Hops with how much character? Quantifying the genetics

Jun 27, 2014
So this is one of those posts where we get technical. This is not a photo of random wildlife on our farms, or a sheep in the gardens, working on her hop-chops.

This is complex and technical hop science. But bear with us, once you get your head into it, this stuff’s fascinating.

As you may be aware HPA has a long history of breeding hops with character – another blog post to come on that. A strong pool of parent stock set up the genetic diversity of our program from its beginnings. In a nutshell, genetic diversity equals diversity in potential flavour hops. But we’ll get to that.

In 2004, as part of a research collaboration with the University of Tasmania (UTAS)(1), we started a project to develop a high throughput genotyping tool. This is a tool that identifies differences in the genetic make-up of plants, in our case hops, allowing us to map the entire family tree. And no, this wasn’t just a cosy hop-history exercise, this data may help us identify young hops with desirable characteristics – those up and coming hops with character.(2)

Diversity Arrays Technology (DArT) was selected as the genotyping tool due to its ease of use, reproducibility and the large number of potential markers available for analysis. For those with an understanding of molecular genetics, DArT is essentially an array based, amplified fragment length polymorphism genetic marker system. For those who don’t, essentially it’s a tool that detects genetic variation.

Initially we gathered DNA samples from approximately 90 significant hop genotypes from around the world; including male and female genotypes, wild genotypes and important cultivars or breeding lines from Europe, Japan, North America and Australia.

DArT then went through their marker discovery process, identifying around 350 unique genetic markers – this results in enough data to melt your average desktop computer. (3)

This is where it gets really interesting – the DArT marker set was expanded and used in experiments to identify links between variations in traits of interest to hop researchers and brewers. This joint project with UTAS in collaboration with hop researchers from Slovenia and New Zealand (published in BMC Genomics in 2013) allowed us to really start putting this data to work.

It’s important to understand the end-game of this research is not the publication of the papers, but our ability to publish this work in scientific journals is indicative of the calibre of the research .The end-game we are going for is to create a tool that will better help us target the development of future hops with character.

Once the DArT marker set had been established, further work by Erin McAdam (UTAS PhD student at the time) was undertaken on the quantitative genetics of hops. Erin wanted to check the validity of the established hop pedigree data we had, so she sampled and fingerprinted 188 accessions from HPA’s proprietary varieties and germplasm collection using the 348 DArT markers. As we used the same markers created in the original DArT marker development study, we could combine the datasets and compare Australian germplasm with the global genotypes.

So why should you care?

Not only did this data allow us to create this beauty below, we can use the genetic fingerprinting technology to ensure we are planting out ‘true to type’ when undertaking our re-planting program. Theoretically we could also check the genetic make-up of a finished hop pellet to infer its variety.

Now that we have some detailed genetic markers, and understand the genetic variation present in hop, we can put this technology to work to understand how genetic variation relates to the characteristics of hop plants that we observe, such as yield or flavour. More collaborative research to come in the future there….

The Genetic Difference by Split Network

Below is our GDS Network displaying the DArT fingerprint data, created using SplitsTree4. (Check out the high res pdf here)

Complex? Yes. Incredible? Also yes. And a much easier way to visualise the complex genetic information than looking at a database.

For those with an insatiable academic bent the paper describing the maths and reasoning behind split networks can be found via the Oxford Journals. We first presented this work in 2012 to the ISHS-Humulus symposium in Zatec, Czech Republic.

For the rest of us, in the Split Network presented, edges represent lineages of descent or events such as hybridisation. The length of line represents how many marker differences there are on the line – a measure of genetic “distance”, and all nodes correspond to hypothetical ancestors.

This work of art and science shows North American wild hops (long branch to the far left) are genetically quite different from most of the hybrids that constitute today’s dominant commercial cultivars (the middle of the network – look for Magnum, Northern Brewer, Columbus, Nugget and Chinook) grown around the world today, and a long way removed from European Landrace genotypes (such as Saaz, bottom right).

So what does it mean for beer?

If you look at where our proprietary hops fall on the family tree you can see we’re spread nicely throughout the genetic pool. With such a breadth of genetic material in our breeding program (read: flavour pool) there’s unbounded potential.

We’re going to keep pursuing genetic diversity, and keep throwing up unique cultivars –hops with character – and that can only mean good things for the diversity of craft beer.

And this is where the math gets simple – we see it thus:

Unique genetic outcomes = unique flavour outcomes for brewers = differentiated beers = happy beer lovers

As ever, (genetic) variety is the spice of life.

Note: don’t bother looking for our newest girl Enigma on this Network – she was but a twinkle in our breeder’s eye when this network was created.

1. We co-funded along with Horticulture Australia

2. In order to do this, a consortium of hop researchers from Australia, Slovenia, the USA and UK was assembled, with members contributing cash, germplasm or laboratory skills.
3.With any new applied technology it is necessary to check that it performs to expectations. In this case we were able to compare the genetic variations we’d found, with what was already known about hop biogeography and genetic variation from studies such as Murakami . Work also published in Theoretical and Applied Genetics in 2011.

HPA Genetic Difference by Split Network – High Res PDF

 

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