U.S. Department of Agriculture
Research News

New Insights into Invasive Plant Management

Over a decade of research at the U.S. Department of Agriculture (USDA) has resulted in the development of a new matrix for invasive plant management. The model was created by scientists with the Agricultural Research Service (ARS) in Burns, Ore., and helps land managers recognize how rangeland degradation processes vary across landscapes. ARS is USDA's chief scientific research agency.

Using the model can also increase the success rate of restoring native vegetation on damaged landscapes, which supports the USDA priority of responding to climate change.

Ecologist Roger Sheley synthesized a range of findings from scientific literature and field research to develop the model, which is called Ecologically Based Invasive-Plant Management (EBIPM). The process is a mix of plant establishment and succession theories, ecological principles, the identification of parameters that contribute to invasive plant management, and management actions that help restore native forage plants for livestock and wildlife. Sheley works at the ARS Range and Meadow Forage Management Research Unit in Burns.

Sheley and his colleagues based EBIPM on three general causes of plant succession: site availability, species availability, and species performance. They identified site-specific ecological processes that influence plant succession dynamics and determined how these processes are modified by environmental and human factors that affect plant establishment and long-term vegetation change. This information can be used to fine-tune the mechanisms and processes influencing plant succession, all of which helps rout invasive plants and support the return of native grasses and forbs.

Sheley and his colleagues tested their model in Montana's Kicking Horse Wildlife Mitigation Area at three sites that had varying degrees and types of damage from invasive plants. Using EBIPM, Sheley was able to increase the chance of restoration success by 66 percent over traditional approaches to invasive weed management. Sheley believes that EBIPM, which is also called "augmentative restoration," could be a valuable new tool for land managers in the western rangelands, where invasive plants like cheatgrass are fueling wildfires and limiting livestock grazing options.

Results from this work have been published in Rangeland Ecology and Management, Journal of Invasive Plant Science and Management, and www.ebipm.org.

Read more about Sheley's research in the February 2012 issue of Agricultural Research magazine.

Corn Gene Helps Fight Multiple Leaf Diseases

A specific gene in corn seems to confer resistance to three important leaf diseases, according to U.S. Department of Agriculture (USDA) scientists and their university colleagues.

This discovery, published in 2011 in the Proceedings of the National Academy of Sciences, could potentially help plant breeders build disease-resistance traits into future corn plants.

The research team included Agricultural Research Service (ARS) plant geneticists Peter Balint-Kurti, Jim Holland and Matt Krakowsky in the agency's Plant Science Research Unit in Raleigh, N.C., and scientists with the University of Delaware, Cornell University, and Kansas State University. ARS is the USDA's chief intramural scientific research agency.

Three diseases-southern corn leaf blight, northern leaf blight, and gray leaf spot-all cause lesions on corn leaves worldwide. In the U.S. Midwest Corn Belt, northern leaf blight and gray leaf spot are significant problems.

The researchers examined 300 corn varieties from around the world to ensure a genetically diverse representation. No corn variety has complete resistance to any of these diseases, but varieties differ in the severity of symptoms they exhibit.

The researchers set out to look for maize lines with resistance to the three diseases to determine which genes underlie disease resistance, according to Balint-Kurti. When they tested the lines for resistance, they found that if a corn variety was resistant to one disease, chances were favorable that it was also resistant to the other two.

The researchers applied a statistical analysis technique called "association mapping" to identify regions of the genome associated with variation in disease resistance. According to Balint-Kurti, the scientists knew there was a strong correlation between resistance of one disease and the other two. They postulated that some resistance genes conferred resistance to two or more different diseases, and they identified a gene that seemed to confer multiple disease resistance.

This gene, a GST (glutathione S-transferase), is part of a family of genes known for their roles in regulating oxidative stress and in detoxification. Both of these functions are consistent with a role in disease resistance.

Read more about this research in the February 2012 issue of Agricultural Research magazine.

Vaccine Protects Against Leptospirosis

Scientists at the U.S. Department of Agriculture (USDA) have found that a commercial vaccine is effective against leptospirosis in cattle.

A widespread zoonotic disease, leptospirosis is transmitted naturally from domestic and wild animals to humans. The contagious disease, which is caused by Leptospira bacteria, is spread through contact with food, water or soil contaminated with urine from infected animals. It can affect all farm animals, rodents and wildlife.

Several years ago, retired microbiologist Richard Zuerner, veterinary medical officer David Alt and their colleagues at the Agricultural Research Service (ARS) National Animal Disease Center (NADC) in Ames, Iowa, tested a version of this vaccine and discovered that it induced some protection against experimental infection with Leptospira borgpetersenii serovar Hardjo, the main cause of bovine leptospirosis.

ARS is USDA's chief intramural scientific research agency, and this research supports USDA priority of promoting international food security.

Alt and his colleagues, who work at the NADC Infectious Bacterial Diseases Research Unit, examined the vaccine's potency in reducing the shedding of bacteria, potentially affecting the spreading of leptospirosis in herds. They vaccinated cattle twice with this vaccine or twice with a standard or control vaccine.

To test the vaccine's ability to induce short- and long-term immunity to infection, cattle were challenged with L. borgpetersenii serovar Hardjo three months or one year after immunization.

Scientists found that the vaccine appeared to be effective at both three-month and one-year periods after vaccination. Although the vaccine did not provide complete protection from shedding at one year after vaccination, it induced greater immunologic responses and protection against shedding of leptospirosis than the standard vaccine.

After cattle were challenged three months after vaccination, bacteria were detected in the urine for several weeks, but the cattle appeared to be capable of clearing the infection, whereas non-vaccinated cattle remained infected, according to Zuerner.

Only one vaccinated animal in the year-long study was shown to have bacteria in the kidney at the end of the live challenge, but most animals had evidence of short-term kidney infections that eventually cleared, according to Zuerner.

Although the vaccine was partially successful in protecting cattle against leptospirosis, scientists agree that improvement is still needed.

Choosing the right vaccine depends on identifying the infecting serovar, according to Alt. The diverse organisms of Leptospira bacteria contain more than 200 serovars that can cause the disease.

Findings from this research were published in Clinical and Vaccine Immunology.

Read more about this research in the January 2012 issue of Agricultural Research magazine.