First report of Monilinia fructicola on peach and nectarine in China

X.Q. Zhu¹, X.Y. Chen², Y. Luo³ and L.Y. Guo¹*

¹ Department of Plant Pathology, China Agricultural University, Beijing 100094, China
² Beijing Plant Protection Station, Beijing 100029, China
³ Department of Plant Pathology, University of California, Kearney Agricultural Center, Parlier, CA 93648, USA

Accepted for publication 05/01/05

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 M. fructicola based on morphological (Lane, 2002) and molecular approaches. The mycelia grew at a linear rate of 7.8 mm per day on potato dextrose agar (PDA) at 25ºC, forming a greyish colony with heavy sporulation showing concentric rings. The conidia were 1-celled, hyaline, lemon-shaped, 15.0 (17.5-11.3) x 10.4 (12.5-9.8) µm on PDA, produced in branched, monilioid chains. Species-specific ITS primers for M. fructicola, M. laxa and M. fructigena (Ioos & Frey, 2000) and a M. fructicola-specific microsatellite primer (Ma et al. 2003) were used to amplify the genomic DNA of these isolates. Sub-clones of the respective ITS regions from each of 3 standard cultures were used as the positive control. A DNA fragment of approximately 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 Ma's M. fructicola-specific primer.

Figure 1: Brown rot disease symptom observed on nectarine in July, 2004 in suburb of Beijing, China

Pathogenicity was tested by inoculating surface-sterilised, mature nectarine fruit with a droplet of spore suspension (5,000 spores per ml) from an isolate. Fruit inoculated with 5 ml of sterile water were used as controls. Inoculated fruit were placed in a sterilised plastic container at room temperature (21-26°C). Six fruit were used in each of two replicated tests. About 50% inoculated fruit developed typical brown rot symptom after 4 days of incubation, while all the control fruit remained healthy. M. fructicola was re-isolated from these inoculated fruit.

Brown rot of stone fruit is commonly caused by one of the three Monilinia species. It was still not clear which is major causal pathogen of stone fruit in China. Although occurrence of Monilinia laxa on peach in China had been documented, this is the first report about the occurrence of M. fructicola on stone fruit in China.

Acknowledgements

This study was supported by the project 948 (2003-T19) of China Agriculture Minister. We thank Dr. Renaud Ioos for kindly supplying the sub-clones of the respective ITS regions of the standard cultures.

References

Ioos R, Frey P, 2000. Genomic variation within Monilinia laxa, M. fructigena and M. fructicola, and application to species identification by PCR. European Journal of Plant Pathology 106, 373-378.

Lane CR, 2002. A synoptic key for differentiation of Monilinia fructicola, M. fructigena and M. laxa, based on examination of cultural characters. EPPO Bulletin 32, 489-493.

Ma Z, Luo Y, Michailides T, 2003. Nest PCR assays for detection of Monilinia fructicola in stone fruit orchards and Botrysphaeria dothidea from pistachios in California. Journal of Phytopathology 151, 1-11.

The British Society for Plant Pathology