The soil nutrients that reduce barley head loss

Gains made in agronomic and genetic control of barley head loss

Agronomy
Professor Chengdao Li inspects barley at a field trial of the genetic, environmental and management factors that reduce head loss. PHOTO DPIRD

Professor Chengdao Li inspects barley at a field trial of the genetic, environmental and management factors that reduce head loss. PHOTO DPIRD

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Having rated barley's varietal susceptibility to head loss, scientists make more advances.

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Help is on its way on multiple fronts to help reduce head loss in barley crops caused by breakage of the straw in the head's support stem or peduncle.

A research project led by Professor Chengdao Li, director of the Western Barley Genetics Alliance, has looked at the problem from the perspective of genetics, soil nutrition, the environment and management practices.

For growers, there is now new information about the importance of copper and potassium nutrition to reduce the incidence of head loss.

The same project also delivered DNA markers and a physical trait to barley breeders, with both able to select for useful levels of head loss resistance.

For growers, there is now new information about the importance of copper and potassium nutrition to reduce the incidence of head loss. - Western Barley Genetics Alliance director Professor Chengdao Li

These findings are the result of GRDC investment in research that involved Murdoch University and the Western Australian Department of Primary Industries and Regional Development (DPIRD), along with assistance from the University of Adelaide for South Australian field trials.

Professor Li says head loss is a complex trait in that its expression draws on dynamic interactions between varietal, seasonal, agronomic and soil factors.

Head loss in the field. PHOTO DPIRD

Head loss in the field. PHOTO DPIRD

"Head loss is a challenging defect to reduce, with the complexity comparable to studying frost damage," he says.

"We see coastal regions particularly affected, with head loss further exacerbated in high-yielding environments, sandy soils and wet, windy seasons.

"That creates a lot of background noise to understanding how we can reduce head loss incidence."

The complexity of the challenge necessitated a multi-stage research program that started in 2012.

Risks to consider

In the first phase, all commercial barley varieties were benchmarked for head loss susceptibility at windy coastal sites with sandy soils, such as Esperance in WA, which helped to induce the expression of the head loss defect.

That work has since been translated into grower guides that help to better explain head loss risks when selecting a barley variety.

"When deciding on a variety, head loss is just one of several factors that need to be weighed up," Professor Li says.

Barley head loss occurs when the straw under the head breaks. PHOTO DPIRD

Barley head loss occurs when the straw under the head breaks. PHOTO DPIRD

"End user preferences for certain malting quality, for example, or yield potential can limit choice.

"So we knew that in addition to rating the varieties we needed to provide practical management solutions while also developing tools to make genetic gain."

Agronomy tactics

In the second phase, now recently completed, field trials in WA's south coastal districts were undertaken to identify agronomic methods to mitigate head loss risks. The focus was on more susceptible varieties and the findings were subsequently validated in glasshouse tests.

The trials found that the same variety could have two to three times greater head loss levels if copper and potassium were deficient in the soil nutrient profile during the crop's stem elongation and head formation stage.

Overall, varieties were found to respond differently to low levels of potassium, suggesting that genetically improving potassium use efficiency in barley varieties will reduce head loss while also enhancing yields and reducing the need for fertiliser.

"This shows the importance of providing adequate levels of these nutrients, particularly during stem elongation and head formation," Professor Li says.

"Up to 30 per cent of soils in WA's cropping regions are deficient in potassium and this can be exacerbated on sandy soils in the south coastal region where nutrients are prone to leaching."

Also during the second phase, tools were developed to help breeders genetically reduce head loss susceptibility in barley varieties.

DPIRD researchers Dean Diepeveen,left, and David Farleigh collect barley straw samples from WA field trials for straw strength measurements. PHOTO DPIRD

DPIRD researchers Dean Diepeveen,left, and David Farleigh collect barley straw samples from WA field trials for straw strength measurements. PHOTO DPIRD

Progress was made relative to observational traits, with Professor Li finding that head loss incidence can be rated relative to two physical straw properties: strength versus flexibility.

"That research suggests barley varieties are less susceptible to head loss if the barley 'peduncle' is bred to be genetically more flexible and equivalent to wheat straw, which is known to withstand weather and moisture for much longer than barley," Professor Li says.

In addition, varieties at the extreme of the tolerance-susceptibility spectrum were crossed to produce a mapping population for genetic analysis.

This allowed the barley genome to be 'fingerprinted' with DNA markers and resulted in the discovery of three regions associated with consistent reductions in head loss incidence in the paddock.

The relevant DNA markers have now been made available to breeders who are in discussion with the researchers regarding the best quantitative trait loci (QTL) to target in various breeding programs.

Varietal head loss risk information is available in sowing guides such as the Barley Sowing Guide for WA, available at http://bit.ly/2MYdYnV, and the South Australian Sowing Guide, available at http://bit.ly/2Y0CEgy.

GRDC Research Code UMU00051, DAW00246

More information: Chengdao Li, c.li@murdoch.edu.au

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