S01 - Session O4 - Apple cultivar breeding for multi-genic resistance to multiple diseases: The New Zealand experience

Authors: Richard Volz *, Natalie Proffit, Chrissy Marshall, Ben Orcheski, Elena Lopez-Girona, David Chagne, Vincent Bus

Breeding for scab ( Venturia inaequalis ) disease resistance in apple has always been a major goal for the New Zealand programme at Plant & Food Research since the programme's inception in the mid-1980s. While initially focusing on the single Rvi6 major gene resistance, parental breeding lines that utilised many other major scab resistance genes were also developed from the mid-1990s. The Rvi2 line was the first to produce suitable selections for use as parents with Rvi6 material, in large-scale cultivar breeding to produce more durable scab-resistant cultivars. Since the late 2000s, two generations of pyramided Rvi2 / Rvi6 seedling populations have been generated and evaluated for their resistances and fruit quality. In the last four years, fire blight ( Erwinia amylovora ) and European canker ( Neonectria ditissima ) disease resistances have been added as breeding targets, so that now cultivar breeding is focused on both multi-genic and multi-disease resistances. Simultaneously, breeding needs to produce a differentiated product of an extremely high quality standard 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 the present cultivar breeding system that attempts to address these challenges. New phenotypic and genotypic selection methods, and also consumer testing, are used at different stages of the programme to optimise breeding performance and efficiency. In particular, a new high-throughput genetic marker for Rvi2 has been developed that is enabling efficient marker-assisted seedling selection for the two pyramided scab resistance genes.