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First Report of Brown Rot of Apricot Caused by Monilia mumecola

In May 2013, apricot (Prunus armeniaca) fruits covered with grayish, conidial masses were collected from an unknown cultivar in an experimental field of Huazhong Agricultural University, Wuhan, Hubei Province. About 3 to 5% of fruit was infected and affected apricots had tan to white zones of sporulation, which resembled brown rot caused by Monilia species. Conidia were harvested from the surface of the sporulating apricot fruit and spread onto shallow potato dextrose agar (PDA) media (about 2 mm in thickness) using sterile cotton swabs. Conidia were lemon-shaped and mean size was 15.7 (10 to 22.5) × 25 (16.25 to 35) μm. Conidia on PDA were incubated at 23°C for 3 h in darkness, then observed under microscope. More than two germ tubes were produced from each conidium, which was the distinctive trait of Monilia mumecola species (2). Single-spore isolates were obtained and 3 isolates were cultured on PDA in petri dishes. Mycelium grew at an average of 15 mm per day, and the colony showed concentric rings of mycelium with lobbed margins at 23°C in darkness. A 712-bp fragment was PCR amplified from β-tubulin gene (TUB2) of all the nine isolates investigated indicative of M. mumecola (2). The ribosomal ITS1-5.8S-ITS2 regions of nine isolates were also PCR-amplified from genomic DNA using primers ITS1 and ITS4 and then sequenced (4). ITS sequences were identical to ITS sequences of M. mumecola from China (HQ908786) and Japan (AB125613, AB125614, and AB125620), but only has 98% and 97% identity with the closest species M. laxa (EU042149) and M. fructicola (HQ908789) according to BLAST search in GenBank. Pathogenicity was confirmed by inoculating mycelial plugs of three isolates into six surface-sterilized apricots wounded with a 6-mm diameter sterile cork borer. Control fruit received plain PDA plugs and was incubated in a moist chamber at 23°C with 12 h light/12 h dark. All inoculated fruit developed typical brown rot symptoms with sporulating areas as described above after 3 days of incubation, while control fruits remained healthy. The developing spores on inoculated fruit were re-isolated and confirmed to be M. mumecola. M. mumecola was first isolated from Prunus mume in Japan in 1982 as an unknown Monilia species (3), then identified and the nomenclature was provided in 2004 (1). To our knowledge, this is the first report of M. mumecola on P. armeniaca indicating that M. mumecola has spread to different hosts.

References: (1) Y. Harada et al. J. Gen. Plant Pathol. 70:297, 2004. (2) M. J. Hu et al. Plos One, 6(9):e24990, 2011. (3) S. Nakao. Kongetsu-no-noyaku, 1:92, 1992. (4) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, San Diego, 1990.