engleski

Genetic Structure and Differentiation in Hop (Humulus lupulus L.)

Hop is cultivated for its female infl orescence (hop cones) with lupulin glands that provide aroma, fl avour and bitterness to beer. Breeding for improved cultivars in terms of yield, high resin content and disease resistance has been a principle aim of hop breeding programs. Germplasm collections have been established in main hop breeding centres, providing valuable starting material in hop breeding. Th ese collections are fundamental resources for studies in genetics and breeding and their exploitation requires a detailed knowledge of the levels and distribution of genetic diversity present and of genetic relationships among available genotypes. We analyzed genetic structure and diversity among hop genotypes using microsatellite markers and a set of wild and cultivated hop accessions. Model-based clustering (Structure) allocated the accessions into fi ve gene pools that correspond to major breeding groups and to accessions showing mixed origin. A Fitch-Margoliash leastsquare tree shows good agreement with pedigree information and fi ve gene pools, and further assigned eight accessions into two additional gene pools.. Th e cultivated hops diff er signifi cantly from the wild ones, although most of the variability was found within groups. Molecular variances within groups of cultivated and wild hops were homogeneous, suggesting that a similar level of molecular variability is found in both groups of accessions. Core sets of cultivated hop accessions that capture maximum allelic richness were defi ned, generally including hop cultivars of ‘ mixed origin’ that combine alleles originating from diff erent gene pools and thus have the greatest allelic richness. Th e above results are consistent with two biogeographically separated germplasms and with the known history of accessions and have so far given a most detailed insight into the structure and extent of genetic diversity present in hop germplasm collections.

model-based clustering; genetic diversity; hop; Humulus lupulus L.

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