Investigation on apple blotch resistance of Malus baccata 'Jackii'

The fungal pathogen Diplocarpon coronariae causes apple blotch and has rapidly spread throughout Europe in recent years. The most sustainable approach to control this disease is breeding cultivars that exhibit high tolerance or resistance to it. Screenings of the Malus germplasm collection from the Fruit Genebank of the Julius Kühn Institute showed that an accession from Malus baccata is resistant to Diplocarpon coronariae. In this study, Malus baccata ‘Jackii’ and two susceptible genotypes were artificially inoculated and evaluated for their resistance to apple blotch in a detached leaf assay. The phenotypic evaluation revealed a difference in the number of necrotic spots among the genotypes. Additionally, after abrading the cuticle with silicon carbide, a higher amount of Diplocarpon coronariae-specific DNA was detectable in the susceptible cultivars compared to Malus baccata ‘Jackii’. This indicates that the resistance mechanism observed in Malus baccata ‘Jackii’ is not restricted to the cuticle.