By DOUG GRAVES
COLUMBUS, Ohio — Among the things plaguing soybean farmers today is the destructive disease called phytophthora root and stem rot. Phytophthora thrives in wet, warm soil, particularly poorly draining soil.
In Ohio, the disease accounts for $50 million in losses each year, ranking as one of the top three most vexing soybean diseases for Ohio farmers.
The rows of petri dishes in Dr. Leah McHale’s lab at Ohio State University just might have the genes to fend off the disease. McHale, director at Ohio State University’s Soybean Breeding and Genetics Lab, said the answer is roughly two years away from being determined.
“As a soybean breeder and geneticist, I aim to develop cultivars with a good profile of disease resistance as well as good yield and good quality traits,” McHale said. “A lot of the cultivars we develop are for the good grade industry so they need high protein and large seed size.”
And phytophthora is one stumbling block standing in McHale’s way of progress, but she’s hoping the soybean roots growing in those petri dishes in her lab will offer a solution. In a month or two the soybean roots will be exposed to phytophthora, then observed to see whether they acquire the disease and die.
If their resistance chances (getting better or worse) then that means McHale and her colleagues, including soybean pathologist Anne Dorrance, have identified another gene that affects resistance to phytophthora. That gene then becomes a building block in creating a new variety of soybean seed that can thwart the disease.
According to McHale, a soybean plant carrying that newly identified gene improving resistance will be crossed with another soybean plant with that same gene. Then the resulting seeds will be grown into plants and tested for their disease resistance.
“You think plants, like soybeans, just sit there and grow, but they have to respond to sunlight, lack of rain, pathogens, insects and other circumstances,” McHale said. “The journey that begins in a petri dish and ends with a new variety of seed that resists phytophthora can stretch to five or more years. That’s partly because a soybean has a surprisingly large number of genes – about 66,000. That’s roughly three times higher than the number of genes humans have. Soybeans are more complex than you might think.”
McHale and Dorrance help identify which combination of genes offer resistance to phytophthora and create that combination in a single plant by crossing varieties of soybeans.
The DNA of the resulting seeds are then analyzed to determine if they have the set of genes that can fight off the disease. Once that’s done, the seeds with the desired genes are allowed to self-pollinate for several generations, and then each resulting plant is tested to see if it can fend off phytophthora.
Dorrance tests the varieties of soybeans that McHale creates by exposing them to phytophthora and seeing how they fare. If a plant survives the exposure, it’s closer to going to market for farmers to purchase.
Researchers have long been studying phytophthora and creating soybean seeds that resist it because the disease evolves. New varieties of soybean seeds are always needed.
“We always have to try to keep one step ahead of the pathogen,” Dorrance said.
After years of research, McHale and Dorrance, along with a team of soybean researchers, are in the final stages of locating which of the tens of thousands of genes in the soybean plant are responsible for resistance to Phytophthora.
“We’ve done a lot to get to this point,” McHale said.
Even though researchers know the location of the soybean genes responsible for resistance, the trait for resistance has low heritability, meaning that the environment weighs heavily on whether the genes will be expressed or not, even if they are present in the plant.
“It’s impossible to gain all the desired traits in one soybean seed, plus make the seed able to resist a number of diseases and offer high yields in any location where it is grown,” McHale said. “It’s never going to be a perfect seed.”
And, they say, two factors are always changing: weather and pathogens.
“It’s a constantly moving target,” McHale said. “Still, we’re always making improvements and those improvements are good for Ohio farmers.”
This year, McHale said the university expects to release two seed varieties, both of which will offer higher protein for production of foods such as tofu and soymilk.