High diastatic power (DP) is a key attribute in the purchase of malting barley to be used to digest cooked starch adjunct in grain distilling. There is a known positive correlation between diastase activity and grain nitrogen content so maltsters typically purchase higher nitrogen grain lots to supply the needs of grain distillers. Progress in breeding for high diastase has stagnated in the UK because the character is generally only measured under nitrogen regimes more typical of malting barley and the market demand is small. In addition, whilst limit dextrinase, alpha-amylase and beta-amylase are known to be the key enzymes affecting diastase activity, repeated selection for good malting quality means there is little variation for the structural genes for these enzymes amongst the current UK elite barley genepool. Nevertheless, there is still considerable variation for diastase activity amongst these lines. The challenge therefore is to identify the genes controlling this variation and devise a selection strategy that can be applied by breeders to identify lines with high diastase, and used by official testing authorities and maltsters to promote and stream these varieties for the benefit of the grain distilling market. This will also benefit those spring barley growers that find it challenging to meet the malting specifications for the distilling and brewing markets, as they can safely apply nitrogen to their crops and realise the extra yield benefit whilst obtaining a malting premium for the high diastase market.
We hypothesise that only a genome-wide genetic analysis of diastase activity will identify the genes that are contributing to the character. Our approach makes use of pre-existing data and resources gathered under projects, such as Association Genetics of UK Elite Barley (AGOUEB; HGCA Project Report 528) and the BBSRC Crop Improvement Club Barley Malt Processability project (BB/J019593/1), to identify subsets of germplasm that contrast for diastase activity. We have collected detailed genotypic data on these lines as part of AGOUEB and IMPROMALT (RD-2012-3776) and will use this data to find variation in barley chromosomal segments that correlate with the variation in DP. Such regions are highly likely to contain different versions of the genes that control DP, with one form pre-dominating in one pool and another in the other pool. Because of the relatively low resolution of the marker platform used to characterise the AGOUEB and IMPROMALT genotypes, this approach will provide an informative but relatively coarse focus view of the key genomic regions. A much finer focus will be required to identify potential candidate genes. This will be achieved by very high resolution analysis of pools of lines contrasting in DP activity for genome-wide variation in gene sequences. This will be achieved using exome capture sequencing (ECS); a genome complexity reduction approach that allows all of the gene space in a barley line to be sequenced easily and cost effectively. By extending ECS to pooled DNAs it provides a rapid and highly cost-efficient profile of the quantitative differences in allele frequencies between the two pools. As ECS provides detailed sequence information for virtually the entire gene complement of barley captured by the enrichment process, we will potentially be able to directly identify likely causal polymorphisms that lead to the differences in diastase activity.
We will use these potential causal polymorphisms to generate allele-specific KASP markers (LGC Genomics), which are currently the breeders’ marker system of choice, for high-throughput selection. We will validate these as predictors of DP using independent germplasm selected from amongst the remainder of the AGOUEB and IMPROMALT sets. We will augment this test by extending the range of germplasm into the winter and six-row genepools where we will rely upon collaboration with the Scotch Whisky Research Institute (SWRI) to provide DP phenotypic data that we can use to test our marker predictions.
We also recognise the need to better understand the interaction of DP with different fertiliser management regimes and the consequent effect upon the key enzymes. We will therefore select a subset of the pools of spring lines for more detailed phenotyping of DP and its component characters under a range of conditions expected to differentiate between high and low DP lines so that we can develop and release an improved assessment protocol to complement the markers in an integrated screening package.
The validated markers will then be released to the breeders, testing authorities, and maltsters for immediate use in their programmes so that improved varieties will start to come through the selection process within 3 years of the project end.
For further information on this project please contact Joanne Russell (email@example.com) from the James Hutton Institute.