The genetics of brewing better beer
GroundCover™ Issue: 104 | Author: Dr Gio Braidotti
Genetic analysis shows that malting barley grown under Australian conditions requires a finer balance between malting quality and pre-harvest sprouting tolerance than its Canadian counterparts
- Molecular tools have been developed that augment
the capacity of barley breeding programs to reduce
grain defect risks
- These include markers that can select for a region-appropriate
balance between pre-harvest sprouting tolerance
and high malting quality
Australia and Canada lead the world in production of malting barley, collectively accounting for 70 per cent of world trade. That makes breeders in these countries especially skilled at offsetting grain defects that cause malting barley to be discounted or downgraded as feed – a problem that costs growers tens of millions of dollars a year.
However, the market has a strong preference for the malting flavour of Canadian barley and is often willing to pay a $50-per-tonne premium for it.
In a recent round of discoveries, Australian researchers have learnt it is not a simple matter of just introducing the Canadian genetics. This is because the genetics that give Canadian malt its commercially preferred flavour can weaken pre-harvest sprouting tolerance in Australian varieties. It is a finding with important implications for Australian barley breeding programs.
The discovery was made by the GRDC ‘Barley Grain Defect’ project and was part of a package of findings. These include more efficient screening techniques for quality traits such as seed dormancy, the development of new molecular markers and better information about the response of varieties to different environments.
Importantly, the findings, from research led by Dr Chengdao Li from the Department of Agriculture and Food, Western Australia (DAFWA), make it possible to reduce – and in some cases even eliminate – grain defects in new Australian malting barley varieties.
Dr Li says that when he started the GRDC project it was a market mystery why Canadian barley had better malting flavour. Genetic mapping of varietal differences in malting quality has partially solved the conundrum, and in the process scientists have implicated variation in genes located at the tip of chromosome 5H as the cause.
“A key factor affecting beer in terms of foam stability and flavour is a gene called LOX [lipoxygenase],” Dr Li says. “Low LOX content is a desirable trait for malting quality. In general, what we see is that Canadian malting barley varieties and their derivatives show lower LOX content compared with Australian varieties.”
Tempted by the promise of improved flavour, Australian barley breeding programs adopted the Canadian ‘low LOX’ trait, including it in new varieties such as Hamelin and Flagship.
However, Dr Li has now shown that the gain in flavour came at a high cost – the Canadian trait also caused increased susceptibility to pre-harvest sprouting.
“We now realise that the low-LOX attribute of Canadian malting barleys, such as Harrington and AC Metcalfe, are only useful in barley-growing areas where pre-harvest sprouting risk is low,” Dr Li says.
“The Canadian barley industry typically experiences significant pre-harvest sprouting problems in Harrington and its derivatives, but this is less damaging in Canada where barley matures under cool conditions and is stored under frozen winter conditions.”
Not so in Australia, where barley varieties have traditionally needed higher levels of pre-harvest-sprouting tolerance to avoid compromising barley’s viability in warmer temperatures.
“So the Canadian pre-harvest-sprouting trait presents a much higher risk to the Australian barley industry than it does in Canada,” Dr Li says.
“New genetic sources of low LOX activity are needed for Australia breeding purposes. That means exploring biodiversity in malting quality traits within the broader barley gene pool or generating new genetic variation for low LOX by mutation approaches.”
The right balance
Detailed mapping of one tip of the cigar-shaped chromosome 5H allowed Dr Li’s team to identify barley candidate genes that affect malting barley quality traits.
These include malt extract, diastatic power (part of the process of converting starch into sugars), free amino acids, nitrogen, alpha-amylase activity, seed dormancy and pre-harvest sprouting. A set of markers were developed to distinguish genetic variation among these genes.
“These markers provide simple and efficient tools to characterise barley biodiversity in quality genes and to select for desirable malting traits,” Dr Li says.
An important outcome is a set of markers that can detect germplasm with a suitable balance between pre-harvest-sprouting tolerance and malting quality in different climatic conditions.
In the medium-to-low rainfall region it was the geneotype found in Gairdner that proved the best option, whereas BaudinA proved a good option for the high-rainfall region and the gene combination of Stirling for the northern region.
“The analysis of Baudin in particular demonstrated that differences in the pre-harvest-sprouting tolerance gene are not always negatively associated with malting quality,” Dr Li says.
Baudin was developed by DAFWA’s barley breeding program from the cross of two Australian malting barley varieties, Stirling and Franklin. Long-term experiments in WA found that Baudin has good levels of pre-harvest-sprouting tolerance and excellent malting quality. It is now the predominant variety grown in WA and traded on international markets. Baudin has also become a major parental variety for many barley breeding programs.
“We found that Baudin's pre-harvest sprouting tolerance trait contributes to higher malt yield,” Dr Li says. “The data says that it should be possible to develop cultivars that combine acceptable malting quality and adequate levels of grain dormancy for protection against pre-harvest sprouting under Australian growing conditions.”
While quality traits such as malt extract, diastatic power, free amino acid nitrogen, alpha-amylase activity, seed dormancy and pre-harvest-sprouting are not only complex in their genetic make-up but also interact with each other and the environment, by targeting a higher-level regulatory gene or group of genes in the genome, Dr Li’s work has been able to provide breeders with tools that make selection for these important malting traits more efficient.
Black point in barley
Kernel colour is an important selection criteria when trading barley on international markets. Kernel discolouration can result in thousands of tonnes of malting barley being downgraded each year worldwide.
Three types of barley kernel discolouration have been observed in Australia. These are colour discolouration, black point, and distinctive spots or staining caused by fungal proliferation.
Black point has been associated with fungal infection in the US, Slovakia and the Czech Republic, but in Australia the dark colour is thought to be caused largely by biochemical responses to warm, humid or rainy environmental conditions, especially during grain-filling stages.
Genetically improving black point and colour discoloration resistance has proven complex in the past. Tolerance to black point and discoloration are controlled by different mechanisms that complicate each other under the field conditions. Breeders also need more efficient analysis methods and an understanding of how genes and environments interact, along with knowledge of the biochemical mechanisms of melanisation.
The GRDC ‘Barley Grain Defect’ project has made progress developing this needed expertise. Researchers have developed a digital image analysis system to measure black point and grain colour discolouration simultaneously. This is expected to improve selection efficiency in breeding programs and also facilitate risk assessments for grain receival agents and marketers.
The project also identified regions in the barley genome containing genes that affect these important traits. The genes were mapped in a population derived from crossing a susceptible and a resistant barley variety, which was grown in Queensland and Western Australia in consecutive years.
Of the mapped regions associated with black point and kernel discolouration tolerance, three proved effective across the environments, making them highly valuable to breeders. Markers for these regions are likely to prove useful for selecting black point and kernel discolouration resistance in breeding materials.
GRDC Research Code: DAW00220
Dr Chengdao Li,
GRDC Project Code DAW00186
Region National, Overseas, West, North