Genetic diversity of the apple leaf blotch fungus Marssonina coronariain Europe

Apple blotch caused by Marssonina coronaria (Mc) is reported in Europe since 2001. It has become a serious problem in organic low input orchards and in cider production areas in Northern Italy, Switzerland, Austria and Germany. It is assumed that is has been introduced from East Asia where it is known since 1907. However, its invasion route to Europe and the genetic diversity of established populations in Europe is unknown. To better understand its epidemiology and to reveal its population genetic structure, we developed Mc specific SSR markers (SSR: short sequence repeats) and studied European samples. They showed the typical genetic signatures of a recently introduced species such as lower number of alleles per SSR markers, and higher clonality compared to samples from Asia. The observed low genetic diversity and high clonality suggests that management strategies (such as resistance breeding) might be successful, always supposing that further introduction of novel M. coronaria genotypes into Europe is prevented.