A new study led by University of Illinois Urbana-Champaign scientists has identified critically low genetic variation for grain yield in one of the primary breeding stocks used to develop corn hybrids in the United States.
The finding involves intermediate-maturity hybrids, which dominate U.S. commercial corn production and account for nearly one-third of global corn production. Researchers said the limited genetic variation could hinder breeders' ability to develop high-yielding hybrids capable of adapting to future climate challenges.
Modern corn breeding relies on heterosis, or hybrid vigor, in which parents from genetically distinct groups are crossed to produce offspring that outperform either parent. For decades, breeders have primarily crossed lines from two heterotic groups, stiff-stalk and non-stiff-stalk.
Although the two groups are genetically distinct from each other, the inbred lines within each group have become increasingly similar. Breeders have repeatedly selected and reused high-performing lines as parents, gradually reducing genetic variability within each group.
Researchers evaluated genetic variation associated with grain yield, plant height, days to silking and days to anthesis in 13 stiff-stalk and 28 non-stiff-stalk inbred lines representing early-, intermediate- and late-maturity types.
The study found that genetic variability associated with yield was lacking in intermediate-maturity stiff-stalk lines. Because intermediate-maturity corn is the most commonly grown maturity group in the U.S. Corn Belt, researchers said the finding could limit the ability of this important heterotic group to contribute to future high-yielding hybrids.
The researchers also found genetic variability remained available across traits in early- and late-maturity inbreds in both heterotic groups. Intermediate-maturity non-stiff-stalk inbreds also retained sufficient variability for yield.
The research originated through the Genomes to Fields initiative, established in 2013 by a group of university corn breeders seeking to collaborate on breeding research. Researchers exchanged breeding materials and tested them across multiple growing environments in the United States and Canada.
The team developed 162 single-cross hybrids using stiff-stalk and non-stiff-stalk inbred lines and evaluated them at more than 30 locations. The resulting phenotypic data across maturity groups was used to characterize remaining genetic diversity.
Researchers said corn breeders should take deliberate steps to reintroduce genetic variability into breeding populations. One potential source is the USDA Agricultural Research Service's Germplasm Enhancement of Maize program, which introduces germplasm from around the world into elite heterotic groups.
The study does not indicate an end to progress in corn breeding, researchers said. Instead, the findings highlight the importance of protecting and expanding the genetic diversity available to breeding programs so breeders can continue developing hybrids adapted to future growing conditions.
Source: University of Illinois Urbana-Champaign, "Illinois study reveals major genetic weakness for future corn breeding"