Genetic Diversity among World Hop Accessions Grown in the USA

have been pursued both within the USA and other countries. The end result of all this activity is a large holding Hop (Humulus lupulus L.) is an important cash crop in the U.S. of hop accessions with little descriptive information Pacific Northwest. Classifying groups of hop accessions presently held in the USDA-ARS world collection is vital toward categorizing newly about their relationships. imported accessions and identifying closely related (if not identical) One method of identifying similar accessions and ascultivars. The objective of this study was to identify hop germplasm sessing genetic and phenotypic relatedness is to perform diversity pools on the basis on morphological and chemical data by a classification on a large collection of individuals using cluster analysis. Eight hop quality characteristics including yield a statistical procedure such as cluster analysis (Ander(YLD), acids, acids, hop-storage index (HSI), cohumulone (CoH), berg, 1973). Multiple characters for each individual are myrcene (M), caryophyllene (C), and humulene (H) were obtained used to group accessions into cluster classes. Individuals from historical databases for 129 accessions from the USDA-ARS within a given cluster class are similar, while individuals hop germplasm field collection located near Corvallis, OR. Three from different classes are not. Similarity measurements distinct genetic diversity pools were identified and named: (i) European, (ii) Wild North American, and (iii) Hybrids. The European among clusters were also determined so that relationpool was divided into English and Continental European subgroups ships between groups can be established. Use of classifidistinguished by their -acids and CoH contents. The Hybrid pool cation data can offer the hop breeder an objective judgwas divided into five subgroups distinguished by their geographic ment when determining which widely differentiated origins. The variables YLD and CoH content differentiated these five individuals to use as parents. It can also be used to classify subgroups (r 0.92; P 0.05). The information presented in our newly introduced accessions into known population study will help categorize newly imported accessions into the current groups and determine similarity or novelty with existing U.S. hop germplasm collection and will help in identifying closely collection holdings. related or similar accessions. Several papers have discussed hop genetic variation using either biochemical or DNA descriptors. In almost all cases, cluster analysis identified two primary groups: H is a dioecious climbing plant with bines that the so-called European and American populations. Sustartwine in a clockwise direction. Plants typically Vozlic and Javornik (1999) analyzed 65 world hop cultigrow on 6-m trellises with the mature female floral strucvars using both random amplified polymorphic DNA ture, called hop cones (or strobiles), as the harvested (RAPDs) and dried hop cone essential oil composition. portion of the plant. Lupulin glands located on the bracThey observed the two primary groupings with further teoles, and to a lesser extent on the bracts, is the source subdivision of the European group into five distinct of commercial value in hops. Resins within these glands clusters corresponding to regions of geographic adaptagive beer its bitterness while the essential oils found in tion. The authors stated that the RAPD data correthe glands contribute flavoring. Hop cones were initially sponded well with essential oil fingerprints groupings. utilized as a preservative in beer brewing. Later, after Murakami (2000) also assayed 51 world cultivars using the advent of pasteurization, hop cones were used as RAPD analysis and identified six clusters that were flavoring agents as people began to associate hop flavor reported to agree with breeding history and country with beer. of origin, although some associations were not readily Most early hop used for beer production in the USA apparent. Seefelder et al. (2000) analyzed 84 world cultiwas imported from European countries, including Gervars and six German experimental lines for genetic relatmany and England. Cultivars such as Fuggle, Saazer, edness using amplified fragment length polymorphism Bullion, and Halletauer Mittelfruh were subsequently (AFLP). Seven AFLP primer pair combinations prointroduced into the USA for production as opposed duced a total of 130 polymorphic fragments that cateto importing hop cones for brewing. Since that time, gorized two main clusters. These first represented Euronumerous foreign-developed cultivars have found their pean aroma-type hop accessions while the second place in the USA hop brewing industry, and production consisted of lines developed via the incorporation of of these cultivars continues in many cases. At the same genes from wild American hop accessions into Eurotime, many new domestic-developed hop cultivars have pean cultivars. Further subgroups were observed in each been released and collections of wild hop accessions primary cluster with the authors stating the resulting dendrogram agreed with pedigree data. Several accesJ.A. Henning and J.J. Steiner, USDA-ARS National Forage Seed sions had identical fingerprints and were therefore indisResearch Center, Oregon State University, Corvallis, OR 97331; K.E. tinguishable from one another. Even though Seefelder Hummer USDA-ARS National Clonal Germplasm Resources, Oreet al. (2000) used German hop collection accessions, gon State University, Corvallis, OR 97331. Received 1 Oct. 2002. *Corresponding author ([email protected]). more than a third covered were not used for breeding or production in the USA, and no wild American accesPublished in Crop Sci. 44:411–417 (2004). sions were included. Jakse et al. (2001) utilized AFLP  Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA techniques to differentiate European and American hop