Now to the root of the matter
GroundCover™ Issue: 115 | Author: Sarah Clarry
Researchers in different cropping regions are studying how to lift nutrient use efficiency by manipulating a crop’s root systems
At the University of New England, Associate Professor Chris Guppy is examining how cereal root growth responds to nutrients placed deep in the soil profile in northern grains systems.
In the south and west, Dr Manny Delhaize from CSIRO Agriculture has discovered that root hairs play a key role in improving the phosphorus use efficiency of wheat in acid soils.
A concerted effort is being made to better understand, and ultimately harness, ways to enhance crop growth by lifting the efficiency of roots.
Associate Professor Chris Guppy from the University of New England explains that conventional thinking has been that shoots govern plant selection: “Root parameters have been largely ignored. So we want to test whether there is a way to phenotype root systems and take advantage of root genetics,” he says.
This means examining whether variations exist within wheat varieties that influence the way the plant roots respond to concentrated patches of nutrients.
Associate Professor Guppy is especially interested in identifying whether cereal roots have the capacity to respond to the deep nutrient placement strategies being developed in the northern cropping region.
His research has examined 10 wheat and five barley varieties with phosphorus banded in the root zone.
“We know that wheat roots will proliferate around nutrients but we don’t know whether there is variation among varieties,” he explains.
“In plant varieties grown in real soil, rather than in a culture medium such as a gel or solution, preliminary data suggests there is variation in root length in patches of higher nutrient density, so we measure root length in that patch.”
To date the research has found older varieties such as Sunvale and LongReach SpitfireA are inherently less vigorous and this is true for their root systems as well.
However, the research is not a straightforward process. Different wheat varieties can differ significantly in the time they take to reach each stage of maturity, so the researchers have to be sure to factor in such growth-stage variations when analysing the data.
The work is currently confined to small pots in a greenhouse, where the plants are grown in styrofoam containers rather than the usual PVC pots. This allows X-rays and CT scans to penetrate the container wall and obtain high-quality images of what the roots are doing.
Associate Professor Guppy hopes the outcomes of his work will allow breeding programs to begin to select for root traits as well as shoot traits, and ultimately find lines that will be able to grow roots in saline, sodic and/or acid soils.
“We want to understand the phenotypic expression of roots so we can find the roots that can punch through,” he says.
He believes most of the gains that can be achieved in leaf area and yield have been made, for now, and that roots provide the next big opportunity.
Dr Manny Delhaize from CSIRO Agriculture is working on developing wheat lines that have different root hair length – a key factor for a plant’s phosphorus use efficiency for acid soils.
Root hairs allow roots to more effectively explore the soil for phosphorus and are an important component of phosphorus use efficiency.
On many acid soils, the aluminium solubilised by the acidity is toxic to the wheat plant and reduces yield. Although many current Australian wheat cultivars possess genes that confer aluminium tolerance to root growth, the rhizosheath (the root hairs and a mucilage secreted from the root that binds soil particles) remains susceptible to aluminium and its growth is reduced.
Previously Dr Delhaize identified Brazilian wheat lines that maintained their rhizosheath in acid soils and were more tolerant to aluminium.
He established a direct relationship between the size of the rhizosheath and the length of root hairs, which enabled him to rapidly screen lines for root hair length by using a simple assay based on the size of the rhizosheath.
Using these methods, Dr Delhaize developed experimental lines that share a similar genetic background but differ in rhizosheath (root hair length) when grown on acid soils.
“We have bred lines that are essentially the same but differ only in root hairs: short versus long,” Dr Delhaize says. “In pot trials, we have shown that wheat lines with longer root hairs do better in terms of taking up phosphorus and building shoot biomass.
“We are now testing the plants in the field and taking them through to yield. We have plants in the ground in Binalong and Wagga Wagga in New South Wales and near Northam in Western Australia.
“In non-acid soils, we are not seeing any major differences, which is an important validation of the trait for acid soils. New germplasm that displays the trait in non-acid soils, however, is also being developed for testing on more neutral pH soils.”
Dr Delhaize is now working on molecular markers that will allow breeders to incorporate the root hair trait into their breeding work.
“Acid soils are a big problem in WA and parts of NSW,” he says. “If root hair length can drive improved phosphorus uptake, it will allow growers to produce better yielding crops with lesser need for fertiliser inputs.”
Associate Professor Chris Guppy
02 6773 3567
Dr Manny Delhaize
02 6246 5047
GRDC Project Code CSP00165, UNE00020
Region South, North