Dataset from the evaluation of resistance/susceptibility of Malus genetic resources to apple blotch disease (Diplocarpon coronariae)

The dataset contains the field evaluation data and data from two artificial inoculation experiments for the evaluation of Malus genetic resources for apple blotch disease. Apple blotch, caused by the fungus, Diplocarpon coronariae, is an economically important disease in organic apple production in Europe. The disease, which occurs worldwide, was first described on leaves of Malus coronaria in Wisconsin, USA. Symptoms of apple blotch are black spots on apple leaves followed by leaf chlorosis and finally severe defoliation before fruit harvest. This weakens the physiological condition of the host, resulting in long-term reduced tree vigour and decreased yields. Currently, apple blotch appears in apple-growing regions in South Germany, Switzerland, Southern Austria and Northern Italy. The only effective method to control the disease is the application of fungicides, which is restricted in organic production. Cultivation of apple blotch-resistant cultivars is a desirable strategy to control the disease but little is known about the resistance of Malus genetic resources. We evaluated the Malus wild species accessions of the gene bank collection from the Julius Kühn-Institut for field incidence of apple blotch (Occurence of D. coronariae JKI 2014_15_16_18.csv) and leaf fall (Leaf fall wild species JKI 2015_16_18.csv) over a time period of four years. To confirm the field observations, only leaves of accessions without symptoms were tested by artificial inoculation with spores of D. coronariae in a laboratory assay. The necrotic leaf area was measured 14 days post inoculation (dpi) using the leaf doctor application (Artificial inoculation D. coronariae_wild species.csv). Most of the evaluated cultivars were susceptible and developed symptoms after inoculation with D. coronariae. Information about the resistance/susceptibility of Malus genetic resources to apple blotch is still insufficient. The data obtained will provide insight into potential resistance donors, which can be used in future breeding programs.