Development of SNP molecular markers targeting the major apple scab resistance gene Rvi14
Abstract
Scab (Venturia inaequalis) is the most damaging disease on apple tree, requiring 15 to 25 phytosanitary treatments per year. Several major resistance genes have been discovered but so far, only the Rvi6 gene has been widely introgressed into commercial varieties. Due to the frequency of its resistance breakdown by virulent strains, many apple breeding programs aim to pyramide other genetic sources (major genes and QTLs) to improve resistance durability. In this context, the Rvi14 scab resistance gene, was previously detected on linkage group LG06 of the German cultivar ‘Dülmener Rosenapfel’. Varieties cumulating Rvi6 and Rvi14 could offer a more durable level of resistance against a wider range of Venturia inaequalis strains. However, the precise location of the gene was so far unknown and only few SSR molecular markers were identified to target it. The present work describes the method used to identify and validate new SNP molecular markers targeting Rvi14. To do so, seven biparental progenies segregating for the Rvi14 gene, including recombinant individuals around the targeted locus derived from a cross between ‘Gala’ and ‘Dülmener Rosenapfel’, were genotyped using assays from the Illumina 20K and Affymetrix-Axiom 480K chips. Genotyping data were correlated with phenotypic scoring obtained after scab inoculation performed in greenhouse on grafted plants. In addition, candidate SNP markers were tested on a large and diverse panel of ~200 individuals from the INRAE/NOVADI breeding program. Validated SNP markers will be used for Marker Assisted Breeding and for further fine mapping of the gene.