Skinning is a grain spoilage condition of much concern to the UK malting barley supply chain. It can result in widespread loss of the UK malting barley crop, which then becomes suitable only for animal feed. Grain skinning causes significant handling and processing problems for maltsters, with significant financial and time costs. Malt produced from skinned grain will be of inferior quality and value. Skinning also reduces the yield of malt per tonne of grain. A modest 1% loss of malt yield across the malting sector would cost the industry £4M. Increased handing costs of skinned grain/malt also extend to the brewing and distilling sectors.
Maltsters assess skinning at intake. In some seasons, it is present in more than 20% of samples, resulting in a significant number of rejections. Even a low national rejection rate of 10,000t per annum (or 0.5% of the UK maltsters average intake) represents a net loss to the industry of about £2M. Breeders have made good progress in improving grain quality, but skinning remains a concern. Breeders will invest £1M to £2M in bringing a new variety to market. A malting barley variety encountering a skinning problem will rapidly lose market share, resulting in failure to re-coup the breeders’ investment.
Skinning, or poor husk adhesion, is a failure of cuticular material from the outer layer of the grain (pericarp) to adhere to the inner epidermis of the husk (palea or lemma). The causal hypothesis is differential tissue development and variation in the amount and/or quality of the wax-lipid deposited on these surfaces from early in grain development and involve synthesis of cuticular material.
Up to 300 spring barley genotypes will be phenotyped for differential expression of skinning. Barley germplasm and genotypic data in the ‘Association Genetics of Elite UK Barley’ project will allow a genome wide association genetic analysis to detect QTL for skinning. This will identify a sub-set of susceptible and resistant varieties for detailed analysis of grain development using light microscopy and TEM.
Grains from the sub-set will be sampled post-anthesis for RNA extraction and transcriptomic analyses, using a newly developed high-density barley microarray based on the Agilent platform. This represents 50,000 gene models from the current barley genome assembly. Additional novel sequences from extensive in-house 2GS transcriptome resources may also be considered.
Transcriptional differences should be expressed as differences in either the type and/or amount of wax being deposited between the pericarp and husk. These tissues will be sampled to extract wax for quantification and characterisation. Transcriptomic data will be combined with biochemical and structural data to identify genes that are up/down regulated and associated with wax differences. Those that co-locate with QTL detected in the association analysis will be re-sequenced to detect possible causal polymorphisms.
Validation will be conducted in an independent pool of genotypes e.g. 20 barley lines, including some known to be susceptible and resistant to skinning. These lines will be phenotyped and genotyped to ascertain whether or not individual SNP polymorphisms are associated with phenotypic differences.
For further information on this project please contact Bill Thomas (email@example.com) from the James Hutton Institute.