Features Agronomy Plant Breeding
Yield gain to double with new selection tool

Researchers have used DNA testing to select for traits like disease resistance ever since marker assisted selection (MAS) techniques were developed 20 years ago. With those defensive-type traits breeders can identify the gene responsible for providing resistance to a certain pathogen and then test to see if it is present in a variety: relatively simple stuff for a researcher or breeder who knows what they are doing and what to look for.

Pioneer Hi-Bred senior scientist Scott Sebastian examines AYT soybeans in field plots. Photo courtesy of Pioneer Hi-Bred.  Advertisement

However, the ability to find the places in the genome that are directly responsible for yield is very new and is being utilized in the Pioneer Hi-Bred soybean breeding program for both eastern and western Canada. Pioneer Hi-Bred has coined this new process the Accelerated Yield Technology (AYT) system.

It is already paying dividends for growers. Bert Rammelaere of Tilbury, Ontario, grew 200 units of Pioneer-brand 92Y80 soybeans in 2008. “They looked a little greener all year and seemed to have more pods on them,” he says.

He grew another high-yielding variety in the same field. “When I ran the combine with the yield monitor on the other variety and took the yield it was 50.5 bu/ac,” says Rammelaere. “I wrote it down, zeroed the yield monitor and then drove down the 92Y80 strip and took 55 bu/ac.”

Pioneer Hi-Bred is using sophisticated genetic testing not only to flag defensive traits, like disease resistance, but also to boost yield. That is new technology and already is translating into big yield gains in soybeans. “In the past, the yield trial winner in a breeder’s plots was the heaviest bag of seed,” says Scott Sebastian, senior scientist at Pioneer Hi-Bred based in Des Moines, Iowa. “But that’s confounded with error. Ten percent of yield is based on genetics but 90 percent is based on environment and things like disease pressure, soil type and the availability of water.”

Sebastian is the inventor of one of AYT’s system at Pioneer. “Yield was an elusive thing because it’s a network of genes working together, not a single gene,” he says. “Now we can quickly find the hotspots in the genome that affect yield.”

He uses a technique where a leaf sample is obtained during the growing season, carefully catalogued, and taken back to the lab. A lab technician grinds it up, extracts the DNA and puts it under a powerful microscope. The technician looks for yield “hotspots” in the genome.

Leon Streit, senior research scientist at Pioneer, has been waiting for this kind of opportunity to make dramatic steps forward in yield. In 2004 he went into the cold storage room at Pioneer Hi-Bred and pulled seeds of soybean varieties from the past 30 years. When he grew them out and charted the yield gain, he found that on average there was a 0.5 bu/ac increase per year for Pioneer products and 0.4 bu/ac increase in yield per year for other varieties.

Then he grew Pioneer-brand varieties that were developed using MAS technology for things like soybean cyst nematode and other defensive traits. The yield enhancement since 1995, when varieties using MAS technology were first released, was 1.2 bu/ac per year.

That is a jump in yield three times the industry average but Streit predicts even better things to come in soybeans developed with the AYT system. “In terms of major advancements in plant breeding this ranks right up there with MAS,” he says. “It’s very important to have disease protection to protect yield. But by moving to the next level and identifying regions in the genome that are responsible for yield improvement, we could double the rate of genetic gain.”

“We use the term genetic gain in plant breeding the same way drivers refer to the speed on their speedometer,” says Dave Harwood, technical services manager for Pioneer Hi-Bred in Chatham, Ontario. “The rate of genetic gain has been around one bushel per year. With AYT soybeans we’re hoping to double the rate of genetic gain by 2010 and increase soybean yields by 40 percent within the next decade.”

Practically, it means that Pioneer plant breeders like Streit can quickly hone in on the best-yielding varieties. “We’re able to go back to a plot and pick the one variety with all the favorable genes,” says Sebastian. “All 1000 pieces of genetic data that we sift through point to that plot, even though it might be the lowest yielding because it’s in a puddle. If you trust the data and select for it, it will win yield trials next year.”

Sebastian draws an analogy with the insurance industry and how they will grill prospective customers before granting a policy. They want to know whether a potential client smokes, is overweight or likes to sunbathe. “You may or may not get cancer but your chances change as they take your risk factors into consideration,” he says. “The insurance companies can make some good decisions on that data.”
Breeders still have to grow out varieties and test them in plots. But with these new tools, selection precision could go up by a factor of 10. That is significant considering that in a traditional breeding program, only one variety out of 20,000 ends up in commercialization. “There’s a misconception about AYT soybeans,” says Streit. “There isn’t this one gene that we’re inserting into all the new soybean lines. It’s a complex set of genes and a combination of traits that we’re identifying”

Streit says in some cases they are not even sure why those particular yield hotspots they identify are boosting yield. It could be that area of the genome helps the plant better absorb carbon or helps in photosynthesis. Or maybe those genes provide resistance to a soil pathogen that science has not yet identified. “For the farmer, all this doesn’t really matter,’ says Streit. “Molecular geneticists challenge me on this. Yes, we’ll figure out why these genes work the way they do but in the end we know the most important thing… that they yield better.”