorus and potassium, the two main elements that can impact a plant's performance if they are in deficient levels.

"In a nutrient-deficient situation, the biochemical reactions are not going to be what they should be under normal conditions. You may get a reduction in protein formation, which is the main building blocks of the plant," said Watson. "A plant will tend to take some nutrient elements from the older leaf tissue and put it toward the younger leaves to compensate, particularly in the case of nitrogen or potassium deficiencies. As a result, you don't get the normal development of the plant and yield is then reduced."

Plants may also run into a nutrient imbalance if nutrient levels are too high in the soil. Nutrient levels are also impacted by soil type (sandy soils have less of a reservoir for nutrients than clay or silt loam soils), as well as the type of crop being planted. For example, corn silage and alfalfa remove more potassium from the soil than grain crops.

New Soybean Line Offers Strong Resistance to Nematodes

By Jim Core, United States Department of Agriculture

A new soybean line from the Agricultural Research Service and the University of Missouri delivers a rare combination of resistance to two leading nematode pests. The release is good news for consumers of edible natto soybeans. The germplasm line, designated S99-3181, was initially bred for resistance to both soybean cyst nematode (SCN) and southern root-knot nematode by Grover Shannon, a soybean breeder at the University of Missouri's Delta Research Center in Portageville, Mo. Prakash R. Arelli, a geneticist at the ARS Nematology Research Unit in Jackson, Tenn., identified S99-3181 for its resistance to SCN.

Natto soybeans get their name from a Japanese fermented soybean dish most commonly eaten at breakfast on top of rice, but it is also used in other dishes and during other meals. Very few soybean lines, especially natto type, have this combination of broad nematode resistance and high yield potential, according to Arelli. In fact, during field trails, its yield was found to be equal to, or higher than, yields of Hutcheson, a popular cultivar. Additionally, the line also has shatter resistance, which means it will hold its seed after maturing.

The new line has broad resistance to SCN, the most destructive soybean pest in the United States, causing annual losses as high as $438 million. The cyst nematodes attack the roots of developing plants. Root-knot nematodes are the second most destructive soybean pest in the southern United States.

The line is expected to be used as a parent in breeding programs to develop new varieties that reduce soybean yield loss and reduce the need for pesticides. But growers might want to plant S99-3181 seeds directly, according to Arelli. The new line is a cross between S93-1344 and Camp. Arelli uses traditional breeding and marker-assisted selection to find new resistant genes in soybeans.