US - Selective breeding of maize over the last century to increase yield may have indirectly led to the evolution of more efficient root systems, according to researchers.
The findings suggest that future breeding efforts that directly select for positive root traits could lead to yield gains, while reducing pollution from excess nitrogen and farmers' fertiliser costs.
About half of the yield gains in commercial corn hybrids in the last 100 years have come from improved plant genetics, explained Dr Larry York, lead author on the study.
The other half came largely from agronomic practices, such as fertiliser use and higher planting densities.
"A lot of research has focused on the shoots of maize plants, such as the direction of the leaves and how they capture light, or how the plants divide matter into ears and kernels," York said.
"We all know roots are responsible for the uptake of water and nutrients. However, relatively little is known about how roots do that."
The researchers hypothesised that during a century of corn breeding aimed at increasing yields, root systems were indirectly selected for architecture and anatomy that are more efficient for nitrogen acquisition.
To test this, they collaborated with DuPont Pioneer, which supplied 16 varieties from the company's collection representing maize grown commercially in the United States from the early 1900s to the present.
The researchers grew all 16 varieties in both high- and low-nitrogen plots at three different densities, representing both historical and modern growing environments.
They measured shoot mass and yield and used a technique known as "shovelomics" to dig up the top portion of the roots so they could measure root quantity, angles, diameters, degree of lateral branching and length.
The researchers found that the newest commercial varieties performed better in every agronomic environment.
These newer varieties also had root characteristics known to make plants more efficient at acquiring nitrogen from the soil, including longer lateral roots and larger cells.
"That the newer material performed better in low-nitrogen environments is a novel result, since researchers tend to focus on high-input cropping systems," Dr York said.
"Although newer varieties were developed for use in high-nitrogen conditions, today's higher population densities mean plants have greater competition for available nutrients."
The researchers said more in-depth research is needed on how specific root properties affect nitrogen uptake and on how these traits influence acquisition of other nutrients, such as phosphorous.
"In addition, we need to know how the optimal root phenotype will depend on different environments - do we need the same roots in Pennsylvania as in Africa?" Dr York said.
You can view the full report and author list by clicking here.
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