Development and validation of the Axiom(®) Apple480K SNP genotyping array

Cultivated apple (Malus x domestica Borkh.) is one of the most important fruit crops in temperate regions, with great economic and cultural values. The apple genome is highly heterozygous and has undergone a recent duplication which, combined with a rapid LD decay, makes it difficult to perform genome-wide association (GWA) studies. Single nucleotide polymorphism arrays offer highly multiplexed assays at a relatively low cost per data point and can be a valid tool for the identification of the markers associated with traits of interest. Here, we describe the development and validation of a 487K SNP Affymetrix Axiom(®) genotyping array for apple and discuss its potential applications. The array has been built from the high-depth resequencing of 63 different cultivars covering most of the genetic diversity in cultivated apple. SNPs have been chosen by applying a focal points approach to enrich genic regions, but also to reach a uniform coverage of non-genic regions. A total of 1,324 apple accessions, including the 92 progenies of two mapping populations, have been genotyped with the Axiom(®) Apple480K to assess the effectiveness of the array. A large majority of SNPs (359,994; 74%) fell in the stringent class of Poly High Resolution polymorphisms. We also devised a filtering procedure to identify a subset of 275K very robust markers that can be safely used for germplasm surveys in apple. The Axiom(®) Apple480K has now been commercially released both for public and proprietary use and will likely be a reference tool for GWA studies in apple. This article is protected by copyright. All rights reserved.