Improving Beer malt quality, a comprehensive breeding effort
Nowadays, beer malts are made from high-performance cultivars (elite cultivars) that produce malts that adhere to the highest quality standards. To breed crop cultivars, geneticists (breeders) make crosses between individual lines (parents). Many of these parents derive from breeding programmes or cultivated collections themselves. The gene pool present in breeder collections (also called germplasm) can be narrow for this reason. The absence of gene diversity in a breeding population can impact your improvement efforts, and you are limited by the amount and quality of the diversity in your collection. The (lack of) diversity raises an important question: how can we enhance diversity in our germplasm?
The solution to this problem is simple: Expand the germplasm collection by incorporating very different lines. In the most extreme case, this means adding plant lines that come from their centre of the origin or have a more direct (or separate) relationship than your current breeding lines.
Wild Barley germplasm, isolated from their centre of origin.
There is a problem with this approach, however, and you may have guessed it already. We have not used wild germplasm for cultivation, and these plants would perform poorly in a crop production setting. Remember the demands of the malt industry? The chances of finding a wild barley plant and harbouring the ideal set of traits (Yield, protein, sugar, Diastatic Power, etc.) are low.
The fact that wild barley plants are not equivalent to elite breeding lines does not mean that wild germplasm has no use in a breeding programme. In most cases, they harbour valuable traits. The question is whether introducing these new attributes impose penalties on the existing characteristics. Will the introduction of disease resistance, for example, impact yield and grain quality? Can we use wild germplasm to enhance current features and improve crop performance or yield? A paper published in 2019 tried to answer these very questions.
Here, the authors investigated the genetics of yield-associated traits (yield, lodging etc.) and nine brewing-associated traits in a population derived from a cross between wild barley and a cultivated line (Harrington). For this, they crossed progeny again from the original cross (2x) with Harrington. This advanced backcross population allows identifying and tracking small pieces of DNA originating from the wild parent and testing their impact on all these traits in the Harrington background (most DNA in these lines will come from Harrington, with a small proportion coming from the wild parent). Since they use an extensive collection of individual lines, they collectively represent most of the wild barley genome.
This mosaic of barley lines allows the researchers to identify the “wild” DNA pieces and determine whether they can improve crops.
Beer Malt quality, the end of the crop improvement road?
What did they find? In a nutshell, none of the yield-associated traits (lodging, seed scatter, etc.) could be enhanced within this population. Domestication and selection of modern cultivars have already incorporated superior alleles into existing cultivars. This means that the use of wild barley lines in a breeding programme may not increase yields. They found the same for most of the traits associated with malting quality. For only three out of the nine quality measures used (diastatic power, free amino nitrogen content, and soluble protein content), the use of wild germplasm may be of benefit.