Researchers crack resistance in soybean pest

Genetic breakthroughs could help prairie producers avoid mistakes made in the U.S. with soybean cyst nematode

ORLANDO, Fla. — Researchers have made a number of breakthroughs in the ongoing battle against the biggest yield-robbing soybean pest.

Soybean cyst nematode (SCN) causes an estimated US$1 billion in yield loss annually as it overcomes traditional sources of resistance in the United States.

“These nematodes are a big problem for our producers,” said Melissa Mitchum, a nematologist at the University of Missouri and part of the SCN Coalition.

The coalition was formed in 2016 because SCN is becoming resistant to PI 88788, the source of resistance used in more than 95 percent of the soybean varieties on the market. The other less common source of resistance on the market is called Peking.

A 15-year study of Iowa soybean fields shows that yields of PI 88788 resistant varieties have declined by 14 bushels per acre as the nematodes overcome the source of resistance.

The good news is crop breeders have discovered two new sources of SCN resistance in wild soybeans and have stacked those genes with the PI 88788 resistance in commercial soybean varieties.

Stacked resistance soybeans have performed well in greenhouse trials and field trials in the U.S. Midwest, reducing the populations of resistant nematodes. There has been no yield drag associated with the new sources of resistance.

The university researchers who discovered the new sources have made the genes available to seed companies so they can breed them into their varieties and get them to market as soon as possible.

Mitchum hopes the new sources of resistance will be made available to growers in Western Canada so they don’t make the same mistake as U.S. farmers by relying solely on the PI 88788 source of resistance to keep the nasty pest at bay.

SCN was first discovered in Missouri in 1957 and has since spread across North America. It was found in Ontario 30 years later and in Quebec in 2013.

Mitchum told reporters at the 2019 Commodity Classic that another “major breakthrough” was the publishing of the reference genome for SCN a few weeks ago.

“It allows us to know all the genes in the nematode. We’ve already been able to look at those genes and identify those that we think could potentially be important,” she said.

That will help researchers understand how the parasite functions and figure out ways to make it a less effective pest.

Mitchum said researchers will soon be able to sequence adaptive populations of the nematode that have overcome the PI 88788 source of resistance and compare those to the reference genome.

That will allow researchers to pinpoint the exact genes that are causing them to overcome the resistance.

Researchers will be able to use the reference genome and other genome sequences to develop molecular diagnostic tools to quickly identify what type of nematode infestation a farmer is dealing with and the best course of action to neutralize the problem.

One other thing researchers have learned is that there are varying levels of effectiveness of the PI 88788 gene, depending on the copy number of that gene. The higher the copy number, the better the resistance.

“All PI 88788 varieties on the market are not created equal,” said Mitchum.

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