Potential Heterotic Groups in Hop as Determined by AFLP Analysis

acid was negatively correlated among 112 female (r 0.78), and among 74 male hop genotypes (r 0.85). Hop (Humulus lupulus L.) is a perennial, dioecious species in Additive genetic variation was detected for yield, and which the female inflorescence (cones) are harvested and used in the beer-brewing process to impart bittering and/or flavoring to beer. -acid content, cohumulone, and hop storage index for Hop breeders have typically utilized clonal selection and hybridization both males and females in a North Carolin Design I to develop new cultivars. The use of genetically diverse parents for analysis of 25 yr of USDA historical data (Henning et al., the purpose of capturing heterosis in the offspring has received little 1997a). They also reported negative genetic correlations attention from hop breeders. The objective of this research was to between -acid and -acid content, and between -acid assign male (N 80) and female (N 26) hop genotypes into potential and hop storage index, and positive genetic correlations heterotic groups using AFLP-generated molecular markers. The six between cohumulone and yield, and cohumulone and AFLP primers used in this study amplified 550 total fragments, of which 490 (89.1%) were polymorphic. A genetic distance (GD) matrix hop storage index. Genetic variation in hop has also was computed from the binary data matrix, and groupings and sumbeen reported for essential oil concentration (Henning mary statistics were calculated from the GD matrix. Two major cluset al., 1997b) and mineral concentration (Keller and ters were observed, one composed primarily of European hops, while Likens, 1955). the second group was composed primarily of European–wild AmeriSeveral molecular marker tools have been employed can hybrids. The two major clusters were further subdivided into 13 to assess genetic diversity in hop, including amplified smaller clusters (two female, nine male, two male and female) based fragment length polymorphsim (AFLP) (Hartl and Seeon a qualitative analysis. These results suggest potential parental combinations for hop researchers and breeders to study heterosis in hop. felder, 1998; Seefelder et al., 2000; Townsend et al., 2000), random amplified polymorphic DNA (RAPD) (Pillay and Kenny, 1996; Seefelder et al., 2000), and microsatelH is a perennial, climbing, dioecious species in lites (Jakse et al., 2001). Previously published hop gewhich the female inflorescence (cones) are harnetic diversity reports based on molecular marker data vested and used in the beer-brewing process to impart have focused on female genotypes. In an analysis of 41 bittering and flavoring to the final product. Hop cultifemale hop accessions by AFLP and microsatellites, two vars are developed for two primary uses; the bittering distinct germplasm groups were observed representing cultivars are used as bittering agents in beer brewing, American and European ancestry (Jakse et al., 2001). while the aroma cultivars are used to impart flavor and In an AFLP analysis of 86 female and four male hop aroma in beer. accessions, two major groups were identified that correEarly hop improvement efforts were mainly conducted sponded to European and European wild American by growers selecting the most desirable genotypes for hybrids, and these were subdivided into numerous smaller use in a given geographic area. Since hop is a vegetasubgroups (Seefelder et al., 2000). tively propagated species, traits can be easily fixed and Predicting hybrid performance, or heterosis with mocultivars are typically released after a single selection lecular markers has not been pursued in hop but has cycle (Haunold, 1981; Neve, 1991). received research attention in other crop species. GeTraits of interest in hop production include high -acid netic distance measured by pedigree, plant morphology, content for bittering hops, low or moderate -acid, and or molecular markers does not necessarily correlate in a desirable combination of essential oils for aroma hops, a linear fashion with heterosis although Lanza et al. storage stability (i.e., low hop storage index), low co(1997) did find a positive correlation between RAPDhumulone (an -acid homolog), high yield, and resisbased GD and maize single-cross hybrid grain yield. tance to downy [Pseudoperonospora humuli (Miyabe et However, GD has proven useful in grouping related Takah.) G. Wilson] and powdery (Podosphaera macugenotypes together that exhibit heterosis when crossed laris Braun & Takamatus) mildews. Genetic variation to genotypes in unrelated groups (Cheres et al., 2000; was found for -acid, -acid, flower weight, and number Fabrizius et al., 1998; Sant et al., 1999). of lupulin glands in 20 male hop clones from 17 different Because accurate pedigree information is not availpedigrees (Brooks and Likens, 1962). Alpha-acid and able for some hop genotypes, molecular markers could be used to assign genotypes to heterotic groups. Once M.S. Townsend, Dep. of Crop and Soil Science, Oregon State Univ., assigned to groups, genotypes could be crossed in a and J.A. Henning, National Forage Seed Production Research Center, systematic manner to establish heterotic combinations. USDA-ARS, Corvallis, OR 97331. Received 19 Dec. 2003. *Corresponding author ([email protected]). The objective of this research was to place 106 male and female hop genotypes into potential heterotic groups via Published in Crop Sci. 45:1901–1907 (2005). AFLP-based GD estimates. Plant Genetic Resources doi:10.2135/cropsci2003.0688 © Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: GD, genetic distance. 1901 Published online August 26, 2005