Detached leaf assay with respect to determine resistance of Malus species against premature leaf fall (M. coronaria)

Premature leaf fall disease is caused by the hemibiotrophic ascomycete Diplocarpon mali (Y. Harada & Sawamura 1974) (anamorph Marssonina coronaria). Breeding for disease resistance and development of resistant cultivars could help to defeat the disease in the future. The first step in resistance breeding is to assess Malus genetic resources for resistance to M. coronaria. The aim was to proof a detached leaf assay as phenotyping procedure. Disease assessment was performed after 14 days post inoculation (dpi). Different symptoms obtained from the inoculated genotypes indicate a high level of susceptibility in Malus cultivars. In contrast, M. baccata accession MAL0419 was tolerant to M. coronaria. Future experiments will show whether the tolerance of M. baccata accession MAL0419 is inherited and if the genotype is a possible donor for resistance breeding toward M. coronaria.