New Hop Cultivars Developed by HortResearch
Beer's bitter flavour is due to the hops used in brewing: the mature female hop cone produces resinous glands which contain a group of compounds called alpha-acids, these are bittering agents. The characteristic aroma of beer comes from a complex mixture of essential oils also contained within these resinous glands. The New Zealand hop and commercial brewing industries are almost totally reliant on new and improved cultivars developed by HortResearch in Nelson.

Hops are a horticultural crop that is gaining attention as a promising New Zealand export. Production of hops has increased significantly in recent years from 274 tonnes in 1986 to 760 tonnes in 1994. Currently around 80% of total production is exported. This represents only 0.6% of the world hop production, so the industry definitely has the potential to expand. There are about 300 ha planted in hops, but the number of growers has reduced from the over 100 growers 50 years ago, to just 26. Those who have stuck with the industry are now seeing rewards in increasing demand and prices. It is not a crop for people looking for fast profit: the capital investment needed to establish farms is considerable, with an expensive high wire trellising system needed to support the hop vines during the growing season, as well as specialized equipment required for harvesting and drying. Hops must be harvested at a critical stage, so sharing of equipment is not always practical.

History of Hops in New Zealand
The predominantly British immigrants in the mid nineteenth century brought hop cultivars from their homeland, and hop plants can be found on the sites of old homesteads throughout New Zealand. As the population increased, the brewing of beer became an industry as opposed to a home activity, and the production of essential ingredients centred in the country's most suitable areas.

The Nelson region has an ideal climate for hop growing - plentiful sunshine interspersed with regular rainfall, and relatively wind-free conditions. Geographical isolation has contributed to a virtual absence of pests and diseases on hops. The only significant pest which attacks Nelson hops is the two-spotted mite. Growers may have to spray for it only once or twice during the season, if at all. Researchers are currently developing non-chemical ways of controlling the mites, so eventually even this may not be necessary. In most Northern Hemisphere hop growing countries, aphids and fungal diseases cause major problems, and hop growers there have to spray 10 to 20 times during the season. In some of the traditional hop growing countries (e.g. Germany), environmental pollution is also creating new problems.

Hops have been grown commercially in the Nelson region for more than 100 years. For the past 40 years, HortResearch (and its parent organization the DSIR) has played an essential part in the success of the industry. Imported hop cultivars from Europe did not do well in New Zealand, mainly because flowering of the hop plant is latitude sensitive, and they were derived from countries that are much further from the equator than New Zealand. By the 1940s all the hops being grown in New Zealand were of American origin. These cultivars yielded well, as they originated from a similar latitude to Nelson, but they were found to be susceptible to a fungal root-rot caused by Phytophthora citricola.

HortResearch Breeding Programme
In 1949 the hop growing and brewing industry approached DSIR to initiate some research on the root-rot disease which was devastating growers' properties in Nelson. A breeding programme was started in 1952 to develop root-rot resistant, high yielding hop cultivars and three resistant cultivars were released from the programme in 1960 (see Table 1).

The focus of the breeding programme then shifted to developing high alpha-acid (or bittering) hop types with a low seed content. Seeds create impurities in the brewing process, and can be a real problem. In Germany, laws prevent the growing of male hops so accidental pollination and formation of seeds in the hops is avoided. In New Zealand, HortResearch has pioneered the development of naturally seedless 'triploid' hops. Triploid hops contain three sets of chromosomes instead of the usual two, and are infertile so they do not develop true seeds. Seven cultivars have been released to date from this programme (Table 1).

A third phase of the breeding programme began in 1975 with the aim of developing low seeded, triploid, aroma cultivars with essential oil profiles similar to European "Noble Aroma" cultivars. This ultimate objective was also to be coupled with improved performance under New Zealand growing conditions. One aroma cultivar has been released to date from this phase of the programme (Table 1).

The New Zealand hop industry now totally relies on five of these cultivars for commercial production: "Superalpha" (35% of total planted area); "Sticklebract" and "Green Bullet" (20%); "Pacific Gem" (25%); and "NZ Hallertauer" (20%). The two main domestic breweries, DB and Lion, have both won prestigious international brewing competition awards with beers brewed using 100% HortResearch-bred hop cultivars.

Dr Ron Beatson of HortResearch's Riwaka Research Centre has been the leader of the hop breeding programme since 1982. The present emphasis is on developing new triploid aroma cultivars, as well as high alpha-acid triploids. Future projects include the application of plant biotechnology to hop breeding, and the introduction of a wider collection of imported hop germplasm.

"Southern Cross", a dual purpose, high alpha-acid/aroma-type hop, was released to growers earlier this year. It is expected to be especially popular with overseas breweries who buy hops from New Zealand. Another, yet to be named, cultivar is expected to be released this spring. It is an aroma-type hop rather like the German "Hallertauer" cultivar, but with the advantage of being seedless and having a better yield. A late maturing high alpha-acid hop, that will help growers to spread the harvest season, is currently being tested in brewing trials in New Zealand, and a further two advanced selections will be trialled this year.

Further Information
For more information about these cultivars and other HortResearch new selections, please contact:

Ron Beatson
rbeatson@hortresearch.co.nz
Scientist, Plant Breeding
HortResearch Nelson Region
PO Box 220
Motueka
Telephone: 03 528 9106
Fax: 03 528 7813

The New Zealand hop breeding programme is supported by the hop and brewing industries, and by the Foundation of Research, Science and Technology.

Table 1.
HortResearch bred hop cultivars.

	Release date	Main characteristics	Ploidy level
First Choice	1960	Root rot resistant, medium alpha	diploid
Calicross	1960	Root rot resistant, medium alpha	diploid
Smoothcone	1961	Root rot resistant, medium alpha	diploid
Green Bullet	1972	Seedless, high alpha	triploid
Harley's Fullbright	1972	Seedless, high alpha	triploid
Sticklebract	1972	Seedless, high alpha	triploid
Super Alpha	1976	Seedless, high alpha	triploid
Alpharoma	1983	Seedless, medium alpha	triploid
Pacific Gem	1987	Seedless, high alpha	triploid
NZ Hallertauer	1988	Seedless, medium alpha	triploid
Southern Cross	1994	Seedless, high alpha	triploid

Source:
The Orchardist, September 1994, Vol: 67, Number: (8):58