Strategies for breeding macadamias in Australia

Abstract

Macadamia (Macadamia integrifolia Maiden & Betche and M. tetraphylla L.A.S. Johnson) is an Australian native, evergreen nut tree adapted to the subtropics. Large tree size and slow maturity of the crop pose particular problems for breeding and selection. Funding for an industry breeding program commenced in 1996 and 20 elite seedlings were selected. A second generation of hybrid seedlings is planned for production using the elite selections identified from previous breeding as parents. Four breeding strategies were compared in terms of the time to commercial deployment of elite selections, cost of breeding and expected rates of genetic gain determined by stochastic modelling. A tandem selection strategy, which selected for kernel recovery in a seedling trial and nut-in-shell yield in a clonal trial, produced the highest gain to cost ratio but was limited in the number of genotypes assessed in the clonal trial. The full assessment and progeny cull strategies, which selected for nut-in-shell yield and kernel recovery in both a seedling and clonal trial were similar in terms of gain per unit cost and a cloned seedling strategy was intermediate in value.