Scientists’ Corn Seed Gets Microbial Coat Against Harmful Fungi

By Jan Suszkiw

BELTSVILLE, Md., Jan. 23--Harmful fungi that try to invade newly sprouted corn seeds may be kept at bay by a new tactic of U.S. Department of Agriculture scientists: seeds coated with helpful microbes that weaken or kill the would-be fungal freeloaders.

“We’ve devised a procedure that uses naturally occurring, beneficial fungi and bacteria to protect corn seed from disease caused by the fungal plant pathogens Pythium and Fusarium,” said plant pathologist Robert Lumsden of USDA’s Agricultural Research Service in Beltsville, Md.

Unchecked, Pythium and Fusarium cause rot diseases that can reduce corn yields 10 to 30 percent, said Lumsden at ARS’ Beltsville Agricultural Research Center (BARC). The fungi are scourges of corn crops throughout the U.S., particularly in the Midwest, he said.

Enlisting multiple species of beneficial microorganisms “is a new form of biological control,” Lumsden said. “In the past, the approach has been to use one biocontrol agent against one plant pathogen.” But this won’t guard against other disease-causing organisms that may also be in the soil, he explained.

So, the scientists coated seed with a combination of helpful bacteria and fungi they isolated from plant roots and surrounding soil. “These microorganisms attack pathogens in a number of ways,” Lumsden said. “They compete with fungal pathogens for nutrients; they make antibiotics that kill or repel the pathogens, or they serve as parasites that invade and consume the pathogens from within.”

And, compared to chemical fungicides, he said, “the beneficial microorganisms pose no environmental hazard and protect plants at least as well as fungicides.”

Lumsden, research leader of the Biocontrol of Plant Diseases Laboratory, led a scientific team that includes soil scientist Jack Lewis, plant pathologist Weili Mao and microbiologists Daniel P. Roberts, Prakash Hebbar and Shin-I Chow. They conducted lab and field tests at the Beltsville center.

The scientists also ran tests in Minnesota, Delaware and Virginia, to learn how microbe-coated seed would fare against the harmful fungi in various soils, climates and other conditions. Collaborators included scientists at the University of Delaware in Newark, Virginia Polytechnic Institute and State University in Blacksburg, and a commercial firm.

Pythium flourishes when soils are cool and wet, such as during the spring. It causes damping-off, a rot disease of seeds and seedlings. Fusarium prefers warm, dry conditions typical of summer. It attacks the roots of corn plants. In one field study, only about half the seeds sprouted and grew to mature plants in plots harboring both fungi.

But in plots where seeds were coated with a combination of beneficial fungi and bacteria, more than 80 percent became full-grown plants. This bettered or equaled the performance of seed protected with coatings of any of several fungicides, said Beltsville researcher Jack Lewis.

Protection by the good microbes continues after the seedling stage. Mature plants in the biocontrol plots had about 25 to 40 percent less damage from root and stalk rot diseases, compared to plants grown from untreated seed, Lewis said.

In their approach, Lumsden’s team uses fermentation to “brew” large amounts of beneficial microbes. Then they formulate the microbes into a mix that can be coated onto the seed.

Lumsden envisions that soybeans, dry beans and some other high-value crops could also benefit from the seed treatment.