Climate change

What are some current advancements in hop breeding?

Common hop – you might call it hops – is a main ingredient in beer responsible for its rich flavor profile. Craft brewers and larger manufacturers alike are always looking for that new flavor. You may not know that a lot of breeding efforts go into those new flavors – but there is additional work being done to make varieties of hop that are disease resistant, as well as drought and heat tolerant.

It’s the fruit of hop that brewers consider when choosing ingredients. The fruit of the female plant is a cone-shaped flower. Many hop varieties are prolific bloomers on perennial vines. The vines can grow over seven feet tall.

While hop is important in the beer industry, not a lot of research has focused on creating a genetic profile of the crop. Over the past decade, several breeders, including myself, have focused on creating genetic maps that outline “markers” to help guide us in our breeding.

person wearing hat inspecting hop vines on tall hop plants
Dr. John Hennig by vines of hop growing at Oregon State University’s trial fields. The team is breeding hop for flavor as well as climate tolerance and disease resistance. Credit: Kayla Altendorf

Markers are locations on genes that predict a specific trait. There are markers for plant height, drought tolerance – and especially that important flavor profile. The study of markers for traits is called genomics, and we’ve made a lot of progress this decade.

For many US crops, markers are used as tools for selecting traits to be bred or researched.

Traits such as disease resistance, growth habit (dwarf vs tall), fruit color and shape or oil content are easily identified in the seedling stage using these markers. This saves breeders a lot of time – since the DNA of a seedling is the same at the adult plant, determining the markers at earlier stages of development saves months in the process.

By creating this profile of genetic markers, breeders can reduce the number of experimental lines that need to be evaluated in the field. This also helps the selection process have greater precision – with seeds likely to produce plants that create the desired fruits.

For popular crops, like wheat, corn, soy, and rice, much of the early work on marker development took place in the late 1990s and early 2000s. The genomes for these crops were fully sequenced, assembled and their genes identified well over a decade ago. Having this basic tool allowed plant breeders to then search for markers to important traits and to increase accuracy in breeding programs for major crops.

large trough filled with cones of harvested hop along with dozens of bagged sets of dried cones
Green cones of harvested hop along with bagged sets of dried cones. Experimental hop lines from USDA-ARS hop breeding program laid out for kilning.  Credit: John Henning

Large internationally owned plant breeding companies will assay over one million seedlings for thousands of markers linked to a plethora of traits for each crop and breeding location. The costs for such analyses are well beyond the scope for a minor crop such as hop. About 40,000-100,000 seedlings are generated annually per breeding program.

Currently, we have only determined the markers for a few hop traits for use in our programs. Some important markers we know for hops are:

  • Sex – this is important because only female lines are cultivated
  • Disease resistance – we know the markers for Hop Powdery Mildew, Hop Downy Mildew
  • Plant height – this is important because dwarf hops can be grown on a short trellis as a hedge—significantly reducing labor inputs
  • Alpha acid levels – these contribute to the bittering potential that a hop will contribute to brewing
  • Prevalent essential oils – these are more compounds that contribute to the flavor of beer

Recent developments in genomic tracing have lowered the cost of the process. More of these traits – and others soon to be identified – will be implemented into routine breeding. This is true for both the public breeding programs as well as private endeavors.

Early efforts at hop genome assembly were only recently published (2015) and the first true draft genome published last year (2020). As a result, efforts at marker development for hops are still in their infancy stage in hops. And this is for only of few of the simpler traits—those controlled by one or just a few genes. Some traits are controlled by three or more genes, which dramatically increases the complexity of gene expression and makes selection for traits much more difficult.

In addition to developing the hop genome and identifying markers for simple traits, recent research in my program has revealed genomic control over water use efficiency—drought response—and its impact upon hop chemistry. 

hop cones growing on tall vines
Hop cones growing on tall vines. Hop gives beer its distinctive flavors. Breeding efforts in both flavor variety and disease resistance have progressed in the past decade due to genomic mapping. Credit: John Henning

We observed the greatest impact on hop bittering acids and other flavoring compounds was during the mid-stage of cone (fruit) development. This means that drought or heat stress during the mid-stages of hop cone development will impact overall yield. Just as important, it will impact bittering acid levels and levels of other flavoring compounds.

While genomics work and marker development are exciting and impactful, regular plant breeding continues to have the greatest impact upon the economic health of the hop industry and brewing world.

The USDA-ARS public breeding program has recently released its latest hop cultivar, USDA Triumph (2020). This cultivar is a new high yielding, disease tolerant public line (available to anyone without royalties). It has an incredible aroma and brewing characteristics for anything from a lager to hazy IPAs.

In addition, my program released another new exciting public hop cultivar—experimental name “074”, to the public in late 2021. This line is a seedless hop, with large cones. It has an incredibly intense tropical fruit with citrus flavor and after-notes of stone fruit. The yields for “074” have far exceeded those of other aroma lines. The crop is adaptable across the US, having been successfully grown and harvested from the Pacific Northwest to Vermont. 

Another experimental cultivar is waiting in the wings for release this year. It has the characteristic of being an extremely early harvested line with broad usage in different brewing styles.

Answered by John Henning, Oregon State University

This blog is based on Dr. Henning’s paper about the development of hop “074” published in the Journal of Plant Registrations.

About us: This blog is sponsored and written by members of the American Society of Agronomy and Crop Science Society of America. Members are researchers and trained, certified professionals in the areas of growing the world’s food supply while protecting the environment. Members work at universities, government research facilities, and private businesses across the United States and the world.

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