First report of Monilinia fructicola on peach and nectarine in China

In 2003 and 2004, peach and nectarine fruit showing typical brown rot symptoms were found in an orchard in a suburb of Beijing, China. The pathogen was identified as Monilinia fructicola based on morphological (Lane, 2002) and molecular approaches. Mycelia grew at a linear rate of 7·8 mm per day on potato dextrose agar (PDA) at 25°C, forming a greyish colony with heavy sporulation showing concentric rings. The conidia were one-celled, hyaline, lemon-shaped, 15·0 (17·5–11·3) × 10·4 (12·5–9·8) µm on PDA, produced in branched, monilioid chains. Species-specific ITS primers for M. fructicola, Monilinia laxa and Monilinia fructigena (Ioos & Frey, 2000) and an M. fructicola-specific microsatellite primer (Ma et al., 2003) were used to amplify the genomic DNA of these isolates. Subclones of the respective ITS regions from each of three standard cultures were used as the positive control. A DNA fragment of ≈350 bp was amplified by the ITS-specific primer for M. fructicola, but no products were obtained using the primers for the other two species; a 468 bp DNA fragment was amplified using the M. fructicola-specific microsatellite primer. Pathogenicity was tested by inoculating surface-sterilized, mature nectarine fruit with a droplet of conidial suspension (5000 spores mL−1) from an isolate. Fruit inoculated with 5 µL sterile water were used as controls. Inoculated fruit were placed in a sterilized plastic container at room temperature (21–26°C). Six fruit were used in each of two replicated tests. About 50% of inoculated fruit developed typical brown rot symptoms after 4 days’ incubation, while all the control fruit remained healthy. Monilinia fructicola was reisolated from these inoculated fruit. Brown rot of stone fruit is commonly caused by one of the three Monilinia species. It is still not clear which is the major causal pathogen in stone fruit in China. Although the occurrence of M. laxa on peach in China has been documented, this is the first report of the occurrence of M. fructicola on stone fruit in China. This study was supported by project 948 (2003-T19) of China Agriculture Minister. We thank Dr Renaud Ioos for kindly supplying the subclones of the respective ITS regions of the standard cultures.