First Report of Brown Rot on Plum Caused by Monilia polystroma in China.

Abstract

In August 2008, mummies of dwarf sweet plum (Prunus aitianli) fruit covered with grayish, conidial tufts were found in an orchard in Mudanjiang City of Heilongjiang in China. Conidial masses were touched with a sterilized wire loop and streaked onto the surface of water agar (WA) plates. After incubating at 22 ± 2°C for 16 to 24 h, individual germinated spores were picked out with a sterilized scalpel blade under a microscope in a laminar flow cabinet, and transferred to potato dextrose agar (PDA) in petri dishes. Mycelium grew an average of 10.7 mm per day on PDA and formed a white-to-grayish colony with irregular, black stroma 12 days after incubation at 22 ± 2°C under 12-h light/12-h dark. The average size of stroma was 8.19 cm2 per petri dish 37 days after incubation in the dark. The conidia were one-celled, hyaline, lemon-shaped, 15.2 (10.8 to 18.9) × 10.9 (8.3 to 16.3) μm, and arranged in branched monilioid chains on inoculated apples. The PCR products of internal transcribed spacer (ITS) region 1 and 2 and 5.8S gene of the ribosomal RNA amplified with primers ITS1 and ITS4 was directly sequenced in both directions using the PCR primers. The sequence of the Monilia polystroma isolate (GenBank Accession No. GU067539) was identical to the reference isolate of M. polystroma (CBS102686), containing five nucleotides that distinguish it from Monilinia fructigena (1,3). The pathogen was identified as M. polystroma on the basis of morphological characteristics (3) and the sequence of internal transcribed spacer (ITS) region 1 and 2 and 5.8S gene of the ribosomal RNA. Pathogenicity was confirmed by inoculating surface-sterilized, mature plum and apple fruit wounded with a nail, with a mycelial plug (5 mm in diameter) of the fungus at each wound. Fruit treated with plain PDA plugs were used as a control. Inoculated fruits were placed in a sterilized moist chamber at room temperature (23 to 28°C). Fifteen plums and nine apples were used in each of two replicated tests. All inoculated fruit developed typical brown rot symptoms 4 days after inoculation, while the control fruit remained healthy. M. polystroma was reisolated from the inoculated fruit and identified by the above methods. M. polystroma was first reported on apple in Japan (3) and it was recently discovered in an apple orchard in Hungary (2). Although the occurrence of Monilinia fructicola, Monilinia laxa, and Monilinia fructigena (teleomorphs of the three Monilia spp.) in China have been documented, to our knowledge, this is the first report of the occurrence of M. polystroma in China.