Apple blotch disease (Marssonina coronaria (Ellis & Davis) Davis) – review and research prospects

Apple blotch, caused by Marssonina coronaria , is a serious and widely distributed fungal disease that causes huge losses to apple production especially in South and East Asia. The pathogen causes black spots on apple fruits, leaves and premature defoliation, resulting in weakened physiological balance of the host, reduced tree vigor and decreased yield. It is not clear when the pathogen first occurred in Europe but the disease has become increasingly important in Europe due to its unexpected occurrences in European organic orchards in the last decade. Hence, information on the pathogen host range and geographical distribution, symptoms, biology and disease cycle, as well as epidemiology is vital in developing control strategies. Only the asexual stage of the pathogen has been observed in Europe to date. Therefore, mating and sexual recombination mechanism of the pathogen as well as its overall evolutionary potential is unknown. Altogether, population genetics, importance of primary inoculum, overwintering and the time point of disease outbreak are less researched issues of this pathogen. Host resistance is thought to be the most reliable means to prevent the further spread of this pathogen in organic orchards. However, knowledge about the disease and its interaction with the host is a prerequisite for breeding durable resistant apple cultivars. This review highlights the information available from previous research on M. coronaria and its occurrence on apple.