Polyploid breeding strategies for developing hop cultivars in New Zealand

The main objective of the New Zealand hop breeding programme is to develop triploid cultivars with unique brewing properties. Created from crosses between diploid and tetraploid parents, these genotypes have the advantage of being seedless as well as high yielding. Population improvement procedures are used independently for both diploid and tetraploid populations. Restricted maximum likelihood statistical procedures are used for the selection of both male and female genotypes for tetraploid and diploid parental material. In this regard, particular emphasis is placed on identifying sexually derived tetraploids to widen the gene pool. Crosses using tetraploids, as both female and male parents, hybridised with diploid genotypes, are described. Gender segregation ratios from recent triploid seedling populations vary considerably. The statistical analysis of triploid seedling female genotypes from these populations for several key traits is presented. A summary of main chemistry features of New Zealand bred polyploid cultivars is presented. Future breeding strategies for triploid hops are discussed.