Multi-dimensional approach against Marssonina coronaria in apple (Abstr.)

Marssonina leaf blotch is a fungal disease of apple caused by the ascomycete Diplocarpon mali (anamorph: Marssonina coronaria). The pathogen origins from Asia where it accounts for crop losses of up to 100%. In Europe it was first detected in Italy in 2001 and is spreading since then in Switzerland and southern Germany (first reports in 2010), mainly in organic apple orchards and in orchards for cider production with a reduced fungicide regime. M. coronaria infects the leaves by using appressoria and shortly afterwards forms haustoria in the host cells. Blackish-violet spots appear on the upper leaf side, sometimes turning into star-like lesions. On the lesions acervuli are produced and eventually the leaves become chlorotic and fall off. First symptoms can be observed in June after a humid period, leaf drop may start two to three weeks later. Severely infected trees can be completely defoliated already in August. The FiBL and KOB Interreg project aims at gaining more knowledge on the biology of the fungus and on control methods in organic farming. For example has the teleomorph Diplocarpon mali not yet been detected in Europe and also the form of overwintering is still unknown. Identification of resistant or less susceptible cultivars, to be directly used in production or as sources of resistance in apple breeding, is a further important pillar in Marssonina control. First results on a population study will be presented