Agro-morphological differentiation between European hop (Humulus lupulus L.) cultivars in relation to their origin

Hop (Humulus lupulus L.) is mainly used as flavoring and aromatic component in beer production. Breeding of new cultivars has focused on economically important characters such as brewing quality, yield potential and resistance to diseases. To broaden the genetic base available for breeding purposes, hop genetic resources with different origin are examined in respect of traits valuable to cultivars improvement. The aim of the research was to recognize the extent of diversity within European hop cultivars on the basis of agro-morphological traits linked with productivity potential as well as chemical compounds desired for brewing. Thirty eight accessions of hop originating from Poland, Russian Federation, Ukraine, Czech Republic and former Yugoslavia grown in the same environmental conditions in Poland were investigated. Many of these accessions are rarely included in the study because they are relatively poorly represented in most germplasm collections of Humulus genus. Five morphological characteristics as well as qualitative traits like alpha acids content, resistance to powdery and downy mildews and term of technological maturity were studied. Cluster and principal component analyses were performed to assess the diversity among studied cultivars. A large variability was observed for most traits. Results of correlation analysis showed significant positive or negative correlations among some important traits. On the basis of principal component analysis, the most significant traits responsible for variation in studied material were the length of lateral branches and the height of cones formation. The wide range of variability indicates a considerable potential for improving hop genotypes for both morphological and qualitative traits. Cluster analysis based on agro-morphological characteristics separated the studied cultivars into two groups reflecting two major breeding objectives, i.e. development of aroma and bitter cultivars. Discrimination based on phenotypic characteristics was generally in accordance with parentage of studied genotypes.