Polyploid breeding and mutagenesis in hop (Humulus lupulus L.)

Two different strategies have been employed to obtain improved hop varieties: polyploid breeding and mutagenesis. Polyploid breeding was used to obtain a breeding population of polyploid plants. Commercial hops in Australia are triploid, usually resulting from a female tetraploid x male diploid cross. Traditionally, female tetraploids have been generated asexually using a genome-doubling agent, such as colchicine. Polyploid breeding involved identifying sexually-derived tetraploids by analyzing progeny from female triploids using flow cytometry. This approach has also permitted the identification of pentaploids as well as diploids and triploids. The mutagenesis strategy involved exposing axillary buds of hop to the mutagenic agent ethyl methanesulfonate (EMS), with the aim of generating lesions at the DNA level. A number of protocols have been employed including EMS exposure to (i) ex vitro material, (ii) ex vitro material subsequently placed in vitro and (iii) in vitro material. Over 1300 EMS-treated plants have been generated to date and many have been transferred to the field for evaluation. The aim of this research is to obtain genetically stable plants with improved characteristics.