Genetics of malting quality: The end of the road for crop improvement?

Genetics of malting quality: The end of the road for crop improvement?

‘Au contraire’ my friends!

In this instalment of the Beerologist, we will look into some of the latest research on Malts or Barley to be more precise. In the last episode of my newsletter, I stated how breeders need to breed malting barley varieties that have to fulfil strict criteria.

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 your breeding population can impact your improvement efforts. 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?

Fig. 1 Genetic map of the Barley genome from Mapping malting quality and yield characteristics in a north American two-rowed malting barley × wild barley advanced backcross population. Extensive breeding, genetic characterisation and sequencing efforts have helped define the genetic blueprint and organisation of the barley genome.

The solution to this problem is simple in principle: Expand the germplasm collection by incorporating lines that are very different. In the most extreme case, this means adding plant lines that come from their centre of origin or have a more direct (or separate) relationship than your current breeding lines.

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Wild 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, harbouring the ideal set of traits (Yield, protein content, sugar content, Diastatic Power etc.) are low.

This 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 traits. Will the introduction of disease resistance, for example, impact on yield and grain quality? Can we use wild germplasm to enhance existing characteristics and improve crop performance or yield? A paper published in 2019 (https://link.springer.com/article/10.1007/s11032-019-1030-3) 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 to identify and track small pieces of DNA, originating from the wild parent, and test 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, allow the researchers to identify the pieces of “wild” DNA and determine whether they can lead to crop improvement.

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 into 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.

Should we stop using wild germplasm?

The brief answer is “no”. Yield and malting quality are important characters, but there are others. Disease resistance, for example, is a critical trait that growers use to control pathogens in the field. Genetically encoded resistance is one of the most environment-friendly ways to prevent disease epidemics and crop losses. Wild germplasm is an extremely rich source of genetically encoded resistance. This necessitates their use in breeding programmes.

Should we stop breeding for malt quality and yields then?

Again, the answer is no. This study only deals with a limited set of wild barley lines. Sampling has not captured all the diversity out there. There may (and probably will) be barley lines out there that carry gene versions of benefit. Significantly, investigating the genetics of malting quality and yield in barley will only enhance our ability to introgress new traits (disease resistance, drought resistance, etc.) into elite cultivars. With a better grasp of barley genetics, we can more quickly select lines that have the right combination of traits. Breeding will continue to play an important role in the improvement of barley in the foreseeable future.

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I hope you enjoyed this read!

Best wishes,

Edgar, The Beerologist.

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The Beerologist Newsletter is part of ExtrAnalytics. ExtrAnalytics is a bespoke scientific consulting service, designed to help (small) businesses & brewers to identify and solve problems that are rooted in (micro)biology. To enlist our help, you can contact us by email: huitemae@protonmail.com

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