Genetic markers take traditional plant breeding to another level
Wheat variety trials from Oklahoma State University (OSU) now include entries with a “D” in the identifier. The experimental lines are the result of doubled haploid (DH) technology, which allows an experimental line to be developed in 16 months, rather than seven to eight years using traditional breeding methods.
“Doubled haploid technology has existed for a number of years and is widely used in Europe, Canada and Australia,” says Brett Carver, regents professor of wheat breeding and genetics at OSU. “We’re just beginning to see it make a broad difference in wheat breeding across the U.S.”
The particular laboratory process used at OSU and many other private and public breeding programs involves crossing wheat with corn to produce a haploid line that will not live unless it is intensively managed in the laboratory, Carver says.
“A haploid cell, say from a pollen grain, contains only half of the DNA normally contained in the plant,” Carver says. “If the haploid cell comes from a wheat hybrid, each cell will be genetically different.
“Doubling the DNA in each haploid cell produces a myriad of genetic combinations in the form of inbred lines, which with further field testing may constitute a ready-made wheat variety,” he adds.
For example, the OSU program is currently working with the Gallagher variety, a 2012 release. They already have field results from crosses with the variety for 2012 through 2015. The same conventional lines aren’t even ready to test in the field.
“I’m on my fourth cycle of doubled haploid plant breeding, and we’ve always gotten something of value out of the process,” Carver adds.
One of the benefits of DH technology is it allows researchers to introduce diverse genetics from traditionally produced hybrid plants and use genetic markers to map various genes in the DH progeny. Through careful cataloging and selection, various traits can be stacked through normal plant breeding methods not using transgenic methods or so-called genetic modification.
Carver is most excited about producing wheat varieties with naturally occurring resistance to greenbugs and other aphids. He is collaborating with USDA–Agricultural Research Service scientists who monitor aphid biotypes threatening wheat. Currently, a Gallagher DH variety from Carver’s program carries stacked resistance to greenbug and Hessian fly damage.
DH technology is expensive, but the industry is involving private laboratories to work on a contract basis.
“We cooperate with Pioneer and Syngenta on projects, but most of our DH effort is being handled through Heartland Plant Innovations Inc. (HPI),” he notes. “HPI can produce up to 50,000 DH plants per year.”
From the 1,100 crosses produced at OSU every year, Carver selects about 10 based on what has the best chance of producing a usable variety and applies DH technology.
“Customarily, we place about eight new varieties in our test trials each year. The next year, two of those will be DH products,” he explains. “Twenty-five percent of our most elite material will be processed with DH. We also develop those same lines with traditional breeding methods and use those years in the field to make further selections as we watch them react to field conditions.”