Breeding Hop Varieties for North Carolina
Interest and commitment from local growers in establishing commercial hop (Humulus lupulus) production in NC have been strong over the past ten years and this parallels the growth of the craft brewing industry in the state. According to the U.S. Brewers Association in 2016, 24.1 million barrels were produced by craft breweries (31 gal per barrel). North Carolina had 200 (33 in 2008, 101 in 2014) breweries out of a total 5234 in the US in 2016, ranked 9th (12th in 2014) and produced 1,269,402 (185,000 in 2008, 372,473 in 2014) barrels, ranking 5th in the nation and with $ 2.04 billion (1.2 billion in 2014) economic impact in the state.
Over the past twelve years, hop yard acreage in NC has grown from just a few acres to more than 40 acres in 2015 (Hop Growers of America). However, NC growers and NC State University researchers in Mills River and Raleigh have experienced low yields compared to the major hop production areas. Dry cone yield in NC is about one-fifth of that in the Pacific Northwest (PNW) (200 to 400 dried lbs per acre in NC compared to 1,000 to 2,000 dried lbs per acre in the PNW for most popular hop varieties Cascade, Nugget, and Chinook). With yields this low, it is doubtful that NC hop production can be profitable over the long term. The low yield is due to available hop varieties being poorly adapted to NC, which is close to the generally accepted southern geographic limit (latitude 35o N) for successful hop production. These varieties, bred and selected almost entirely from and for the major hop production regions in the PNW, either suffer from poor vegetative growth and/or low flower production (low cone yield) in NC. Adjusting cultivation methods, such as cutting down new growth in spring to delay flower initiation, appears to be able to control the timing of flower initiation but has limited impact on improvement of cone yield.
So, it is clear that without varieties that can adapt well to NC environments, which during the growth season are usually warmer, more humid, and shorter in photoperiod than hop production regions in the PNW, hop production in the state will not grow beyond the niche crop status it has now. Therefore, for long term growth and success of hop production in NC, development of varieties through breeding and selection in its own environments may be the only solution for the establishment of a strong hop industry in the state.
Having germplasm that possesses the genetics for growing well vegetatively and reproductively (producing high cone yield) in NC is the most important and fundamental factor for determining the validity to start and maintain a hop breeding program. Ideal germplasm candidate(s) for this purpose must also have relatively good brewing qualities to yield rapid results. Based on observations from the last several years in our experimental hop yard at the Mountain Horticultural Crops Research and Extension Center in Mills River, NC, we identified a hop variety Canadian Red Vine (CRV) which has performed well in vegetative growth and produced very high cone yields. Cone yield of CRV was impressively high compared to the other varieties included in the trial. One plot of five plants produced 19.3 lbs of fresh cones in the first year (2013) and 25.6 lbs the following year (2014). Its first year yield was more than three times that of the second best producing variety Zeus (3.9 lbs vs 1.1 lbs per plant) in 2011 and the second year yield was close to 4 times of the best variety Nugget (5.1 lbs vs 1.4 lbs per plant) in 2014. However, CRV is currently rarely used in the brewing industry because it has a reputation for having a high cohumulone content, which may cause a harsh aftertaste in the beer.
It is generally believed, and has been evidenced in the practice of hop breeding and cultivation, that the hop plant is very sensitive to day length and local environmental factors such as temperature or soil conditions and, as a result, varieties usually do not perform well outside the original area where they were developed. Therefore, hop improvement programs needed to be in the geographic areas in which the varieties will be grown. CRV was probably developed in Canada (ARS, USDA). Therefore, the origin of this variety suggests that its testing and selection site were not with low humidity and plenty of sunlight during the growth season like that in the PNW. This indicates that the breeding (especially selection) site is very important in development of hop varieties that can adapt to a local or even a broad environment. The important role played by selection site is also evidenced in the breeding of the hop varieties ‘Southern Brewer’ and ‘Southern Promise’ in South Africa. These varieties were developed from crossing the existing hop variety Fuggle in the United Kingdom with unspecified male hops under local conditions in George, South Africa, at a southern latitude similar to NC.
With the background information in mind of high impact on economy and having promising germplasm, we started a breeding project for the purpose of developing hop varieties that will adapt well to the environments of NC and other south Atlantic states with high cone yield, acceptable disease resistance, and good brewing quality. In this project we are breeding and selecting by combining the genetics for plant growth and cone yield from CRV with current commercially important hop varieties such as Cascade, Chinook, and Nugget for new variety development.
Breeding work in 2016 and 2017
Our breeding work started in 2016. The 2016 work was initiated with no funding for the purpose of generating new male and female germplasm for use in further breeding steps, particular for generating males that are selected in NC environments. Plants were grown in pots (≥ 5-gallon) at the Mountain Research Station, Waynesville, NC (Figure 1a). Female parents with aromatic properties (Cascade, Tettnang) and bittering (Columbus, Southern Brewer), and ZR4P1MR (ZM, a dwarf selection) were chosen to cross with a male selection YAW2 (Figure 1b). CRV plants generated from soft cuttings failed to flower in 2016 because they were started late. The male plant (YAW2) flowered in late June and overlapped with the five varieties. Open pollination was performed. Cones appearing to bear seeds were harvested in September to early October 2016, placed in paper bags, and dried at room temperature. Seeds were collected in December 2016 and Jan. 2017. Since only one male was involved, pedigrees of the seeds are known. From these crosses 1,495 seeds were collected.
Seed collection was done by hand. Matured hop seed is covered with lupulin powder, sitting on the peduncle enclosed by a small fold of the bearing bracteole. Cleaned seeds (with no bracteole but is sticky due to lupulin) were put in paper seed envelopes and stored in an environmentally controlled seed storage room until needed.
Before germination, the seeds were stratified under moisture-cold (~40o F) conditions (Figure 2). Seeds were spread on the soil surface in 1-gallon garden containers and covered with 0.5 cm of the soil. The soil was then thoroughly moistened with tap water and placed in a walk-in cooler. The pots were regularly checked and moistened when needed. The stratification lasted for about 8 weeks.
In 2017, totally 939 seedlings were obtained from these seeds. After initial screening for disease (downy mildew) resistance by growing in four inch pots, about 20% of the seedlings were transferred to 1-gallon pots for further evaluation (Figure 3). From these, six female plants were selected and cuttings were made to grow additional plants. Eleven plants from the cutting were transferred to the hop yard in June 2017 and flowered that season. Seven male plants were also identified in the 2017 population.
Crosses made in the 2017 growth season focused on between CRV and selected males (three 2016 selections of SB-m1, ZM-m1, ZM-m2, and YWA2) through open pollination. By October 2017, >3,000 seeds were collected from these crosses. On November 6, 2017, 110 seedlings obtained from first batch of 239 seeds and were transferred to 4 inch pots and grown in a greenhouse. On December 4-5 2017, 72 seedlings were repotted into 1-gallon pots and trained on to strings in a low trellis system in the greenhouse. These plants grew up to 9 feet high with 16 nodes in about 40 days (Figure 4). Burr stage was observed on a seedling on Jan. 23, 2017. Additional seedlings will be developed in the coming months.
In 2018, we are expecting to obtain more than 2,000 seedlings from the CRV crosses and after screening for downy mildew resistance, about 10% will be planted in pots or in soil for evaluation. Selected female plants will be propagated by soft cuttings for increasing plant numbers for evaluation in next growth season. Male plants with disease resistance and flowering time (prefer late flowering) will also be selected for use in breeding.
Crossing back these selected males with hop varieties will increase the chance for the progeny to possess more good traits of the established varieties and less of the undesired characters from CRV. In 2018, we are going to use several selected hop varieties in such crosses.
At a latitude of 35.58o N, Mills River is close to the southern limit of regions considered suitable for successful hop production. Because of high elevation (2,425 feet) of the trial site, we have a relatively cooler summer than at lower elevation areas at the same latitude. However, compared to the Yakima Valley (Yka) in WA, our location still appears to be less favorable for promoting hop growth and cone yield (Table 1). During the growing season from April to September, our site has a similar day-high temperature but much higher night-low temperature than the Yka, which may have negative impact on nutrition accumulation in the plants for growth and reproductive production as have been seen in other crops; during growth season our day length is about 60 min shorter than Yka and our precipitation is >10 times than Yka which means less available sunlight in addition to the shorter day length because of more cloudy/rainy days.
Except CRV, all the hop varieties we grew in Mills River performed poorly compared to when they are grow in the PNW. Most of the varieties did not grow to the desired height and the ones that reached the height developed less flowers and/or short side arms, on which hop cones are borne (Table 2). Therefore, low yields were produced by these varieties (Figure 5).
However, vegetative and reproductive growth of CRV appeared not be affected in Mills River. The plant grew on average of about 0.5 feet a day and reached 20 feet high in about 40 days before flowering (Figure 6). Its side arm development went along with the main bine’s growth and the length of a side arm was often more than 60 inches with 18 nodes.
Another growth and development feature of CRV is its secondary side arm development on the original side arms (Figure 3). These secondary side arms can develop on up to the 6th nodes counted from the arm base (Figure 7 and b) and up to 24 cones can develop on a single arm.
2019 Hops Breeding Update
We have made significant progress in our hop breeding program over the last few years. We established a breeding hop yard at the research station in Mills River in 2018 (Figure 1a) and expanded the one at the Mountain Research Station in Waynesville in 2019 (Figure 1b). We have used these hop yards to screen first year hybrid seedlings and make initial selections.
We made selections in 2018 and 2019. Compared to the hop varieties that most growers produce in our region, these selections produced higher yields and exhibited moderate downy mildew resistance (an important trait for this region). Brief descriptions of our four advanced selections are provided in Table 1.
We propagated these advanced selections in 2019 and transplanted the propagules in the hop yards in May. The plants flowered in early to mid-June. Cones were hand harvested in late August to early September. Yields from our variety trials and those reported by growers in NC and VA are in the 300-500 dried lbs/acre range. Estimated yields from our new selections are more than three times what we usually harvest from Cascade, the most widely grown variety in the region
After we collected all of our yield and quality data and submitted samples to the lab for analysis, we provided cones to Sideways Farm and Brewery in Etowah, NC to determine if these selections made good beer.
Jon Schneider, master brewer at Sideways, used two selections to make single hop beers. Here are his comments: “Brewing with the two new varietals of hops developed by the NC State [Research and] Extension center at Mills River has been an amazing honor. NC-1707 gave the beer a wonderful aroma of ripened tropical fruit and will make for a wonderful dual purpose hop. NC-1601 has a slight piney and floral aroma and will be a great bittering hop addition. Both of these varietals are an amazing achievement for the [Research and] Extension center as well as the local craft beer industry.”
These results indicate that we have made significant progress in breeding hops for lower latitudes. We will continue our breeding to increase yield, quality, and disease resistance and conduct more on-farm trials and tests with breweries.