Genome-wide association studies identify genetic loci for apple blotch symptom development

Apple blotch disease caused by Diplocarpon coronariae poses a significant threat to apple production, particularly in low-input production systems. The fungus spreads on leaves, resulting in symptoms such as chlorosis, necrosis, premature defoliation and fruit spots, which severely reduce the yield when infestation occurs in early summer. Apple cultivars are susceptible to apple blotch; however, differences in susceptibility have been identified, as symptom development differs in a temporal manner. Apple blotch symptom progression data from laboratory experiments of 555 apple cultivars was used to conduct a genome-wide association study for the identification of regions in the apple genome associated to symptom delay. This study identified SNP markers associated with a delay in symptom development, with strong significant associations on chromosome 12, as well as on chromosomes 3, 13, and 16. The high heritability of the analyzed traits and the association of the genetic markers with several phenotypic traits highlight the potential for marker-assisted selection for this disease. These results support the development of sustainable breeding strategies for disease-resistant apple cultivars.