Genetic Diversity among World Hop Accessions Grown in the USA

Abstract

Hop (Humulus lupulus L.) is an important cash crop in the U.S. Pacific Northwest. Classifying groups of hop accessions presently held in the USDA‐ARS world collection is vital toward categorizing newly imported accessions and identifying closely related (if not identical) cultivars. The objective of this study was to identify hop germplasm diversity pools on the basis on morphological and chemical data by cluster analysis. Eight hop quality characteristics including yield (YLD), α acids, β acids, hop‐storage index (HSI), cohumulone (CoH), myrcene (M), caryophyllene (C), and humulene (H) were obtained from historical databases for 129 accessions from the USDA‐ARS hop germplasm field collection located near Corvallis, OR. Three distinct genetic diversity pools were identified and named: (i) European, (ii) Wild North American, and (iii) Hybrids. The European pool was divided into English and Continental European subgroups distinguished by their α‐acids and CoH contents. The Hybrid pool was divided into five subgroups distinguished by their geographic origins. The variables YLD and CoH content differentiated these five subgroups (r = 0.92; P ≤ 0.05). The information presented in our study will help categorize newly imported accessions into the current U.S. hop germplasm collection and will help in identifying closely related or similar accessions.

Susceptibility of Hop Cultivars to Downy Mildew: Associations with Chemical Characteristics and Region of Origin

“…Assessments of downy mildew phenotype were conducted in experimental plots near Corvallis, OR. The plot contained 110 cultivars that are or were widely grown in the United States, Europe, or Australasia as described by Henning et al (2004a). Each cultivar was planted in single plant plots, from rhizomes or young potted plants, with four replicate plants.…”

“…These cultivars were collected over a period of 25 years, and all cultivars evaluated had been established since at least 1999. Plots were maintained using standard production practices for hop as noted by Henning et al (2004a). However, no fungicide applications were made for at least four years before disease assessments began.…”

“…Further, conducting these assessments on established plants in the same location over a period of three years reduces the likelihood that a cultivar would escape infection if susceptible and also captures potential decline in vigor over time due to crown infection. Henning et al (2004a) previously identified five clusters of hop diversity on the basis of yield and chemical characteristics of cones, and these diversity groups were largely related to region of origin, namely United Kingdom, Continental Europe, United States, Japan, and former British Commonwealth countries (e.g., Australia and New Zealand). Seventy-nine cultivars were included in the prior analysis by Henning et al (2004a) that were also assessed for downy mildew susceptibility and shoot production in this study (Table 2).…”

“…Regional effects are known to exist for certain agronomic and chemical traits of cultivars that are developed and adapted to growing in particular areas (Neve 1991). Henning et al (2004a) used phenotypic data of 129 world hop cultivars grown in Oregon and identified five diversity groups (clusters) of hop cultivars with similar characteristics that were largely explained by geographic origins. While disease assessments were not conducted in the study by Henning et al (2004a), it is possible that there is an association between region of origin and downy mildew resistance (Neve 1991).…”

“…Henning et al (2004a) used phenotypic data of 129 world hop cultivars grown in Oregon and identified five diversity groups (clusters) of hop cultivars with similar characteristics that were largely explained by geographic origins. While disease assessments were not conducted in the study by Henning et al (2004a), it is possible that there is an association between region of origin and downy mildew resistance (Neve 1991). Collecting disease assessments in one location greatly increases the accuracy and value of the data because cultivars can behave differently in different environments.…”