First Report of Brown Rot Caused by Monilinia fructicola on Apricot in a Swiss Orchard.

Abstract

Monilinia fructicola (G. Wint.), causal agent of brown rot on stone and pome fruits, is a quarantine pathogen in Europe (EPPO A2 quarantine pest). Since it was first discovered in French orchards in 2001, this pathogen has been officially identified from orchards in Austria (eradicated), Spain, Czech Republic, Italy, and Germany. M. fructicola has also been reported on imported fruit in Hungary and Switzerland (2). Orchard surveys in Switzerland in 2003 and 2005 found no evidence of natural infections (2). From July to August 2008, a large-scale survey of orchards was conducted in the primary apricot- (Prunus armeniaca Linn.) production region of Switzerland (Canton Valais). Apricots showing brown rot symptoms were collected from 57 different orchards at packinghouses (152 samples). In addition, mummies and fresh fruits showing brown rot symptoms were directly collected from three orchards (70 samples). All samples were tested using the PCR-based assay of Côté et al. (3). Ten apricots, originating from an orchard where the samples were directly collected from the trees, tested positive for M. fructicola. These apricots showed brown, sunken lesions covered with grayish pustules. The remaining brown rot samples were identified as M. laxa and M. fructigena. The positive samples were confirmed by the M. fructicola PCR protocols of Hughes et al. (4), following the EPPO diagnostic protocol (1). Eight amplicons obtained with the PCR protocol of Hughes et al. (4) were sequenced, compared with each other, and blasted to the NCBI database. These amplicons were identical to each other and had a 100% match to 16 M. fructicola isolates originating from several countries including the United States, New Zealand, Japan, and China. The unicellular, hyaline, lemon-shaped conidia of three isolates grown at 22°C on PDA averaged 14.4 ± 1.3 μm long and 8.8 ± 0.77 μm wide, therefore fitting the description for M. fructicola (1). Koch's postulates were fulfilled by reproducing brown rot symptoms on mature apricots inoculated with conidia. Six days after inoculation, typical brown rot symptoms appeared on inoculated fruits while control fruits remained healthy. Molecular tests performed with the protocol of Côté et al. (3) and Hughes et al. (4) confirmed the presence of M. fructicola on the inoculated fruits. In 2009, the presence M. fructicola in the orchard where the pathogen was detected in 2008 was verified. One hundred and thirty-seven apricots showing brown rot symptoms were collected and tested (3). M. fructicola was recovered from two samples, indicating the persistence of the pathogen in the orchard. To our knowledge, this is the first report of natural infection of M. fructicola in a Swiss orchard.