The sleeping dog within the wheat genome

8 February 2017

Special research measures were needed when environmental factors were discovered to trigger a prevalent but normally dormant defect in the wheat genome. When activated, the defect can cause a punishing downgrade of wheat grain quality.

 

Key points:
  • Late maturity alpha-amylase (LMA) is a genetic defect that may reduce grain Falling Number but is only expressed under certain environmental conditions.
  • Researchers can trigger LMA with a cold shock midway between flowering and harvest-ripeness.
  • A new project is now underway at the University of Queensland to determine the environmental triggers of LMA under field conditions and develop a predictive model for LMA risk and incidence across wheat producing regions.

A genetic defect that harms wheat grain quality has quietly accumulated in the wheat breeding gene pool worldwide. The defect has mostly escaped detection because it lies dormant, lurking in the genome waiting for the right environmental conditions to strike. The defect is called ‘late maturity alpha-amylase’ (LMA) and it was first detected and characterised in Australia by Dr Daryl Mares and Dr Kolumbina Mrva of the University of Adelaide.

Dr Mares explains that in LMA-affected wheat varieties, the grain starts making the starch-digesting enzyme, alpha-amylase, in the middle of grain development. This premature enzyme activation in otherwise normal looking grain then adversely affects Falling Number, the internationally accepted grain trade quality specification. This can potentially cause a $20-$50 per tonne penalty if the grain is segregated into the General Purpose or Feed grades instead of the regular Australian Prime White (APW) grade.

Besides grain growers, LMA has impacts right through the value chain. Dr Mares says there is no simple way to differentiate low Falling Number due to LMA at receival from other causes, such as preharvest sprouting and possibly frost during grain ripening. “Processors are understandably wary of grain that fails to meet receival limits,” he says.

“LMA impacts are especially detrimental to the Australian grains industry since Australia exports a high proportion of its wheat into quality-sensitive markets in Asia where shipments containing low falling number wheat are problematic.”

Wheat breeders are also affected as LMA can result in advanced breeding material, with high yield potential, having to be culled late during development.

At a controlled-environment screening facility in Adelaide, Dr Mares has targeted LMA for intensive analysis and can trigger it using a cold shock midway between flowering and harvest-ripeness.

“This involves a phenotyping protocol in which the lines are grown in a glasshouse and tagged when they flower,” he says. “At around 26 days after flowering, pots or tillers are transferred to the controlled environment facility and subjected to a cold shock for one week. The plants are then allowed to mature back in the glasshouse and the grain analysed for the presence of the alpha-amylase enzymes using specific antibodies.”

Based on this procedure, 650-700 advanced breeding lines a year are screened at the University of Adelaide on behalf of the Australian wheat breeding companies, in a process that is helping to reduce LMA incidence in the wheat gene pool.

Now a new project is underway led by Dr Andries Potgieter at the University of Queensland that uses six field trial sites across Australia to survey the environmental conditions that trigger LMA under paddock conditions. The study is being undertaken with advanced wheat lines registered in the National Variety Trials (NVTs) alongside LMA-prone cultivars selected by Dr Mares as controls. It also draws on results from experimental trials at the University of Adelaide, as well as LMA-specific trials conducted by breeding companies and the GRDC at 70 sites around the country.

Dr Potgieter says the new study is a purely climate driven project, explaining that LMA triggers are more diverse in open paddocks compared to Dr Mares’ controlled experimental facilities and they are not properly understood.

“We want to understand what it is about environmental conditions within the wheat growing regions that can trigger LMA,” Dr Potgieter says. “To that end, we are collecting weather data at the six selected NVT sites and checking for the incidence of LMA. The aim is to use that combined information to develop simulation models that can predict the risk and incidence of LMA at the shire level across the wheatbelt.”

Dr Mares says the study should provide valuable information. “It is clear that there is a strong environmental influence in the occurrence of LMA,” he says. “In our controlled environment facility, temperature is important. But we know that out in the field, it seems that temperature is not the only trigger controlling LMA. This new study should help us work out what is.”

Monitoring at the six NVT sites took place during the 2015 season and continues in 2016, with weather conditions during these two season providing highly contrasting conditions that could result in a data-rich analysis.

At the end of each season, falling number is measured to identify wheat lines that need to undergo LMA testing by Dr Mares. “We hope this study will provide clarity about LMA risks in the paddock for different environments, allowing us to determine what drives LMA at each location and to identify the causative triggers,” Dr Potgieter says.

With sources of LMA constantly entering the Australian wheat gene pool from international breeding companies, a deeper understanding of environmental triggers for different genotypes should help the grains industry better manage risks without sacrificing yield gains or quality premiums.


More information: Dr Andreis Potgeiter, a.potgieter@uq.edu.au

The Queensland Alliance for Agriculture and Food Innovation (QAAFI) is a research institute of The University of Queensland (UQ), supported by the Queensland Department of Agriculture and Fisheries. 

 

 

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