Detecting sudden death in soybeans

A simple, cheap laboratory test developed at Southern Illinois University Carbondale can unerringly detect Sudden Death Syndrome, a costly fungal disease, in soybean seedlings. Once commercialised, its use will help breeders produce SDS-resistant soybean varieties much faster than they can now.

“You can do a reliable assay in the greenhouse in a plastic cup and four weeks later, you’ll see the result,” said David A Lightfoot, a biotechnologist in SIUC’s College of Agricultural Sciences who developed the procedure.

“The seedlings develop the leaf symptoms and the root rot or they don’t. It works every time, and the labour cost is very low — about $1 per assay.”

Lightfoot received a patent for the assay October 31, which will allow the university to negotiate with private companies to license it.

“Now that the important things about the assay are protected, we can use it without fear of infringement by others,” Lightfoot said.

“When you don’t patent your discoveries, companies can do so, and it really kills research if what you have been working with now belongs to someone else. It’s very difficult to get grant money, for one thing.

Not long ago, breeding SDS-resistant soybean varieties was pretty much hit or miss. Breeders would plant a bunch of beans in a flock of fields and hope the disease would show up somewhere by the end of the growing season. If it did, they could make breeding crosses with the survivors and repeat the process during the next season.

But sometimes the disease didn’t appear, and sometimes when it did, it didn’t behave normally, disappearing mid-season. In addition, SDS resistance is not the only part of the equation. Breeders also must incorporate other traits, such as yield and adaptability, when developing new lines. Lightfoot and colleagues Khalid Meksem and Paul Gibson (now retired) figured starting out with disease-resistant breeding lines would cut the time it took breeders to produce marketable new varieties. In 1994, they began working on an assay that could quickly pinpoint seedlings that could withstand SDS.

“People had done two things wrong in the past (in attempts to develop an assay). They’d grown the fungus on rich media, so it wasn’t hungry (which could lead to false negatives). The other mistake was to just jab the plant with the fungus or put it in humongous quantities in the ground, making the disease inevitable (leading to false positives). The amount of fungus and its aggressiveness are critical parameters in SDS — much more so than in other diseases,” Lightfoot said.

Lightfoot grows his fungus on a mix of cornmeal, sand, mineral salts and agar, a jelly-like substance made from algae. That’s enough to keep it alive but not “fat, lazy or happy”, Lightfoot said. Graduate students, armed with spades and pails of the mix, then dig that mix into piles of soil, turning it until the fungus-laden growing medium is distributed evenly throughout. Vulnerable seedlings planted in that infected soil will contract the disease; seedlings with resistance potential won’t.