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Biotech Trick or Treat

September 30, 2011
By: John Buckner, Farm Journal Executive Editor
disease soybeans
Soybean embryos grown in the Crop Genetic Transformation Lab at the University of Georgia in Athens from germplasm will hopefully lead to future generations of flood-tolerant plants with resistance to Phytophthora.  

This soybean research project plays some pranks to fool Phytophthora

They’re eerie, as in spooky, and are patiently waiting in dark, earthy loam and clay. This class of fungi-like organisms with a funny name—oomycetes (oh-oh-my-seats)—is responsible for about half a billion dollars worth of soybean yield suppression in the U.S. in 2010.

It’s known as the tongue-twisting Phytophthora, a Latin name that only Daffy Duck would enjoy pronouncing, spit and all.

"Phytophthora is the most devastating disease over any other disease in the U.S., except for the effects of the soybean cyst nematode," says Allen Wrather, a plant pathologist at the University of Missouri Delta Research Center in Portageville, Mo. "Yield suppression in the U.S. last year from the fungus was 38.8 million bushels."

Wrather says the Phytophthora species sojae is becoming more of a threat because more acres are expected to be planted to soybeans in the future. Also, saturated soils cater to the increase of the disease where it is found naturally, in specific crop fields, so chronic wet spring weather doesn’t help the situation. Phytophthora is known to wipe out entire soybean fields from the

resulting root and stem rot.

Hopefully, the disease will be neutralized by a group of researchers and Extension agents armed with a $9.28 million grant from USDA’s National Institute of Food and Agriculture. The research and outreach program is coordinated by Brett Tyler of the Virginia Bioinformatics Institute at Virginia Tech and involves interdisciplinary teams at 18 institutions.

"This project isn’t as much about new discovery as it is applying our recent discoveries to make real-world improvements," Tyler says.

Seek and destroy. So how does Phytophthora sojae seek and destroy? Found naturally in the soil, it produces spores by asexual reproduction on rotten root tissues when the soil is flooded. Mobility of the spores is achieved with whiplike filaments, which allow them to swim in a corkscrew path in water, seeking host plants. They become attracted to chemicals released by soybean roots and germinating seeds. Like a magnet to steel, they make contact with the soybean root surface, where they shed the mobile filaments and form a cell wall. The spores germinate and fibrous strands penetrate into the root and begin rotting the tissue.

Tyler and his research group at Virginia Tech analyzed the genetic material in Phytophthora and found the location of a superfamily of deadly genes involved in the infection of plants. These genes produce virulent proteins that disable the immune systems of their victims as part of an

attack strategy, much as the HIV virus does in humans.

According to the research, these lethal proteins are able to easily enter a soybean plant cell across the cell membrane without any additional attack effort from the killer. These proteins also carry the "entry mechanism" that disables the cell that is necessary for the deadly fungal microbes to infect the plants.

Serving as the lead institution for this research, Virginia Tech is responsible for discovering new resistance genes, while the University of Georgia is responsible for soybean transformation.

"We know there is a protein that a soybean makes, which the fungus uses to recognize that the plant is a soybean plant. That becomes a welcome mat for this fungus," says Wayne Parrott, researcher and professor of plant pathology at the University of Georgia in Athens (UGA). "One research target is to see if we can alter that welcome mat or get rid of it: Then the fungus will not recognize that it’s on a soybean and will not attack it."

Out-of-the-box fix. Another approach that might be effective to combat the fungus involves a natural mechanism that plants have to "turn off" genes in viruses that attack them. A retired professor from UGA came up with the idea to use this same system, tweaking it so that it would work on the nematodes.

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FEATURED IN: Farm Journal - October 2011
RELATED TOPICS: Soybeans, Agronomy, Research, Production

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