HISTORY

Hop research in New Zealand began in the late 1940’s. This was in response to a request from the Nelson based hop industry, which was being severely affected by a soil born fungus disease called Phytophthora root rot. The cultivar grown at that time, Californian Late Cluster, was particularly susceptible to the disease. Plant breeding solved the disease problem quickly. This was achieved by hybridising Californian Late Cluster, which had good yield potential, with root rot resistant male selections derived from "old line" European cultivar sources. By the early 1960’s, three disease resistant cultivars had been released and were becoming wide grown by NZ hop growers and accepted by the domestic breweries.

SEEDLESS CULTIVARS

After the disease problem had been solved the hop breeding programme changed its emphasis to the development of genetically seedless hop cultivars. In fact, New Zealand hop breeders pioneered this work which has resulted in a string of very successful cultivars being released to the NZ hop industry. Initially the triploid seedless cultivars developed from this programme had high alpha acid contents. More recently the hop breeding effort has centred on developing seedless triploid aroma-type cultivars.

A total of nine triploid cultivars have been released since the early 1970s. They include seven high alpha types and two aroma types.

CURRENT GOALS

The hop breeding programme continues to aim at improving the quality of high alpha types with a particular emphasis on developing new late maturing (late March) cultivars. The aroma breeding programme seeks to develop a range of cultivars with brewing qualities similar to the "noble aroma" (old line) cultivars from Europe such as Golding, Fuggle, Saazer, Teltnanger, Spalter, and Hallertauer. The noble aroma cultivars generally perform very poorly under NZ conditions and are highly seeded. As a starting point, these old line cultivars are being used as parents in the hybridization programme which aims at improving the agronomic performance above that of the parents.

SELECTION CRITITERIA

For the aroma breeding programme particular emphasis is placed on obtaining a chemistry profile which closely matches the noble aroma cultivars mentioned above. The most important characters examined are the cohumulone content of the alpha acids, as well as humulene content of the essential oils. A cohumulone content of less than 30% and a humulene content of less that 30% is considered desirable.

The alpha breeding programme aims to select triploid hybrids which have alpha acids in excess of 12% with a cohumulone content of less than 30% and a humulene content of less than 20%. In both the alpha and aroma programmes a seed content of less than 2% and good agronomic (yield) performance are also sought.

PRESENTLY GROWN COMMERCIAL CULTIVARS

Main attributes of the seven presently grown commercial cultivars are summarised in Table 1.

Of particular interest are the two new cultivars, Southern Cross, a high alpha type and Pacific Hallertauer, an aroma type. Pacific Hallertauer has a chemistry profile very similar to its mother, Hallertauer mitterfrueh.

In conclusion, the hop breeding programme has provided a good supply of hop cultivars to the NZ industry enabling it to develop a significant export industry. At the same time domestic brewers have enjoyed the use of unique hop cultivars with good chemistry attributes.

The programme aims to continue developing improved cultivars and expanding the portfolio of aroma types to meet the demands from the hop and brewing industry as the 21st century approaches.

Table 1:
Chemical Characteristics of NZ Hop Cultivars

	Pacific Hallertauer	NZ Hallertauer	Green Bullet	Pacific Gem	Southern Cross	Sticklebract	Super Alpha
Alpha acids	6.2	9.5	13.7	15	14.2	14.1	13.6
Beta Acids	6.2	7.7	7.2	8.3	6.9	7.7	8.4
Cohumulone	27	36	43	41	27	45	38
Oil content	1.14	0.88	1.19	1.27	1.2	1.18	1.35
Essential Oils
Humulene	35.35	12.89	18.03	17.84	13.98	10.34	20.76
Caryophyllene	11.95	6.58	5.84	6.19	4.26	5.37	6.19
Farnescene	0	4.98	0.08	0.09	4.73	5.24	0.09
Myrcene	33.63	43.92	56.12	53.38	56.43	52.36	50.65
Oxidation Products	1.65	1.31	1.05	0.96	0.89	0.96	1.13
Floral-Estery	1.26	2.58	1.67	1.42	1.68	1.99	1.72
Citrus Piney	3.79	5.49	2.5	2.86	2.27	7.57	2.89
Other	12.43	22.24	14.7	17.25	15.75	16.19	16.57

Where all figures are %:
oxidation products = oxidation products of caryophyllene and humulene
floral-estery = linalool, geranyl acetate, geranyl isobutyrate and geraniol
citrus-piney = limonene, d-cadenine, g-cadenine, muurolene, selinene