First Report of Brown Rot of Apple Caused by Monilinia fructicola in Germany.

Abstract

Monilinia fructicola (G. Wint.) Honey is a causal agent of brown rot of stone fruits but may also affect pome fruits. M. fructicola is common in North America, Oceania, and South America as well as in Asia, but it is listed as a quarantine pathogen in Europe (3). Since its first discovery in Europe in 2001 (France), it has been reported in Spain, Slovenia, Italy, and Switzerland. Recently, the fungus was also detected in orchards of blackberries and plums in the State of Baden-Württemberg, Germany (4). In July 2010, apples (Malus domestica Borkh.) of the cultivar Jonagold were found in a residential backyard in Fronhausen an der Lahn located in the State of Hessen, Germany with symptoms resembling brown rot caused by Monilinia species. Affected apples were at or near maturity with brown decay that had spread throughout the fruits. On the surface of the decaying apples was tan to white zones of sporulation. Upon isolation, the mycelium grew at a linear rate of 9.2 mm per day at 22°C on potato dextrose agar forming branched, monilioid chains of grayish colonies with concentric rings and little sporulation. The lemon-shaped spores had an average size of 14 × 9 μm, a shape and size consistent with M. fructicola. The ribosomal ITS1-5.8S-ITS2 region was PCR-amplified from genomic DNA obtained from mycelium using primers ITS1 and ITS4. A BLAST search in GenBank revealed highest similarity (99%) to M. fructicola sequences from isolates collected in China, Italy, and Slovenia (GenBank Accession Nos. FJ515894.1, FJ411109.1, GU967379.1). The M. fructicola sequence from the apple isolate was submitted to GenBank (Accession No. JF325841). The pathogen was also identified to the species level and confirmed to be M. fructicola using two novel PCR techniques based on cytochrome b sequences (1,2). Pathogenicity was confirmed by inoculating three surface-sterilized, mature apples cv. Gala with a conidial suspension (105 spores/ml) of the apple isolate. Fruit were stab inoculated at three equidistant points to a depth of 10 mm using a sterile needle. A 30-μl droplet was placed on each wound; control fruit received sterile water without conidia. After 5 days of incubation at room temperature in air-tight plastic bags, the inoculated fruits developed typical brown rot symptoms with sporulating areas (as described above). The developing spores on inoculated fruit were confirmed to be M. fructicola. All control fruits remained healthy. To our knowledge, this is the first report of M. fructicola on apple in Germany and more indication of further geographical spread of the quarantine disease in Germany.