Apple cultivar breeding for multigenic resistance to multiple diseases: the New Zealand experience

Breeding for scab (Venturia inaequalis) disease resistance has been a major goal for the New Zealand apple (Malus × domestica) programme at Plant & Food Research since the programme’s inception in the mid-1980s. Initially focusing on the single Rvi6 major gene resistance, parental breeding lines utilising many other major scab-resistance genes were also developed from the mid-1990s. Since the late 2000s, two generations of pyramided Rvi2/Rvi6 large scale seedling populations have been generated and evaluated for their resistances and fruit quality in the cultivar breeding programme. In the last four years, fire blight (Erwinia amylovora) and European canker (Neonectria ditissima) disease resistances have been included in the breeding target, so cultivar breeding is now focused on both multigenic and multi-disease resistances. Simultaneously, breeding needs to deliver a differentiated apple fruit of very high quality tailored to the consumers’ needs in the market(s) of interest, while meeting growers’ expectations for regular high-yielding crops in commercial orchards. Combining all these requirements present both breeding and logistical challenges for the breeding programme. This paper describes the development of our cultivar breeding system that attempts to address these challenges. New phenotypic and genotypic selection methods, combined with consumer testing, are used at different stages of the programme to optimise breeding performance and efficiency. In particular, new high-throughput genetic markers are enabling efficient marker-assisted seedling selection for the two pyramided Rvi2 and Rvi6 scab resistance genes.